Pinyon Jay Gymnorhinus cyanocephalus
Version: 2.0 — Published March 19, 2020
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Walking, Hopping, Climbing, etc.
Upon leaving the nest, fledglings usually hop on relatively strong legs among branches and on the ground. Soon after, they walk, a common pattern of locomotion for this species. The slow, deliberate gait of Pinyon Jays with careful steps placed one in front of the other, the slight sideways wattle of the body, and the erect posture of the entire body are trademarks of this species. This gait may be a specialized adaptation for moving slowly over the ground while searching for small food items (120).
Pinyon Jays are exceptionally strong flyers, compared to other southwestern jays. All flights from vegetation are preceded by facing the direction of flight, performing “intention movements” of flexing and extending legs ≥ 2 times before extending wings and spreading tail to initiate flight. Flight behavior occurs in three main contexts:
(1) Tree to Ground. Birds perform this during foraging bouts when food items are carried into trees before being consumed. Flights to the ground are characterized by a jump from the branch, 1 or 2 modest flight strokes, followed by a glide with wings partly extended. The flight path inscribes an inverted J as the wings flair slightly before landing (RPB).
(2) Ground-Foraging (Figure 6). Flocks spend considerable time foraging as a unit on the ground, usually moving in a single direction. They typically “leapfrog” as they progress over the substrate. Birds at the rear of the flock fly up from the ground and, with slow deep wing beats, interspersed with short glides with wings partly extended, move to the leading edge of the flock. As long as this behavior is performed, the flock is predictably sedentary (88).
(3) Long-Distance Flights. While vocalizating (see Sounds and Vocal Behavior: Vocalizations), individuals fly from ground to high branches where the flock assembles in a staging response. Flock members fly high into the air in a steep ascent. The flock forms into a relatively tight ball at 100–200 m and on strong wing beats (without gliding) circles the area and then flies up to 4 km. These flights are reminiscent of flights by flocks of European Starling (Sturnus vulgaris; 88).
Preening, Head-Scratching, Stretching
Immediately before and during molt, Pinyon Jays preen vigorously over the back, belly, wings, and legs. During most of the year, preening is a midday event. A mate may invite its partner to allopreen by sidling up to it with bill pointed directly upward. They stretch symmetrically with both leg and wing extended on same side of body and then on the other.
The bill is wiped from base to tip, alternating left and right sides in quick succession, often: (1) during pine-seed harvest when pine pitch may be present on cones and seeds, (2) after digging up caches when soil sticks to bill, and (3) after feeding young when particles of food and saliva may stick to the bill (RPB).
During hundreds of hours of observations when individuals were near open water, Balda and associates never observed bathing. Normally, after bathing, individuals must shake, preen, and sunbathe, to dry their feathers—all behaviors that could slow a bird from departing with the flock. Also, a bird made heavy with wet feathers is probably not able to fly as fast as a bird with dry ones. This may be an example of the premium placed on birds to stay within the flock at all times. Dust-bathing is rarely observed but may be common.
Synchronization of behaviors is common in Pinyon Jay flocks (2). Individuals in a flock that obtain food, water, or other resources (including the reproductive energy to breed) faster than other flock members must suppress further activity and wait for slower flock members, as a lone bird or pair may be more vulnerable to predators or less efficient in tracking variable resources than when in a group.
Sleeping and Roosting
Roosting is usually preceded by a flight of 2–6 km. A flock may arrive at the roost site 1 h before actually going to roost. Often a portion of the flock forages for a time near a roosting area while other birds sit and hop among lower branches of trees. Birds alternate ground foraging and arboreal behavior. About 20 min before roosting, all birds ascend into the trees, with many climbing to the tips and then gliding to the lower branches of nearby trees.
A loud Krawk, common when the flock arrives, is then heard only rarely; most birds become silent. About 5 min before roosting starts, groups of two to four individuals begin selecting sites, sometimes sitting silently, then moving to a new branch or tree. Then, as if on cue, all birds stop moving and the flock is still until morning. If disturbed by an owl or domestic cat, jays may give a loud danger call and fly off, even in the middle of the night.
