Island jay

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Island jay
Island jay (Aphelocoma insularis)

Island jay ( Aphelocoma insularis )

Systematics
Order : Passerines (Passeriformes)
Subordination : Songbirds (passeri)
Superfamily : Corvoidea
Family : Corvids (Corvidae)
Genre : Bush jay ( Aphelocoma )
Type : Island jay
Scientific name
Aphelocoma insularis
Henshaw , 1886

The island scrub jay ( Aphelocoma insularis ) is a medium sized Singvogelart from the family of corvids , which only Santa Cruz Iceland off the coast of Southern California found. Together with the yellow-billed magpie ( Pica nuttalli ), the island jay is one of the two bird species endemic to California .

Compared to its closest mainland relatives, the western bush jay ( Aphelocoma californica ), the Woodhouse's scrub jay ( Aphelocoma woodhouseii ) and the Florida bush jay ( Aphelocoma coerulescens ), the island jay is significantly larger and its feathers are darker in color. In addition, its voice is louder than that of the Western Bushjay and its brooding is not cooperative like that of the Florida Bushjay. Among the passerine birds , the island jay stands out with its exceptionally high annual survival rate of 95 percent in adults .

Since the distribution of the population estimated at 2,400 to 3,000 individuals in 2008 and 2009 is limited to the only 250 square kilometer Santa Cruz Island, the species is classified as endangered by the IUCN . The species is potentially threatened by land fires and the West Nile virus .

features

Build and color

Adult island jay

Adult island jays reach a length of around 33 centimeters. Male specimens weigh 100–147 grams, while females weigh 100–117 grams. The animals have long tail feathers, disproportionately long beaks and long legs. The plumage of the island jay is colored matt ultramarine blue on the crown and neck, as well as on the sides of the chest, wings, upper tail-coverts and on the tail . The upper chest area and the neck are white, the lower chest area is colored gray. The sides of the head are black with a thin white stripe over the eyes . The shoulder wings are colored dark gray. The underside of the tail feathers is bluish in color. The iris is brown; The bill and legs are black. The plumage of juvenile animals is brownish-gray with a blue crown and dark blue wings and tail.

Compared to the western bush jay ( Aphelocoma californica ), the island jay is overall larger and has a longer beak. In addition, the island jay is darker in color and instead of a white color on the underside of its tail feathers has a light blue color.

Vocalizations

The island jay's voice resembles that of its closest relative, the western bush jay ( Aphelocoma californica ). This is a picture of a western bush jay in Strawberry , Marin County.
Sonogram of the above picture of a western bush jay.

Island jays have a wide repertoire of vocalizations. A high-pitched "Shek-shek-shek" is used to mark the territory and is often heard when flying between different branches. Females often respond to this "shek-shek-shek" from their partner with a loud and harsh chuckle.

In case of danger - for example from birds of prey or snakes - both sexes of the island jay make a screeching sound that is picked up by other individuals within the territory. The animals show twitching of their wings and tail feathers.

In spring and summer, territorial individuals of both sexes utter a quiet series of trills of up to 10 seconds. In courtship, male individuals feed their female partners. During courtship feeding , the females make a short, quiet sound that is described as "panting", which is similar to the begging call of nestlings of the island jay.

The voice of the island jays is generally louder than that of their relatives on the mainland, which is probably due to the size of the species.

distribution and habitat

Chaparral in the Santa Ynez Mountains near Santa Barbara

Island jays are found exclusively on Santa Cruz Island off the southern California coast, where they live year-round. With a size of around 250 square kilometers, Santa Cruz Island is the largest of the islands belonging to the Channel Islands National Park . The island jays prefer habitats overgrown by chaparral . This type of vegetation, specially adapted to the Mediterranean climate of California, is dominated by Quercus pacifica ("Island scrub oak") and oak forests and covers around 18 percent of Santa Cruz Island. In addition, island jays can also be found in parts of the island that are overgrown with a mixture of pine and scrub. The island jays, however, are less common in those parts of the island that are dominated by grassland. Compared to its relatives, the island jay is represented in a wider range of habitats than the Florida bush jay and in a narrower range than the western bush jay.

