Introduction
Of the over 500 species of birds that breed in North America, only one, the island scrub-jay, occurs on a single island—Santa Cruz Island in Channel Islands National Park. This makes it the only island endemic bird species in North America. Compared to its mainland cousin, the California scrub-jay, the island scrub-jay is larger, darker blue in color, and has a distinctive call, making it the most differentiated of all the island endemic birds. This species is the only scrub-jay on the Channel Islands and occupies more habitats than do scrub-jays on the mainland.
Quick and Cool Facts
The island scrub-jay lives only on Santa Cruz Island, which means it has the smallest range of any North American bird species.
The island scrub-jay belongs to the family Corvidae, which includes crows and ravens, are remarkable for their intelligence, memory and curiosity.
A genetic analysis indicates that this species diverged from its closest relative, the wide spread California scrub-jay about 150,000 years ago.
Island scrub-jays are monogamous and may stay with a mate for their entire lives.
The island scrub-jay can live as long as twenty years.
The island scrub-jay is noticeably larger than its mainland related species of scrub jays.
Appearance
Measuring 13 inches, the island scrub-jay is distinguished from other scrub-jays by its larger size—almost 1/3 larger than its mainland counterpart. This species is also brighter and more vibrant blue than other scrub-jays. It has a broad head with ultramarine-blue nape, crown, upper wing and tail, a white upper breast, chin, and throat, and a large gray-brown patch on the upper part of its back. Other characteristics include a distinct blue collar below the throat which is nearly complete, and a disproportionate large black bill, and a long tail typical of most other jays. Juveniles are grayish-white overall, but have blue wings and tail. Island scrub-jays have a raspy "shreep" call and a undulating flight pattern.
Range
The island scrub-jay is restricted to Santa Cruz Island, the largest and most topographically diverse of the Channel Islands. Santa Cruz Island is 18 miles off the coast of California and directly south of Santa Barbara. The Channel Islands are uniquely important for the preservation of this endemic bird and others. There are no recent records of scrub-jays occurring on other islands, but a fossil jay bone has been found on nearby Santa Rosas Island, and an ornithologist from the Smithsonian Institution who visited Santa Rosa Island in 1892 noted that the rancher there reported jays on the island. It is unclear at what point jays went extinct on Santa Rosa Island (Collins 2009).
Habitat
This species breeds in coast live oak woodland or chaparral dominated by scrub oak. On the park property of Santa Cruz Island island scrub-jays are commonly seen in in upper Scorpion Canyon and at Prisoners Harbor. Most foraging and other maintenance activities occur inside territory boundaries, with territory boundaries being stable from year to year. Agonistic behaviors for defending territories include mostly vocalizations and chasing, although dominant jays have been observed pecking subordinate individuals.
Feeding
The large bill of the island scrub-jay is related to its diet, of thick-shelled acorns which they bury, or cache, in the fall and eat months later. They also eat insects, spiders, snakes, lizards, mice, and other birds' eggs and nestlings.
Reproduction
These birds are monogamous, often having the same mates all their lives. They are also territorial. Breeding habitat appears to be saturated on the island, causing young individuals to delay breeding for up to several years. Until breeding space becomes available, unmated individuals use marginal habitats not suitable for breeding. Non-breeders do not defend territories, but rather forage and roost in loose groupings or on their own.
Nesting peaks during the last two weeks in March when the chaparral plants are flowering and growing new leaves. This period also coincides with an increase in arthropod abundance, indicating that this may be a strong influence on the timing of nesting in island scrub jays. Nests are located in dense bushes and trees and are often well-concealed. Nests are constructed of coarse sticks, lined with finer twigs and rootlets, and can be placed anywhere from ground level to 40 feet off the ground.
Females lay two to five eggs in a nest that they incubate for about twenty days. While the female sits on the eggs, the males spends time hunting and defending the nest from predation by gopher snakes, island spotted skunks, island foxes, common ravens, and other island scrub jays. In fact, nest predation is the biggest limit onisland scrub-jay reproductive success, and the extent to which a nest isconcealed affects the likelihood of predation (Caldwell et al. 2013). Vegetation recovery on Santa Cruz Island may eventually reduce the impact of predation. Once the chicks fledge, average life expectancy is 4.8 years and can be as long as twenty years.
Conservation Status
Since the island scrub-jay occurs only on one island that makes it susceptible to any major disaster, a disease outbreak, or widespread land-use changes, any of which could potentially extirpate the species or cause a severe population decline. The island scrub-jay is classified as Near Threatened on the IUCN Red List.
The uniqueness of this jay is the focus of an ongoing research and monitoring effort by personnel from the Smithsonian Institution, Colorado State University, the UC Davis WildlifeHealth Center, and The Nature Conservancy. The most insidious threat to island scrub-jays is the possible introduction of West Nile Virus to Santa Cruz Island. The island scrub-jay's mainland cousin,the western scrub-jay, is extremely susceptible to West Nile Virus, which is carried by certain species of mosquitoes. Ambient temperatures on Santa Cruz Island are currently to low to support those mosquito species, but would be high enough to support those species when global warming occurs. The threat of this has prompted some conservation biologists to propose establishing a second, redundant population of island scrub-jays on Santa Rosa Island (Morrison et al. 2011). Another possible mitigation for West Nile Virus is annual vaccination of a core group of island scrub-jays against the disease, though the expense and availability of an appropriate vaccine and the difficulty of recapturing jays for booster shots make this less attractive as a treatment (Boyce et al. 2011, Wheeler et al.2011).
Boyce, W.M., W. Vickers, S.A. Morrison, T.S.Sillett, L. Caldwell, S.S. Wheeler, C.M. Barker, R. Cummings and W. Reisen.Vector-borne and Zoonotic Diseases 11(8): 1063-1068.
Caldwell, L., V.J. Bakker, T.S. Sillett, M.A.Desrosiers, S.A. Morrison and L. M. Angeloni. 2013. Reproductive ecology of theisland scrub-jay. The Condor 115(3): 603-613.
Collins, P.W. 2009. Historic and prehistoricrecord for the occurrence of island scrub-jays (Aphelocoma insularis) on the northern Channel Islands, Santa Barbatra Island,California. Santa Barbara Museum of Natural History. Rechnical report no. 5.
Morrison, S.A., T.S. Sillett, C.K. Ghalambor,J.W. Fitzpatrick, D.M. Graber, V.J. Bakker, R. Bowman, C.T. Collins, P.W.Collins, K.S. Delaney, D.F. Doak, W.D. Koenig, L. Laughrin, A.A. Lieberman,j>W. Marzluff, M.d. Reynolds, J.M. Scott, J.A. Stallcup, W. Vickers and W.M.Boyce. 2011. Proactive conservation management of an island-endemic birdspecies in the face of climate change. BioScience 61(12): 1013-1021.
Wheeler, A.S., S. Langevin, L. Woods, B.D.Carroll, W. Vickers, S.A. Morrison, G.J. Chang, W.K. Reisen and W.M. Boyce.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(8):1069-1080.