A flock may use the same roosting area for 2–3 mo (121), while at other times it uses a different area every night. All roosting birds may be clustered in 4–6 large pine trees in an area of about 2 ha. Large flocks (100–200) of European Starlings may roost nearby. In ponderosa pine (Pinus ponderosa) habitat in northern Arizona, they normally roost in small clumps in the middle heights of the ponderosa pines and on south sides of trees, facing south or west into the setting sun. This roosting orientation may allow individuals to take advantage of the last rays of the sun for warmth and to continue vigilance later into the evening. With arrival of spring, individuals roost progressively higher in trees. At this time, roost sites are similar to nest sites in height and orientation (121).
During roosting, the legs are flexed, and partly covered by belly feathers. The neck is retracted and bill pointed straight forward. Scapular, anterior spinal, flank, and dorsal belly feathers are slightly elevated, giving the bird a rounded appearance.
Some individuals on some nights changed from the above posture to one in which bill was placed on or near the skin of the dorsal apterium, between spinal and humeral feather tracts, with bill and anterior part of head covered. Small females do this earlier and on more nights than do larger males, suggesting that this behavior may reduce heat loss from head and nostrils. In an outdoor cage, females went to roost before males and placed their bills under their scapulars earlier and on more nights than males did (121).
Daily Time Budget
Although not studied for the entire year, observations on the time of roosting and arousal in fall, winter, and early spring indicate that Pinyon Jays arise later and roost earlier than many other passerines in their habitat. As the nesting season approaches, they arise earlier than predicted from sunrise and go to night roosts later than predicted from sunset (M. L. Morrison, T. R. Bement, RPB, unpublished data).
In northern Arizona, observations of aggression measured as displacements at a well-stocked feeder provided data on phenology, frequency, dominance hierarchy, and individual differences in threat displays. From these data, dominance relationships within the Town Flock were determined. “Winners” were defined as birds that maintained their positions at the feeder after an encounter and “losers” as birds that either left the feeder or gave an appeasement posture during an encounter. Winners most often won simply by turning toward the subordinate, looking at it, then taking a step toward it. Winning was most often swift and efficient. Losing was much more complicated and time-consuming, as losers often employed six different acts in an attempt to maintain their position on the feeder. Losing was slow and inefficient (2).
The following statements are based on > 4,000 recorded aggressive encounters taken throughout the year for both sexes and age classes. During all times of the year, adult males are the most aggressive class, followed by yearling males. The least aggressive class is females, with yearling females being the most passive. Aggression is highest in fall and lowest during courtship and breeding during late winter and early spring. From June through September, when the flock contains juvenile birds, they are highly aggressive; they fight often with each other and are often deferred to and tolerated by older birds. Most of these encounters are initiated by young males. This special social position ends abruptly in autumn with levels of aggression waning in this cohort and other cohorts no longer tolerating the exuberant behavior of the juveniles (116, 2).
Adult males fight more frequently than any other cohort and mainly with each other; consequently, more data have been gathered for them. One male was notably the “alpha male,” 7 other males were clearly dominant, another seven were subdominant, and the remaining 39 males could only be classified as subordinate. The alpha male was the largest male in the flock but not the most aggressive; thus it was difficult to identify him. Consequently, aggressiveness and status are not correlated. Bill size, but not body mass, is correlated with dominance status. In aviary contests between two males, dominant individuals were heavier and had larger bills (25).
Adult females show a much less linear arrangement even though a diligent search was made for one (contra 122), which may indicate that they have a much more complex social organization than males. In laboratory tests between two females, dominance was weakly associated with brightness of the malar feathers and weight (123).
Threat displays are subtle and relatively inconspicuous, but easy to identify. The most common threat display involves the dominant bird turning its body to face the subordinate bird, raising its head slightly and staring at the subordinate. A second threat display involves a simple step toward the subordinate. Serious threat displays (seldom used) including flying at, chasing, or pecking at the subordinate (89, 2).
The “Chin-Up” Display is given by a subordinate bird in conflict situations. It is given silently as the submissive bird points its bill straight up toward the sky and stands motionless. Body-feathers are held tightly to the body, tail folded in, and the white throat bib is exposed with throat-feathers slightly raised. Occasionally, a slight quiver of the wings accompanies this act. This display is given uncommonly by very subordinate adult males, adult females, and yearlings of both sexes and is seldom given by dominant males when challenged by other dominant males. Juvenile birds do not give this display.
The “Begging” posture is also an appeasement display given by a subordinate individual when birds are in close contact. The body is partly flattened, wings are partly outstretched, and primaries are pointed posteriorly. The tail is often touching the ground, but folded, whereas the neck is slightly extended with the bill opened wide. The wings are quivered rapidly as bird gives the female Begging Chirr loudly and persistently. When used by a female during courtship and nesting, she advances toward her mate. When used as an appeasement posture, the bird is still. Juvenile birds, females, and subordinate males use this signal. Sick or injured individuals in captivity also use this signal (KJ). More dominant males were never seen to use this posture.
Territoriality is not observed in this species except over nesting material, which pairs vigorously defend once it is in place. Flocks maintain a well-defined home range most of the year, but boundaries are not defended conspicuously. Flocks may intermingle at home-range boundaries but depart with their home flocks. Home-range size is highly variable among flocks, depending on flock size, habitat quality, amount of human use, etc. In Arizona, the Town Flock home range measured about 8 × 8 km (6,400 ha). Another flock near Flagstaff, Arizona, had a home range of about 4 × 4 km (1,600 ha). At three sites in New Mexico, home ranges documented using radio-telemetry were 2,042 ha and 4,419 ha (breeding season), 2,060 ha and 4,599 ha (nonbreeding season), and 3,580 ha, 4,033 ha, and 5,978 ha (breeding and nonbreeding season) (66, 124). In years when pine cone crop is spotty, birds may leave the home range in search of cone crops at local “hot spots” and travel many kilometers outside the home range (2).
Mating System and Sex Ratio
Pinyon Jays are socially monogamous, though genetic studies on paternity have not been done to date. Pairs generally mate for life, with divorce extremely rare. The adult sex ratio in northern Arizona was always male biased, with on average 57% of all adults in January being males. Ligon and White (13) reported a similar ratio for an unprovisioned flock in New Mexico. Sex ratio varies among years and may result from higher mortality among females. Yearling sex ratios are far more variable and may act to drive emigration of the more numerous sex to other flocks in some years (87; see Migration Overview).
The permanent pair bond is the most stable association between 2 Pinyon Jays and may have profound influence on an individual's fitness. During the nonbreeding season, however, it is difficult to identify pairs within the flock. Yearling jays may court for more than 6 months before forming a permanent pair bond. Most birds initiate nesting when 2 yr old, and none after 3 years of age. Some yearling females breed, most often with older males. The average pair bond duration in Arizona was 2.5 yr; the maximum duration was 10 yr. Males averaged 1.63 mates/life; females averaged 1.43 (125).
Although both sexes compete for mates, males are slightly more competitive. In an aviary population, males with longer bills and heavier mass were dominant and more successful in obtaining mates than other males. Males preferred large, dominant females, but females preferred brightly colored males (25, 25). Results from field studies suggest that males prefer larger females but females prefer smaller males (15). Age strongly influences mate choice. Individuals tend to mate with birds of their age; this applies even to older birds in subsequent pairings. For example, a yearling female mated with a yearling male lost her mate when she was a 4 yr of age and mated with another male, also a 4 yr old. Two years later, this male disappeared and the now 6-yr-old female mated with a 6-yr-old male. Possibly the most important determinant of mate selection was past breeding performance. For 32 males and females in the Flagstaff, Arizona, Town Flock, the complete pair-bond history was known. After losing a mate, 75% of previously successful males (those that had produced at least one yearling) and just over 50% of previously successful females re-mated with previously successful birds. In contrast, only 18% of previously unsuccessful females and 33% of previously unsuccessful males re-mated with previously successful mates. This suggests birds have knowledge of past reproductive efforts of flock members (15).
