Pinyon Jay Gymnorhinus cyanocephalus
Version: 2.0 — Published March 19, 2020
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Diet and Foraging
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Main Foods Taken
Pinyon Jays are omnivorous, taking pine seeds, some acorns, juniper berries, other wild berries, cultivated grains (including sunflower seeds and other commercially supplied seeds from bird feeders), arthropods, lizards, snakes, nestling birds, and small mammals (93, 88, 4).
Microhabitat for Foraging
A flock forages together year-round, except when nesting, when males forage together in small groups and return to the colony to feed their mates on the nest. In northern Arizona, Pinyon Jays foraged on 5 different substrates (this does not include food previously cached): walking on the ground peering intently at objects; turning over leaves, pine cones, pieces of bark, and decaying branches; probing directly in the soil; maneuvering on herbaceous and shrubby vegetation gleaning seeds, berries, and small arthropods from these surfaces; searching on downed and standing dead tree branches and trunks, with and without bark; and searching leaves, twigs, needle clusters, and branches in live trees. During late autumn, they are attracted to salt licks for cattle. Foraging locations vary seasonally (94; Table 1).
Habitat types visited in northern Arizona during foraging include meadows and grasslands, woodlands, ponderosa pine (Pinus ponderosa) forests, and mixed coniferous forests (including burned areas). In New Mexico, they harvested seeds of pinyon pines in persistent pinyon–juniper woodlands during the fall, retrieving caches in these habitats during spring, summer, and winter. They spent more time in lower-elevation pinyon–juniper savannas during winter, where they foraged for insects and juniper berries (69, 67).
Food Capture and Consumption
Pinyon Jays are able to open ripe green pine cones and remove seeds (see Diet and Foraging: Food Selection and Storage). They also probe deep into crevices in bark and soil and kill small vertebrates with swift, well-directed blows of the bill to the head and upper neck. A foraging group often scares up grasshoppers and crickets (Orthoptera), beetles (Coleoptera), and katydids (Tettigoniidae), which are quickly snatched, and they sally forth from foliage to capture flying insects. They have been seen to insert the bill and forehead under downed, dead tree branches and lift them to expose the underside, which may contain termites (Isoptera); these are then delicately picked from the branch. Small, mobile mammals and lizards are captured by group effort, but one jay, presumably the most dominant, feeds on the kill (RPB).
Major Food Items
None available for adults.
Food Selection and Storage
Pinyon Jays are morphologically, physiologically, and behaviorally well equipped for the harvest, transport, storage, retrieval, and use of the seeds of pinyon pines. Physiologically, the presence of pine seeds and green cones reverses gonadal regression and stimulates testis growth in wild and experimental birds from central New Mexico (3, 4). The Pinyon Jay possesses a strong, sharp bill used to: (1) hack open tightly closed pine-cone scales, (2) extract pine seeds from pine cones, (3) thrust the seeds into the substrate, and (4) probe into the soil to recover hidden seeds. The bill is featherless at its base (hence the genus name Gymnorhinus, which means bare nostrils). This allows individuals to probe deep into pitch-laden cones without fouling the feathers that usually cover the nostrils. A specialized jaw articulation allows the Pinyon Jay to open seeds and absorbs the impact of pounding on the seed hull (38). Unusually strong, long wings assist in extended flights when searching for pine cones, which are often widely scattered and clumped, and returning to traditional caching areas on its home range (B. Pavlick, P. Bednekoff, RPB, unpublished data). A flock may transport seeds up to 11 km before caching them. The upper two-thirds of the esophagus expands when packed with pine seeds, allowing a single bird to carry about 40 (83) or > 50 (4) whole, unhulled seeds in a single trip. The sympatric Woodhouse's Scrub-Jay (Aphelocoma woodhouseii) can cram only 3–5 seeds in its mouth and throat.
