Gray jay

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This article is about the bird. For the article about the Cree mythological figure, see Wisakedjak.
Gray jay
Perisoreus canadensis mercier2.jpg
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Corvidae
Genus: Perisoreus
Species: P. canadensis
Binomial name
Perisoreus canadensis
(Linnaeus, 1766)
Subspecies

11 subspecies; see text

Perisoreus canadensis range.png
Gray Jay range

The gray jay (Perisoreus canadensis), also grey jay, Canada jay or whiskey jack,[2] is a 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.

Distribution[edit]

Subspecies P. c. capitalis (left), and P. c. obscurus (right); illustration by Keulemans, 1877

The gray jay is a native resident from northern Alaska east to Newfoundland and Labrador and south to northern California, Idaho, Utah, east-central Arizona, north-central New Mexico, central Colorado, and southwestern South Dakota. It is also a native resident in northern Minnesota, northern Wisconsin, northern Michigan, northern New York, and northern New England. The gray jay may wander north of the breeding range. In winter it travels irregularly to northwestern Nebraska, central Minnesota, southeastern Wisconsin, central Michigan, southern Pennsylvania, central New York, Connecticut, and Massachusetts.[3][4]

  • P. c. albescens is a resident from northeastern British Columbia and northwestern Alberta southeastward, east of the Rocky Mountains to South Dakota (Black Hills). It is casual in northwestern Nebraska.[3]
  • P. c. arcus is a resident in the Rainbow Mountains area, and headwaters of the Dean and Bella Coola Rivers of the central Coast Ranges, British Columbia.[3]
  • P. c. barbouri is a resident on Anticosti Island, Quebec.[3]
  • P. c. bicolor is a resident in southeastern British Columbia, southwestern Alberta, eastern Washington, northeastern Oregon, northern and central Idaho, and western Montana.[3]
  • P. c. canadensis breeds from northern British Columbia east to Prince Edward Island, and south to northern Minnesota, northern Wisconsin, northern Michigan, northeastern New York, northern Vermont, northern New Hampshire, and Maine. It winters at lower altitudes within the breeding range and south to southern Ontario and Massachusetts, casually to central Minnesota, southeastern Wisconsin, northwestern Pennsylvania, and central New York. Perisoreus c. canadensis is accidental in northeastern Pennsylvania (Philadelphia).[3]
  • P. c. capitalis is a resident in the southern Rocky Mountains from eastern Idaho, south-central Montana, and western and southern Wyoming south through eastern Utah, and western and central Colorado, to east-central Arizona and north-central New Mexico.[3]
  • P. c. griseus is a resident from southwestern British Columbia and Vancouver Island south through central Washington and central Oregon to the mountains of north-central and northeastern California.[3]
  • P. c. nigracapillus is a resident in northern Quebec (Fort Chimo, Whale River, and George River), throughout Labrador, and in southeastern Quebec (Mingan and Blanc Sablon).[3]
  • P. c. obscurus is a resident in the coastal belt from Washington (Crescent Lake, Seattle, and Columbia River) through western Oregon to northwestern California (Humboldt County).[3]
  • P. c. pacificus is a resident in north-central Alaska (Kobuk River, Endicott Mountains, and Fort Yukon), northern Yukon (Arctic Circle at the International Boundary), and northwestern Mackenzie (Mackenzie Delta and lower Horton River) south in Alaska to latitude 60° N.[3]
  • P. c. sanfordi is a resident in Newfoundland and Nova Scotia.[3]

Habitat and distribution[edit]

Perisoreus canadensis obscurus in Mount Rainier National Park

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 lower elevations of 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.

Behavior[edit]

Mating[edit]

Gray jays typically breed at two years of age. Pairs are monogamous and remain together for their lifetime, but a male or female will find another mate following the disappearance or death of their partner.[4] Gray jay pairs breed during March and April, depending on latitude,[4][5][6] in permanent, all-purpose territories.[4][5][6][7] Second broods are not attempted, perhaps allowing greater time for food storage.[4][5]

Gray jays cooperatively breed.[6][8][9] Strickland[6] studied cooperative breeding of gray jays in Algonquin Provincial Park, Ontario, and La Verendrye Provincial Park, Quebec. In early June, when broods were 55 to 65 days old, the young fought amongst themselves until dominant juveniles forced their siblings to leave the natal area. Dominant juveniles, known as "stayers", remained with their parents, and "leavers" left the natal territory to join an unrelated pair who failed to breed. Two-thirds of "stayers" were male.[6]