As Pinyon Jays are monogamous and mate for life, they must be highly selective about mate quality. Choice of a mate is an important decision for Pinyon Jays because: (1) a jay that successfully obtains a high-quality mate is more likely to leave offspring; one with a low-quality mate will repeatedly fail; (2) mate fidelity is strong even after several years of poor breeding performance (126); (3) most Pinyon Jays (57% of males and 65% of females) mate with only one partner in their lives. Thus, the variety and intensity of courtship displays performed by Pinyon Jays is great. One major problem to be overcome by such a social bird is to find “privacy” where subtle courtship can be conducted. As courtship progresses, courting birds separate more frequently and farther from the foraging flock. Just before nest-building starts, the foraging flock consists of only a few adult birds and many yearlings.
Courtship displays as described by Balda and Bateman (89) for birds near Flagstaff, Arizona, and by Berger and Ligon (118) for birds from central New Mexico are presented below. Most displays were observed and/or confirmed to occur in the wild; a few displays were observed only in captive birds (J. Muskat, personal communication; RPB). The descriptions of these behaviors roughly follow the chronological sequences observed in the wild.
Silent Food Transfer. This display is observed before breeding, first appearing in mid-November when the photoperiod is shortening. This inconspicuous display involves one bird holding a tidbit of food at the end of its bill and its mate quickly snatching it. Although the male is the predominant provider in this display, in captive pairs some females readily fed their mates (102). Occasionally a slight quivering of the wings, and rarely a soft Chirr is given by the recipient. Early performances occur most frequently on the ground, at the periphery of the foraging flock. As the breeding season approaches, frequency of Silent Food Transfer increases and occurs at greater distances from the foraging flock.
Courtship-Begging. Starting in mid-December, females become more vocal and animated during Silent Food Transfer. Females crouch before their males with their heads slightly extended, open bills pointed slightly upward, wings flapping or fluttering, and tails motionless or slightly quivering against or near the substrate. Females vocalize loudly with Kaws and Courtship Chirrs. By January, females chase males on the ground and through the foliage performing this display. This is an intense, ritualized display given during courtship, nest-site selection, nest-building, egg-laying, incubation, and brooding. Because breeding males forage as a flock and return synchronously to feed their incubating females, a cacophony of Courtship-Begging calls may be heard at the nesting colony during feedings.
Silent Sitting. This subtle display becomes common as the nesting season approaches and the above two displays become regular. Pairs leave the foraging flock and fly to a perch, where they sit silently next to one another. This may occur ≤ 200 m from the flock. Individuals sit quietly, facing the same direction, with contour feathers compressed or slightly elevated. On occasion, one bird points its bill at its mate. The mate then raises its bill upward at a 50–70° angle, exposing the white throat bib in a display labeled a Chin-Up posture (89). Both members of the pair may alternate Chin-Ups. During Silent Sitting the pair also allopreens, preening the sides of the head and nape of the neck with slow, deliberate bill movements. Silent Sitting birds also perform a sidle display as one bird attempts to move closer to its mate (118). In early courtship, the female may sidle away or remain stationary, whereas later she may sidle toward her mate and the two may sidle back and forth, performing a slow, weaving dance.
Occasionally this display is interrupted by a soft, musical song given by one or both mates. This song is the most musical heard from these birds and is similar to the soft subsong given by juveniles (see Sounds and Vocal Behavior: Vocalizations).
Swagger Walk. This visual display occurs on open ground, where one bird follows its mate or the pair walks side by side, using an exaggerated posture and strut. Both birds are upright, tails elevated and wings and tail vibrated intermittently, and contour feathers mostly compressed, as they display their bright malar feathers and white bibs (118).