The Pinyon Jay can discriminate between full and empty pinyon pine seeds by hull color, which signals the quality of the contents: A dark, chocolate-colored seed hull indicates a full, well-formed seed, whereas a light yellow-brown seed hull indicates an empty seed hull. Of 655 seeds removed from Pinyon Jays' throats, all were dark brown and fully edible (83). Seeds remaining in open cones invariably have yellow hulls. However, some brown seeds are also empty, but Pinyon Jays use a series of sophisticated techniques to assess seed quality, including “bill clicking” or “bill weighing.” In the latter, seeds are held mid-length in a motionless bill. In the former, seeds are held mid-length in the bill and the upper and lower mandibles are rapidly clicked. This may reveal weight directly or produce a hollow sound, indicating an empty seed (95).
All behaviors performed during foraging for conifer seeds are performed synchronously by the flock. Once birds have filled their esophagi, a series of Kaws signals their departure. Birds quickly ascend to the tops of trees with throats bulging with seeds. They join in a series of Kaws and fly off to one of several traditional caching areas on their home range. Pinyon Jays carrying large numbers of seeds in their throats fly with a distinctive position, with the head tilted back (KJ).
Modern pinyon pines and Pinyon Jays appear to have coevolved a number of traits that interact to produce an efficient harvest of pine seeds. Pinyon pines apparently have a suite of characteristics that attract birds to the cones (referred to as “enticer traits” (96, 97). Seed-hull color is one of those traits (see above), but seed-hull thickness is less than expected for a seed this large (98). Pinyon pine seeds are wingless, and, after the cone opens, the seeds are held tightly in place by a small flange on the cone scale. Cones are positioned outward and upward on branches for easy access by bird dispersers. Cone scales radiate evenly from a central axis, making the seeds easy to see, and they contain no sharp spines. Within a season, cones open asynchronously within a tree and habitat, thus providing a continuous supply of seeds over time. Pinyon pine trees are highly synchronized in the annual production of seeds; some years every tree for hundreds of square kilometers will produce abundant cones, and the next year almost all trees will be barren. All of the above characteristics appear to serve one purpose: rapid and efficient seed removal and planting in the soil by jays (97).
In years of a large crop of seeds, individuals first eat seeds each morning, then begin collecting them. Early in autumn, they peck open green cones to extract seeds, with strong jabs of a partly opened bill, accurately directed at the junction between two cone scales and accompanied by much bill-wiping. These scales are soon shredded. This time-consuming behavior requires the flock to be sedentary while birds work on tightly closed cones. In early autumn, birds attempt to remove cones from branches by either twisting the cone or hammering at the pedicel until it breaks. The cone is then carried to a nearby crotch, where it is tightly wedged and held with the toes. Dark brown seeds are extracted with the bill, which is then held upward and opened, allowing seeds to fall into the esophagus. Often the same “vice” is used repeatedly and a pile of shredded cones accumulates below, suggesting these birds use tools.
Later in the season when the cones have opened naturally, birds move rapidly through the habitat, peering into cones in search of dark-brown seeds. Flocks are known to ascend mountains into mixed-coniferous forest in search of seeds from limber pine (Pinus flexilis) and bristlecone pine (Pinus aristata; 63, RPB)
Most seeds are cached in thick litter and needle layers covering the ground; some are placed in tree crevices and needle clusters. Caching areas are often relatively open, containing sparse vegetation, patches of bare ground, and good drainage. Each flock appears to have a group of caching areas, some that are used each year and others less frequently. These areas often contain a scattering of seedling and sapling pinyon pines. The Town Flock had between 8‒10 traditional caching areas. The number of harvest, transport, and cache cycles performed per day is highly variable, depending on weather conditions, size of cone crop, and distance between harvest and caching areas.
Pinyon Jays sometimes prefer to cache at the base of large trees (often on the south side), large boulders, or at the base of cliffs where less snow accumulates and melts off rapidly when the sun reappears (88). Caching sites are frequently protected spots conducive to germination (4).
Of 128 caching bouts observed in northern Arizona, 70% were multiple, consecutive seed caches (99). During recovery bouts, however, birds seldom recovered from multiple sites. Birds are highly accurate at recovering their cached seeds, even under snow (88).
During caching, the flock is usually silent, moving in one direction. Birds walk slowly and, at 3‒6-s intervals, thrust their bills into the substrate, placing a seed therein. Most caches contain one seed. At times, a bird thrusts its bill into the substrate but does not deposit a seed. False caching and moving cached seeds, observed in captivity, may serve to deceive individuals attempting to retrieve another’s cache (KJ). A single cache can be created in about 2 sec (RPB). Birds in the wild do not return to these caches until they are harvested.
