This discussion was first published as part of the 2012 update, and remains open for comment in the hope that we will receive enough information to reassess the species in 2014.
Yellow-billed Magpie Pica nuttalli is endemic to the state of California, USA, where it occurs in a variety of wooded and grassland habitats, including suburban areas (e.g. Airola et al. 2007). It is listed as being of Least Concern on the basis that it did not appear to approach the thresholds for Vulnerable under any of the IUCN criteria.
This species has a large range, and hence does not approach the thresholds for Vulnerable under the range size criteria (B and D2: Extent of Occurrence of less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appeared to be stable, and hence the species did not approach the thresholds for Vulnerable under the population trend criteria (A: at least a 30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criteria (C and D1: fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).
There is now evidence that this species has suffered high levels of mortality and a severe population decline owing to a high susceptibility to West Nile virus (Airola et al. 2007, Crosbie et al. 2008), since its documented arrival in California in summer 2003 (Reisen et al. 2004), with data suggesting a decline of 42-49% from 2004 to 2006 (Crosbie et al. 2008). Christmas Bird Count (CBC) data from the Lower Sacramento Valley suggest that numbers of this species declined by 48% between 2004/2005 and 2005/2006, with surveyed numbers in 2005/2006 having declined by 38% compared to the previous 10-year average when accounting for the effects of bad weather (Airola et al. 2007). The analysis of CBC data by Airola et al. (2007) suggests that the species had been increasing on average between 1980/1981 and 2001/2002, but an analysis of CBC data from Califronia’s Central Valley indicates a steady decline of c.10% annually on average between 1995 and 2006. It is unclear, however, if the very rapid recent decline has continued beyond 2006, and whether this would be expected to continue into the future. Other threats cited for this species include habitat loss, rodent poisioning and direct persecution (Crosbie et al. 2008, Beedy et al. 2009 and references therein).
The evidence suggests that this species has undergone a population reduction equivalent to at least a 30-49% decline over three generations, estimated by BirdLife to be 21 years (based on an estimated generation length of c.7.1 years [BirdLife International unpubl. data]). However, the decline has probably been more severe. A reduction of at least 50% over 21 years would warrant uplisting of the species to Endangered, while any indication of a decline of at least 80% over 21 years might mean the species should be uplisted to Critically Endangered.
Comments are invited on the potential uplisting of this species under criterion A, and further information is requested, particularly on whether the observed rapid decline and high mortality have continued up until the present.
Airola, D. A., Hampton, S. and 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.
Beedy, T., Estep, J., Sterling, J. and Smallwood, S. (2009) Species Account: Yellow-billed Magpie (Pica nuttalli). Yolo Natural Heritage Program: http://www.yoloconservationplan.org/yolo_pdfs/speciesaccounts/birds/yellow-billed-magpie.pdf
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. and Ernest, H. B. (2008) Early impact of West Nile Virus on the Yellow-billed Magpie (Pica nuttalli). Auk 125: 542-550.
Reisen, W., Lothrop, H., Chiles, R., Madon, M., Cossen, C., Woods, L., Husted, S., Kramer, V. and Edman, J. (2004) West Nile Virus in California. Emerging and Infectuous Diseases 10: 1369-1378.
The attached figure was sent by Walt Koenig to accompany his comments posted on 26 January 2012: