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The Gray Jay is member of the crow and jay family (Corvidae) found in the boreal forests across North America north to the tree-line and in subalpine forests of the Rocky Mountains south to New Mexico and Arizona. It is one of three members of the genus Perisoreus, the others being the Siberian Jay, P. infaustus, found from Norway to eastern Russia and the Sichuan Jay, P. internigrans, restricted to the mountains of eastern Tibet and northwestern Sichuan. All three species store food and live year-round on permanent territories in coniferous forests.
Additional recommended knowledge
Although the Gray Jay can fluff up its dense plumage and give the impression of large size, it is actually one of the smallest jays in the world, males weighing about 76 grams and females only about 68 grams. Both sexes typically have light gray underparts, medium-gray upperparts, and a partial black cap on the back of an otherwise white head. Birds on the Pacific coast of Washington and Oregon states have more extensive black on the head and noticeably darker backs with conspicuous white streaks. Individuals from the southern Rockies have black caps that fail to reach forward as far as the eye, giving that race a noticeably more white-headed appearance. Juvenile plumage (retained until August) is sooty gray all over, though slightly darker on the head.
Gray Jays live in pairs, each defending a large (25-100 hectares) permanent territory against its neighbours. Often a pair is accompanied by a third bird, usually the dominant young from the pair’s own previous nesting, but sometimes it is an unrelated immigrant expelled from another territory. The pair or trio (rarely quartet) moves through the forest in a loose group, scanning the surroundings for food and keeping a sharp eye out for predators.
Gray Jays build a new nest every year over a three-week period beginning in February or early March. The structure is a large, bulky platform of twigs, supporting an inner nest of bark strips, lichens, and feathers. From 2 to 5, but most often 3 or 4 greenish gray eggs with brownish speckles are laid laid at intervals of 26 hours. The female sits beginning with the first egg (apparently to keep them from freezing) and initiates true incubation only with the last egg, thereby assuring that the entire clutch hatches out in just a few hours. A typical 3-egg clutch requires 20 days from the first egg to hatching. The female sits very tightly during this time but is fed by the male only about once a day. Hatchlings are pink and naked except for wispy dorsal down. The male does all of the initial feeding with the female starting to accompany him on foraging trips when the nestlings are about a week old. By two weeks, the nestlings are well feathered and are often left alone for an hour or more between joint parental feeding visits. The young usually fledge when 23 days old. They are capable of level flight but spend most of their time huddled together waiting for food and only gradually begin to accompany the adults. Their tails are fully grown by the age of 42-45 days, at which time they are skilful fliers and are no longer fed by their parents.
Food and Food Storage
Food falls into four main categories: insects and spiders, berries and mushrooms, nestling birds or other small live animals such as mice or toads, and carrion. Gray Jays cannot open cones and do not rely on boreal seed crops. Although some food is eaten directly, many individual items or pieces are coated with sticky saliva and fastened in thousands of individual hiding places up in the trees, often in bark crevices. These food stores make it possible for Gray Jays to avoid the perils of migration and to have an annual adult survival rate (about 80%) that is much greater than for most other comparably small birds. Surprisingly, most Gray Jay deaths occur, not in the harsh and apparently foodless boreal winter, but in the summer, probably because of migratory, bird-eating hawks.
The vast majority of Gray Jays live where there is a strong presence of one or more of: black spruce (Picea mariana), white spruce (P. glauca), Englemann spruce (P. engelmanni), jack pine (Pinus banksiana), or lodgepole pine (P. contorta). Gray Jays do not inhabit the snowy, coniferous, and therefore seemingly appropriate Sierra Nevada of California where no spruce and neither of the two named pines occur. Nor do Gray Jays live in coastal Alaska or British Columbia dominated by Sitka spruce (Picea sitchensis). The key habitat requirements may be sufficiently cold temperatures to ensure successful storage of perishable food and tree bark with sufficiently pliable scales arranged in a shingle-like configuration that allows Gray Jays to wedge food items easily up into dry, concealed storage locations. Storage may also be assisted by the antibacterial properties of the bark and foliage of boreal tree species. An exception to this general picture may be the well-marked subspecies P. c. obscurus, once given separate specific status as the “Oregon Jay”. It lives right down to the coast from Washington to northern California in the absence of cold temperatures or the putatively necessary tree species. One may speculate that it depends much less on stored food than the other, more typical races of the Gray Jay.
Relationship with Humans
Gray Jays readily capitalize on novel food sources, including humans living on or passing through their territories. To the frustration of trappers using baits to catch furbearing animals or early travelers trying to protect their winter food supplies, and to the delight of modern campers, many individual Gray Jays quickly learn that we can be an excellent source of food, even coming to the hand for bread, raisins, or cheese. Such familiarity has inspired a long list of colloquial names for the Gray Jay. In addition to the once official ‘Canada Jay,’ there are, meat-bird, camp robber, venison-hawk, moose-bird and, most notable of all, ‘whiskeyjack’. This a corruption of an aboriginal name, variously written as wiskedjak, whiskachon, wisakadjak, and many other variants, of a mischievous prankster prominent in Algonquian mythology.
Gray Jays are widespread in boreal and subalpine habitats only lightly occupied by humans. Significant human impacts may nevertheless occur through anthropogenic climate warming. Gray Jays at the northern edges of their range may benefit from the extension of spruce stands out onto formerly treeless tundra. A published study has documented a decline at the southern edge of the Gray Jay’s range, however, and plausibly linked a local decline in productivity to warmer temperatures in preceding autumns. Such warm temperatures may encourage spoilage of the perishable food items stored by Gray Jays upon which success of late winter nesting partly depends.
Three Important Questions
There are three perplexing features of Gray Jay breeding and social behaviour that pose interesting challenges to a central concept of evolutionary biology, namely that an organism should exhibit behaviour that maximizes the production of surviving offspring.