Ligon (4) calculated a flock of 250 Pinyon Jays can store about 4.5 million pine seeds in one autumn, when seeds are plentiful. Balda (100) calculated a single Pinyon Jay caches about 2,600 seeds in a single autumn, when cones are abundant.
Although impossible to observe in the wild, mated pairs appear to coordinate their caching so that cache locations are mutually known to each other, especially the male. Data from aviary observations and experiments confirm this (101, 102).
In some years, especially when pinyon pine cones are rare or absent, jays harvest and cache large numbers of ponderosa pine seeds in northern Arizona (and Jeffrey pine [Pinus jeffreyi] in southern California). These cones are armed with sharp spines, and cone scales do not have flanges to hold the seeds; consequently, seeds are quickly released from the cones. Seeds have wings that must be removed. Pinyon Jays are efficient foragers on these species, but no detailed studies are available (88).
Cached seeds are hidden from view and present no clue as to their location. Field observations reveal that birds are extremely accurate at digging up hidden seeds. This behavior cannot be studied in the wild, as it is impossible to follow specific birds to specific cache sites over time (86).
Laboratory studies on the details of this memory system have employed experimental rooms with floors which were either sandy or contained numerous holes that could serve as cache sites. When placed into such a room and presented with pinyon-pine seeds, jays readily cached. Pinyon Jays performed well above chance levels when recovering seeds, even when individuals were forced to cache in specific holes and the retention interval was assigned by the experimenter (103). Birds were highly accurate over long periods of time (104) when tested in an analog of the radial maze test (105) and a 3-dimensional maze (106, 107). Tests revealed that birds do not need to employ odor, site-marking, preferences, rules, or route reversal to accurately recover caches. Individual jays use landmarks to aid them in their search for caches. Pinyon Jays were found to use the sun compass as an aid to finding caches (108). When Woodhouse's Scrub-Jay (Aphelocoma woodhouseii), Mexican Jay (A. wollweberi), Pinyon Jay, and Clark's Nutcracker (Nucifraga columbiana) were tested together, Pinyon Jays and nutcrackers significantly outperformed the other two jays (103, 109, 104). This similarity is evidence that these four species demonstrate convergent and divergent evolution (see Systematics: Related Species) and that species most dependent on cached seeds for winter survival and early reproduction have more accurate spatial memories than species less dependent on cached food (86).
Nutrition and Energetics
Seeds of two-needle pinyon (Pinus edulis) are 61% fat, 16% protein, and 16% carbohydrate (110), and 90% of the fat is unsaturated (111). Little (112, 113) determined that a pinyon-pine seed contained 74,410 cal/g or 31 kJ/g (98).
Metabolism and Temperature Regulation
Metabolic rates of Pinyon Jays have not been determined. A study of thermoregulation revealed a Lower Critical Temperature of about –5°C for female Pinyon Jays (114). Birds shiver at and below this temperature, which is common from mid-October to mid-April across their range. The use of the south sides of trees for roosting and nesting, sitting in the tops of trees early in the morning, and shivering are all behavioral adjustments to low ambient temperatures. At high temperatures, Pinyon Jays pant and open and droop their wings (RPB).
Drinking, Pellet-Casting, and Defecation
Pinyon Jays drink open water and eat snow; they have been seen chipping at ice with heavy strokes of the bill. Petersen et al. (115) note that Pinyon Jay colonies are typically located near a source of drinking water, and water availability may be one reason for the location of nesting colonies in habitat which otherwise appears suboptimal.
Pellet-casting has been observed in the laboratory. Defecation is unremarkable, but individuals make very slight movements of the body when defecating perpendicular to a perch. Pinyon Jays have the ability to propel feces up to 1 m. When doing this, legs are flexed and then extended, and feces are propelled horizontally or slightly upward. The reason this occurs is unknown, but it may have a social function. Birds defecate during roosting, as at arousal some birds (possibly those lower in the roost tree) have guano on heads, backs, and tails.