Stick Manipulation. The male picks up a stick, a twig, or tuft of grass, approaches his mate, often flies to a branch, and sits motionless with the material in his bill. If the female does not respond, he drops the material and returns to the female's side. As the season progresses, the female may follow her stick-toting mate into the trees. The male places the sticks in front of the sitting female. As courtship proceeds, stick manipulation increases in frequency and becomes suggestive of nest-building. Pinyon Jays use sticks as a part of courtship more than do Florida Scrub-Jays (127) or Mexican Jays (128).
Crotch-Sitting. The male places a stick in front of his mate as she sits quietly in a crotch. Pairs may visit 3 or 4 crotches in succession. Silent Food Transfer and soft singing are interspersed with Crotch-Sitting. These sites are sometimes used by more than one pair, but seldom become nest sites. Occasionally these sites contain a number of sticks and twigs that superficially resemble the early stages of a nest. Crotch-Sitting becomes more common as the breeding season approaches.
Display Flights. Simultaneous with the appearance of Stick Manipulation, this bold display becomes evident. From 2‒12 individuals fly rapidly through and above trees, emitting loud Krawks as they perform steep dives and sharp turns above the foraging and courting birds. These flights contain yearlings and adult jays and always seem to contain one or more leaders and a group of followers. Upon landing, individuals continue to chase each other up and down through the tree branches in sharp spiral patterns before initiating another flight. These flights last from 1‒45 min. Sometimes multiple display flights occur simultaneously. The function of these flights is unclear, but if performed by noncourting birds in the midst of courting ones, it may aid in mate assessment by demonstrating the comparative vigor and stamina of performers.
Leg- and Belly-Pecking. This behavior is performed only by males and commences shortly before nest-building begins (J. Muskat, personal communication); it has been described only in captive birds courting in a large aviary. The male gently pecks his mate on or near her belly with a quick, direct peck. The female often responds with a Rick or Rack vocalization. In Leg-Pecking the male pecks at his mate's tarsal area. The female often sidles away from her mate and emits Chirrs. The function of these displays is not clear; they may serve to motivate the female to start nest-building and/or to encourage feather loss in the brood-patch area.
Copulation is the most striking display given by Pinyon Jays. This behavior has rarely been seen in the wild, but is confirmed by descriptions from captive jays (Figure 7.; 118; J. Muskat, N. Stotz, personal communication). The displaying male assumes a hunched-over body position in a tree or on the ground, with wings partly extended in a caped position and the tail spread and upright. The male stays close to the female and circles around her while holding this posture. As the male jumps from branch to branch or walks around the female, his head and back feathers are erect. During circling, the male twists and turns to expose his back and wing feathers to the female. The female remains still, in an upright posture, feathers sleek to body, except for erect head-feathers. She intently watches the male as he circles and may crouch and softly give Begging Chirrs. If the female remains still and no distractions or interruptions occur, the male steps onto her back and copulates. Both members of pair wing-quiver during copulation. After the male dismounts, the female may give a Chirr.
Temporal and Spatial Components of Courtship
In northern Arizona and New Mexico, flocks often traverse their large home ranges during courtship. As courtship proceeds, flock movement becomes more restricted, and fewer long-distant flights are performed. Each flock has one or more traditional breeding and caching areas within its home range, and courtship is performed on or near both traditional areas (88, 89).
The duration and intensity of courtship is related to the number of pine seeds cached the previous autumn, availability of alternate foods, sex ratio of the flock, and only minimally to winter climate. In years when food is abundant, courtship occupies a shorter duration than when food is scarce (for details, see 88, 89, 4).
Duration and Maintenance of Pair Bond
Pinyon Jays are socially monogamous, but final judgment on the genetic mating system awaits genetic testing. No more than two adults (excluding second-year helpers at the nest) have been seen tending a nest, and only rarely do color-banded males attempt to mate with females other than their mates. Extra-pair copulations are common in Mexican Jay (Aphelocoma wollweberi; 128), but are not found in Florida Scrub-Jay (A. coerulescens; 127).
