The data behind mysterious bird deaths in New Mexico
by Jenna McCullough
Last week, the Rocky Mountain states experienced a strong storm that brought with it snow, near hurricane force winds, and unseasonable record-breaking cold temperatures. In Albuquerque on September 8, it was sunny and a record-high 96ºF. The next afternoon, a severe windstorm tore through the region. The Albuquerque airport measured windspeed of over 70 mph, and temperatures plummeted to historic lows. Albuquerque broke a 100-year record low temperature when the mercury dropped to 40ºF. While snowfall was heaviest in the northern Rockies from Montana to Colorado, New Mexico received several inches of heavy, wet snow as far south as the Sandia Mountains east of Albuquerque.
My colleagues and I spent the morning of Thursday 10 September picking up dead birds in the Sandias. We found several dead Empidonax flycatchers of three species, a Vesper Sparrow, and a Townsend’s Warbler. Some birds were wet from the overnight snow, but others were completely dry, huddled in the corners of buildings. A Dusky Flycatcher sat dazed in the parking lot.
We first thought little of it: mortality is expected for migratory birds, and we didn’t find more than a handful of carcasses. But social media told a grimmer story that night. We read reports of widespread mortalities across the state: dead swallows along a bike path in Albuquerque, a half-dozen Empidonax flycatchers and swallows in one park in Clovis, and a local news report of 300 carcasses recovered by researchers from New Mexico State University and nearby White Sands Missile Range. It was soon apparent that a significant mortality event had occurred.
But one video on Twitter recorded by local journalist Austin Fisher stood out to me: several dozen swallows dead in an arroyo in Velarde, approximately 40 miles north of Santa Fe. It was only when I reached out to Austin for the purposes of this report that I realized the video wasn’t taken the week before during the cold snap, but rather the previous night, on 13 September. To see it for myself, fellow ornithology grad student, Nick Vinciguerra, and I drove the hour and a half north that night.
When we arrived at midnight, we found a macabre scene. Several hundred Violet-green Swallows were strewn across the bank of the Rio Grande. Dozens of birds had stuffed themselves into the few natural cavities, and many more were dead amongst the vegetation. In total, we found 305 individuals of six species, all of which were insectivores: 258 Violet-green Swallows, 35 Wilson’s Warblers, six Bank Swallows, two Cliff Swallows, one Northern Rough-winged Swallow, a MacGillivray’s Warbler, and two Western Wood-Pewees. These proportions are similar to what was reported by researchers at NMSU.
Several hypotheses are emerging to explain this mass mortality event in New Mexico. Recently, heightened attention has been given to the possibility that historic wildfires across western North America are to blame, and wildfires certainly pose a major disruption to migratory birds. For instance, a wildfire could cause birds to flee an area before they’ve replenished their fat stores. Indeed, anecdotal reports from banding stations suggest that wildfires contribute to unusual migrant influxes into areas that are free from fire. Michael Hilchey, a volunteer bander at the Rio Grande Bird Research Station in Albuquerque, noted a significantly higher volume of migrants over the past two weeks than has been over the last 10–15 years. Smoke is covering nearly all of the lower 48 states, and while we experienced heavy smoke in Albuquerque the night before the storm arrived, fires are not new or unexpected during the height of fall migration. Indeed, wildfires are common and increasing in frequency.
There is, I believe, a much more plausible reason for large numbers of birds to die during migration: lack of food.
The 55–60ºF temperature swing observed in New Mexico combined with hurricane force winds and with wet snow very likely caused hypothermia in some birds, especially juveniles. Furthermore, cold temperatures also affect the food supply for insectivores, as insects (which become dormant or dead) are then covered by snow. Certainly, they are not flying through the air, as swallows and pewees need. Dave Leatherman, a former entomologist for the state of Colorado, noted marked behavioral differences in foraging insectivorous birds during the week’s snowstorm. In addition, a 2007 study by Ian Newton found that unseasonably cold weather can have a negative effect on migrating birds. While cold temperatures and snow cut off the food supply for naïve migrants, resident birds not stressed by migration typically have both fat reserves and local knowledge of where to find shelter.