During the nest-building phase of the subsequent breeding season, approximately 65% of gray jay trios included "stayers" from the previous spring and their parents, and approximately 30% of trios included an unrelated "leaver". Occasionally, two nonbreeders accompany a pair of adults. "Stayers" may eventually inherit the natal territory and breed, and "leavers" may eventually fill a vacancy nearby or form a new breeding pair on previously unoccupied ground.[6] The role of "stayers" is to retrieve caches and bring food to younger siblings;[8][9] however, this is only allowed by the parents during the postfledgling period.[6][8][9] Until then, parents are hostile toward the "stayer". This may reduce the frequency of predator-attracting visits to the nest when young are most vulnerable. The benefits of allofeeding may include "lightening the load" for the breeding pair, which may possibly increase longevity, reducing the probability of starvation of nestlings, and detecting and mobbing predators near the nest.[8]

Nesting[edit]

Gray jay in late spring

Nesting typically occurs in March and April.[4][5] Male gray jays choose a nest site in a mature coniferous tree[7] and take the lead in construction.[4] Gray jay nests were found in black spruce (Picea mariana), white spruce (Picea glauca), and balsam fir (Abies balsamea) trees in Ontario and Quebec, with black spruce predominating.[4][5] Cup-shaped nests[7] were constructed with brittle dead twigs pulled off of trees, as well as bark strips and lichens. Cocoons of the forest tent caterpillar (Malacosoma disstria) filled the interstitial spaces of the nest.[4] Nests are usually built on the southwestern side of a tree for solar warming and are usually <1 nest diameter from the trunk.[5] Nest height is typically 8 to 30 ft (2.4–9.1 m) above the ground.[5] The average height of 264 nests surveyed in Algonquin Provincial Park was 16 ± 9.2 ft (4.9 ± 2.8 m) above ground.[5]

Clutch size is 2 to 5 eggs. The mean clutch sizes of gray jays in Algonquin Provincial Park and La Verendrye Provincial Park were 3.03 and 3.18 eggs, respectively. Incubation is performed only by the female[5] and lasts an average of 18.5 days.[4]

Fledging[edit]

Gray jay young are altricial. Nestling growth is most rapid from the fourth through the tenth day following hatching. Young are fed food carried in the throats of both parents.[4][5] They are fed by the accompanying nonbreeding third bird ("stayer") only during the postfledgling period.[8][9] Food is a dark brown, viscous paste containing primarily arthropods.[4][5] Young gray jays leave the nest between 22 and 24 days after hatching.[4] Juveniles reach full adult measurements within 5 months.[10] Natal dispersal distance for the gray jay is a median of 0.0 mile for males, 1.7 miles (2.8 km) for females, and a maximum distance of 7.0 miles (11.3 km) for males and females.[6]

Survival[edit]

In studies conducted in Ontario and Quebec, the mortality rate for nonbreeding dominant juveniles ("stayers") was 52%, and mortality was 85% for nonbreeding "leavers" between fledging in June to approximately mid-October. From fall to the following breeding season in March, further nonbreeder mortality was 50%. Territory-holding adult gray jays experienced low mortality rates (15.1% and 18.2% for males and females, respectively).[6] The oldest known female gray jay was 16 years old, and one male was at least 14 years old.[4] Food-storing birds such as the gray jay may live longer than other species due to the increased probability of food availability.[11]

Gray jays are omnivorous.[4][5] Foods eaten include arthropods,[4] small mammals,[12] nestling birds,[13][14][15] carrion,[4][5] fungi,[4] fruits such as chokecherry (Prunus virginiana),[5] and seeds.[5] Two gray jays were seen eating slime mold (Fuligo septica) near Kennedy Hot Springs in the Glacier Peak Wilderness, Washington. This was the first report of any bird consuming slime mold in the field.[16]

Occasionally, gray jays eat live prey. Lescher and Lescher[12] witnessed a gray jay kill an unidentified, live small rodent in Wisconsin. Barnard was the first to witness an in-flight gray jay capture of a magnolia warbler (Dendroica magnolia) for consumption.[17]

