Archived 2018 topic: Allen’s Hummingbird (Selasphorus sasin): revise global status?

Currently listed as Least Concern (BirdLife International 2018), Allen’s Hummingbird (Selasphorus sasin) comprises two subspecies. One is migratory, breeding in coastal western U.S.A. from Oregon to California, and wintering in central Mexico (see Altshuler et al. 2018). The other is resident to the extreme south-west of California and extreme north-west of Mexico, as well as adjacent offshore islands (see Altshuler et al. 2018). It generally occurs in scrubland and bushy slopes, as well as into open woodland (Altshuler et al. 2018), while garden plants and artificial feeders may be bringing the species into more urbanised areas (Clark and Mitchell 2013).

Partners in Flight list the two key threats to the species as climate change and urbanisation (Rosenberg et al. 2016), although from Clark and Mitchell (2013) it appears that these threats are currently being offset by the increase in available nectar for the species directly as a result of human activities. Thus, while these threats may be the most important for the species, it is unsure whether they are having an impact.

Following the publication of Partners in Flight 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 Categories and Criteria. As the data presented come from long-term trends (Partners in Flight trends come from between 1970 and 2014), where possible we have also used data from the North American Breeding Bird Survey (Sauer et al. 2017) to collate more recent trends. Having completed this review, Allen’s Hummingbird appears to potentially warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

 

Criterion A – The information regarding the population trend appears to be very contradictory. Rosenberg et al. (2016) estimate the population reduction between 1970 and 2014 to be 83%, which equates to a reduction of 43.3% over three generations (14.1 years). Partners in Flight also estimate the half-life of the species to be only 17 years, and so this would roughly equate to decreases of 43.7% over three generations.

Short term (2005-2015) data from Sauer et al. (2017) also suggests a rapid decline, with annual declines of 4.11% (1.58-6.95%). This would equate to declines of 44.7% (20.1-63.8%) over three generations. Sauer et al. (2017) do also show year by year records, and so we can extrapolate trends for any three generation period. Three generations ago was approximately 2004. Therefore, we can extrapolate the trends between 2004 and 2015 to 2018 in order to estimate the population trend over the past three generations. Between 2004 and 2015 the population has been, in general, decreasing with a significant, estimated annual decrease of 4.10% (1.81 to 7.03%) (Sauer et al. 2017). This would equate to a reduction of 44.6% (15.4-64.2%) over three generations.

This data alone would appear to suggest that the species clearly warrants uplisting to Vulnerable under this criterion. However, surveys between 1980 and 2000 by Howell and Gardali (2003) found the population of this species to be stable over that time period at least. Clark and Mitchell (2013) even suggest that the main impacts of human activity, e.g. introduced species and artificial feeders in urbanised areas are leading to population increases; and they suggest that declines based on the Breeding Bird Survey data may be a result of artefacts of survey technique.

Therefore, it is not clear what the species’s trend really is, and we request further information and insight to better assess the species against this criterion.

 

Criterion B – The species’s range is too large to warrant listing under this criterion (Extent of Occurrence [breeding/resident] = 214,000km2; Extent of Occurrence [non-breeding] = 456,000km2).

 

Criterion C – Rosenberg et al. (2016) estimate the population size to be 1,700,000 mature individuals. This is far too large to warrant listing under this criterion.

 

Criterion D – The population size and range of this species 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, Allen’s Hummingbird potentially warrants uplisting to Vulnerable, although there is contradictory evidence that suggests the population may be stable (at least up to 2000) or even increasing. We welcome any comments or further information, especially regarding this contrasting information regarding population trends. Please note though 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 about the proposed listing.

 

References

Altshuler, D. L., Kirwan, G. M.; Boesman, P. 2018. Allen’s Hummingbird (Selasphorus sasin). 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/55675 on 6 March 2018).

BirdLife International. 2018. Species factsheet: Selasphorus sasin. Downloaded from http://www.birdlife.org on 06/03/2018.

Clark, C. J.; Mitchell, D. E. 2013. Allen’s Hummingbird (Selasphorus sasin), 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.501.

Howell, S. G.; Gardali, T. 2003. Phenology, sex ratios, and population trends of Selasphorus hummingbirds in central coastal California. J. Field. Ornith. 74(1): 17-25.

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.; 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: Allen’s Hummingbird (Selasphorus sasin): revise global status?

  1. James Westrip (BirdLife) says:

    Tim Meehan has kindly provided analyses of Christmas Bird Count data. Taken from long-term trends (1966-2017), these data suggest an annual increase of 16.77% (15.44-18.15% annual increase) in this species. This would equate to an increase of 790.07% (656.98-950.50%) over three generations.

  2. Claudia Hermes (BirdLife International) says:

    Preliminary proposals
    Based on available information, our preliminary proposal for the 2018 Red List would be to list:
    Allen’s Hummingbird as Least Concern.
    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 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.

Comments are closed.