Recommended citation
Carmody, Michael. 2021. “New Distributional and Temporal Records for Birds of the Mexican State of Guerrero.” <https://wp.me/p8iY2g-bNd> North American Birds. 72:2.

As early as 1944, William B. Davis, the curator of the Texas Cooperative Wildlife Collections, acknowledged the paucity of information concerning the birds of the Mexican State of Guerrero (Gro), yet almost a half-century would pass before researchers affected comprehensive studies within the state’s unique habitats. Adolfo G. Navarro-Sigüenza (1992) provided invaluable data with altitudinal surveys in the Sierra de Atoyac. Concurrent studies in the Sierra Norte de Guerrero by J. E. Morales-Pérez and A. G. Navarro-Sigüenza (1991) augmented awareness of the avifauna north of the Río Mezcala (alternate names Atoyac River and Balsas River). Notwithstanding these significant contributions, the body of knowledge concerning the avifauna of Gro remains arguably less complete than for any other of Mexico’s 32 political jurisdictions.

This article details 94 species of birds (Appendix A), of which 41 are first records for Gro (five previously published elsewhere, seven attributed to eBird, and 27 are newly brought forward). Nine species are resident, though not attributed to the state by Howell and Webb (1995), the systematic compendium of modern Mexican ornithology, and 53 species are addressed for Gro as either data deficient (24), with populations in parts of the state where unmapped by Howell and Webb (22), or their status in the state is currently misrepresented in print (7).

Additionally, I list 78 species found to occur in the Sierra Norte de Guerrero that were not attributed by Howell and Webb (referred to in this article as H&W; Appendix B). I spent 349 days in Gro leading tour groups with multiple participants, first having visited Taxco during August 1994. I explored 73 of the state’s 81 municipalities, and I boated the offshore waters 16 times (while doing so, personally recorded 499 species in Gro). Field reports detailed herein are largely the result of these comprehensive studies though I incorporate information drawn from published articles, reports contributed through eBird, and personal communications with field observers.

The taxonomic sequence and species list adhered to in this article follows the 7th edition (1998) of the AOS Checklist of North and Middle American Birds as of the 2020 (61st) supplement. 

Black-bellied Whistling-Duck (Dendrocygna autumnalis) – H&W do not map this species for interior Gro. I observed a group of 43 birds at Laguna de Tuxpan, Iguala, on 21 Mar 1996. During 46 subsequent visits encompassing all seasons of the year, minimum and maximum numbers observed were 16 (25 Apr 1999) and 3,000 (14 Apr 2017). This species is to be expected at large impoundments in interior Gro.

Banded Quail (Philortyx fasciatus) – In Gro this species occurs primarily in the interior, reaching the central Pacific coast through the arid Chilpancingo–Tierra Colorada–Acapulco corridor (H&W). I observed six birds on the northwest Gro coast near Los Achotes, Zihuatanejo, on 22 Apr 2014, and four at nearby Barra de Potosí on 7 May 2018. On 14 Apr 1996, a pair crossed the Atoyac Road above El Rincón de las Parotas [17.2488, -100.3753]. There are five eBird reports (Isaín Contreras, photo) for the northwest Pacific slope, including two by Chester C. Lamb in 1949 (Atoyac) and 1955 (Tacpan).

Northern Bobwhite (Colinus virginianus) – The distinctive races are sometimes treated as separate species. H&W detail two subspecies groups for Gro, C. v. coyolcos (black-headed males) along the southeast coast, and an isolated pocket of C. v. nigripectus [graysoni/nigripectus Group] in the state’s northern interior. I observed pairs of the former taxon along the central coast north to Coyuca de Benítez (21 Mar 1996), and on the central Pacific slope to 1,575 ft (480 m) at Tierra Colorada (11 Jul 2019). The later taxon is more widespread in Gro than previously understood, with personal observations of pairs or small groups along the México/Morelos border at El Mogote (10 Oct 1998), Taxco (29 Jul 2000), and Laguna de Tuxpan (18 Jun 2008), and to 3,215 ft (980 m) in the interior Sierra Madre del Sur along the Puebla/Oaxaca borders (two eBird sight reports). The occurrence of this taxon in northeastern Gro is unsurprising as Friedmann et al. (1950) record it for the southern halves of the neighboring states of México, Morelos, and Puebla.

Least Grebe (Tachybaptus dominicus) – H&W map this species for the length of the Pacific coastal slope, addressing it as irregular within interior Mexico north of the Isthmus. I encountered this species in interior Gro on numerous occasions, the first being on 28 Mar 2001 with 24 birds at Presa Valerio Trujano. On 21 Apr 2003, eight birds were observed at Laguna de Tuxpan, where this species has been recorded during 28 subsequent visits, including confirmed breeding, with an adult and two chicks on 13 Apr 2011.

Eurasian Collared-Dove (Streptopelia decaocto) – This species arrived in Mexico through the northern border states during the early 2000s, and within a decade it appeared in nearly all 32 states. Likely the first sighting for Gro is my observation of two birds at Coyuca de Benítez on 7 Apr 2011. Almazán-Núñez and Carlos (2014) noted its preference for human settlements while they were evaluating the rapid advance of S. decoacto within Gro for possible effects on native species.

Ruddy Ground Dove (Columbina talpacoti) – H&W map this species for the state only for the Pacific coastal slope. On 3 May 1995, I observed two birds at a permanent water seepage location near Iguala. Between two and eight birds have been observed 33 times during return visits to northern interior Gro where this species is an uncommon resident, being most easily found near freshwater.

Striped Cuckoo (Tapera naevia) – This species is unrecorded in western Mexico north of the isthmus. During the morning of 31 Mar 2005, in a scrubby field near the Acapulco airport [16.7507, -99.7627], I heard the spontaneous hollow phrases of a Tapera/Dromococcyx cuckoo. The use of playback resulted in a prolonged view of a bird perched atop a low bush singing twice more its flat triple escalating song. This sighting is the first such report for T. naevia in Gro, and the northernmost occurrence in western Mexico. The location is now a housing development, though abandoned fields continue to dominate the coastal landscape of Gro.

Mangrove Cuckoo (Coccyzus minor) – H&W lists this species in Gro only along the Pacific coastal slope. I located individual calling birds in interior Gro during early summer at Xochipala (11 Jul 2019), Laguna de Tuxpan (9 Jul 2019), RMO Tiuribe, Iguala (20 Jun 2008 and 10 Jul 2019), San Juan Union (18.4310, -99.6268] (19 Jun 2008), and Milpillas [17.7676, -99.5624](29 Jun 2020), suggesting that in Gro, C. minor is a seasonal visitor and likely rainy season breeder (Jun–Jul) within the Río Mezcala drainage.

Black-billed Cuckoo (Coccyzus erythropthalmus) – H&W list this species as an uncommon transient through southern Mexico, with relatively few records due to its inconspicuous habits. Friedmann et al. (1950) report an undated Gro reference with the note “generally overlooked.” On 30 Apr 1998 near Chilpancingo [17.5980, -99.5399], I observed red eyering of a bird perched of this species at a 15 ft (3 m) distance, and observed the solidly brown underwings as it took flight. This sighting serves as the only specific report for C. erythropthalmus in Gro.

Common Nighthawk (Chordeiles minor) – H&W map this species as a summer resident for Gro, noting their personal sightings in the neighboring states of Michoacán and México . The sole Gro reference is a series of sightings by Dixon and Davis (1958) resulting in the collection of three birds between 11 Jun and 1 Jul 1954 at Agua de Obispo and Almolonga (both locations near Chilpancingo in the central Sierra Madre del Sur). Selander and Alvarez del Toro (1955) assign the three specimens to C. m. neotropicalis, the southernmost breeding race in Mexico. More recently extensive studies in the Sierra Norte de Guerrero by Morales-Pérez and Navarro-Sigüenza (1991) and Almazán-Núñez (2009) failed to detect this species. I failed to record this species within the state; and there are no eBird reports for Gro, though three recent migration period sightings (Jun and Sep) are listed for nearby Morelos. The U.S. Department of Interior publication, The State of the Birds 2014 Report, addresses C. minor among those in steep decline throughout North America. The absence of records during the past 66 years suggests the Gro nesting population has disappeared, and it is not likely to be expected as a migrant within the state.

Common Pauraque (Nyctidromus albicollis) – H&W map this species for the coastal slope, and present its status in the interior as uncertain. Friedmann et al. (1950) reference it for interior Gro without details. During the early evening of 13 Apr 2003, I saw three birds at Ciudad Altamirano; and on 17 Mar 2010, a single calling bird was spotlighted at Presa Valerio Trujano, Tepecoacuilco. Rojas-Soto et al. (2009) reported one bird at Campo Morado on 18 May 2006; and eBird holds an additional eight sightings for interior Gro, including one by Chester C. Lamb on 14 May 1941 (Zirándaro). Of note, N. albicollis has been encountered locally throughout the length of the Río Mezcala system, with nearly 50 eBird reports from Morelos, the oldest being three reports by Chester C. Lamb along the Río Amacuzac (Oct 1946).

