This discussion was first published as part of the 2018 Red List update. At the time a decision regarding its status was pended, but to enable potential reassessment of this species as part of the 2019 Red List update this post remained open and the date of posting has been updated.
Cerulean Warbler (Setophaga cerulea) is a wide-ranging migratory songbird of the Americas. It breeds in North America, in southern Ontario and Quebec (Canada) and throughout central and eastern U.S.A., and migrates to spend the non-breeding season in northern and western South America, as far south as Bolivia (see Curson et al. 2018). The species breeds in mature deciduous forests (see Curson et al. 2018), and overwinters in submontane forest on the eastern slope of the Andes, and occasionally in adjacent lowlands, plantations and secondary forest (Curson et al. 2008).
The species is impacted by several threats, but foremost among them is habitat loss and degradation. This is driven through conversion of land for urban and agricultural development, as well as disease impacting key tree species (see Buehler et al. 2013). As a result, the species has been thought to be undergoing a rapid decline, and as such is currently listed as Vulnerable under criterion A (see BirdLife International 2018).
Following the publication of Partners in Flight (PiF) Landbird Conservation Plan (Rosenberg et al. 2016) and The State of North America’s Birds 2016 (North American Bird Conservation Initiative 2016) we have reviewed the new information held in these publications, particularly regarding population trends. This has allowed us to reassess the species outlined in these publications against IUCN Red List Categories and Criteria. As the PiF data are long-term trends (1970-2014), where possible we have also used data from the North American Breeding Bird Survey (Sauer et al. 2017) to assess more recent trends over the period relevant to the Red List. Having completed this review, Cerulean Warbler appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.
Criterion A – Rosenberg et al. (2016) estimate the population reduction between 1970 and 2014 to be 72%, which roughly equates to 26.8% over three generations (10.8 years). Short term population trends from Sauer et al. (2017) show an annual decline of 1.31% (3.70% decrease to 1.83 increase) between 2005 and 2015. This would equate to a reduction of 13.3% (33.4% decrease to 21.6% increase) over three generations, which does not approach the threshold (>30%) for Vulnerable under this criterion.
Even when looking at year by year records from Sauer et al. (2017), the species’s rate of decline has not met or approached the threshold for Vulnerable (reduction of 30% over three generations) since 2008, and so the rate of decline has been below the threshold for Vulnerable for some time. Therefore, the species should no longer warrant listing as such under this criterion.
Partners in Flight do estimate the half-life of the species to be 26 years (Rosenberg et al. 2016), though, which would equate to a decline of 25.0% over three generations. Therefore, it may be precautionary to propose listing the species as Near Threatened under criterion A3c.
Criterion B – The species’s range is far too large to warrant listing under this criterion (Extent of Occurrence [breeding] = 2,540,000km2; Extent of Occurrence [non-breeding] = 4,130,000km2).
Criterion C – Rosenberg et al. (2016) estimate the population to be 570,000. It is not clear whether this refers to mature individuals or all individuals, but either way it would be too large to warrant listing under this criterion.
Criterion D – The species’s population size and range are too large to warrant listing under this criterion.
Criterion E – To the best of our knowledge there has been no quantitative analysis of extinction risk conducted for this species. Therefore, it cannot be assessed against this criterion.
Therefore, Cerulean Warbler potentially warrants downlisting to Least Concern based on current information, but because of the potential for moderately rapid declines in the future it is instead proposed to list the species as Near Threatened. We welcome any comments or further information, but please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’s Red List status. Therefore, please make sure your comments are about the proposed listing.
BirdLife International. 2018. Species factsheet: Setophaga cerulea. Downloaded from http://www.birdlife.org on 08/03/2018.
Buehler, D. A.; Hamel, P. B.; Boves, T. 2013. Cerulean Warbler (Setphaga cerulean), version 2.0. In: Rodewald, P. G. (ed.). The Birds of North America. Cornell Lab of Ornithology, Ithaca, New York, U.S.A. https://doi.org/10.2173/bna.511.
Curson, J.; Christie, D. A.; Sharpe, C. J. 2018. Cerulean Warbler (Setophaga cerulea). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/61491 on 8 March 2018).
North American Bird Conservation Initiative. 2016. The State of North America’s Birds 2016. Environment and Climate Change Canada, Ottawa, Ontario.
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. and Will., T. 2016. Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee.
Sauer, J. R.; Hines, J. E.; Fallon, J. 2003. The north American breeding bird survey, results and analysis 1966-2002. version 2003.1. USGS Patuxent Wildlife Research Center. Downloaded from http://www.mbr-pwrc.usgs.gov/bbs/bbs2002.html.
Sauer, J. R.; Niven, D. K. ; Hines, J. E.; Ziolkowski, Jr, D. J.; Pardieck, K. L.; Fallon, J. E.; Link, W. A. 2017. The North American Breeding Bird Survey, Results and Analysis 1966 – 2015. Version 2.07.2017 USGS Patuxent Wildlife Research Center, Laurel, MD.