Notably, and understandably, this type of die-off commonly affects swallows. In several documented cases of swallow mortality events (Newton 2007), a sudden drop in temperatures caused insects to become dormant (and stop flying). In Kazakstan during the fall of 2000, cold and snow killed thousands of Barn Swallows (Berezovikov and Anisimov 2002). Severe cold snaps in 1931 and 1974 killed “hundreds of thousands, possibly millions” of swallows and martins in central Europe (Alexander 1933, Ruge 1974, Bruderer and Muff 1979, Reid 1981, Newton 2007). Specifically, Newton (2007) states, “When short of food in cold weather, swallows and swifts often seek shelter in buildings, huddle together for warmth, and may suffer from hypothermia and starvation. Other migratory insectivores also die in such conditions, but less conspicuously.”
Sudden and dramatic unavailability of food caused by a historic and drastic cold snap is, I believe, a more parsimonious explanation than a widespread, smoke induced, mass mortality event. While we do not have data on how fast smoke inhalation would kill birds hundreds of miles away from the fires themselves, what we do have are data from the 258 Violet-green Swallows that Nick and I collected in Velarde this week.
If a lack of food contributed to the mortality event, birds would have less fat and no protection against hypothermia. Indeed, of the hundreds of birds we assessed, none had fat stores on their bodies. Furthermore, many birds also showed signs of breast muscle atrophy, which points to starvation and dehydration. The average mass of an adult male Violet-green Swallow is 14.4 g; females are slightly lighter at 13.9 g. In addition, I used an open-access museum collections database, Vertnet, to find data on thirty specimens collected July–September, and their average weight was 15 g. We weighed 234 swallows which showed only minor signs of decomposition, and their average mass was dramatically lighter: 9.5 g, or about two-thirds the weight of normal birds. Though we have yet to perform any toxicology analyses or inspect their lungs for signs of smoke inhalation, I think it is safe to say that these birds were starved and succumbed to hypothermia. When USFWS autopsies of other birds are reported in the coming weeks or months, we suspect they will reveal a similar cause of death.
Christopher Witt, Professor at UNM and Director of the Museum of Southwestern Biology, waxed poetical with me this week about how fall 2020 has brought a spectacular array of fall migrants to Albuquerque, noting that it’s been the “Best I’ve seen in years.” As a birder myself, I also benefitted from this better than average migration with my lifer Blackpoll Warbler on the University of New Mexico campus this week. Our influx of migrants may or may not have been due to wildfires, but I have no doubt that they were affected by the extreme cold and high winds in New Mexico. Though the fires and extreme weather events are influenced by human-induced climate change, it is unlikely that the wildfires alone caused the death of thousands of birds in New Mexico.
Jenna McCullough is a 3rd year PhD student at the University of New Mexico and the Museum of Southwestern Biology, where she studies avian evolution and systematics of birds in the South Pacific. Jenna is a third-generation female birder and regularly birds across the western U.S. and internationally. She can be reached on Twitter @Jenna_merle or via email at mcculloughj@unm.edu
I witnessed this on September 9 driving hwy 10 from La Junta to Walsenburg CO. Snow on the ground birds in the road. In that 60 mile stretch, going 10 miles under the speed limit I still must have hit almost a dozen. For an avid birder it broke my heart!
In the future, use your horn. Birds respond to loud sounds, while having no concept of a vehicle coming at them at high speed. Of course, when birds are really thick along a road, it’s hard to avoid hitting them at any speed.
Please honk your horn!!!!
They’ll fly off!
So honk your horn continually for 60 miles? Come on guys, have a little compassion. This is unreasonable and unrealistic.
Great article. Thank you for your hard work. I was appalled when I first read about this fearing a new avian disease.
Illuminating & heartbreaking.
How long of an event does it need to be to lose that much weight? Was there any banding north if there that have logged weights of birds?.
Probably not very long. I’ve observed songbirds put on 10-20+% of their mass in a matter of days while banding at migration stopover sites. And if the birds had already been working hard migrating when the bad weather change arrived they were probably low on energy stores to begin with. Margins can be pretty thin during migration season.
Thank you for the research. I had found 8 dead birds, swallows and Wilson Warblers, on the west side of the river from Velarde. Couldn’t figure out why.