Why do Gray Jays breed so early?
Breeding Gray Jays build nests and lay eggs in March or even February, when snow is deep in the boreal forest, temperatures may plunge far below freezing, and there is no obvious food to support reproduction. In spite of such hostile conditions, Gray Jays have a high rate of nest success and the young typically leave the nest in late April, well before most boreal birds have even returned from the south, let alone begun nesting themselves. Just as strange, Gray Jays never bring off a second brood in the same season even though there would probably be time to do so and therefore to produce more young per year than they actually do. Stored food enables nesting jays to feed their young even during a blizzard but this only explains how Gray Jays can get away with nesting in late winter and contributes nothing to understanding why it is advantageous to do so. Among other possible benefits, early nesting Gray Jays have nesting over and done with at a correspondingly early date and can invest more food storage effort into their territories before the following winter. Assuming much of the stored food lasts until the onset of cold temperatures, storing more food on the territory should mean that early nesting jays have a better prospect of making it through the long, seemingly foodless boreal winter by staying at home and therefore avoiding the dangers of migration. This might mean that fewer young would be produced each breeding season (than if nesting occurred in June) but if it means that early nesting Gray Jays live longer and nest more often, they may still produce more surviving young in the long run than if they re-nested, or nested just once but later in the season).
Why do young Gray Jays turn on each other?
When young Gray Jays leave the nest in late April, they huddle together for warmth at first and later gradually start moving through the forest as part of a cohesive family group. Then, when they are about 55 days old (five weeks out of the nest) they start to fight among themselves and within ten days, one of them has expelled its siblings from the natal territory. The dominant juvenile will continue to accompany its parents through the first fall and winter (and sometimes longer), benefiting from their experience and protection. The expelled siblings sometimes succeed in finding an unsuccessful pair that will tolerate them but most fail to do so and about 80% of them are dead by fall (as opposed to just 50% of the dominant juveniles that have stayed at home with their parents). Since siblings share 50% of their genes (as many as a parent shares with its offspring) an explanation is required for any behaviour in an individual that results in a high death rate in that individual’s brothers and sisters.
For the Gray Jay, one possible explanation concerns the problem of storing enough food for a young bird’s first winter. Although young Gray Jays start storing food when they are just a few weeks old, they almost certainly aren’t very good at it and may plausibly require a parental subsidy to avoid starving to death in the cold season. If so, and if the parental subsidy is sufficient for the sure survival of only one extra bird, there will be grounds for conflict in deciding which sibling will be the one to benefit. The question then becomes ‘why not wait until fall before ejecting the weaker siblings?’ That way, the dominant juvenile could reap the benefits, not only of his food storage efforts (and it usually is a male since they are larger and tend to win the dispersal fights), but also of the food stored all summer by the about-to-be ejected losers.
The relevant consideration here may be how the parental subsidy is acquired. If Gray Jays find stored food by random searching, evicting siblings at either the beginning or the end of the summer-and-fall food storage season would probably be ineffective. To be sure, a dominant juvenile could probably keep its weaker siblings from accompanying the family group but it could do little to prevent them from sneaking around the huge thickly forested territory and finding stored food on their own. If Gray Jays recover stored food by memory, however, it would pay a dominant juvenile to get rid of the competition at the beginning of the food storage season. That way, the weaker siblings would never know where the extra food was hidden and there would be no point in trying to stay on in their parents’ territory. On the contrary, it would be in their best interest, once they had lost the fight with their dominant sibling, to leave in search of another territory without an extra juvenile and where they might be tolerated by the local pair. In so doing, they would have at least a fighting chance to acquire access to a winter food subsidy of their own. The fact that dominant juveniles do expel their siblings in June, at the beginning of the food storage season, and the fact that expelled juveniles do leave right away and try to win acceptance from unrelated pairs suggests that Gray Jays do, in fact, recover stored food by memory.
Why don’t nonbreeders help feed nestlings?
When Gray Jays start building their nests in February or March, 20 percent or more of all pairs are still accompanied by a third, nonbreeding individual, usually the dominant juvenile from the pair’s own previous nesting. Many other bird species, particularly in the tropics, and notably including jays, also have retained young that have been unable to find territories of their own. Typically, such birds help feed their parents’ new nestlings and participate in defending them from nest predators. In many cases, such help has been shown to improve the production of surviving young. Since the extra young are younger siblings of the nonbreeding helpers, the nonbreeders have, in effect, increased their own genes in the next generation, just as they would have if they had had young of their own.
In Gray Jays, however, nonbreeders do not help their parents to raise younger siblings. Instead, they usually stay well away from the nest and if they do approach it, the adults energetically drive them away. But, if helping by nonbreeders is so beneficial in other birds with similar demographic circumstances, why not in Gray Jays? If anything, it should be even more important in a bird that nests in the cold, apparently foodless conditions of late winter. Even more puzzling, although a pair will prevent the nonbreeder from feeding the nestlings, it will allow such feeding as soon as the young have left the nest. This strange reversal of behaviour may be explained as follows. First, extra trips to the nest with food will be dangerous if they give the location away to a predator that then cannot be driven away by the combined efforts of the pair and the nonbreeder. This is supported by the fact that adult Gray Jays also help to keep the nest inconspicuous in much the same way—by bringing maximum possible food loads in what are therefore very infrequent trips to the nest. Second, if the nest predator driving this behaviour is a mammal, it will be much less dangerous once the young can fly and have left the nest. This may explain why, after the young fledge, breeding Gray Jays start allowing feeding visits to the young by the nonbreeder and also why they themselves start making more frequent visits (with smaller food loads).
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Gray_Jay". A list of authors is available in Wikipedia.|