White-fronted Swift (Cypseloides storeri) – Navarro-Sigüenza et al. (1992) describe a new species of swift for Mexico based on a Gro specimen. To prompt critical observation concerning the status and distribution of Cypseloides swifts, Howell et al. (1997) describe the flight pattern of a single bird judged to be this taxon observed in Michoacán on 12 Sep 1995 amid a mixed-species flock. Howell notes in particular direct and heavy flight without frequent or abrupt changes in direction and almost hurried wingbeats. On 2 Aug 2020, I studied a bird viewed from above, in good light, believed to be C. storeri at 4,675 ft (1,425 m) elevation, 4.4 mi (7 km) southwest of Xochipala [17.7754, -99.7008]. My notes read “with eight Great Swallow-tailed Swift (Panyptila sanctihieronymi), whitish forehead, tail not forked, no long body beyond wing … flight pattern/size most like Chestnut-collared Swift (Streptoprocne rutila), head stocky/blunt, wings thick at base … tail never fanned, continual series of rapid wing beats, short/direct guides, wings never uplifted.” The similar flight descriptions, in particular the “hurried” wingbeats, support the occurrence of C. storeri in the interior slope of the northern Sierra Madre del Sur.

Green-breasted Mango (Anthracothorax prevostii) – H&W report this species as rare north to southern Gro, mapping it for the winter months along the south coast. eBird lists five verified Gro sightings for this species (Nov–Aug), all from the feeders at Refugio de Potosí, Zihuatanejo [17.5644, -101.4317]. On 19 Aug 2017, an adult male was photographed by Isaín Contreras (pers. comm.), the first such documentation for Gro.

Lucifer/Beautiful Hummingbird (Calothorax lucifer/pulcher) – H&W map these sibling species for interior Gro, stating that C. lucifer winters (Aug–Apr) to the Balsas Drainage, and C. pulcher is a seasonally common resident from interior Gro south to Oaxaca. It is believed C. lucifer migrates north as far as the U.S. border to nest, and C. pulcher is resident south of the transverse volcanic range, with both species partially sharing their winter range in Gro, Puebla, and Oaxaca. I observed Calothorax hummingbirds in Gro on seven dates, with birds believed to be winter migrants at El Mogote on 20 Jan 1998 (1M) and 24 Feb 2018 (1F), at Taxco el Viejo on 21 Jan 1998 (1M, 4F), and Puente Mezcala on 28 Jan 1998 (1M). Birds judged either migrants or residents were observed at Sasamulco on 30 Mar 2019 (1F), Puente Mezcala on 3 May 1996 (1M), and Chichihualco on 26 Mar 1996 (1M). Sierra-Morales et al. (2016) model habitat preferences for 22 species of Trochilidae (including C. lucifer) for Gro, but they add that C. pulcher could not be modeled “for lack of records of its presence within the state.” Additionally, Berns and Adams (2013) identify C. pulcher among 32 hummingbirds in the Mellisugini clade as the species with the most significant sexual dimorphism in bill size and shape. Further critical review is entreated for two main reasons. First, there’s a paucity of information concerning the nonbreeding range of C. lucifer and the complete life history for C. pulcher. Second, current field study criteria does not support the identification of nonbreeding Calothorax hummingbirds to species based on either physical location or bill size/arc.

Ridgway’s Rail (Rallus obsoletus) – Sierra-Morales et al. (2020) reports this species (photo) at Barra de Potosí on 14 Jun 2016, the first record for the state. On 3 Oct 2021, likely a different individual was videotaped near the same location by Baltazar Castro.

Russet-naped Wood-Rail (Aramides albiventris) – This species is listed by H&W on the Pacific slope from central Oaxaca south. GBIF (2020) lists an undated/unsexed specimen for the Royal Ontario Museum (ROM#654) tagged for San Geronimo, Gro. Along the sylvan edge of the marsh at El Carrizal [16.9947, -100.1991] on 27 Apr 2009, I located two birds in a forested slough. My notes read “seemingly a pair, Aramides size, red legs, red eyes, golden-brown body, with prominent grayish face, upper breast, and neck.” This sighting represents the first detailed report for this species in Gro, and it supports the earlier specimen as likely having been collected in the state.

Aztec Rail (Rallus tenuirostris) – Sierra-Morales et al. (2020) reference a report by Dickerman (1971) of a male specimen from Laguna de Tuxpan. Dickerman resided in Mexico (1961–1965) when the natural freshwater lake likely provided sufficient habitat for Rallidae. However, the GBIF (2020) lists the specimen location “not available,” the basis of record “unknown,” the term “recorded date invalid,” and the recorder “unknown.” Caution withholds imparting gravitas on the Dickerman specimen as the sole report for R. tenuirostris in the state.

Limpkin (Aramus guarauna) – H&W do not record this species for Gro. Howell (1994) details the discovery of this species in Colima, the initial awareness of a dynamic push along the Mexican west coast north to Nayarit. eBird lists 17 sightings for coastal Gro since 2005 (three with photos). Additionally, I’ve encountered this species at two locations away from the coastal plain, one bird on 18 Mar 2010 flushed from freshwater marsh at a 870 ft (265 m) elevation near Tierra Colorada [17.1620, -99.5293]; and two birds in interior northern Gro at Laguna de Tuxpan on 4 May 2016, and singles there on 14 Apr 2017 and 30 Mar 2019 (possibly the same long-staying individual). 

Killdeer (Charadrius vociferus) – H&W report this species is a common breeder south to interior northern Gro. On 27 Apr 2009, I encountered an adult in distraction behavior with two chicks on a dike within the marsh at El Carrizal [16.9986, -100.1645], this being the first observation of breeding on the Gro coast.

Collared Plover (Charadrius collaris) – H&W identify this species as an uncommon visitor (Oct–Mar) in interior Gro. At Laguna de Tuxpan on 20 Apr 2003, I encountered two pairs, with individuals and/or pairs having been observed an additional 16 times (Mar–Oct) at the two Iguala area impoundments, where abundant shoreline habitat for nesting is available. Of note, Almazán-Núñez et al. (2017) mistakenly use C. collaris photographic documentation from Ciudad Altamirano to report Wilson’s Plover (C. wilsonia) for interior Gro. Adjusting for this error (discounting C. wilsonia), as per the photograph, the details of the 28 Oct 2013 sighting of seven birds, three performing courtship displays, should be attributed to C. collaris.

Northern Jacana (Jacana spinosa) – This species is listed by H&W as extending locally inland, and “possibly resident” within the Río Mezcala drainage. On 22 Jan 1998, I observed a single adult in a wet meadow at Laguna de Tuxpan, though none have been observed during 48 subsequent visits. eBird holds six reports (Mar–Oct) near Ciudad Altamirano of up to 13 birds on 11 Apr 2020. Numbers suggest the possibility of nesting locally; however, within the interior, little suitable habitat exists as most fresh water is impounded with shorelines trampled by livestock.

Semipalmated Sandpiper (Calidris pusilla) – This species is unrecorded for Gro. On 12 Apr 2008 at Playa Paraíso Escondido, I studied an adult in alternate plumage, noting “small, straight bill, strong eyeline, rufous cap and scapular centers, black legs, rounded head, pale blackish streaking on breast.” This sighting represents the first such report for Gro, with individual birds observed by me since, at Laguna de Tres Palos, Acapulco on 6 Apr 2011, and at Coyuca de Benítez on 8 Apr 2017. During spring passage, C. pusilla is likely a rare misdirectional visitor along the Gro coast because most birds traveling the Pacific coast use the Isthmus of Tehuantepec to move northward along the Atlantic coast.

Bonaparte’s Gull (Chroicocephalus philadelphia) – This species is unrecorded for Gro, though it has a propensity to wander, being photographed seven times in Central America and once in Ecuador (eBird, photos). On 22 Apr 2000 at the yacht basin in Acapulco Bay [16.8493, -99.9032], I observed a small, buoyant gull with reddish legs and a delicate black bill at 100 ft (30 m) distance among feeding Laughing Gulls (Leucophaeus atricilla). My notes, in part, read “overall pale body, narrow black tail band, dark primary trailing edges … face pattern: extensive black ear-patch reaches partly around nape.” These details represent the first record for C. philadelphia for the state, with a second being an adult in winter plumage photographed by Amelia Arreguín (pers. comm.) at Playa Marquelia [16.5585, -98.8039] on 9 May 2021.