Pinyon Jays maintain pair bonds with the same partner for life. During 18 years of study, Balda and others ( 2,125) documented > 100 pair bonds, containing 279 pair-years; only three pairs divorced or dissolved their bonds. One bond was between the most dissimilar-sized birds in all bonds, and another occurred after the male developed a physical impairment. On average, pairs remained together for 2.5 yr ± 1.8 SD (n = 107) before the death of a partner, but 10% of all pairs remained together for > 5 yr, and 1 pair maintained bond for 10 yr in northern Arizona. One male that lived for at least 16 yr had 6 known mates. Pairs unsuccessful in producing young do not dissolve their bonds. In northern Arizona, 5 pairs remained mated despite producing no fledglings for 4 or more consecutive years. The social environment may constrain mate desertion. Flock members recognize each other as individuals, and pairs may assess breeding success or failure of other pairs; hence, unsuccessful jays probably have little chance to gain a better mate (129). Selection of a mate involves multiple criteria and takes a relatively long time; this may explain why Pinyon Jays show little increase in reproductive success with pair duration (125). Retention of mates serves to reduce competition and increase harmony and cooperation, beneficial factors for flock members.
None reported. No DNA testing has been done to date, although microsatellites have been developed for Pinyon Jays (130).
Social and Interspecific Behavior
When choice food items are presented at feeding stations, or when cones are densely packed on tree limbs, Pinyon Jays crowd together to collect these morsels. Each individual is bent on obtaining as much food as possible, with minor attention paid to other flock members, in scramble competition. In contrast, Clark's Nutcrackers and Steller's Jays attempt to defend these clumps of food, by driving off conspecifics, thus demonstrating interference competition, supporting the hypothesis that social species perform the former and asocial species the latter (131, 132, 133).
Degree of Sociality
Pinyon Jays are extremely social, with highly synchronized flocking behavior throughout the year. Each flock has permanent members, consisting of family clans, which remain stable over many years. Most males remain in their natal flocks, and many females do likewise (see Migration Overview). Social associations are first made shortly after leaving the nest, when young gather in nursery crèches. After about 1 yr of age, all except a few females will remain in the same flock. The function of the flock varies at different times in the annual cycle.
During years of heavy or modest pine cone crops, flocks may occupy a home range measuring about 8 × 8 km (see Spacing). When cone crops fail, an entire flock may leave its home range in search of pine seeds. Where crops exist nearby, flocks return periodically throughout the day to cache seeds and roost on their home range. When cone crops are poor, highly scattered, or nonexistent, numerous flocks may unite into massive groups of up to 1,000 birds that may range over 30 km/d (RPB). The “flock” is a complex structure. Flock composition and dynamics have been studied extensively only in the Town Flock near Flagstaff, Arizona. This flock averaged 165 birds and ranged from 121 to 292 birds during a 9-yr period from 1974 to 1982. In New Mexico, birds from two or three nesting colonies joined to form a winter flock (67).
Fall (August–October). The major fall behavior of the flock is to locate, harvest, transport, and cache pine seeds in individual sites. Many observers have been puzzled by these regular autumnal movements, which may sometimes number thousands of birds from numerous flocks (134). After caching ceases, birds forage as a synchronized unit. Flocks are largest and most variable in size during this period because of the variability in juveniles produced within the flock and the number of juveniles immigrating from other flocks. Over a 9-yr period in northern Arizona, autumn flock size ranged from 102 to 427 individuals and averaged 200. The largest number occurred in 1978, when hundreds of juveniles born elsewhere joined the Town Flock. Adult birds were the most stable cohort and averaged 70 birds over the 9 years (range 50–80). At this time of year, the flock contained an average of 27 yearlings (range 10–60 over 9 years).
