An ABA Area Big Year shall start at 12:00 AM on 1 January of that year and end at 11:59 PM, 31 December of that year, based on the local time of the location of the birder at each time threshold. Each species counted by the participant must have been encountered in accordance with the ABA Recording Rules current at the time the species was encountered. Each species counted must have been on the ABA Checklist during the Big Year, with the following exception: A non-exotic species encountered that is new to the ABA Area can be retroactively counted for the Big Year if and when that species is added to the ABA Checklist and if the bird seen represents the accepted new ABA record or is another individual of the species seen after the initial record. Any ABA Area Big Year lists submitted to the ABA must be in accordance with these rules.

The following are two real and two hypothetical examples that clarify the countability of species in some potentially confusing situations:

1. In November 2010, Pacific Wren (Troglodytes pacificus) was officially added to the ABA Checklist following its split from Winter Wren (Troglodytes troglodytes, sensu lato). Thus, Pacific Wren is a countable species for a 2010 Big Year, no matter when it was encountered during 2010. For example, if Big Year birders encountered a Pacific Wren in March 2010 (before it was officially on the ABA Checklist), they may count it on their final Big Year lists. However, if the split had occurred in 2011, Pacific Wren would not be a countable species for a 2010 Big Year.
2. Hypothetically, if Northwestern Crow (Corvus caurinus) were lumped with American Crow (Corvus brachyrhynchos) and removed from the ABA Checklist in November 2018, Big Year birders could still count Northwestern Crow on their Big Year lists for 2018. Even if Northwestern Crow were not seen until December 2018 (after its hypothetical removal from the ABA Checklist), it would still be considered countable for a 2018 Big Year. However, if the lump had occurred in 2017, Northwestern Crow would not be a countable species for a 2018 Big Year.
3. Hypothetically, if a Happy Wren (Pheugopedius felix) were discovered in Tubac, AZ, in April 2015 and another one in Miller Canyon in June 2015, and the April record were accepted by the ABA Checklist Committee as a new ABA record, then both birds would be considered countable for a 2015 Big Year. If the April record is rejected or not reviewed by the Checklist Committee and the June record is accepted, then only the June bird may be counted for a 2015 Big Year. The future date of the Checklist Committee’s acceptance of the new species does not affect its ultimate Big Year countability, but the new species may not be officially counted for a past Big Year until it is added to the ABA Checklist.
4. In late 2003, the ABA Checklist Committee removed Crested Myna (Acridotheres cristatellus) from the ABA Checklist. If Big Year birders encountered the last two Crested Mynas in 2003 in Vancouver prior to the birds’ demise in mid-February, the birders may count Crested Myna for their 2003 Big Year. Additionally, in accordance with Recording Rule 2B(iii), Big Year birders that encountered Crested Mynas in previous years may keep the species on their Big Year lists (i.e., removal of the species from the Checklist in 2003 does not affect the Big Year countability of the species from previous years when the species was still on the Checklist).