Heermann’s Gull (Larus heermanni) – This species is not mapped by H&W for Gro, though Miller et al. (1957) record it for the state. I observed an adult with roosting larids at Barra de Potosí on 10 Apr 2018 (Mark Hoffman, Raymond Jeffers, photo), being the first such documentation for Gro. This species appears to be the most likely vagrant gull to occur in the state, with seven eBird sightings.

Western Gull (Larus occidentalis) – H&W reference Erickson (1994), who reports the first Gro record for this species at Acapulco on 25 Jun 1992, an injured bird. On 4 May 2018 at Playa Paraíso Escondido, I observed an adult of the L. o. wymani subspecies (Aidan Kelly, photo), only the second record for Gro.

Forster’s Tern (Sterna forsteri) – H&W notes this species is an uncommon coastal transient and winter visitor the length of the Pacific coast. At Laguna de Tuxpan on 22 Jan 1998, I located two winter plumage birds resting on wooden stakes within the lake, noting “small size, black bill, red legs … black mask.” This sighting is the only such report for interior Gro.

Sandwich Tern (Thalasseus sandvicensis acuflavidus) – H&W map this species on Mexico’s west coast south from the Isthmus of Tehuantepec. They do not list it for Gro, yet note it occurs irregularly north along the Pacific to Jalisco. On 27 Jan 1998, I observed two birds fishing the surf at Pie de la Cuesta, Acapulco [16.9144, -100.0017], likely the first observation for Gro, with subsequent sightings on 27 dates the length of the Gro coast. Blancas-Calva et al. (2018) detail the first published Gro sightings (2011–2015), and eBird lists more than two dozen reports of this uncommon visitor throughout all seasons of the year. Of note, following Efe et al. (2009), the International Ornithological Congress (IOC) World Bird List treats the Old World (T. sandvicensis) and New World (T. acuflavidus) taxa as separate species, the later named Cabot’s Tern. 

Common Loon (Gavia immer) – Listed as possibly rare and irregular for Gro by H&W, this species is reported by Gómez de Silva (2002a), with three birds in basic plumage at Pie de la Cuesta, Acapulco on 8 Dec 1999, the first Gro record for this species. There are also a series of eBird reports at Barra de Potosí, 25–29 Jun 2017, including the first photograph (Nicola Souza) for this species in the state.

Juan Fernandez Petrel (Pteradroma externa) – H&W address this species as “probably uncommon” in Colima waters (Apr–Oct). Per Beven (2006), Tropical Storm Otis became a hurricane off the southern tip of the Baja peninsula at 2 a.m. on 30 Sep 2005, as the Norwegian Cruise Line vessel Norwegian Star sailed south into Mexican waters. On 3 Oct 2005, while in deep water, I studied at 150 ft (45 m) distance three birds of this species, with two passing by, below observation-deck height, as close as half the stated distance, giving excellent dorsal views in good light. This is the first specific report for P. externa in Gro waters.

Cook’s Petrel (Pterodroma cookii) – On 2 Oct 2005 during the Hurricane Otis phenomenon, this relatively small procellariiform was the most numerous petrel in Colima waters, with up to 40 individuals passing the vessel, possibly attracted by more than 100 sulids that fished the wake throughout the day. In Gro waters on 3 Oct 2005, I studied two birds two hours apart. During the first observation period, both this species and P. externa were viewed in direct comparison, allowing for clear study of the differences in size, wing loading, and plumage pattern. H&W list this species as fairly common (Mar–Oct) off Baja California Sur south to Nayarit. This sight report is the first such for Gro, and the southernmost report for P. cookii in Mexico.

Black-vented Shearwater (Puffinus opisthomelas) – H&W do not map this species for the state but state it is “rare in Gro.” An alert beached bird studied by Wesley Hochachka (pers. comm.) at Playa Diamante, Acapulco, on 1 Jan 1984, represents the first report for Gro. eBird holds more than a dozen sightings (Isaín Contreras, photo), Aug–Apr, primarily in near-shore waters, with molting birds lacking full flight capabilities during Apr (pers. obs.).

Wood Stork (Mycteria americana) – This primarily coastal species is not mapped by H&W for interior Gro. On 2 Apr 2003 while at Presa Valerio Trujano, Tepecoacuilco, I observed a single adult standing at the shore. There are five additional eBird reports (two with photos) for interior Gro, including a party of 43 birds reported by Alan Palacios (pers. comm.) on 28 May 2015 at El Cristo [17.9981, -99.7682]. It is reported as well (Aug–Mar) near Ciudad Altamirano by Almazán-Núñez et al. (2017). Of interest is a 14 May 2013 eBird report of two birds flying at 7,215 ft (2,200 m) elevation at Omilteme (alternate name Omiltemi) that may imply strong flyers, such as storks and pelicans, venture into the interior via direct flight over the Sierra Madre del Sur.

Masked Booby (Sula dactylatra) – H&W report this species nesting in western Mexico off Baja California Sur and the Revillagigedo Islands (Colima). Castillo-Guerrero et al. (2007) detail the first report of nesting in Gro with a series of observations at Los Morros de Potosí beginning on 4 Jan 2006, adding the prescient conjecture that a new colony was likely forming. Visiting the islets at least annually since 2017 (Mar–Jul), I observed as few as one adult (18 Mar 2020), and as many as 100 total birds (13 Jul 1999), with an estimated count of 40 fledglings among that number. 

Red-footed Booby (Sula sula) – H&W broadly address this species in western Mexico as a fairly common offshore visitor from Baja California Sur to Central America. eBird lists eight reports, including an immature at sea [16.6008, -100.0591] on 4 Mar 2020 by Noam Markus (pers. comm., photo), the first such documentation for Gro.

American White Pelican (Pelecanus erythrorhynchos) – This species is not mapped for interior Gro by H&W, though stated to be an uncommon winter visitor to inland Mexico south of the transverse volcanic range. On 9 May 2002, I observed two birds resting on the water of Laguna de Tuxpan. Three other records for inland Gro come from Ciudad Altamirano with a report by Almazán-Núñez et al. (2017) of large parties on 16 Oct 2011 (63) and 6 Oct 2012 (28), and an eBird report of nine birds on 17 Feb 2019.

Brown Pelican (Pelecanus occidentalis) – This coastal species has been found to wander deep into the Mexican interior, with personal sightings of single immatures at Laguna de Chignahuapan/Almoloya, México, on 19 Apr 2008 and 19 Apr 2018, and at Laguna el Rodeo, Morelos, on 13 Mar 1997. On 1 Apr 2003, I watched three birds at Presa Valerio Trujano, two adults and one juvenile, resting together at the shoreline, and on 27 Feb. 2016 at Laguna de Tuxpan, I observed a juvenile (brown neck, dull bill) both in flight and at rest on the water. These are the sole reports for P. occidentalis in the interior of Gro.

Tricolored Heron (Egretta tricolor) – H&W list this species as rare and irregular throughout the Mexican interior but do not map it for interior Gro. I’ve encountered this species in northern interior Gro during all seasons of the year; it being first noted at Laguna de Tuxpan on 22 Jan 1998 with two birds, and at nearby Presa Valerio Trujano with a single bird on 21 Apr 2003. Up to four individuals have been recorded at one or both of the Iguala area impoundments during 32 of 45 subsequent visits. On 21 Mar 2020, I observed a single bird along the river edge at Mezcala (pueblo) [17.9356, -99.5842]. This species is an expected visitor to permanent freshwater habitat throughout the state’s interior.

King Vulture (Sarcoramphus papa) – H&W list this species as rare on the Pacific slope south from Gro. I observed an adult on 16 Mar 2004 while at 3,150 ft (960 m) elevation on the Atoyac Road near San Vicente de Benítez [17.3180, -100.2645]. I have since recorded 22 additional sightings on 18 dates, with six juveniles among that total. All observations have taken place between 2,800 ft (850 m) and 4,425 ft (1,350 m) elevation along the massive Arroyo Grande, with all birds being seen soaring overhead. The Gro population is best understood to be small, viable, and wholly isolated within the Sierra de Atoyac, surviving 475 mi (760 km) north of the nearest extant population in the Sierra Madre de Chiapas. 

Lesser Yellow-headed Vulture (Cathartes burrovianus) – H&W map this species north to central Oaxaca along the Pacific coast. On 9 Oct 2003, I observed eight birds, five adults and three dark-headed juveniles, resting together on low palms and fence posts near El Carrizal [16.9693, -100.1550], representing the first report for this species in Gro. I observed single adult birds flying low over the same marsh on 26 Mar 2007 and 14 Apr 2008. Since, this species has been located on an additional 11 dates, and it appears today to be an uncommon resident within a narrow 20-mi (35-km) coastal wetland corridor along Highway 200 between Coyuca de Benítez and Laguna Mitla.

