Evening Grosbeak (Hesperiphona vespertina): revise global status?

Evening Grosbeak (Hesperiphona vespertina) is endemic to continental North America. An irruptive species, it breeds in conifer forest in a band across northern U.S.A. and southern Canada, as well as western U.S.A. and into western and southern Mexico. In winter it will migrate, with its range expanding to include most of continental U.S.A. (see Clement 2018).

The species is currently considered Least Concern (see BirdLife International 2018), but there is now a growing amount of information showing that the species may in fact be undergoing rapid declines (Bonter and Harvey 2008, Ralston et al. 2015, Rosenberg et al. 2016, Sauer et al. 2017); and it has been placed on the Yellow Watch List by Partners in Flight (Rosenberg et al. 2016). The cause of these decline has not been identified yet, although habitat alteration, disease and control of its insect prey (e.g. Spruce Budworm) have been put forward as potential contributors (Bonter and Harvey 2008).

Given these potentially rapid declines we have therefore reassessed the species here against all criteria to see whether it may warrant a change in Red List status.

 

Criterion A – Rosenberg et al. (2016) present that the species may have declined 94% over the 44 years 1970-2014. This would roughly equate to a decline of 65.2% over three generations (16.5 years). Additionally, data from the North American Breeding Bird Survey suggests significant short term declines (between 2005  and 2015) of 2.9% per year (0.09-5.45% per year) (Sauer et al. 2017), roughly equating to a decline of 38.5% (1.5-60.3%) over three generations.

Sauer et al. (2017) also provide year by year records, and so we can extrapolate reductions over any three generation period. Three generations ago (pre-2018) is approximately 2001. Therefore, we can extrapolate the trends between 2001 and 2015 to 2018 in order to estimate the population trend over the past three generations. Between 2001 and 2015 the population has been, in general, decreasing with a significant, estimated annual decrease of 5.5% (3.35% to 7.6% decrease) (Sauer et al. 2017). This would equate to a reduction of 60.6% (43.0-72.9%) over three generations.

Bonter and Harvey (2008) also show using data from Project FeederWatch that the species may have disappeared from 50% of recorded sites between 1988 and 2006, and where the species remained, abundance dropped by 27%. All of these data are only for continental U.S.A. and Canada though, and so the population trends in Mexico are not included.

The threshold for listing as Vulnerable under this criterion is a reduction of 30% over 3 generations, while the threshold for Endangered is a reduction of 50% over the same time period. Therefore, it may be appropriate to tentatively suspect that the species approaches or meets the threshold for Endangered based on past declines. However, the short term data from Sauer et al. (2017) suggests ongoing declines may only meet the threshold for Vulnerable. Therefore, it is proposed that the species be listed as Endangered under criterion A2ac with the potential for subcriterion (e) to be used too given the tentative proposed threats (although further evidence may be required to support this). We do though request any further comment as to whether the rate of ongoing decline may in fact be >50% over three generations so as to better decide whether the species could warrant listing under criteria A3c+4ac too.

 

Criterion B – The species’s range is far too large to warrant listing under this criterion.

 

Criterion C – Partners in Flight (Rosenberg et al. 2016, Partners in Flight 2018) estimate the population size to be 3,400,000 mature individuals in U.S.A. & Canada out of a global total of 2,600,000. Therefore, the population size 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, it is proposed that this species be uplisted to Endangered under Criterion A.

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’ Red List status. Therefore, please make sure your comments are relevant to the information that is sought, or about the species’ Red List status.

 

References

BirdLife International. 2018. Species factsheet: Hesperiphona vespertina. Downloaded from http://www.birdlife.org on 31/01/2018

Bonter, D. N.; Harvey, M. G. 2008. Winter survey data reveal rangewide decline in Evening Grosbeak population. Condor 110(2): 376-381.

Clement, P. 2018. Evening Grosbeak (Hesperiphona vespertina). 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/61427 on 31 January 2018).

Partners in Flight. 2018. Avian Conservation Assessment Database, version 2017. Available at http://pif.birdconservancy.org/ACAD. Accessed on 05/02/18.

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 northern United States. Biological Conservation 187: 270-278.

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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