Gray jays have been seen landing on moose (Alces alces) to remove and eat engorged winter ticks (Dermacentor albipictus) during April and May in Algonquin Provincial Park. Researchers also found a gray jay nest containing a brooding female, three hatchlings, and three warm, engorged winter deer ticks. Because the winter deer ticks were too large for the hatchlings to eat, it was hypothesized that the ticks may have served as "hot water bottles", keeping hatchlings warm when parents were away from the nest.[18]

Gray jays are suspected but not proven to prey on nests of the threatened marbled murrelet (Brachyramphus marmoratus) in coastal areas of the Pacific Northwest.[19]

Foraging behavior[edit]

Gray jays do not hammer food with their bill as do other jays, but wrench, twist, and tug food apart. Gray jays commonly carry large food items to nearby trees to eat or process for storage, possibly as defense against large scavengers.[4] They are "scatterhoarders", caching food items among scattered sites for later consumption.[20][21]

Any food intended for storage is manipulated in the mouth and formed into a bolus (rounded mass) that is coated with sticky saliva, adhering to anything it touches. The bolus is stored in bark crevices, under tufts of lichen, or among conifer needles.[5]

Risk and energy expenditure are factors in food selection for gray jay, which selects food on the basis of profitability to maximize caloric intake. Increased handling, searching, or recognition times for a preferred food item lowers its profitability.[20]

The gray jay takes advantage of man-made sources of food, hence the names "camp robber" and "whiskey jack". According to Maccarone and Montevecchi,[20] human observers do not inhibit gray jay's feeding behavior; however, Rutter[5] claims that "once having identified man with food it does not forget". He found that after a nesting female was accustomed to being fed by humans she could be enticed to leave the nest during incubation and brooding.[5]

Predation[edit]

Gray jays commonly prey on nestling birds.[15][19] Nests are located visually by moving from perch to perch and scanning surroundings.[4] Gray jay predation on nestling birds is temporally homogeneous throughout the passerine breeding season. Avian nest predation by gray jays is not necessarily higher in fragmented versus unfragmented forest.[13][14][15]

Boulet and others [13] examined bird nest predation in a commercially fragmented boreal black spruce forest intermixed with jack pine, balsam fir, quaking aspen, and paper birch near Lake Saint-Jean, Quebec. Gray jays directed their attacks on artificial arboreal nests more often than artificial ground nests. Depredation of nests was positively related to the presence of the lake and jack pine. Gray jays may have preferred preying on avian nests in jack pine versus black spruce habitat because jack pine forests were more open, and trees did not conceal nests as well. Gray jays may have favored foraging along lakeshores and moist patches due to the high density of insects. No relationship was found between the fragmented forest and predation.[13]

The potential for egg predation by gray jays was greater in riparian forest strips than in clearcuts in a second-growth boreal balsam fir forest in Montmorency Forest, Quebec.[22]

Stuart-Smith and Hayes[14] examined the influence of residual tree density on predation of artificial and natural songbird nests. The study took place in the White River and Lussier River Watershed, southeastern British Columbia, in a forest dominated by Douglas-fir, white spruce, and western larch. Twenty-four plots of similar age were chosen (16 logged, 8 burned by wildfire); they varied in residual tree density between 0 and 180 trees/ha. Residual trees apparently did not increase predation on nesting songbirds by the gray jay. However, a moderate increase in nest predation occurred in logged plots adjacent to or surrounded by mature conifer forest, which is the preferred habitat for gray jays.[4][5] Retaining residual trees would outweigh the possible increased risk of nest predation, except in areas where nesting birds are at very low numbers and potential risk by gray jays is high.[14]

When predation rates on bird nests by the gray jay were compared in clearcut, green-tree retention stands, and mature western hemlock stands in the west-central Oregon Cascade Ranges, predation rates were highest in green-tree retention stands. This may have been due to increased availability of perch sites for avian predators such as the gray jay.[15]

Caching[edit]

Gray jays cache thousands of food items every day during the summer for use the following winter.[6][9][23][24] Caching behavior is thought to have evolved for several reasons. It allows for permanent residence in boreal and subalpine forests,[4] ensures a food source in areas with high elevations and cyclic availability of food resources, and favors the retention of young and a kin-selected social organization.[11] In southern portions of the gray jay's range, food is not cached during summer because of the chance of spoilage and the reduced need for winter stores.[4] Cached items can be anything from carrion to bread crumbs and are formed into a bolus before being cached.[5] Cached food is sometimes used to feed nestlings and fledglings.[5]