White-tailed Kite (Elanus leucurus) – H&W map this species for Gro along the southeastern coastal corridor, where eBird lists more than 20 verified reports. In interior Gro, I observed single adults in hovering flight on 20 Aug 1994 and 20 Jan 1998 at El Mogote (18.7290, -99.6083], and a perched adult at Laguna de Tuxpan on 3 May 1995. Almazán-Núñez et al. (2017) report it being “frequently” observed near Ciudad Altamirano during a two-year bird survey. Within the Río Mezcala system this species now appears to be locally uncommon, favoring open grassland habitats affected by seasonal agriculture.

Double-toothed Kite (Harpagus bidentatus) – This species is listed by H&W for the mid-to-upper elevations of the northern Sierra Madre del Sur. On 14 Apr 2017, I encountered an adult bird on the Tetipac Road, Taxco in the Sierra Norte de Guerrero. On 23 Feb 2018, two birds were engaged in nest building, and on 12 Apr 2018, a bird was observed on the nest (18.5956, -99.6210]. The following year (29 Mar 2019) the nest was abandoned, and H. bidentatus was not detected. During the past two decades this species managed stepping-stone advances through the major west Mexican ranges north to the Sierra Madre Occidental, Sinaloa (Mark Stackhouse, pers. comm.). However, the series of observations over two years from the Sierra Norte de Guerrero represent the first awareness of this species in interior Mexico north of the isthmus.

Cooper’s Hawk (Accipiter cooperii) – H&W map this species resident south to Nayarit and Jalisco, and they write “possibly” to Gro. I observed single birds near Corral de Bravo, at an 8,900-ft (2,715-m) elevation, along the interior slope of the Sierra Madre del Sur [17.6238, -99.8475], on 7 May 1996 (M), 2 Aug 2000, and 8 Jun 2008 (M). Nick Lethaby (pers. comm.) observed this species at the same location on 29 Jul 2012. The series of sightings (May–Aug) suggest A. cooperii is an uncommon resident within the pine-oak summits of the northern Sierra Madre del Sur. Additionally, I studied an adult female with a full crop in flight above Taxco at an 6,075-ft (1,850-m) elevation on 27 Jun 2020, likely a summering individual in the Sierra Norte de Guerrero.

Northern Goshawk (Accipiter gentilis) – H&W map this species “resident” in the northern Sierra Madre del Sur, erroneously referencing Blake (1950), who states it “winters casually” to Gro. Confusion may result from the English name “Mexican Goshawk” used by W. B. Davis (1944) for the then-attributed subspecies of Gray Hawk (Asturina nitida plagiata) (since assumed into the monotypic Buteo plagiatus). Regardless of ascribed status or understood taxon, there are no specific Gro records for this Accipiter, and as such it should not be considered resident, and probably not included among the avifauna of Gro.

Mississippi Kite (Ictinia mississippiensis) – This species migrates north each spring along the Caribbean coastal plain, though during fall passage I have noted a greater propensity for it to wander with Sep–Oct sightings for the states of Nayarit, México, and Quintana Roo. On 25 Apr 2000 while at Coyuca de Benítez, I observed a kite-shaped bird overhead flying at migration altitude. Favorable late-morning light allowed for viewing the “pale head, soft gray body, dark gray underwing primaries, … straight-edged dark tail.” This sighting represents the first such report for I. mississippiensis in Gro. Of note, I recorded a second summer (dark band at tip of tail) bird at Singayta, Nayarit on 6 Jun 2019. Furthermore there are two Jun–Jul eBird sightings in the Cape District of Baja California Sur (both with photos), raising the question as to whether these individuals overshot their westward movement after passing north along the Caribbean coast—or some individuals arrive in the northwestern Mexican states via the Pacific coast.

Black-collared Hawk (Busarellus nigricollis) – H&W map this species as resident for Gro noting it “rare and local on the Pacific slope from Sinaloa south,” presumably relying upon Blake (1950) and Friedmann et al. (1950), both of whom list this species without details for only two of the west Mexican states (Sinaloa and Gro). There are nine eBird sightings from Nayarit and Colima since 1980 (none with photos) that may represent vagrants, but more likely these should be understood as equivocal. As there are no specific Gro records, and the nearest resident population in Pacific Mexico is 500 mi (800 km) south in Chiapas (Reserva de la Biosfera la Encrucijada), prudence prevails in not listing this species among the resident avifauna of the state.

Snail Kite (Rostrhamus sociabilis) – H&W do not list this species for Gro. Hernández-Vázquez et al. (2013) detail 2010–2011 surveys in Jalisco and Colima that expand the then-published distribution of this species 560 mi (900 km) north along the west Mexican coast. eBird lists 10 records (three with photos) from the wetlands of Parque Ecológico Aztlán, Ixtapa, where two birds seen on 9 Mar 2011 by Pete Hoeger (pers. comm.) represent the first report for Gro. On 1 Jul 2020, I studied an adult male in flight at this location, where this species appears to be an annual (Jul–Mar at least) visitor dependent upon the summer rains that fill the seasonal wetlands.

Harris’s Hawk (Parabuteo unicinctus) – H&W do not map this species for the state’s Pacific slope. Gómez de Silva (1998) reports an adult near Acapulco on 9 Aug 1991, though he allows for the possibility of an escapee. On 26 Apr 1998, I studied an adult with no jesses or obvious signs of human influence at Coyuca de Benítez, with two perched birds together at the same location on 26 Mar 2004. It appears this species wanders north on occasion from the resident population in the isthmus, taking advantage of the relentless burning along the narrow coastal plain.

White-tailed Hawk (Geranoaetus albicaudatus) – This species is not mapped for Gro by H&W, though Friedmann et al. (1950) report it as a local Gro resident in “open, grassy, or mesquite country.” I observed individual adults at Tierra Colorada on 7 Oct 2003 and 31 Mar 2005 [17.1879, -99.5456], at El Mogote on 24 Feb 2018, and at Sasamulco on 30 Mar 2019. There are 10 eBird reports for this species from either interior Gro or along the Chilpancingo-Tierra Colorada corridor, including a report by Chester C. Lamb at Mezcala (pueblo) on 8 Feb 1955. Sight reports from eBird along the northwest coast, and in the Sierra Madre del Sur north of the arid Río Papagayo drainage, lack photographic documentation and are best understood to be equivocal, as Short-tailed Hawk (Buteo brachyurus) is common throughout, and light phase birds exacerbate confusion.

Black-and-white Owl (Strix nigrolineata) – There were no records for this species in Gro, though it has been reported infrequently in Nayarit since 2013 (Mark Stackhouse, pers. comm.). On 6 Mar 2021, Daniel Garza Tobón, Angel Montaño, and André Sebastián Fuentes Vega photographed an individual on the Atoyac Road near Nueva Dehli [17.4221, -100.1944], the first documented report for this species in Gro.

Ringed Kingfisher (Megaceryle torquata) – This species is not mapped by H&W for the Gro interior. eBird lists more than a dozen recent (2016–2020) reports within the four-state area (Gro, Michoacán, México, and Puebla) encompassed by the tributaries of the Río Mezcala. The cluster of recent sightings (Jan–Oct) within the Río Mezcala system support an understanding that this species is colonizing the interior.

Laughing Falcon (Herpetotheres cachinnans) – H&W map this species for coastal Gro, noting it is uncommon on the Pacific slope south from Sinaloa. On 28 Apr 1998, I located a calling bird near Chilpancingo [17.6003, -99.5506], and on 27 Apr 2000, an individual was encountered north of the Río Mezcala near San Juan Tetelcingo [17.9676, -99.5409]. eBird also records a bird near Mezcala (pueblo) by Chester C. Lamb (28 Jun 1947).

Aplomado Falcon (Falco femoralis) – This species is unrecorded for Gro. On 18 Feb 2018, I observed a pair (Brendan Ryan, photo) 3.7 mi (6 km) southeast of Cuajinicuilapa [16.4474, -98.3514], for the first Gro record. Sandy Astrid Medina Valdivia (pers. comm., photo) studied an adult bird on 28 Jul 2018 at Carrizal de Cinta Larga [17.1760, -100.7333], for the northernmost record along the Pacific coast. This species appears to be expanding northward along the Pacific coastal strip as acceptable grassland habitat replaces arid subtropical forest in the constant cycle of burning, short-term farming, and abandonment.

Monk Parakeet (Myiopsitta monachus) – eBird monitors this species on the expectation that escaped birds will establish within Mexico. The initial awareness of this species in Gro comes from a report by Almazán-Núñez et al. (2015) of seven birds in an African Tulip (Spathodea campanulata) at Chilpancingo on 6 May 2014. eBird lists 10 sightings (two with photos) involving between two and five birds from urban parks in both Chilpancingo and Acapulco.

