|Scientific Name:||Aphelocoma insularis|
|Species Authority:||Henshaw, 1886|
|Red List Category & Criteria:||Vulnerable D2 ver 3.1|
|Reviewer/s:||Butchart, S. & Symes, A.|
|Contributor/s:||Desrosiers, M., Fitzpatrick, J., Langin, K., Morrison, S., Sillett, S. & Stallcup, J.|
This species has been uplisted to Vulnerable because it occupies an extremely small range, being found on only one island, and is susceptible to the arrival of West Nile virus, which has resulted in high mortality in other corvids. This plausible threat could conceivably cause the species to qualify as Critically Endangered or Extinct within one or two generations if adequate intervention is not carried out. Given the limited efficacy of the vaccines available, a stable sub-set of several hundred vaccinated birds would probably be required to safeguard the species from such a fate.
Aphelocoma insularis is endemic to the California Channel Islands, U.S.A., being extant only on Santa Cruz Island (250 km2). Evidence suggests that the species could have been extant on Santa Rosa Island until perhaps the early to mid-20th century (Morrison et al. 2011). The species’s population was previously estimated to number c.9,000 individuals (Rich et al. 2004), of which 7,000 were thought to be breeders (Kelsey and Collins 2000, Rich et al. 2004). However, survey results from 2008 and 2009 suggest there may actually be fewer than 3,000 individuals, and perhaps only c.2,400, probably including fewer than 1,000 breeding pairs, but with no clear evidence of a decline (Morrison et al. 2011, The Nature Conservancy 2011, S. Sillett in litt. 2012).
|Range Map:||Click here to open the map viewer and explore range.|
The species's population was previously estimated to number c.9,000 individuals (Rich et al. 2004), including c.7,000 breeders (Kelsey and Collins 2000, Rich et al. 2004). However, the analysis of survey results from 2008 and 2009 suggests there may actually be fewer than 3,000 individuals, and perhaps only c.2,400, probably including fewer than 1,000 breeding pairs (Morrison et al. 2011, The Nature Conservancy 2011, S. Sillett in litt. 2012). Based on this information, the number of mature individuals is estimated at c.2,000.
|Habitat and Ecology:||It occurs throughout nearly all of the woody vegetation on the island, but is especially abundant in canyons and on north facing slopes dominated by Quercus trees.|
Very little is known about the species's historic status or ecology; however, there is evidence to suggest that it was lost from Santa Rosa Island in the early to mid-20th century owing at least partly to the impacts of livestock on native vegetation (Morrison et al. 2011). Vegetation on Santa Cruz has been severely degraded by introduced sheep and pigs, but is recovering since their control. It may be susceptible to catastrophic fires and the introduction of diseases. There is particular concern over the potential danger from West Nile virus, which arrived in mainland southern California in 2003, but has not yet become established on Santa Cruz Island (c.30 km from the mainland) (Boyce et al. 2011, Morrison et al. 2011). It is unclear whether this is simply because a vector, most likely an infected bird, has not yet carried the virus to the island or because the climate there is too cool for efficient virus replication in mosquitoes, potentially providing the island’s avifauna with a thermal refuge (Boyce et al. 2011, Morrison et al. 2011). If this latter explanation is correct, it may be only temporary, owing to the potential effects of projected climate change (Morrison et al. 2011). The establishment of West Nile virus on Santa Cruz Island is expected to be catastrophic for the species, assuming a lack of adequate intervention, as it is likely to be at risk of high mortality from the virus, given the lethal impacts in other corvid species (e.g. Kilpatrick et al. 2007, LaDeau et al. 2008). It has been recommended that over 100 individuals in the population be vaccinated each year (Boyce et al. 2011). Climate change may also make the island’s vegetation more susceptible to wildfire. In addition, the species is potentially susceptible to the introduction of rats (Rattus spp.), which are absent from Santa Cruz and Santa Rosa islands, but are extant on three of the other six Channel Islands, having been eradicated from another (Morrison et al. 2011).
Conservation Actions Underway
Conservation action is now controlling introduced sheep and pigs, and in many areas the vegetation is recovering dramatically, but the impact of these ecological changes on the status of this species requires careful monitoring. A programme of vaccination against West Nile virus amongst the population was initiated in 2008 (Morrison et al. 2011), with at least 100 birds vaccinated so far (The Nature Conservancy 2011). However, this is considered a precautionary early measure using a vaccine that has been tested on Western Scrub-jay A. californica with only modest success (Morrison et al. 2011, Wheeler et al. 2011).
Conservation Actions Proposed
Continue to implement a vaccination programme, with the aim of establishing a stable sub-set of several hundred vaccinated birds. Continue to monitor the population for any signs of decline. Eradicate rats from the Channel Islands. Manage the threat of wildfire.
|Citation:||BirdLife International 2012. Aphelocoma insularis. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 19 May 2013.|
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