Archived 2018 topic: Blackpoll Warbler (Setophaga striata): revise global status?

Currently listed as Least Concern (see BirdLife International 2018), Blackpoll Warbler (Setophaga striata) is an extremely abundant passerine, breeding in boreal forest throughout Canada and Alaska, and into the extreme north-east of U.S.A. too (see Curson 2018). It is a migratory species, overwintering across north-eastern South America, utilising a range of habitats including lowland forest, cloudforest, secondary growth and plantations (see Curson 2018).

Given its wide range of habitat use in the non-breeding range, forest loss/degradation there is not thought to be a key threat (see DeLuca et al. 2013). The remote nature of its breeding range would also appear to make logging there unlikely to be a significant threat too (see DeLuca et al. 2013). The species is frequently reported as suffering mortality by colliding with large structures during migration, but this in part could be a result of the species’s abundance, and so the impacts of this on its overall population dynamics may in fact be trivial (see DeLuca et al. 2013).

The species’s habitat requirements for breeding may be being affected by climate change though, as habitat shifts potentially bring other species into competition with Blackpoll Warbler, and turn lower-elevational areas into population sinks (see DeLuca et al. 2013). In fact, modelling has suggested a three degree rise in average temperature could lead to the loss of nearly all high-elevation conifer habitat in the species’s breeding region (Rodenhouse et al. 2008 per DeLuca et al. 2013).

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, Blackpoll Warbler appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

 

Criterion A – The species has undergone a statistically significant decline (Ralston et al. 2015), and Partners in Flight estimates that while the 46 steeply declining North American landbirds may have lost a combined 1.5 billion individuals since 1970, nearly half of these individuals have been Blackpoll Warblers (Rosenberg et al. 2016). This equates to a reduction of 92% between 1970 and 2014, or 45.3% over three generations (10.5 years), assuming a constant rate of decline. Short term trends from Sauer et al. (2017) as less conclusive, due to a significant data deficiency (particularly given the species’s remote breeding range). Sauer et al. (2017) do show a non-significant annual decline of 2.21% between 2005 and 2015, which would equate to a decrease of 20.9% over three generations. However, the confidence intervals for this value range from a 17.43% annual decline (86.6% decrease over three generations) to a 12.03% annual increase (229.6% increase over three generations).

Sauer et al. (2017) also holds historical year by year records, and so we could extrapolate population trends for any three generation period. Three generations ago (pre-2018) is approximately 2007. Therefore, we can extrapolate the trends between 2007 and 2015 to 2018 in order to estimate the population trend over the past three generations. Between 2007 and 2015 the population has been, in general, decreasing with a non-significant, estimated annual decrease of 1.16% (17.46% increase to 16.38% decrease) (Sauer et al. 2017). Moving the three generation period forward though, the reduction between 2009 and 2015, and 2010 and 2015 would exceed 25% over three generations when extrapolated to 2018, although these are not significant.

Partners in Flight do predict a future half-life for the species of only 16 years, which would equate to a decline of 36.5% over the next three generations, assuming a constant rate of decline (Rosenberg et al. 2016). This is not necessarily in contradiction to trends from Sauer et al. (2017), but the data deficiency highlighted for the species in the North American Breeding Bird Survey does make it difficult to accurately assess recent trends.

Given these worrying trends, and the potentially extremely large population crash since 1970, the species potentially warrants uplisting to a higher threat category than Least Concern. The data presented by Rosenberg et al. (2016) appears to suggest that the species could warrant listing as Vulnerable, but the uncertainty over recent trends due to data deficiency makes it difficult to clearly assess current trends. The species could warrant listing as Vulnerable because of predicted future trends, but again these are based on data for recent trends (see Rosenberg et al. 2016). Therefore, we request any further comments or information regarding recent population trends for the species, particularly whether they may meet the threshold for Vulnerable (reduction of 30% over three generations [10.5 years]). In the absence of this though, it may be appropriate to list the species as Near Threatened under criteria A2ac+3c+4ac.

 

Criterion B – The species’s range is far too large to warrant listing under this criterion (Extent of Occurrence [breeding] = 11,900,000km2; Extent of Occurrence [non-breeding] = 4,870,000km2).

 

Criterion C – Rosenberg et al. (2016) estimate the population size to be 59,000,000 mature individuals. This is far too large to warrant listing under this criterion.

 

Criterion D – The species’s population size and range are far 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, Blackpoll Warbler potentially warrants uplisting, but it is difficult to estimate recent trends based on the available information. We therefore request any further information about the magnitude of recent trends. We also welcome any other 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. We recognise that this is still an extremely common bird, but Red List assessments are not solely based on abundance and any potential listing for this species is entirely based around the population trend.

 

References

BirdLife International. 2018. Species factsheet: Setophaga striata. Downloaded from http://www.birdlife.org on 13/03/2018.

Curson, J. 2018. Blackpoll Warbler (Setophaga striata). 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/61490 on 13 March 2018).

DeLuca, W.; Holberton, R.; Hunt, P. D.; Eliason, B. C. 2013. Blackpoll Warbler (Setophaga striata), 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.431.

North American Bird Conservation Initiative. 2016. The State of North America’s Birds 2016. Environment and Climate Change Canada, Ottawa, Ontario.

Ralston, J.; King, D. I.; DeLuca, W. V.; Niemi, G. J.; Glennon, M. J.; Scarl, J. C.; Lambert, J. D. 2015. Analysis of combined data sets yields trend estimates for vulnerable spruce-fir birds in norterhn United States. Biological Conservation 187: 270-278.

Rodenhouse, N. L.; Matthews, S. N.; McFarland, K. P.; Lambert, J. D.; Iverson, L. R.; Prasad, A.; Sillett, T. S.; Holmes, R. T. 2008. Potential effects of climate change on birds of the Northeast. Mitigation and Adaptation Strategies for Global Change 13 (5-6): 517-540.

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.; 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.

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2 Responses to Archived 2018 topic: Blackpoll Warbler (Setophaga striata): revise global status?

  1. Claudia Hermes (BirdLife International) says:

    Based on available information, our preliminary proposal for the 2018 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.
    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.
    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.
    The final 2018 Red List categories will be published on the BirdLife and IUCN websites in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  2. I am surprised at this proposal, especially considering the large confidence intervals in these trend data. It is not clear if the perceived decline is real or an artefact of low sample size (BBS trends are essentially non-significant so inferring any population loss is risky). This seems to point towards Data Deficient rather than Near-threatened (recognising that BBS is not surveying the bulk of the species’ core range). Manitoba Breeding Bird Atlas data show that in core areas average point count abundance can exceed one individual per point count and we still consider this species to be “secure” (provincial S-rank of S5).

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