Winter and Early Spring (December–March). Winter and spring are times of variable and complex behaviors, including seed recovery from caches, intense foraging for arthropods and seeds, predator surveillance and mobbing, pair-bonding by yearlings, courtship-feeding, nest-building, egg-laying, and feeding of nestlings (which were not counted in flock membership at this time). A flock may exhibit major movement patterns, covering up to 25 km in a single day as it forages, visiting some parts of its home range 2‒3 times per day and other parts only once or twice per week. Annual fluctuation in flock size is damped during this period, and the flock is at its lowest density. The Town Flock averaged 144 birds and ranged from 98‒270 birds during this period, with the high number reflecting a great influx of juveniles in one year. Adult populations were especially stable and ranged from 50‒75 birds over 9 years. Juvenile numbers fluctuated wildly, ranging from a high of 180 in 1978 to a low of 35 in 1976.
Summer (March–July). During spring and summer, adults are stressed by the need to feed their young. Until young begin to thermoregulate, females brood while males forage as a unit. Yearlings are in a nonbreeding flock that moves throughout the home range. Some yearling males help at their parents' nests. When young begin to thermoregulate, females join their mates foraging for the nestlings. During warm afternoons, birds from adjoining nests may form a small flock and move through the colony silently, stopping at nests, peering in, probing nestlings and occasionally feeding them. These visits may allow adults to assess the density of the flock and reproductive competence of the nest owners. At this time, pairs which have failed would now be off re-nesting in satellite colonies. By midsummer, the once-cohesive flock is subdivided into numerous factions, including: multiple crèches of young (each crèche containing young of similar age), a yearling flock, and a few pairs still attempting to nest in small satellite colonies. The Town Flock was most disjointed at this time, when food is most abundant and uniformly distributed over the landscape. In northern Arizona, flock size was highest in years when many juveniles were produced (1974, n = 88; 1977, n = 95; 1978, n = 95); flock size was lowest when few juveniles were produced (1975, n = 27; 1982, n = 50). The Town Flock contained on average 19 yearlings (range 10–25) and 66 adults (range 55–75).
Life in a stable, highly organized social group selects for cognitive abilities that bestow differential fitness (135). Social interactions and organization of the flock as a collection of extended families may have evolved to cope with high environmental variability (129) and/or the complexities of social living. Social species are generally expected to do better on some cognitive tasks than less social species (135 ).
Food Sharing. Pinyon Jays share food with other individuals, an example of prosocial behavior. Males feed their mates during courtship, incubation and brooding, but active sharing also occurs between unrelated adults (136). Although Pinyon Jays share preferentially with some individuals, the above study found no evidence of reciprocity. In some trials, dominant individuals shared more than subordinates (136), but this effect was not universal. Administration of high levels of mesotocin increased food sharing behavior (137).
Observational Learning. Bednekoff and Balda (138, 139) allowed Clark's Nutcrackers (Nucifraga columbiana), Pinyon Jays, and Mexican Jays to observe conspecifics as they cached in an experimental room. After 1 or 2 days, the observer birds were allowed into the room to search for these hidden caches. During the retention interval, all signs of activity were removed from cache sites. Mexican Jays and Pinyon Jays were more accurate than nutcrackers at locating caches made by another bird, even though nutcrackers were most accurate when recovering their own caches.
Two corvids of different social organization were tested for social learning abilities. The abilities of the Clark's Nutcracker (less-social) were compared to those of the Pinyon Jay (more-social). Birds of both species were tested under individual and social learning conditions. Pinyon Jays learning a novel task were facilitated by being able to observe conspecifics performing the same task, but Clark's Nutcrackers were not (140).