Way of life

nutrition

Island jays are omnivores ; their diet consists mainly of acorns and invertebrates , although they occasionally eat vertebrates as well as eggs and nestlings . In autumn, acorns are the most important food source. Like all corvids , island jays have an innate hiding instinct. Excess acorns, but also lizards and small mice, are hidden individually. The search for food takes place by jumping movements on the ground or in the branches of bushes and trees.

Social behavior

Brooding island jays live in pairs and are not supported by other animals during breeding, as is the case with 12 of the 30 species of New World jays . Non-breeding animals show no territorial behavior and can form swarms. These make up around 50 percent of the total population and use those habitats that are largely unsuitable for breeding, such as grassy areas. The swarming of these animals can be observed especially in the late afternoon or at sunset. Island jays, which gather in swarms, show hardly any aggressive behavior towards their fellow species.

During the breeding season, island jays show aggressive behavior towards other bird species, such as the acorn woodpecker ( Melanerpes formicivorus ) or the golden woodpecker ( Colaptes auratus ), which are driven from the vicinity of nests.

Island jays show little shyness towards humans. Individuals attracted by peanuts sometimes perch on the hand or on the head of people. Island jays have also been observed breaking into houses or cars while looking for food.

Reproduction

Island jays live monogamous , with around 10 percent of sexually mature animals choosing a new partner every year - despite the survival of both partners. The nests, which are about 30 centimeters wide and 10 centimeters high, are created by both partners at a height of 2 to 3 meters above the ground in bushes or trees (preferably oaks). The light bluish-green eggs are laid between the months of March and July; the clutch comprises between 2 and 5 eggs. After a breeding period of around 18 days, the young hatch, which are then fed by both partners for a period of 4 to 7 weeks.

The island jays on Santa Cruz Island do not breed for years after reaching sexual maturity because the number of available territories is limited. The first brood takes place late at an average age of 3.6 years. Only 14.6 percent of the animals breed at the age of 1 to 2 years and roughly the same number of island jays only breed at the age of 5 to 6 years. This means that the breeding of the animals on Santa Cruz Island takes place later than the western bush jays on the mainland, which usually breed for the first time at the age of two.

A 2013 study on the nesting success of island jays in relation to their habitat showed that predators have the greatest influence on successful reproduction. At 92 percent, they are by far the most important cause of unsuccessful attempts at reproduction. The same study found that only 15.6 percent of the attempts were successfully completed and at least one nestling survived. However, due to the fact that the island jays made a new attempt with a high probability (females nested up to 6 times in one breeding season and laid up to 18 eggs), the average number of fledged pups per breeding pair per year was 1.8 .

Predators and causes of mortality

The survival rate of juvenile island jays (aged six months to one year) is around 52 percent, while the survival rate of adults observed for 11 years was 95 percent. This means that the average survival rate of the island jays is significantly higher than that of their relatives on the mainland.

The island gray fox ( Urocyon littoralis ), the western spotted skunk ( Spilogale gracilis ) and snakes such as the tree-climbing gopher snake ( Pituophis catenifer ) are known to attack nests of the island jays. In addition, hibernating corner-tailed cows ( Accipiter striatus ) are predators of both juvenile and adult animals.

Taxonomy

First described the island scrub jay by the American Ornithologists was Henry W. Henshaw in 1886 in the journal The Auk . From a brief visit to Santa Cruz Island in 1875, Henshaw had brought three specimens of the bird with him, which he - after some hesitation - initially identified as western bush jays ( Aphelocoma californica ). More than ten years later, while Henshaw stayed at the National Museum of Natural History , the ornithologist Robert Ridgway pointed out that certain morphological features of the bird hides he had brought with him differed from all the hens known to him, whereupon Henshaw published his first description.

While the American Ornithologists' Union led the island jay under the name "Santa Cruz Jay" as an independent species in the first half of the 20th century, it classified it as a subspecies of Florida in the 5th edition of its Checklist of North and Middle American Birds -Buschhahers, Aphelocoma coerulescens insularis . Since 1998 the organization has been managing the island jay again as an independent species.

