Archived 2011-2012 topics: Island Scrub-jay (Aphelocoma insularis): does it qualify as Vulnerable?

Initial deadline for comments: 31 January 2012.

BirdLife species factsheet for Island Scrub-jay

Island Scrub-jay Aphelocoma insularis is endemic to the Channel Islands, California, USA, being extant on Santa Cruz Island, where it inhabits virtually all woody vegetation types. It is listed as Near Threatened under criterion D2, on the basis that it has an extremely small range, being retricted to one location (Extent of Occurrence c.250 km2), but with no known plausible threats that could result in it qualifying as Critically Endangered or Extinct within one or two generations (one generation estimated at c.14.4 years; BirdLife International unpubl. data), although it is considered susceptible to stochastic events in general.

The species’s population was estimated to number c.9,000 mature individuals (Rich et al. 2004), although 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, but with no clear evidence of a decline (Morrison et al. 2011, The Nature Conservancy 2011). It may be susceptible to catastrophic fires and the introduction of diseases, and 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 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). 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).

A programme of vaccination against West Nile virus amongst the Island Scrub-jay 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). Nevertheless, it has been recommended that over 100 individuals in the Island Scrub-jay population be vaccinated each year (Boyce et al. 2011). Given the limited efficacy of the vaccines available (Wheeler et al. 2011), it may be said that until there is a stable sub-set of several hundred vaccinated birds in the population, this plausible threat could conceivably cause the species to qualify as Critically Endangered or Extinct within one or two generations.

For the reasons stated here, the species potentially qualifies for uplisting to Vulnerable under criterion D2. Comments are invited on this potential category change and further information would be welcomed.


Boyce, W. M., Vickers, W., Morrison, S. A., Sillett, T. S., Caldwell, L., Wheeler, S. S., Barker, C. M., Cummings, R. and Reisen, W. K. (2011) Surveillance for West Nile Virus and Vaccination of Free-Ranging Island Scrub-Jays (Aphelocoma insularis) on Santa Cruz Island, California. Vector-Borne and Zoonotic Diseases 2011:1063-1068.

Kilpatrick, A. M., LaDeau, S. L. and Marra, P. P. (2007) Ecology of West Nile virus transmission and its impact on birds in the Western Hemisphere. Auk 124: 1121-1136.

LaDeau, S. L., Marra, P. P., Kilpatrick, A. M. and Calder, C. A. (2008) West Nile Virus Revisited: Consequences for North American Ecology. BioScience 58: 937-946.

Morrison, S.A., Sillett, T. S., Ghalambor, C. K., Fitzpatrick, J. W., Graber, D. M.,  Bakker, V. J., Bowman, R., Collins, C. T., Collins, P. W., Delaney, K. S., Doak, D. F., Koenig, W. D., Laughrin, L., Lieberman, A. A., Marzluff, J. M., Reynolds, M. D., Scott, J. M., Stallcup, J. A., Vickers, W. and Boyce, W. M. (2011). Proactive Conservation Management of an Island-endemic Bird Species in the Face of Global Change. BioScience 61: 1013-1021.

Rich, T. D., Beardmore, C. J., Berlanga, H., Blancher, P. J., Bradstreet, M. S.W., Butcher, G. S., Demarest, D.W., Dunn, E. H., Hunter, W. C., Inigo-Elias, E. E., Martell, A. M., Panjabi, A. O., Pashley, D. N., Rosenberg, K. V., Rustay, C. M., Wendt, J. S. and Will, T. C. (2004) Partners in flight: North American landbird conservation plan. Ithaca, NY: Cornell Lab of Ornithology.

The Nature Conservancy (2011) No Denial about West Nile: Protecting the Island Scrub-Jay.

Wheeler, S. S., Langevin, S., Woods, L., Carroll, B. D., Vickers, W., Morrison, S. A., Gwong-Jen J. Chang, Reisen, W. K. and Boyce, W. M. (2011) Efficacy of Three Vaccines in Protecting Western Scrub-Jays (Aphelocoma californica) from Experimental Infection with West Nile Virus: Implications for Vaccination of Island Scrub-Jays (Aphelocoma insularis).Vector-Borne and Zoonotic Diseases 11: 1069-1080.