Military Macaw (Ara militaris) – H&W list this species for the Pacific slope of northwest Gro but do not map it for the interior. eBird lists 10 reports for the Río Mezcala basin, including sightings by Chester C. Lamb near Mezcala (pueblo) on 8 Jun 1947 and 8 Feb 1955. A series of Feb–Apr sightings between 2017 and 2019 of up to 39 birds (Alan Palacios, pers. comm.) at Papalutla [18.0220, -98.9051], are of interest both for the high number of birds and for the upriver location near the Puebla border.

Ivory-billed Woodcreeper (Xiphorhynchus flavigaster) – This species is unreported by H&W for interior Mexico north of the isthmus. I observed single birds near Xochipala on 28 FEB 2016 and at RMO Tiuribe, Iguala, on 9 Jul 2019. eBird lists nearly 20 reports for interior Gro, and another 20 for the tri-state border region that encompasses México, Morelos, and Puebla. The paucity of reports preceding the current decade indicates a recent, dynamic push into the interior throughout the Río Mezcala tributary system.

White-eyed Vireo (Vireo griseus) – This species is unrecorded for Gro. On 21 Mar 1996 at Coyuca de Benítez (Colonia el Salto) [16.9977, -100.0671]. I studied an adult at 15 ft (5 m) distance in a Tamarind (T. indica) with a small party of passerines that approached in response to pygmy-owl toots. Notes read “white-eye, bright yellow lores and sides, two vivid wingbars… similar to Pacific Mangrove Vireo (V. pallens) … yellow more obvious and extensive.” This sighting represents the first report for V. griseus in Gro.

Yellow-throated Vireo (Vireo flavifrons) – H&W map this species as a winter visitor north on the west coast to central Oaxaca. On 30 Mar 2001 I located an individual of this species on the Atoyac Road at 2,790 ft (850 m) elevation near Río Santiago, [17.2785, -100.2942]. Notes include “bulk of Solitary Vireo (V. solitarius), eye ring, lores, and throat bright yellow, nape, crown, and face greenish yellow, two distinct wingbars”. This sighting represents the first Gro record for this species. On 8 Dec 2018 I observed an individual on the Atoyac Road at 3,710 ft (1,130 m) below Paraíso [17.3272, -100.2447], and eBird holds three sightings, Feb though early Apr, including two (pers. comm.) at sea level on the northwest Gro coast by Nick Lethaby on 2 Apr 2015 and Amy Worell on 16 Mar 2020.

Sinaloa Martin (Progne sinaloae) – Lethaby and King (2010) summarize the current status of this species with the sobering observation that the complete lack of recent records of sizable breeding colonies suggests a significant decline in the breeding population. On 19 Jun 2008 at 6,070 ft (1,850 m) elevation, I studied a pair dipping at a small reservoir on the Tetipac Road (18.5671, -99.6205]. This sighting represents the first record of Gro. On 14 Apr 2011, shortly before sunset, three males were observed feeding over Taxco. During subsequent visits, on 11 dates over a seven-year (2014–2020) period between Mar 31st and Jun 28th, one to four birds were observed in this fashion. At Laguna de Tuxpan on 17 Mar 2010 I studied a female in flight at 100 ft (30 m) distance, and on 28 Apr 2018 and 9 Jul 2019 individuals were observed “dipping” there late in the day. A partial awareness of the migration route of P. sinaloae may be deduced through eBird passage reports with three birds on 31 Mar 2019 near the Gro/Oaxaca border at Xicuhuetztlan (18.0263, -98.8653], and sightings by Paul Lewis (pers. comm.) on four dates between 29 Feb 2016 (photo 1M), and 20 Jul 2015 (15 birds) at Paso Ancho, Mich (19.4974, -100.9175]. Birds nesting in Jalisco, Nayarit, and Sinaloa apparently traverse the southern highlands via an interior route that includes western Oaxaca (Xicuhuetztlan), northern Gro (Taxco/Laguna de Tuxpan), and southeast Michoacán (Paso Ancho), altogether avoiding the Mexican west coast between the isthmus and the Transvolcanic Belt ranges.

Purple Martin (Progne subis) – H&W states this species is an uncommon transient on the Pacific slope from Sonora south through Mexico. On 24 Apr 2010, I observed an adult male at 30 ft (10 m) distance with several hundred Gray-breasted Martin (P. chalybea) at a night roost in city center Atoyac de Alvarez [17.2133, -100.4333]. This sighting is the only specific report for this species in Gro. eBird contains only two photographic reports for this species in western Mexico south of their known breeding range, amazingly both in winter: individual males on 17 Feb 2005 (Colima) and 17 Jan 2018 (Nayarit). The lack of west coast sightings during migration may infer P. s. hesperia, the desert race breeding in Baja California Sur and Sonora, transits the length of northern Mexico while passing along the Caribbean slope during migration, thus avoiding central west Mexico, and as such P. subis should be understood to be very rare in Gro.

Barn Swallow (Hirundo rustica) – H&W list this species as a common breeder south to central Mexico, though I’ve been found it to nest as far south to San Cristobal de las Casas, Chiapas (Gómez de Silva, H. 2002b). In interior Gro I have repeatedly observed this species attending nests at four locations. The dates for first sightings for each location are El Mogote (24 Apr 1999), Taxco (4 May 1995), Iguala (30 Apr 1998), and Xochipala (26 Apr 2000). H. rustica should be understood to nest throughout the Río Mezcala drainage, favoring locations near human habitation.

Cave Swallow (Petrochelidon fulva) – There are no records for this species in Gro, though H&W acknowledge the further need to study movements. Kirchman et al. (2000) suggest extensive seasonal movements of the northernmost P. f. pallida subspecies based on birds found roosting communally, 1 Nov through 10 Dec, at two locations on the El Salvador Pacific coast. During the morning of 18 Mar 2020 at Barra de Potosí, I studied a feeding flock of swallows as close as 65 ft (20 m) that included Northern Rough-winged Swallow (Stelgidopteryx serripennis) and Barn Swallow, with fewer than 10 individuals each, while the majority of the swallows, at least 40 birds, showed tan throats and rumps (Amy Worell, photo). Careful viewing found no Cliff Swallow (P. pyrrhonota) among the party. This report represents the first record for Cave Swallow in Gro. To encourage critical observation of migrating Petrochelidon swallows in western Mexico I add additional sightings of P. fulva from the Pacific states with feeding flocks in Chiapas at Puerto Arista on 16 Feb 2013 (30+ birds), and Mapastepec on 4 Feb 2018 (20+ birds), and a nesting colony at Bahia Kino, Sonora on 10 Jun 2013 (50+ birds using the interior of an abandoned stone building).

Pygmy Nuthatch (Sitta pygmaea) – This species is unrecorded for Gro. On 17Apr 2017, at 6,430 ft (1,960 m) elevation on the Filo de Caballo road shortly below Campo de Aviación [17.6649, -99.8125] on the arid east slope of the northern Sierra Madre del Sur, I observed two birds in pine-oak woods. Following a hard, cold, hailstorm, the noisy, twittering birds moved together from tree to tree as part of a sizable mixed-species flock. This sighting represents the first record for S. pygmaea in Gro, though the earlier discovery of a isolated population in the Sierra Madre de Oaxaca by G. Alcántara-Salinas et al. (2015) allows for the Gro sighting, only the second south of the transverse volcanic range, to be interrupted as expected.

Bewick’s Wren (Thryomanes bewickii) – H&W do not include this species for Gro. Miller et al. (1957) lists the T. b. murinus subspecies as common in the adjacent Morelos plateau. J. E. Morales-Perez and A. G. Navarro S. (1991) report T. b. murinus from study sites in the Sierra Norte de Guerrero, the first report for this species in Gro. I encountered two birds in a Taxco hotel garden (18.5445, -99.6022] on 19 Aug 1994, with others there on 1 May 1998, 2 May 2014, and 18 Apr 2018, and on the arid south-facing slope of the lower Tetipac Road (18.5693, -99.6206], he found individuals on 18 Apr 1996 and 29 Mar 2007. This species is an uncommon resident above 4,900 ft (1,500 m) elevation in the Taxco vicinity. Reports away from the north central interior presented by P. Sierra-Morales et al. (2020) require confirmation.

Gray-barred Wren (Campylorhynchus megalopterus) – H&W do not list this species for Gro. J. E. Morales-Perez and A. G. Navarro S. (1991) report it from the Sierra Norte de Guerrero, the first such notice of this species for the state. On 19 Aug 1994, I located a family group on the Tetipac Road (18.5955, -99.6247]. This species has been encountered in small parties at the same location on 22 subsequent dates, including twice at active nest sites (1 May 1998 and 2 May 2014).

