Common Grackle (Quiscalus quiscula): revise global status?

Currently listed as Least Concern (BirdLife International 2018), the Common Grackle (Quiscalus quiscula) is found solely in North America, with the vast majority of its range in U.S.A. and Canada. In the south of its range it is resident, but other populations will make short to medium range movements (Fraga 2018). It may have originally occupied wooded habitats near watercourses (Fraga 2018), but with the intensification of agriculture and clearance of woodland the species can now be found in a range of habitats including rural and residential areas (Fraga 2018).

It is common to abundant throughout its range and it will feed on agricultural produce to such an extent that it is considered a major pest (see Peer and Bollinger 1997), and as such it is under control measures in some areas (see Peer and Bollinger 1997, Fraga 2018). The roost sites for the species can also hold the fungus Histoplasma capsulatum, which can cause the lethal human respiratory disease histoplasmosis (see Peer and Bollinger 1997). This has been used as a justification for the killing of large numbers of roosting birds (Peer and Bollinger 1997).

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

 

Criterion A – Partners in Flight put the overall population reduction between 1970 and 2014 at 54% (Rosenberg et al. 2016). This would roughly equate to a reduction of 25.7% over 3 generations (16.8 years). Rosenberg et al. (2016) also propose a half-life of 33 years (i.e. the population is predicted to halve in 33 years). This would equate to a population reduction of 29.7% over 3 generations.

Sauer et al. (2017) do show year by year records, and so we can extrapolate trends for any three generation period. Three generations ago 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 1.40% (1.11-1.68%) (Sauer et al. 2017). This would equate to a reduction of 21.1% (17.1-24.8%) over three generations, which does not approach the threshold for Vulnerable sufficiently to warrant listing under criterion A2.

Some extrapolated trends over three generations that include both time in the past and in the future do imply a reduction that approaches the threshold for Vulnerable. For instance, data from 2005-2015 show an annual decline of 1.87% (1.47-2.26% decline) (Sauer et al. 2017). This would equate to a reduction of 27.2% (22.0-31.9% reduction) over 3 generations. However, some more recent annual declines appear to be lower, and so declines of this rate are not suspected to continue into the future.

Therefore, the species appears to approach the threshold for Vulnerable under this criterion (reduction of 30% over 3 generations), and so would warrant listing as Near Threatened under criteria A4ad.

 

Criterion B – The species’s range is far too large to warrant listing under this criterion (Extent of Occurrence [breeding/resident] = 12,100,000km2; Extent of Occurrence [non-breeding] = 5,510,000km2).

 

Criterion C – The population size of the species, based on Partners in Flight is 69,000,000 mature individuals (Rosenberg et al. 2016). 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, Common Grackle potentially warrants uplisting to 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’ Red List status. Therefore, please make sure your comments are about the proposed listing.

 

 

References

BirdLife International. 2018. Species factsheet: Quiscalus quiscula. Downloaded from http://www.birdlife.org on 05/03/2018.

Fraga, R. 2018. Common Grackle (Quiscalus quiscula). 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/62283 on 5 March 2018).

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

Peer, B. D.; Bollinger, E. K. 1997. Common Grackle (Quiscalus quiscula), 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.271.

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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