Well, why is there a loss of food for the birds. Are the insects, etc. affected by the wildfires, extreme temperatures, wind storms? I have now seen less cockroaches, less grasshoppers early on but now huge grasshoppers, lots of spiders and lots of lizards. Lots of hawks but less finches and wrens.
In all humility, does your question imply that you did not read how the insects were not flying due to cold temperatures and snow? Even those insects that don’t fly would be less noticeable since they would be moving less and possibly covered by snow.
Did you read the article? She explains that it was a sudden cold snap.
Thank you for your work and for sharing your information. One quick question….” Sudden and dramatic unavailability of food caused by a historic and drastic cold snap is, I believe, a more parsimonious explanation”…….why parsimonious?
She’s a writer, they like multisyllabic words. Could have said frugal or simple or brief.
Starvation due to a cold snap… simpler than some theory of smoke pollution and biological frailty and disease.
I think she means in an “Occam’s Razor” way.
The rest of the article effectively explains why. The extent of smoke and wildfires were not something that could impact insect availability as much as an extreme cold front would.
Is there anything we can do to help these birds? I’m guessing they only feed on flying insects, not seeds? It’s extremely upsetting.
Is there anything that we humans can do to help birds in this type of situation? Any way to anticipate a killing disaster before it happens? Does it take bowls and bowls of mealworms or can birdseed help feed them? I know it’s a huge number of birds affected.
Planting native plants– supporting native plants in public projects– provides food for birds, which mostly eat insects and berries. Turns out insects don’t eat plants from other ecosystems– totally plants have almost no insect predators, hence they don’t support birds. When you can, plant natives. It won’t prevent disasters, but it will likely fatten up and maybe improve breeding success of your local migrants! For more, check out http://www.bringingnaturehome.net
All the dead birds I’ve seen have been insectivorous. I suspect pesticide poisoning as being at least a contributing factor to this mass mortality episode. The reduced mean weights of these carcasses could be due to dehydration after death. Smoke inhalation and the sudden drop in temperature could also be contributing factors. None of these factors rule out others but it does seem suggestive that insectivores have died while granivores of similar size and range seem to have been spared.
Thank you for this reporting and analysis. Let’s hope we can all help birds get enough food by planting more plants that support their food web.
This is the same thing we used to witness on the Gulf Coast during Spring migration when a weather event, typically a strong cold front in late April or early May, would slam into birds flying across the Gulf from the Yucatan. You would find thousands of dead birds in the tideline if you took the time to drive the beach. Laughing Gulls relished this demise. The birds drowned most likely, but because they had already dpeleted their fat stores in their long flight before encountering the counter frontal winds, they would fall into the water. You could sometimes stand… Read more »
thanks. fine discussion
Will the collected birds be also tested for herbicide and pesticide residue, that they might have picked up in insects? If not, why? My neighborhood has been affected by drifts of herbicides this year. Many different plants died. Many of those who didn’t die showed growth problems and deformations and were much less attractive to insects. For example no monarch larva thrived on curled milkweed. Now that the season is ending I am also noticing that seed formation on surviving plants is affected. No seed at all, fewer smaller seeds on some. We are NOT located near any agricultural areas… Read more »
Testing for chemical residue in physical tissue takes big money and there are usually no set parameters for what constitutes a fatal or sickening dose, even in humans or in the water. At least this was my experience when I thought I’d test for Rx drug levels in the local water supply as a master’s project.
Fascinating, and thanks for your research. The migrant birds we found dead in Chimayó were pine siskins, which had swamped our feeders for a week or two prior to the cold event, consuming huge amounts of seed. We had noticed that a few seemed lethargic. I know they also eat insects. Perhaps insects contribute more to their fat stores than seeds do?
Thanks for the info. I live on the river a few miles north of Velarde, and have seen some dead birds, but only an individual here and there. All insectivores, including a black phoebe. Our migration has been spectacular as well, with very many Yellow-rumped, Wilson’s next in number, and lesser numbers of Townsend’s and MacGillivrays warblers. Also Williamson’s sapsuckers, Crissal thrasher, Brewer’s and Lincoln’s sparrows, Green-tailed towhees and more.