Spotted Wren (Campylorhynchus gularis) – H&W address this species as “possible” for extreme northern Gro. J. E. Morales-Perez and A. G. Navarro S. (1991) list it for the Sierra Norte de Guerrero based on a male specimen reportedly taken along the Ixcateopan-Taxco road (FC-UNAM #456) GBIF (2020). A record search for this specimen lists two different collection dates for the same event (12 Jun 1986 and 26 Jul 1986). A second museum specimen (BMNH-U of M #3673) GBIF (2020) reportedly collected by R. W. Dickerman on 23 Oct 1964 near Omilteme is hampered by a dubious location, as the broadly studied Sierra Madre del Sur has no other reports of this species. I failed to detect this species during 48 days of fieldwork in the Sierra Norte de Guerrero, and sections of western Morelos and southwest México, though two wrens of the genus Campylorhynchus were found to occur, Gray-barred Wren in the upper elevation humid woodlands of the Sierra Norte, and Boucard’s Wren (C. jocosus) in the mid-elevation Juniperus (sp) zone. R. C. Almazán-Núñez (2009) did not include C. gularis among the 101 species recorded during research in the northwest Sierra Norte. As such, with the nearest known population of this sedentary species on the México/Michoacán border, 60 mi (100 km) north of Gro, awaiting unassailable confirmation of its presence in the state seems the appropriate position.

Cabanis’s Wren (Cantorchilus modestus) – Greg Homel (pers. comm., photo) located an individual of this species on the Atoyac Road near Paraíso on 5 Jun 2016, the first Gro record, and the only known location for this species north of the isthmus. I observed pairs of this species near Nueva Delhi at 5,790 ft (1,765 m) on 5 May 2018 and on 19 Mar 2020 [17.4904, -100.2025], and a single bird above Paraíso at 3,615 ft (1,100 m) on 12 Jul 2019 [17.3681, -100.2028]. Competition with Happy Wren (Pheugopedius felix) and Sinaloa Wren (Thryophilus sinaloa), both common to 1,000 m elevation, may restrict C. modestus to an elevation above that preferred by other Troglodytidae. Until recently, only one seasonal road, deeply rutted and often impassable, accessed the Sierra Madre de Atoyac above the coffee plantation zone, thus allowing C. modestus to go undetected during more than 25 years of active scientific research.

Aztec Thrush (Ridgwayia pinicola) – This species is mapped by H&W as resident in the northern Sierra Madre del Sur, noting that it may withdraw (Oct–Feb?) from northwest Mexico. I observed between 3 and 12 birds in Gro on seven dates (Jan–Apr) with sightings best judged sporadic and unpredictable. Of interest is a series of observations over a four-day period, beginning on 30 Mar 2004 with nine birds at 7,625 ft (2,325 m) elevation above Corral de Bravo [17.5823, -99.8470] feeding in a large Monkey’s Hand (Chiranthodendron pentadactylon) tree. The following day in cold, sleeting rain more than 200 birds were present in the same area, including 50 birds blanketing the flowering tree. Two days later, on 2 Apr 2004, with the stormy weather unabated, a party of 40 birds was discovered on the Tetipac Road near Taxco in the Sierra Norte de Guerrero (18.5956, -99.6210]. Both the large number of birds traveling together, and the sole Gro report away from the Sierra Madre del Sur support the H&W conjecture that birds “withdraw” south as circumstances require.

Red-flanked Bluetail (Tarsiger cyanurus) – I encountered a probable female or first-year male (William Mertz, photo) on 25 Feb 2021 at Troncones [17.8174, -101.7192]. Per Carmody et al. (2021) this represents the first occurrence of this species for Mexico, and for the Neotropics.

Gray Catbird (Dumetella carolinensis) – P. Sierra-Morales et al. (2020) report individuals of this species at Barra de Potosí on 3 Dec 2015 and 14 Dec 2016, the only two records for the state.

Ocellated Thrasher (Toxostoma ocellatum) – This species is not listed for Gro by H&W, though J. E. Morales-Pérez and A. G. Navarro S. (1991) record it for the Sierra Norte de Guerrero with two preserved specimens from Los Jarillos on 11 Sep 1986 (FC-UNAM #5589, #5590) GBIF (2020), where local residents are known to keep this vocal species in cages (pers. obs. 1994–1999). I failed to detect it during 48 days of fieldwork in the tri-state border area (Gro, Morelos, México), and R. C. Almazán-Núñez (2009) does not include T. ocellatum among the 101 species recorded during studies within the Sierra Norte. The lack of sightings suggests that T. ocellatum is not currently part of the Gro avifauna, as this species suffers greatly from human disturbance and may be extirpated from Gro, or the specimens may not result from naturally occurring birds.

Pine Siskin (Spinus pinus) – Though this species is resident in the neighboring states of México and Morelos, there are no published records for Gro. On 1 Mar 2021 André Sebastián Fuentes Vega photographed a group of three birds near Chilpancingo at Ejido el Calvario [17.4658, -99.5142], the first such documentation for Gro. Two additional eBird reports (one with photos) followed during the spring of 2021.

Lesser Goldfinch (Spinus psaltria) – H&W map this species as resident for most of Gro, but do not include it for the coastal plain. I have recorded this species numerous times on the Gro coast beginning with two birds on the lower Atoyac Road on 29 Apr 1995. eBird lists more than 100 verified sightings (three with photos) throughout the Gro Pacific slope, with the majority of reports coming from the northwest coast.

Rosy Thrush-tanager (Rhodinocichla rosea) – H&W report this species as a fairly common resident on the Pacific slope from Sinaloa to Michoacán. A. Townsend Peterson et al. (2004) document “an unreported population near Laguna de Tres Palos, Acapulco,” using 19 Gro specimens (Delaware Museum of Natural History [15], Occidental College Moore Laboratory of Zoology [3], and U. S. National Museum of Natural History [1]). On 22 Apr 2010, at Lomas de Chapultepec [16.6949, -99.6177], I studied at length a pair, first heard, then seen, of “female tossing leaves, male twice singing from perch.” On 7 Apr 2011, at the same location, following tape playback, a pair was seen in flight, as both the male and female crossed the track. The habitat was severely altered sometime before the following visit with no birds detected (23 Apr 2012).

Black-chested Sparrow (Peucaea humeralis) – In Gro, this species is primarily found within the interior, though it reaches the Pacific coast in western Oaxaca (H&W). I located this species on three dates at the edge of thorn forest on the central Gro coast near El Papayo [17.0212, -100.2411] on 26 Apr 1998 (two birds), 1 Apr 2001 (three birds), and 13 Apr 2008 (one bird) before their displacement as result of burning for seasonal farming. On 22 May 2010 two birds were studied on the Atoyac Road at 2,870 ft (875 m) elevation above El Rincón de las Parotas [17.2488, -100.3753]. These sightings, plus six eBird reports along the Pacific slope support the rare and local residency of P. humeralis north at least to central Gro.

Green-striped Brushfinch (Arremon virenticeps) – This species is not listed by H&W for Gro. J. E. Morales-Pérez and A. G. Navarro S. (1991) record it from the Sierra Norte de Guerrero, the first report for the state. On 19 Aug 1994, I located a pair on the Tetipac Road, Taxco [18.5955, -99.6247], with additional sightings during 38 subsequent dates (using tape playback). The Sierra Norte de Guerrero is the southernmost location for which this species is known to be resident.

White-throated Sparrow (Zonotrichia albicollis) – This species is an uncommon winter visitor to northern Mexico. On 29 Mar 2019 near Omilteme [17.5517, -99.7012] at 7,800 ft (2,380 m) elevation, I studied an adult bird (John Hopkins, photo) on a corn stalk at the edge of a harvested field. This sighting is the first record for this species in Gro, and one of very few reports from south of the transverse volcanic range in Mexico.

Canyon Towhee (Melozone fusca) – H&W do not record this species for Gro, though Miller et al. (1957) record it at Taxco (laying, Jul 25), and J. E. Morales-Pérez and A. G. Navarro S. (1991) report it from the Sierra Norte de Guerrero. Since first being observed on the Tetipac Road on 4 May 1995 (one bird), and in Taxco on 24 Mar 1996 (two birds,) I have encountered M. fusca with regularity in suitable habitat above 6,000 ft (1,830 m) elevation in the Taxco area.

White-throated Towhee (Melozone albicollis) – H&W note this species as a common resident in the interior from eastern Gro to central Oaxaca. On 13 May 2013 Paul van Els saw a bird at 7,800 ft (2,380 m) elevation at Omilteme [17.5561m -99.6853], the first observation of this species for the northern Sierra Madre del Sur (north of Chilpancingo). I located this species on at Amojileca [17.5695, -99.5737] on 30 Apr 2018 (one bird), and at Omilteme on 29 Mar 2019 (two birds), 10 Jul 2019 (one bird), and 30 Jun 2020 (one bird) where it favors close proximity with human habitation.