Caching is inhibited by the presence of Steller's jays[25] and gray jays from adjacent territories,[23][24] which follow resident gray jays to steal cached food.[25] Gray jays carry large food items to distant cache sites for storage more often than small food items. To prevent theft, they also tend to carry valuable food items further from the source when caching in the company of one or more gray jays.[24] Scatterhoarding discourages pilferage by competitors. Cache thievery increases with increased cache density.[23]

When exploiting distant food sources found in clearings, gray jays temporarily concentrated their caches in an arboreal site along the edge of a black spruce forest in interior Alaska. This allowed a high rate of caching in the short term and reduced the jay's risk of predation. A subsequent recaching stage occurred, and food items were transferred to widely scattered sites to reduce theft.[21]

Predators[edit]

Gray jays are consumed by several bird species including great gray owls (Strix nebulosa), northern hawk-owls (Surnia ulula),[26] and Mexican spotted owls (Strix occidentalis lucida).[27] Gray jay remains were found in the nest sites of fisher (Martes pennanti) and American marten (Martes americana).[28] Red squirrel (Tamiasciurus hudsonicus) eat gray jay eggs.[5]

Gray jays warn each other of predators by whistling alarm notes, screaming, chattering, or imitating, and/or mobbing predators.[4]

Relationship with humans[edit]

Cultural significance[edit]

Bold gray jay, typical of those individuals accustomed to humans

Gray jays readily capitalize on novel food sources, including food sources introduced by humans living on or passing through their territories. To the frustration of trappers using baits to catch fur-bearing 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 humans 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, lumberjack, meat-bird, camp robber, venison-hawk, moose-bird, gorby and, most notable of all, 'whiskeyjack'. This is a variant of an aboriginal name, variously written as wiskedjak, whiskachon, wisakadjak, and other forms, of a mischievous prankster prominent in Algonquian mythology.

Conservation[edit]

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[edit]

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?[edit]

Female incubating her eggs

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?[edit]

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.

Gray, sooty plumage of a juvenile

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?[edit]

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.

Pair of jays feeding their nestlings

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).

References[edit]

 This article incorporates public domain material from the United States Department of Agriculture document "Perisoreus canadensis".