Could the birds have stopped migrating due to not being able to use star migration because of the smoke, then hit by the storm.
Good speculation, though I’m not sure the smoke had been widespread and bad enough in the areas of NM and CO where these mortalities have been observed to be a significant issue in that way.
Sadly, I just discovered a similar situation in New Jersey today. would the wildfires at West have caused a problem on the East Coast?
Where is that? I’m in western Essex County and curious how far that is from me.
I have picked up 13 dead birds of various species around our house this week after the storms. We had snow and 2 nights of freeze. A factor in my immediate area was a plague of grasshoppers from late May to July. Millions of them. They devoured everything in sight including stripping bare a mature apple tree. I’ve never experienced grasshoppers in that quantity. I doubt they left much for the birds to eat. Our property is located approximately at NM 55 and Riley Road neat Estancia. I do have 4 birds in my freezer
Those wind chargers to make electricity are killing the birds also
Nice that these birds can be used for bird collections. Send my regards to Andy Johnston. Dawie de Swardt, National Museum, Bloemfontein, South Africa
Climate change takes its toll on wildlife. It’s a pity that after surviving the last great extinction, the cretaceous, the last of the Dinosaurs should be extinguished by humans burning fossils (fuel)
Excellent article. Thank you. Regarding people asking about dead birds found that were not pure insectivores (ie, finches, siskins), the cold and wet weather combined with the winds alone is more than enough to kill many songbirds. Whenever we have weather like that, it kills some songbirds, they have a higher core temperature than mammals and are very susceptible to hypothermia. When we get cold icy windstorms in Albuquerque, one can easily find wet, cold near-dying (or already dead) small birds in various “hot spots” in the city. I try to make a habit to checking those hot spots when… Read more »
how long did it take for the birds to starve to death?
I think this explanation makes a lot of sense for recent mortality events, but it seems like there’s more to the story still. What’s curious to me is that the NMSU observations of dead birds from White Sands, which is what originally prompted this story in news media outlets, came from mid/late August, well before the historic cold snap. Was that just a separate localized incident, whereas the reports of more widespread mortality in the reason have occurred after the cold front came through? Or might there be some other underlying factors at play?
Your acute observations in the field and lab are beginning to elicit the deeper and broader questions of long term cause, rather the immediacy of applying bandages per population, per event. There are patterns becoming clearer almost daily across the spectrum of life not only in our country but throughout the world. Yet we keep doing the things known to create dramatic shifts in our waters, our earth, our air. And many among us still deny that we as a species are willfully changing our climate. We are literally playing with earth, fire, wind, water and all the life dependent… Read more »
Hour north of Toronto Ontario Canada and the smaller species of birds are starving and I can’t believe only had one!!! Yes one humming bird all season??? What’s going on is obvious!!!!! Between the chemicals dumpped over the skies ???? I know 5g has zapped untod species into almost instant death! What we are seeing is a tota assault on all species without any regaurd but maybe a evil planned kill off of everything including humans by some really sick induvidualds who have way too much power and no regaurd for life except theirs!!!1 Just sickning to whitness the downfall… Read more »
2020 has seen reduced flights. That means less aircraft pollution, not more.