Spotted Towhee (Pipilo maculatus) – H&W do not map this species for the state though J. E. Morales-Pérez and A. G. Navarro S. (1991) record it from the Sierra Norte de Guerrero, the first report for Gro. On 19 Aug 1994 I located a pair at 7,100 ft (2,165 m) elevation on the Tetipac Road, Taxco (18.5955, -99.6247], with additional sightings on 33 subsequent dates. The Sierra Norte de Guerrero is a geologically isolated unit of the transverse volcanic range with a similar ecology to the Sierra del Ajusco-Chichinauhtzin (México, Morelos, and Ciudad de México) with average summits ca. 8,860 ft (2,700 m). The presence of Grey-barred Wren, Green-striped Brushfinch, and P. maculatus in both ranges, and nowhere else in Gro, attest to the antecedent connection of the two ranges. With some species, such as Transvolcanic Jay (Aphelocoma ultramarina) not present in Gro, it can be deduced that the arid steep sided barrancas of the Río Chontalcoatlán (tributary of the Río Mezcala) at only 4,900 ft (1,500 m) elevation have historically functioned as an effective barrier between the two mountain ranges. Uncertainty regarding the full expanse of time that the “olive-backed” population in Gro has been genetically isolated from P. m. macronyx of the Sierra del Ajusco-Chichinauhtzin invites molecular study of the outlier population to further resource continued interpretation of the Pipilo complex.

Orchard Oriole (Icterus spurius fuertesi) – H&W note that Icterus spurius fuertesi, Ochre Oriole, winters from the Balsas basin south to Chiapas on the Pacific slope, and Baker et al. (2003) state that I. s. fuertesi breeds in Tamaulipas and Veracruz, and migrates (if at all) only a short distance to the coast of Gro and Chiapas. Away from breeding sites only the adult males of this taxon can be identified to form. I observed birds at Laguna de Tuxpan on 28 Jan 1998, at Coyuca de Benítez on 26 Mar 2007, and on the Atoyac Road at 3,115 ft (950 m) elevation on 19 Feb 2015, with each sighting involving a single male, apart for other icterids, feeding in a flowering tree. Following Baker et al. (2003), the IOC treats the Mexican endemic race, I. spurius fuertesi, as a separate species (Ochre Oriole) from the more numerous and widespread I. s. spurius (Orchard Oriole).

Brewer’s Blackbird (Euphagus cyanocephalus) – There are no records for this species in Gro though it is encountered with regularity during winter in nearby Michoacán and México. At Presa Valerio Trujano on 28 Mar 2007 I located a female (Jim Livaudais, photo) on a putting green of an undeveloped golf course. This report represents the first record for this species in Gro.

Worm-eating Warbler (Helmitheros vermivorum) – P. Sierra-Morales et al. (2020) report this species (photo) at Barra de Potosí on 31 Oct 2017, the only record for the state.

Prothonotary Warbler (Protonotaria citrea) – H&W do not list this species for Gro. The author observed an individual (Jacqui Probst, photo) at 8,900 ft (2,710 m) elevation near Corral de Bravo [17.6035, -99.8341] on 31 March 2004. It was seen feeding on the ground in a meadow with Yellow-rumped (Setophaga coronata) and Townsend’s (S. townsendi) warblers, with the birds noticeably distressed by a storm manifesting unseasonal sleet and bitter cold. This report documents both the first record for this species in Gro, and a significant high elevation occurrence. A second Gro record for this species comes from typical coastal mangrove habitat at Tres Palos, Acapulco (Bob Freidrichs, photo) on 9 Nov 2017.

Kentucky Warbler (Geothlypis formosa) – There are no published records for this species in Gro. On 22 Mar 2011 in the coffee zone at 4,430 ft (1,350 m) elevation on the Atoyac Road near Paraíso [17.3971, -100.1992] Matt Brady, Ryan Shaw, and Charlie Wright (pers. comm.) studied a “SY female…distinctive helmeted black cap, and typical ‘KEWA’ call”. This eBird sight report from experienced observers is the only record for Gro. The lack of other reports is more likely the result of relatively few Gro observers, as the heavily studied coffee fincas of Nayarit have produced more than 50 winter sightings of this species, three with photos (eBird).

Hooded Warbler (Setophaga citrina) – R. Carlos Almazán-Núñez et al. (2017) reports this species at Barra de Potosí with the observation of a male on 13 Nov 2008, and a second individual (specimen) on 14 Nov 2010. These are the only records for this species in Gro.

Northern Parula (Setophaga americana) – H&W do not list this species for Gro. On 14 Dec 2017 an individual was photographed as Barra de Potosí (Gustavo Contreras Cuevas, pers. comm.) for the first state record. I have observed single males on three March dates, once along the coast at Ixtapa on 23 Mar 2019, and twice in the interior at Presa Valerio Trujano on 30 Mar 2019 and on 21 Mar 2020.

Magnolia Warbler (Setophaga magnolia) – H&W list this species as uncommon on the Pacific slope (winter) from Nayarit south to Central America, and eBird lists more than a dozen coastal Gro sightings. In interior Gro, I have recorded this species twice with a full plumage male at Laguna de Tuxpan on 29 Mar 2007, and a female at nearby Presa Valerio Trujano on 2 Mar 2020.

Yellow Warbler (Setophaga petechia rhizophorae) – H&W map the local subspecies S. p. rhizophorae for the west coast south from Baja California Sur and Sonora, but report as “uncertain” its status along the Gro coast. On 27 Jan 1998, I observed up to 10 individuals in extensive mangrove habitat at Pie de la Cuesta, and on 4 Oct 2005 a male was studied in mangroves at Punta Diamonte, Acapulco, the latter area having been destroyed since. At Barra de Potosí on 5 Dec 2017 Isaín Contreras located an immature male (pers. comm., photo), the first such documentation for the state. Following Browning et al. (1994), the IOC regards the taxon (S. petechia rhizophorae) as a separate species, Mangrove Warbler, from the more widespread American Yellow Warbler (S. p. aestiva).

Chestnut-sided Warbler (Setophaga pensylvanica) – There are no published reports for this species in Gro. On 25 Jan 1998, I observed a winter plumage adult with “chestnut flanks, upperparts yellowish lime, and cocked tail” on the Atoyac Road above Vicente de Benítez [17.3271, -100.2447] for the first Gro record. On 1 Apr 2018, I located a bright male (black face mask) on the Atoyac Road above Río Santiago [17.2708, -100.3003]. These sightings represent the only reports for this species in Gro.

Blackpoll Warbler (Setophaga striata) – This species is not listed for Gro by H&W, but R. C. Almazán-Núñez et al. (2009) report it for the state. The sight report is most likely equivocal based on elevation (at 8,020 ft [2,640 m], as extralimital records in Mexico come from sea level), season (March, spring passage occurs during mid-to-late May), number (two, vagrant warblers in general occur as individuals), and description (non-breeding plumage, by Mar birds show pre-breeding molt). Lacking additional reports, caution suggests that S. striata not be included among the state’s avifauna.

Palm Warbler (Setophaga palmarum) – H&W note that this species is a vagrant (Oct–Apr) on the Pacific slope from Baja California Sur south to Oaxaca. Hubbard (1972) reports a female collected in Iguala on 11/28/48 (Delaware Museum of Natural History [8133]). I studied a western form bird near Tres Palos, Acapulco [16.7800, -99.7920] on 15 Apr 2003, and a likely returning individual the following spring on 15 Mar 2004. In interior Gro, on 18 Apr 2010 at Presa Valerio Trujano, I studied a breeding plumage individual, “fresh bird, brown crown, eye-stripe, yellow throat and vent…strongly marked”. eBird lists five sightings for coastal Gro, including one at Barra de Potosí on 17 Dec 2017 by Nick Lethaby (pers. comm., photo). In Gro, S. palmaruma shows a preference for freshwater edges.

Yellow-rumped Warbler (S. c. coronata) – H&W list S. c. coronata (Myrtle Warbler) as uncommon on the Pacific slope from Baja California Sur to Central America, but they do not map it for Gro where there are no specific reports. The IOC regards this taxon as a separate species from Audubon’s Warbler (S. c. auduboni), and following Brelsford, A., and Irwin (2009), this taxon is treated as a separate species. On 21 Mar 2020, I studied a winter plumage bird on Presa Valerio Trujano, noting “diffuse dark streaks on white breast, clear white throat, noticeable yellow rump, clear blackish streaks on soft gray back, two white wingbars. An overall colorless bird, the whites being brighter than the relatively dull grays”. This report serves to recognize the Myrtle Warbler form for the Gro.

