Yellow-billed Magpie (Pica nutalli) is endemic to California, U.S.A., west of the Sierra Nevada Mountains (Marzluff and Sharpe 2018). It is native to oak savanna, with trees scattered among expanses of pasture or grassland, but it also makes use of cultivated areas and orchards, and is increasingly utilising suburban areas (Marzluff and Sharpe 2018).
Habitat loss through urban and agricultural developments, as well as the impacts of Sudden Oak Death, summer droughts and poisons used to kill ground squirrels were thought to be potential threats to the species (see Marzluff and Sharpe 2018). These may have caused minor local declines, but the species was still abundant in other areas (Marzluff and Sharpe 2018), such that these threats were thought to have no/negligible impacts on the species as a whole and the population was deemed to be stable, although Airola et al. (2007) suggest the species may have even increased between 1980/81 and 2001/02.
However, in the mid-2000s the population underwent a very rapid decline as West Nile Virus swept through the population. It was first noted in 2003 (Reisen et al. 2004) and continued to impact the species until 2007/08, after which potentially some recovery has been seen (W. Koenig in litt. 2012). Some data suggested that the species decreased by 42-49% between 2004 and 2006 (Crosbie et al. 2008), or 48% between 2004/05 and 2005/06 (Airola et al. 2007). This led to the species being listed as Near Threatened (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, Yellow-billed Magpie appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.
Criterion A – Given that the main population reduction took place over a very short period of time, it would be inappropriate to look at the long term data presented in Rosenberg et al. (2016). Breeding Bird Survey data between 2005 and 2015 shows an annual decline of 6.07% (2.73-9.52%) (Sauer et al. 2017), which would equate to a reduction of 46.5% (24.2-63.2%) over that ten years.
Year by year records from Sauer et al. (2017) show that the species may have actually continued to decline since the end of the West Nile Virus outbreak, although the decline is deemed non-significant. Using the year by year records also means that we can track back to three generations ago (1997) and calculate the population reduction up to 2015. Sauer et al. (2017) show that between 1997 and 2015, the average annual decline was 4.92% (3.00-6.92%), although of course the majority of this was concentrated during the West Nile Virus outbreak. Assuming population stability between 2015 and 2018 would still give a population reduction of 59.7% (42.2-72.5%) over the past three generations. If this rate of decline were to be projected to 2018, the overall reduction would be 65.9% (47.7-78.3%).
It appears that the main reduction has ceased and is reversible, and we do know the cause of the reduction. However, there do remain other potential threats to the species and, although non-significant, declines may still be occurring. For instance, between 2009 and 2015 the population trend was a non-significant annual decline of 2.98% (8.27% decrease to 2.67% increase), which would equate to a reduction of 47.5% (84.1% reduction to 75.3% increase) over three generations.
The threshold reduction size for listing as Vulnerable is 30%, for Endangered is 50%, and for Critically Endangered is 80%. Therefore, the species would warrant listing as Endangered under criterion A2ace+4ace.
Criterion B – The species’s range is too large to warrant listing under this criterion (Extent of Occurrence = 105,000km2).
Criterion C – Rosenberg et al. (2016) estimate the population size to be 90,000 mature individuals. This is too large to warrant listing under this criterion.
Criterion D – The species’s range and population size 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, Yellow-billed Magpie potentially warrants listing at least as Endangered. 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.
Airola, D. A.; Hampton, S.; Manolis, T. 2007. Effects of West Nile Virus on sensitive species in the Lower Sacramento Valley, California: An evaluation using Christmas Bird Counts. Central Valley Bird Club Bulletin 10: 1-22.
BirdLife International. 2018. Species factsheet: Pica nutalli. Downloaded from http://www.birdlife.org on 09/03/2018.
Crosbie, S. P.; Koenig, W. D.; Reisen, W. K.; Kramer, V. L.; Marcus, L.; Carney, R.; Pandolfino, E.; Bolen, G. M.; Crosbie, L. R.; Bell, D. A.; Ernest, H. B. 2008. Early impact of West Nile Virus on the Yellow-billed Magpie (Pica nuttalli). The Auk 125(3): 542-550.
Marzluff, J.; Sharpe, C. J. 2018. Yellow-billed Magpie (Pica nutalli). 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/60755 on 9 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.
Reisen, W.; Lothrop, H.; Chiles, R.; Madon, M.; Cossen, C.; Woods, L.; Husted, S.; Kramer, V.; Edman, J. 2004. West Nile Virus in California. . Emerging and Infectuous Diseases10: 1369-1378.
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.