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5 Responses to Archived 2011-2012 topics: Island Scrub-jay (Aphelocoma insularis): does it qualify as Vulnerable?

  1. I strongly support the proposed change to ‘Vulnerable’ status. I addition to the pertinent facts well presented in this fact sheet, it bears emphasis that the Island Scrub-Jay appears to be immunologically naive in that all individuals that have been tested were lacking antibodies to any of the various insect-borne viruses known from mainland California (Walter Boyce, unpubl. data personally communicated to JWF). Given the climatic regime of the northern Channel Islands, it is reasonable to suppose that their immune systems have remained unchallenged by potentially lethal arboviruses for many generations, perhaps for as long as the species has been isolated (~150,000 years; Delaney and Wayne 2005). Moreover, genetic variability of the Island Scrub-Jay is significantly lower than in mainland jays (Delaney and Wayne 2005), presumably reducing the population’s ability to respond rapidly via natural selection to a novel pathogen. Until a second, geographically isolated population is established (e.g., on Santa Rosa Island, where the jay was almost certainly extirpated by human-induced landscape change) the single Island Scrub-Jay population on Santa Cruz Island must be considered highly vulnerable, and its level of vulnerability will continue to increase as climate change improves conditions for reproduction and population growth of mosquitos and biting-midges on that island.

    For comparison, populations of the closely related Florida Scrub-Jay are known to suffer periodic spikes in mortality (once approaching 50% of breeders and 100% of juveniles) apparently caused by arboviruses long endemic to Florida (Woolfenden and Fitzpatrick 1991). In the event that a novel arbovirus such as WNV spreads across Santa Cruz Island, it is highly likely that mortality of naive Island Scrub-Jays would be much greater than these numbers.

  2. After review of the existing and emerging threats to the Island Scrub-Jay, and the criteria for “Vulnerable” status, I strongly support uplisting this species to “Vulnerable.”

  3. I believe that given conservation threats faced by the Island Scrub-Jay, it is advisable to change the species’ status to “vulnerable.” Historical analyses of extinction events have shown that species endemic to islands are particularly vulnerable; for example, approximately 90% of the bird species that have gone extinct since the time of European colonization were island endemics (Johnson and Stattersfield 1990 Ibis). Island Scrub-Jays face many of the same problems that plagued these other species, including (1) a restricted geographic range with limited spatial separation between sub-populations (which enhances the threat posed by fire), and (2) an evolutionary history lacking selection for defenses against novel mainland threats (e.g. diseases). It is for these reasons that I strongly support the proposal to elevate the conservation status of the Island Scrub-Jay to “vulnerable.”

  4. I strongly support listing the Island Scrub-Jay as vulnerable. Our recent island-wide survey (in review at Ecological Applications) indicates that the current population size is less than 2400 individuals. This figure includes territorial breeders and non-territorial juveniles. Thus, the total number of breeding pairs is well under 1000.

  5. Projected climactic changes on Santa Cruz Island lead me to support the proposed change to “vulnerable” status for the Island Scrub-Jay. Island species are known to harbor less genetic diversity than mainland species (Frankham 1997), and this has been demonstrated empirically in the Island Scrub-Jay (Delaney & Wayne 2005). Genetic diversity is the best predictor of long-term survival of species (Newman & Pilson 1997), as it allows for survival in the face of climactic change or introduced predators and pathogens. It is conceivable, given climactic projections that West Nile Virus may establish on Santa Cruz Island. The impact on the Island Scrub-Jay if this were to happen is expected to be severe. West Nile Virus is known to be especially harmful to Corvid species. Another California endemic, the Yellow-Billed Magpie, suffered a 50% decline when exposed to this disease (Crosbie et al 2008). The Island Scrub-Jay is restricted to Santa Cruz Island, and like many island species, has lost the ability to disperse in the face of adverse environmental change or catastrophic stochastic events such as fire (Diamond 1981). I believe that a change to “vulnerable” is timely.

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