Blue Seedeater (Amaurospiza concolor relicta) – The A. c. relicta (Slate-blue Seedeater) taxon is listed by H&W for the highlands of southwest Mexico, including the Sierra Madre del Sur. Away from known localities in the Sierra de Atoyac I observed this form at four locations in the Río Mezcala basin, first dates for each location are near Chilpancingo [17.6231, -99.5798] at 5,085 ft (1,550 m) on 26 Apr 1999, near Xochipala [17.7942, -99.6840] at 4,560 ft (1,390 m) on 19 Mar 2004, near Taxco (18.5694, -99.5220] at 5,840 ft (1,780 m) on 21 Jan 1998, and at 4,365 ft (1,330 m) elevation at RMO Tiuribe, Iguala, on 4 Oct 1998. Playback of the A. c. relicta song resulted in sightings of birds closely associated with bamboo, whether green or dry, on more than thirty dates during all seasons of the year. In addition to the distinctive song of this subspecies, R. T. Orr and M. S. Ray (1945), note “there is no overlap between A. relictus and any of the Central American specimens of A. concolor examined in regard to length of wing and length of tail, A. c. relictus being decidedly larger in these respects. In color the adult male of A. c. relictus is decidedly grayer and duller than any of the adult males of races of A. concolor examined by us.” This taxon invites further critical review as it occurs within a limited range, sings a unique song, and manifests both plumage and body structure unlike its congeners. Of note, following Klicka et al. (2009), the IOC recognizes Cabanis’s Seedeater (A. concolor) as distinct from Ecuadorian Seedeater (A. aequatorialis) and lists two subspecies of A. concolor that occur in Mexico, with the form north of the isthmus being A. c. relicta, Slate-blue Seedeater.

Blue-gray Tanager (Thraupis episcopus) – This species is mapped by H&W for western Mexico south of the isthmus. On 30/Mar 2005 at Playa Diamante [16.7929, -99.8063] I studied two birds in a ficus tree, likely the first sighting for this species in Gro. Epifanio Blancas-Calva et al. (2017) suggests breeding with two birds on 28 Mar 2016 at San Luis Acatlán, followed by four on 20 Dec 2016, two being perceived post-juveniles. eBird holds 14 reports from the Gro coast (Robin Oxley, photo), with 10 reports entered since 2017. Epifanio Blancas-Calva et al. (2020) report the anticipated 14 May 19 discovery of an adult carrying food to a nest in a Manila Palm (A. merrillii) at urban Zihuatanejo. The rapid increase in the number of sightings, and the recent confirmation of breeding, demonstrate colonization along the Gro coast, with this species taking advantage of ornamental plantings in populated centers and parkland habitats such as golf courses.

DISCUSSION

The high number of species addressed in this article is the consequence of increased fieldwork within the state and the rapid changes in avian distribution resulting from habitat alteration. Broadly viewed, I interpret four distinct avian regions within Gro: the coastal plain, the Sierra Madre del Sur, the Río Mezcala basin, and the Sierra Norte de Guerrero. The narrow Gro coastal plain serves as a pathway for birds expanding their range northward along the west coast of Mexico. Recent arrivals include Lesser Yellow-headed Vulture, Russet-naped Wood-Rail, Snail Kite, Limpkin, and Aplomado Falcon, with Double-striped Thick-knee (Burhinus bistriatus), Clay-colored Thrush (Turdus grayi), and Melodious Blackbird (Dives dives) expected to join this northward advance of Caribbean species into the state. The northwest coast of Gro sustains one of the few remaining west Mexican populations of Yellow-headed Parrot (Amazona oratrix), is the center of abundance of a localized race of White-bellied Wren (Uropsila leucogastra pacifica), and is the southern limit along the immediate coast for the Yellow Grosbeak (Pheucticus c. chrysopeplus) (resident) and the Black-capped Vireo (Vireo atricapilla) (winter visitor).

Isolated populations of Banded Quail, Rosy Thrush-Tanager, and Black-chested Sparrow on the central Gro coast are increasingly imperiled by unbridled habitat alteration, while requirements for Harris’s Hawk and White-tailed Kite are increasingly made available. The mid-elevation Pacific slope of the northern Sierra Madre del Sur sustains the Gro endemic Short-crested Coquette (Lophornis brachylophus), and outlier populations of taxa which are otherwise found only on the Atlantic slope of Mexico; among them Violet Sabrewing (Campylopterus hemieucrus), Northern Barred Woodcreeper (Dendrocolaptes sanctithomae sheffleri), and Unicolored Jay (Aphelocoma unicolor guerrerensis). Cooper’s Hawk, White-fronted Swift, and Pygmy Nuthatch occur in the less studied summits of the sierra where cryptic species such as Northern Saw-whet Owl (Aegolius acadicus) and Hooded Yellowthroat (Geothlypis nelsoni) may yet be detected. The Río Mezcala drainage is the most likely region to encounter extralimital wintering species such as Burrowing Owl (Athene cunicularia), Say’s Phoebe (Sayornis saya), Eastern Phoebe (S. phoebe), Marsh Wren (Cistothorus palustris), American Pipit (Anthus rubescens), Phainopepla (Phainopepla nitens), and Yellow-headed Blackbird (Xanthocephalus xanthocephalus), all of which are broadly mapped for the region by H&W but for which no specific Gro records exist. In addition, the riparian edges of the large impoundments near Iguala are superb vagrant traps with Brewer’s Blackbird, Northern Parula, and Magnolia and Palm warblers among species of note encountered with little comprehensive coverage. 

The Sierra Norte de Guerrero, the southernmost outlier range of the Transvolcanic Belt, supports three species found nowhere else in the state, Gray-barred Wren, Green-striped Brushfinch, and Spotted Towhee. Additionally, per Appendix B, the range supports classic highland species such as Mexican Whip-poor-will (Antrostomus arizonae), Whiskered Screech-Owl (Megascops trichopsis), Mountain Trogon (Trogon mexicanus), White-striped Woodcreeper (Lepidocolaptes leucogaster), Pine Flycatcher (Empidonax affinis), Gray-collared Becard (Pachyramphus major), Chestnut-sided Shrike-Vireo (Vireolanius melitophrys), Red Warbler (Cardellina rubra), Hooded Grosbeak (Coccothraustes abeillei), and Cinnamon-bellied Flowerpiercer (Diglossa baritula). Vagrants to the sierra like Double-toothed Kite and Aztec Thrush may portent the arrival in the state of Red-shouldered Hawk (Buteo lineatus), Black-backed Oriole (Icterus abeillei) and Green-tailed Towhee (Pipilo chlorurus). In summary, this paper reports details for 92 species that either update or contribute new information toward the understanding of the birds of Gro as presented in H&W. In addition, it makes current the list of birds known to occur in the Sierra Norte de Guerrero, and discusses by region within the state patterns of possibility concerning some birds yet to be recorded for Gro. 

ACKNOWLEDGMENTS

I gratefully acknowledge Hector Gómez de Silva for his assistance in accessing reference materials and his thoughtful review of an earlier draft of this manuscript. Appreciation is expressed to those independent observers whose contributions to this article are the result of hundreds of hours in the field. These observers include Matt Brady, Isaín Contreras, Gustavo Contreras-Cuevas, Bob Friedrichs, Hector Gómez de Silva, Wesley Hochachka, Pete Hoeger, Nick Lethaby, Alan Palacios, Ryan Shaw, Mark Stackhouse, and Charlie Wright. Those that contributed photographs include Amelia Arreguín, Neil Broekhuizen, Baltazar Castro, Isaín Contreras, Gustavo Contreras-Cuevas, Luis Uriel Correa Vera, Neto Espinossa, Bob Friedrichs, Alejandra Salazar-Hernández, Mark Hoffman, John Hopkins, Raymond Jeffers, Steve Juhasz, Aidan Kelly, Nick Lethaby, Paul Lewis, Jim Livaudais, William Mertz, Noam Markus, Robin Oxley, Alan Palacios, Jeff Peters, Jacqui Probst, Brendan Ryan, Kevin Schwartz, Nicola Souza, Daniel Garza Tobón, Sandy Astrid Medina Valdivia, André Sebastián Fuentes Vega, and Amy Worell. Finally, the author acknowledges with gratitude each of the 262 tour participants who shared their observations and company in the field during 44 birding tours organized by Legacy Tours to the Mexican State of Guerrero between 1995 and 2021.

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Michael D. Carmody has served for 28 years as the principal guide for Legacy Tours, which specializes in bird tours to Mexico, and which he co-owns with his wife Susan. During that time, he has shared his knowledge with more than 1,200 clients over nearly 200 tours, and he has spent more than five years of his life in Mexico learning the subtleties of its birds. He has studied birds within all 32 Mexican states and has visited nearly all of Mexico’s major islands; along the way, he has encountered more than 1,000 species within the country.