The early research assumed that individual individuals of the genus Aphelocoma could have reached Santa Cruz Island by flying and then trained their own species there. However, this thesis has been questioned by various authors with a view to the limited flight ability of the birds and the relatively large distance from Santa Cruz to the mainland.

Genetic studies from 2005 and more recent theories on the history of the California Channel Islands now support the assumption that the island jay and the western bush jay go back to a common ancestor who lived at least 100,000 years before our time. The island jay probably emerged as a separate species in the late Pleistocene around 20,000 to 11,000 years ago. During the then cold period , the sea level was lower and the now separated northern islands formed a common land mass that was closer to the mainland, which made colonization by local animal species easier.

Today research assumes that the island jay forms a superspecies together with the western bush jay and the Florida bush jay ( Aphelocoma coerulescens ) .

Persistence and Threat

The geographically narrow range of the island jay is one of the main reasons for the classification of the species as "endangered".

While the island jay only occurs on Santa Cruz Island today, it is believed that it was also located on the island of Santa Rosa Island further west until the middle of the 20th century . The intensive cultivation of Santa Rosa Island with non-native domestic sheep ( Ovis aries ) is assumed as a possible reason for its disappearance there . These were introduced on Santa Rosa Island in the 1840s and by the end of the 19th century had reached 80,000 to 100,000 animals. As a result of the intensive cultivation, the diversity of the native flora on Santa Rosa Island had declined, which with the destruction of the habitats of the island jay later probably also led to its disappearance from the island.

While the total population of the island jay was roughly estimated at 9,000 individuals in 2004, after more precise counts in 2008 and 2009, a population of 2,400 to 3,000 individuals and 1,000 breeding pairs is now assumed. However, there are no clear indications of a decline in the population.

The International Union for Conservation of Nature and Natural Resources (IUCN) classifies the island jay as endangered (VU = vulnerable). This is mainly due to the fact that the species only occurs on a single island and the population is therefore threatened by natural disasters such as forest fires. The IUCN suspects that the risk potential from forest fires in the course of climate change could increase further in the future.

In addition, the species is susceptible to the West Nile virus , which has already caused high mortality rates in other corvids, but has not yet occurred on Santa Cruz Island. After the virus first reached Southern California in 2003, scientists began vaccinating the island jays against the virus in 2008 in an effort coordinated by the UC Davis Wildlife Health Center , the Smithsonian Institution, and Colorado State University .

Another potential danger for the island jay is a possible colonization of Santa Cruz Island with rats ( Rattus spp.). These have so far neither occurred on Santa Rosa Island nor on Santa Cruz Island, but are on three other of the six Californian Channel Islands already advanced.

