VU
Yellow-billed Magpie Pica nutalli



Justification

Justification of Red List Category
This species is currently listed as Vulnerable. Between 2003-2008, the species underwent a rapid population reduction owing to mortality caused by West Nile Virus. While the species now appears to be recovering, recent records suggest it is still declining moderately.

Population justification
The species's population was estimated at c.180,000 individuals in 2003, but is thought to have been reduced by 49% by 2006 (del Hoyo et al. 2009) owing to West Nile Virus. Partners in Flight estimate the population to be 90,000 individuals (Partners in Flight Science Committee 2013). The population now appears to have stopped its decline and may have recovered somewhat (W. Koenig in litt. 2016), thus the population is placed in the band for 50,000-99,999 mature individuals, which is assumed to equate to c.75,000-150,000 individuals in total.

Trend justification
The species suffered high levels of mortality and a severe population decline owing to an outbreak of West Nile virus (Airola et al. 2007, Crosbie et al. 2008). Following the documented arrival of the virus in California in summer 2003 (Reisen et al. 2004), data have suggested 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 population appeared to reach a low in 2007-2008, and since then has shown signs of recovery, although it was still depleted in 2010/2011 compared to data collected since the late 1950s (W. Koenig in litt. 2012). 

Year by year records from Sauer et al. (2017) show that the species may have continued to decline since the end of the West Nile Virus outbreak, although the decline is deemed non-significant, and instead the species may be considered to be stable. 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.

Distribution and population

This species is endemic to California, USA, occurring west of the Sierra Nevada mountains (del Hoyo et al. 2009, Marzluff and Sharpe 2018). The species's population, estimated at c.180,000 individuals in 2003, is thought to have been reduced by 49% by 2006 (del Hoyo et al. 2009), owing to the impacts of West Nile Virus. Following a low in 2007-2008, the population now appears to have stopped its decline and may have recovered somewhat (W. Koenig in litt. 2016), even though observational data suggest a moderate ongoing decline (Sauer et al. 2017).

Ecology

This species inhabits oak savanna, with large trees scattered among broad expanses of open grassland and pasture (del Hoyo et al. 2009, Marzluff and Sharpe 2018). Over recent decades, it has been increasing in suburban settings, notably in the Sacramento Valley. It forages in cultivated fields and orchards. This omnivorous species feeds on a range of items, including invertebrates, small mammals, bird eggs and nestlings, carrion, food discarded by humans, grains, fruits, nuts and other seeds. Nest-building takes place from December through to March, with egg-laying from March to May (del Hoyo et al. 2009).

Threats

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).

Conservation actions

Conservation Actions Underway
This species has been the subject of monitoring through citizen science surveys. The species is included on the 'Watch List' of the State of North America's Birds as a species of high conservation concern (NABCI 2016).

Conservation Actions Proposed
Continue to monitor the species's population trend through regular surveys. Protect areas of suitable habitat.

Acknowledgements

Text account compilers
Westrip, J., Derhé, M., Ekstrom, J., Ashpole, J, Hermes, C., Butchart, S., Sharpe, C.J., Symes, A., Taylor, J.

Contributors
Meehan, T., Koenig, W.


Recommended citation
BirdLife International (2019) Species factsheet: Pica nutalli. Downloaded from http://www.birdlife.org on 15/12/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 15/12/2019.