This discussion was first published as part of the 2017 Red List update. At the time a decision regarding the status of several was pended, but to enable potential reassessment of these species as part of the 2018 Red List update this post remains open and the date of posting has been updated.
Golden-cheeked Warbler (Setophaga chrysoparia) is a Neotropical migrant species that is a breeding endemic to Texas, U.S.A., and overwinters in southern Mexico and Central America. Dependent on juniper-oak woodland during breeding (Lockwood 1996), its Area of Occupancy (AOO) is currently considered to be very small (350 km2) and given habitat loss within its range the species’s AOO, Extent of Occurrence, habitat area/quality and population size are all considered to be in decline. As such it is currently listed as Endangered under criterion B2ab(i,ii,iii,v) (see BirdLife International 2017).
Reviewing this current listing, this Area of Occupancy value appears to be a large underestimation. Records within its breeding range cover a far larger area than this (see eBird 2017), and Mathewson et al. (2012) present multiple estimations of the amount of suitable habitat there is for this species, all of which are >1,000km2 but the most recent was 552,195 hectares (or 5,521.95km2) (SWCA Environmental Consultants 2007 in Mathewson et al. 2012). While this value does not directly relate to an AOO by IUCN guidelines (see IUCN Standards and Petitions Subcommittee 2016) it still strongly suggests that the area where this species breeds is far larger than currently used to assess this species’s Red List status, and potentially does not even approach the threshold for listing as Vulnerable under criterion B2. Therefore, this species requires re-assessing against the other criteria to see whether it warrants maintaining its listing as threatened.
Population figures from the recent Partners in Flight publications (Rosenberg et al. 2016) suggest that the species would not warrant listing under a threatened category based on population size (criteria C and D). The ‘population estimate’ provided in Rosenberg et al. (2016) is 21,000, but it is uncertain whether this refers to total number of individuals or just mature individuals. If this number refers to number of mature individuals, then it would not approach the threshold population size for listing as Vulnerable under criterion C (<10,000 mature individuals). However, if this were to refer to the total number of individuals then this would roughly equate to 14,000 mature individuals and so, given that the species may be considered to consist of only one subpopulation because of its migratory behaviour, then the species could warrant listing as Near Threatened under criterion C2a(ii). This said, the ‘population estimate’ of Rosenberg et al. (2016) appears to be considerably at odds with other population estimates displayed by Mathewson et al. (2012). Mathewson et al. (2012) themselves estimate the number of singing males alone at 262,013 (223,164-301,081) (although depending on model selection range expands to 191,658-301,081). Other estimates of the potential population that could be supported in the available habitat range from 4,822-16,016 pairs (Wahl et al. 1990 in Mathewson et al. 2012) to 228,426 individuals (Rappole et al. 2003). These more recent estimates of Rappole et al. (2003) and Mathewson et al. (2012) then both suggest that the population size would far exceed the 10,000 mature individuals threshold, and so would not even warrant listing as Near Threatened under criterion C.
To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species, and so it cannot be assessed against criterion E. This leaves only criterion A, which assesses the species against rates of decline. Partners in Flight, in their Appendix, do not provide a species ‘half-life’ or % decline, but earlier in the publication suggest that the species has undergone a decline of >50% over 44 years. As this leaves still a very large range of potential decline over this period, this makes it very difficult to assess the rate of decline over 3 generations (c.11 years). However, as an example, if a decline of 50% over 44 years is used, then this would only equate to a decline of 15.6% over 3 generations, which again would not qualify this species as even Near Threatened.
Thus it appears likely that in the absence of any other information this species may warrant downlisting to Least Concern. However, we do urgently request any further information, particularly regarding the rate of decline over the past 10-15 years and the very large disparity between population size estimates which could at least mean this species may deserve listing as Near Threatened.
BirdLife International. 2017. Species factsheet: Setophaga chrysoparia. Downloaded from http://www.birdlife.org on 21/04/2017.
eBird. 2017. eBird: An online database of bird distribution and abundance [web application]. eBird, Cornell Lab of Ornithology, Ithaca, New York. Available: http://www.ebird.org. (Accessed: April 21, 2017).
IUCN Standards and Petitions Subcommittee. 2016. Guidelines for Using the IUCN Red List Categories and Criteria. Version 12. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf
Lockwood, M. W. 1996. Courtship behavior of Golden-cheeked Warblers. Wilson Bulletin 108: 591-592.
Mathewson, H. A.; Groce, J. E.; Mcfarland, T. M.; Morrison, M. L.; Newnam, J. C.; Snelgrove, R. T.; Collier, B. A.; Wilkins, R. N. 2012. Estimating breeding season abundance of golden-cheeked warblers in Texas, USA. The Journal of Wildlife Management 76: 1117-1128.
Rappole, J. H.; King, D. I.; Diez, J. 2003. Winter- vs. breeding-habitat limitation for an endangered avian migrant. Ecological Applications 13: 735-742.
Rosenberg, K. V.; Kennedy, J. A.; Dettmers, R.; Ford, R. P.; Reynolds, D.; Alexander, J. D.; Beardmore, C. J.; Blancher, P. J.; Bogart, R. E.; Butcher, G. S.; Camfield, A. F.; Couturier, A.; Demarest, D. W.; Easton, W. E.; Giocomo, J. J.; Keller, R. H.; Mini, A. E.; Panjabi, A. O.; Pashley, D. N.; Rich, T. D.; Ruth, J. M.; Stabins, H.; Stanton, J.; Will., T. 2016. Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee.
SWCA Environmental Consultants. 2007. Preliminary deliverable golden-cheeked warbler status review. Texas Department of Transportation, San Antonio, USA.
Wahl, R.; Diamond, D. D.; Shaw, D. 1990. The golden-cheeked warbler: a status review. Texas Parks and Wildlife Department, Austin, USA.