This makes sense. As you say, it is the most parsimonious explanation. And you note the lack of fat stores on the dead birds collected. But I do wonder if the fires and the smoke could have exacerbated a bad situation. Might these birds have begun their journey with lower than expected fat stores and so been more susceptible to the sudden cold? Only a comparison of migrants in a season without the fires would help answer that question. I study a nonmigratory Insectivorous bird in Portland and am anxious to see if the smoke has affected their winter survival.… Read more »
I am a permitted rehabilitator just outside Albuquerque. Indeed, I have contributed hundreds of specimens to the Museum of Southwestern Biology.I find it interesting that the dead birds were underweight. I received several Wilson’s Warblers and Barn Swallows into rehab in the weeks before the cold snap. Each had been found down, unable to fly. Each was emaciated, only about 60% of their expected healthy weight. Unfortunately each too far debilitated to save.No doubt a bird in that condition could not survive the added stress of the plunge in temperature. But the larger question is why are they starving? Is… Read more »
My wife and I have some property on Glorieta Mesa, twenty some miles SE of Santa Fe. As we are on a major migratory flight path, we have been feeding and watering the birds for years. This has been the sparsest year yet for birds coming through on their way to Bosque Redondo. We are feeding mostly locals (dove, pinyon jays and ravens, and the little guys I still cannot name). There was a huge influx of hummers this year. Most decided to stay and we were quite busy with syrup for a while. When the cold came, they almost… Read more »
Very good point… the toxins from western fires are increased this year as so many more than usual homes and businesses burned. I live in Oregon and we lost a half dozen TOWNS! I am used to trees burning, but this is the first time in my life I was concerned for my home. The smoke was so thick in the Willamette Valley for two weeks I was worried about all the birds. They had no where to go. The entire state from the ocean to the Rockies was covered in thick smoke. It was at a quarter mile visibility… Read more »
[…] birds that died for no obvious reason. Recently, a likely explanation has been published in this ABA Report , which is well worth […]
Thanks billion for the article, the work. Living in East Mtn, i did not see any birds. However, i spent those days bringing in all my patio plants, hanging baskets, and trees, then 3 days later bringing them all back out. Labor Day luncheon 90 plus (at 7,000) then freezing 24 hours later….no fall season!
Super quiet next few days. Now tons of birds everywhere, packed at my bird baths, so many , I put up a couple of new baths. Aaaaaaaaaa
i want to find birds not dead tho i want to be a bander
In El Prado (5 minutes NW of Taos), I have found at least 8 deceased in my yard – but about half were the yellow ones. And a panting finch (mixed plumage, female) at my door in respiratory distress, whom I got to the wildlife center in Espanola. If you need to blood test a live bird for disease, she may be a candidate.
I counted 54 Wilson’s Warblers in between Santa Fe and Taos dead on the road route 62 the morning after the storm.
I work with horses and live on a horse property and this year there were not many flies. I noticed this in June actually. It continued through August with a little spike in population at my friends Ranch that has 25 horses. It only lasted a week. I can’t speak for all the places since I only saw about six properties. It was significant enough to notice. It was super dry. I wonder if mosquito populations were also down.
And then there is government testing of sonic weapons. What is the proximity to military bases and flock deaths? Southern Colorado… etc
None of note.
I live in Washington state the Pacific Northwest. We had lots of smoke for about 4 days. We found 4 dead birds on the 3nd day of smoke. I believe they were swallows. We had many hummingbirds and that have completely disapeared. The honey bees that are usually in my bee gardens have only a few showing up. The Bees I watch are lethargic or they have crawled inside a flower petal.
No, it was not the lack of food.. dang
Yes, it was.
Yes it suck sucks but with these thing we won’t be having a balance of life.
parallel to this, 1 million birds die every year in Germany, because they crash agianst the windows of modern buildings, also near 27 millions in the EU! and how many are killed by the cats in the cities and all around? I wonder that some of them can subsist!
Of course, there is the ongoing problem of some people using glue sticks to kill songbirds for humans to eat. Up to 25 million birds are illegally slaughtered in the Mediterranean each year on migration between Africa and Europe.
https://www.discovery.com/nature/how-the-mediterranean-became-a-corridor-of-death-for-birds
The survivor’s behavior has been erratic also. I commute to Santa Fe from EM and have hit 3 birds and had 2 near misses since Monday. I normally will go more than a year without hitting a bird.
They seem to be oblivious and give almost no time to react. It is diffocult for me to leave smoke off or even down the list. It has been exceptionally bad and depriving me of sleep.
[…] the hundreds of birds we assessed, none had fat stores on their bodies,” wrote McCullough on the American Birding Association […]
A few days ago, the New Mexico Department of Game and Fish released a summary of the necropsied birds, titled “Starvation, unexpected weather to blame in mass migratory songbird mortality”. Here is the link: https://content.govdelivery.com/accounts/NMDGF/bulletins/2afbc3e?reqfrom=share
[…] was marked by unprecedented bird records, extreme temperature swings across the region resulting in mass die off of insectivorous migratory birds, and an ongoing global pandemic—making Fall 2020 one of the most exciting and challenging […]