literature

Web links

Commons : Island Jay ( Aphelocoma insularis )  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c For this and the following, unless otherwise stated, cf. John Marzluff , Island Scrub-jay (Aphelocoma insularis) , in: Handbook of the Birds of the World Alive, ed. by J. del Hoyo / A. Elliott / J. Sargatal / DA Christie / E. de Juana, Barcelona 2013 (paid access; last accessed on August 4, 2014).
  2. ^ Robert L. Curry / Kathleen Semple Delaney, Island Scrub-Jay (Aphelocoma insularis) , section "Distinguishing Characteristics", in: The Birds of North America Online, ed. by A. Poole, Ithaca 2012 (access with costs; last accessed on September 20, 2014)
  3. ↑ On this and the following cf. Curry / Semple Delaney, Island Scrub-Jay (Aphelocoma insularis) , section “Distinguishing Characteristics”, in: The Birds of North America Online, Ithaca 2012.
  4. ↑ On this and the following cf. Curry / Semple Delaney, Island Scrub-Jay (Aphelocoma insularis) , section “Sounds”, in: The Birds of North America Online, Ithaca 2012.
  5. ↑ On this and the following cf. Curry / Semple Delaney, Island Scrub-Jay (Aphelocoma insularis) , section "Habitat", in: The Birds of North America Online, Ithaca 2012.
  6. ^ R. Kelsey, Territory size, habitat use, and population size of the Island Scrub-Jay (Aphelocoma insularis) , Master's Thesis. California State Univ. Long Beach 1998, quoted here from Curry / Semple Delaney, Island Scrub-Jay (Aphelocoma insularis) , section “Habitat”, in: The Birds of North America Online, Ithaca 2012.
  7. ↑ Jonathan L. Atwood: Social Interactions in the Santa Cruz Island Scrub Jay , in: The Condor 82, 4 (1980), pp. 440-448. accessed via JSTOR
  8. ↑ a b c d On this and the following Curry / Semple Delaney, Island Scrub-Jay (Aphelocoma insularis) , section “Behavior”, in: The Birds of North America Online, Ithaca 2012.
  9. ^ AB Howell / AJ van Rossem, Further notes from Santa Cruz Island , in: The Condor 13 (1911), pp. 208-210.
  10. ↑ a b c For this and the following cf. Curry / Semple Delaney, Island Scrub-Jay (Aphelocoma insularis) , section “Demography and Populations”, in: The Birds of North America Online, Ithaca 2012.
  11. ^ Luke Caldwell [et al.], Reproductive Ecology of the Island Scrub-Jay , in: The Condor 115, 3 (2013), pp. 603-613, doi: 10.1525 / cond.2013.120028
  12. ^ A b Caldwell, Reproductive Ecology of the Island Scrub-Jay , p. 607.
  13. ^ Caldwell, Reproductive Ecology of the Island Scrub-Jay , p. 611.
  14. ^ A b c Henry Wetherbee Henshaw, Description of a New Jay from California , in: The Auk 3, 4 (1886), pp. 452f.
  15. ↑ a b See Avibase: Island Scrub-Jay (Aphelocoma insularis) Henshaw, 1886 , last accessed on August 15, 2014.
  16. ↑ The previous state of research is summarized in Jonathan L. Atwood, Breeding biology of the Santa Cruz Island Scrub Jay, Aphelocoma coerulescens insularis , originally published as Master's Thesis, California State University, Long Beach 1978, pp. 675f.
  17. ↑ For a discussion of the research cf. Atwood, Breeding biology of the Santa Cruz Island Scrub Jay , Long Beach 1978, pp. 675f.
  18. ↑ On this and the following cf. Kathleen S. Delaney / Robert K. Wayne, Adaptive units for conservation: Population distinction and historic extinctions in the island scrub-jay , in: Conservation Biology 19 (2005), pp. 523-533.
  19. ^ Claymore M. Moore, Paul W. Collins: Urocyon littoralis. In: Mammalian Species 489, 1995. pp. 1-7.
  20. ↑ Marzluff, Island Scrub-jay (Aphelocoma insularis) , in: Handbook of the Birds of the World Alive, Barcelona 2013.
  21. ↑ On this and the following cf. Scott A. Morrison [et al. a.], Proactive Conservation Management of an Island-endemic Bird Species in the Face of Global Change , in: BioScience 61 (2011), pp. 1013-1021, here p. 1014, doi: 10.1525 / bio.2011, December 61, 2011 .
  22. ^ Morrison [u. a.], Proactive Conservation Management of an Island-endemic Bird Species , p. 1014.
  23. ↑ T. Scott Sillett / Richard B. Chandler / J. Andrew Royle / Marc Kéry / Scott A. Morrison, Hierarchical distance-sampling models to estimate population size and habitat-specific abundance of an island endemic , in: Ecological Applications 22 (2012 ), Pp. 1997-2006, doi: 10.1890 / 11-1400.1 .
  24. ↑ a b c d e Aphelocoma insularis , in: The IUCN List of Threatened Species, 2012 (last accessed on August 5, 2014).
  25. ↑ Steve Chawkins: Taking a rare jay under their wing , in: Los Angeles Times, October 16, 2010, last accessed August 7, 2014.
This version was added to the list of articles worth reading on September 30, 2014 .