California scrub jay

Habitat

True to its name, the California scrub jay inhabits areas of low scrub, preferring pinyon-juniper forests, oak woods, and edges of mixed evergreen forests. It also inhabits suburban gardens.

Urbanization Effects

Urbanization alters behavior, diet, and social interactions along with the way of life for wildlife, including the California scrub jay. However, urbanization can reduce natural habitat, increasing exposure to hazards including traffic, domestic pets, and human disturbance. But, scrub jays are among the bird species that can live in and take advantage of urban landscapes.

In coastal southern California, residential development has divided native coastal sage scrub and chaparral habitat into smaller fragments, and many shrubland birds have declined in these fragments. Scrub jays, however, can use the surrounding urban areas and do not appear to be sensitive to the size of habitat fragments. In surveys of coastal sage scrubs in San Diego County, they were more abundant near the urban edge than in the interior of large habitat blocks.

Urban parks and gardens provide additional food sources for the jays. These include bird feeders set up by humans for recreation or for conservation purposes. California scrub jays are known to be accustomed to human presence and take advantage of the resources provided by these residential areas. Their ability to remember locations of hidden caches help the jays use resources across different environments.

Because they are more common along edges, scrub jays have been named as possible nest predators of other birds. However, a study of rufous-crowned sparrow nests found no difference in nest predation between edge and interior habitat, and most of the predation events observed were by snakes.

Foraging

California scrub jays usually forage in pairs, family groups, or small non-kin groups, outside of the breeding season. They feed on small animals, such as frogs and lizards, eggs and young of other birds, insects, and (particularly in winter) grains, nuts, and berries. They will also eat fruit and vegetables growing in backyards.

Vocalization

The vocalizations of corvids are typically referred to as calls rather than songs, and evidence that they learn their species-specific calls has been limited. In one reported case, a hand-raised California scrub jay housed in an aviary with Florida scrub jays produced two call types that closely matched those of the Florida birds, rather than any known California scrub jay calls. The authors interpreted this as evidence of vocal learning and suggested that some geographic variation in scrub jay calls may be traditional.

Food storing

California scrub jays, like many other corvids, exploit ephemeral surpluses by storing food in scattered caches within their territories. They rely on highly accurate and complex memories to recover the hidden caches, often after long periods of time. In the process of collecting and storing this food, they have shown an ability to plan ahead in choosing cache sites to provide adequate food volume and variety for the future. Western scrub jays are also able to rely on their accurate observational spatial memories to steal food from caches made by conspecifics. Food-storing birds implement a number of strategies to protect their caches from potential 'pilferers.'

Anecdotally, scrub jays – and corvids more generally – are known for an attraction to, and thievery of, brightly colored objects. Recent research debunks, or at least casts doubt, on this idea. Corvids have been observed taking acorns from acorn woodpecker caches. Some scrub jays snatch acorns from the hiding places of other jays. When these birds go to hide their own acorns, they check first that no other jays are watching. Other protection methods include moving the cache in the presence of an observer, storing inedible decoys like small stones instead of food, and hiding the cache once a scavenging bird is no longer watching; these behaviors are thought to vary based on the presence or absence of potential pilferers (like other corvids) as well as what kind of animal might pilfer the cache, implying strategic and socially complex motives behind different kinds of caching behavior.

Intelligence

Recent research has suggested that western scrub jays, along with several other corvids, are among the most intelligent of animals. The brain-to-body mass ratio of adult scrub jays rivals that of chimpanzees and cetaceans, and is dwarfed only by that of humans. Scrub jays are also the only non-primate or non-dolphin shown to plan ahead for the future (known as metacognition), which was previously thought of as a uniquely human trait. Scrub jays have also been shown to look for information about the location of hidden food more often when they were uncertain, similar to apes in a comparable task. Whether tasks like this truly measure metacognition is still debated. Other studies have shown that they can remember locations of over 200 food caches, as well as the food item in each cache and its rate of decay. To protect their caches from pilfering conspecifics, scrub jays will choose locations out of sight of their competitors, or re-cache caches once they are alone, suggesting that they can take into account the perspective of others.

California scrub jays also summon others to screech over the body of a dead jay, according to research from the University of California, Davis. The birds' cacophonous "funerals" can last for up to half an hour.

Scrub jays have also been tested on self-control. In a large comparative study of motor self-regulation, California scrub jays and Eurasian jays performed relatively poorly compared with mammals, but three other corvid species tested later ranked among the top performers, which suggests that a few species may not represent the whole group.

Scrub jays more recently have been tested for mirrored self-recognition, and ability thought to be linked to more complex social thinking. In a study of seven captive jays, the birds cached more food when another jay was watching than when a mirror was present, and they did not protect their caches more with a mirror than when caching alone. This suggests the jays may not have treated their reflection as another bird. However, in a “mark test,” where a sticker was placed on the throat, the jays did not try to remove a red mark more often in front of a mirror than without one, so the study found no clear evidence of mirror self-recognition. The authors described the results as mixed and noted that the mark test may not work well for every species.

Nesting

Nests are built low in trees or bushes, 1–10 m (3.3–32.8 ft) above the ground, primarily by the female, while the male guards her efforts. The nests are sturdy, with an outside diameter of 33–58 cm (13–23 in), constructed on a platform of twigs with moss and dry grasses lined with fine roots and hair. Four to six eggs are laid from March through July, with some regional variations. There are two common shell color variations: pale green with irregular, olive-colored spots or markings; and pale grayish-white to green with reddish-brown spots. The female incubates the eggs for about 16 days. The young leave the nest about 18 days after hatching.

Life span

The life span of wild California scrub jays is approximately 9 years. The oldest known western scrub jay was found in Castaic, California, in 1991 and raised in captivity. "Aaron" lived to be 19 years, and 8 months old.

Diseases

Populations are being adversely affected by the West Nile virus, particularly in California's Central Valley.