  1. ^ BirdLife International (2012). "Perisoreus canadensis". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
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  3. ^ a b c d e f g h i j k l American Ornithologists' Union. 1957. Checklist of North American birds. 5th ed. Baltimore, MD: The Lord Baltimore Press, Inc
  4. ^ a b c d e f g h i j k l m n o p q r s t u v w x Strickland, Dan; Ouellet, Henri. 1993. Gray Jay. In: Poole, A.; Stettenheim, P.; Gill, F., eds. Birds of North America, No. 40. Philadelphia, PA: The Academy of Natural Sciences; Washington, DC: The American Ornithologists' Union.
  5. ^ a b c d e f g h i j k l m n o p q r s t u v Rutter, Russell J. (1969). "A contribution to the biology of the Grey Jay (Perisoreus canadensis)". Canadian Field-Naturalist 83 (4): 300–316. 
  6. ^ a b c d e f g h i j Strickland, Dan (1991). "Juvenile dispersal in Grey Jays: dominant brood member expels siblings from natal territory". Canadian Journal of Zoology 69 (12): 2935–2945. doi:10.1139/z91-414. 
  7. ^ a b c Hobson, Keith A.; Schieck, Jim (1999). "Changes in bird communities in boreal mixedwood forest: harvest and wildfire effects over 30 years". Ecological Applications 9 (3): 849–863. doi:10.1890/1051-0761(1999)009[0849:CIBCIB]2.0.CO;2. JSTOR 2641334. 
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  9. ^ a b c d e Waite, Thomas A.; Strickland, Dan (1997). "Cooperative breeding in Gray Jays: philopatric offspring provision juvenile siblings". The Condor 99 (2): 523–525. doi:10.2307/1369960. JSTOR 1369960. 
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  11. ^ a b Roberts, Robert Chadwick. 1976. Ecological relationships in the acorn woodpecker (Melanerpes formicivorus), with reference to habitat characteristics, foraging strategies, and the evolution of food-storing behavior. Davis, CA: University of California. Dissertation
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  13. ^ a b c d Boulet, Marylene; Darveau, Marcel; Belanger, Louis (2000). "A landscape perspective of bird nest predation in a managed boreal black spruce forest". Ecoscience 7 (3): 281–289. 
  14. ^ a b c d Stuart-Smith, A; Hayes, John P. (2003). "Influence of residual tree density on predation of artificial and natural songbird nests". Forest Ecology and Management 183: 159. doi:10.1016/S0378-1127(03)00104-X. 
  15. ^ a b c d Vega, Robyn M. S. 1993. Bird communities in managed conifer stands in the Oregon Cascades: habitat associations and nest predation. Corvallis, OR: Oregon State University. Thesis
  16. ^ Sutherland, John B.; Crawford, Ronald L (1979). "Gray Jay feeding on slime mold". The Murrelet 60 (1): 28. 
  17. ^ Barnard, William H. (1996). "Juvenile Grey Jay preys upon magnolia warbler". Journal of Field Ornithology 67 (2): 252–253. 
  18. ^ Addison, E. M.; Strickland, R. D.; Fraser, D. J. H. (1989). "Gray Jays, Perisoreus canadensis, and common ravens, Corvus corax, as predators of winter ticks, Dermacentor albipictus". The Canadian Field-Naturalist 103 (3): 406–408. 
  19. ^ a b Raphael, Martin G.; Mack, Diane Evans; Marzluff, John M.; Luginbuhl, John M. 2002. Effects of forest fragmentation on populations of the marbled murrelet. Studies in Avian Biology. 25: 221–235
  20. ^ a b c Maccarone, Alan D.; Montevecchi, W. A. (1986). "Factors affecting food choice by Gray Jays". Bird Behavior 6 (2): 90–92. doi:10.3727/015613886792195216. 
  21. ^ a b Waite, Thomas A.; Reeve, John D. (1997). "Multistage scatter-hoarding decisions in the Gray Jay (Perisoreus canadensis)". Bird Behavior 12 (1/2): 7–14. doi:10.3727/015613897797141335. 
  22. ^ Darveau, Marcel; Belanger, Louis; Huot, Jean; Melancon, Eric; DeBellefeuille, Sonia (1997). "Forestry practices and the risk of bird nest predation in a boreal coniferous forest". Ecological Monographs 7 (2): 572–580. doi:10.1890/1051-0761(1997)007[0572:FPATRO]2.0.CO;2. JSTOR 2269522. 
  23. ^ a b c Waite, Thomas A. (1988). "A field test of density-dependent survival of simulated Gray Jay caches". The Condor 90 (1): 247–249. doi:10.2307/1368458. JSTOR 1368458. 
  24. ^ a b c Waite, Thomas A. (1992). "Social hoarding and a load size-distance relationship in Gray Jays". The Condor 94 (4): 995–998. doi:10.2307/1369297. JSTOR 1369297. 
  25. ^ a b Burnell, Kristi L.; Tomback, Diane F. (1985). "Steller's jays steal Grey Jay caches: field and laboratory observation". Auk 102 (2): 417–419. doi:10.2307/4086793. JSTOR 4086793. 
  26. ^ Rohner, Christoph; Smith, James N. M.; Stroman, Johan; Joyce, Miranda; Doyle, Frank I.; Boonstra, Rudy (1995). "Northern Hawk-Owls in the Nearctic boreal forest: prey selection and population consequences of multiple prey cycles". The Condor 97 (1): 208–220. doi:10.2307/1368997. JSTOR 1368997. 
  27. ^ U.S. Department of the Interior, Fish and Wildlife Service. 1995. Recovery plan for the Mexican spotted owl: Vols. 1–2. Albuquerque, NM: U. S. Department of the Interior, Fish and Wildlife Service
  28. ^ Henry, Stephen E.; Raphael, Martin G.; Ruggiero, Leonard F. (1990). "Food caching and handling by marten". The Great Basin Naturalist 50 (4): 381–383.  PDF copy

Further reading[edit]

  • Madge, S. and H. Burn. 1994. Crows and Jays: A Guide to the Crows, Jays and Magpies of the World. Boston, Houghton Mifflin.
  • Strickland, D. and H. Ouellet. 1993. Gray Jay – Perisoreus canadensis. The Birds of North America No. 40.
  • Waite, T.A. and D. Strickland. 2006. Climate change and the demise of a hoarding bird living on the edge. Proc. Roy. Soc. B. 273: 2809–2813.

Additional photos[edit]

External links[edit]