Socially Neutral Tests for Intelligence. In serial reversal learning, subjects learn to respond differentially to two stimuli, then reward contingencies are reversed, requiring the subject to relearn the altered associations. The ability of a species to adapt to this regimen has been considered an indication of behavioral flexibility. Serial reversal learning of two-choice discriminations was contrasted in 3 related species of North American corvids: Pinyon Jay (highly social), Clark’s Nutcracker (relatively solitary, but specialized for spatial memory), and California Scrub-Jay (Aphelocoma californica; ecological generalists). Pinyon Jays displayed significantly lower error rates than did nutcrackers or scrub-jays after reversal of reward contingencies for both spatial and color stimuli (141). The results are consistent with an evolutionary association between behavioral flexibility and social complexity. In a transitive inference test, the performance of Woodhouse’s Scrub-Jays (A. woodhouseii), Clark’s Nutcrackers, and Azure-winged Magpies (Cyanopica cyanus) was compared to that of Pinyon Jays. Social complexity and reliance on caching were significantly and independently associated with relational inference (142).
Pinyon Jay occasionally “play fly” like Common Raven (Corvus corax) in strong declivity currents near canyon sides and steep mountain slopes. Fledglings are highly inquisitive and play with objects such as fox and rabbit scat, feathers, string, pieces of bark, discarded paper, empty aluminum cans, pine needles and cones, leaves, twigs, beetles, and other insects. Often these objects are presented to other young and a tug of war may result (N. Stotz, personal communication). At 4 wk post-fledging, jays begin hiding objects in soil or tree crevices. These are largely inedible and this behavior has been labeled “play caching” (80). Pinyon Jays are occasionally seen flying in tight flocks performing rolls and swirling wildly with sharp turns, steep ascents, and descents, for no apparent purpose (17), although this could be a description of mating display flights (see Courtship Displays).
Nonpredatory Interspecific Interactions
Flocks of Pinyon Jays harvesting pine seeds are often joined by Clark's Nutcrackers, Steller's Jays (Cyanocitta stelleri), and Woodhouse’s Scrub-Jays. Nutcrackers are exceptionally adept at opening green cones and extracting seeds (143). Woodhouse’s Scrub-Jay, with its relatively weak bill, is unable to open green cones. As a result, Woodhouse’s Scrub-Jays sit silently nearby watching Pinyon Jays and nutcrackers open cones. When a cone is about opened, the Woodhouse’s Scrub-Jay screams loudly and flies at the unsuspecting forager. The startled bird often drops the opened cone, which is then retrieved by the scrub-jay. In this manner, they are able to share in the early pine-seed harvest with Pinyon Jays and Clark's Nutcrackers (83,86).
Kinds of Predators; Manner of Predation
In northern Arizona, eggs and nestlings were taken by gopher snake (Pituophis catenifer), American Crow (Corvus brachyrhynchos), and Common Raven, all egg eaters; Steller's Jay, an egg pecker (RPB); Northern Shrike (Lanius borealis; 17); Abert's squirrel; rock squirrel (Spermophilus variegatus), coyote (Canis latrans), and gray fox (Urocyon cinereoargenteus). The latter two species were seen jumping at nests far out on low drooping branches of ponderosa pine (2). In New Mexico, bobcat (Lynx rufus), Barn Owl (Tyto alba), and Woodhouse’s Scrub-Jay are reported as potential predators (144).
American Crows and Common Ravens cruise just above the treetops intently scanning the foliage below. One Common Raven returned once a day for 3 consecutive days to take 3 nestlings from a Pinyon Jay nest. A Common Raven was seen flying off with a nest, filled with young. Abert's squirrels eat and carry off nestlings (89). During an 11-yr study near Flagstaff, Arizona, yearly nest predation varied from 5–60%. The greatest threats to fledgling Pinyon Jays are Northern Goshawk (Accipiter gentilis) and Cooper's Hawk (A. cooperii); both are apparently attracted to a crèche by the loud begging calls of the young.
Response to Predators
Nest predators such as American Crow, Common Raven, and Northern Goshawk are not deterred by adult Pinyon Jays. When adult jays are present at their nest during a predation event, they give loud Rackas and Multiple Racks, which may attract parents from other nests to join mobbing. Shortly thereafter, however, these vocalizations gradually change to begging calls. At first thought to be an inappropriate behavior performed in the “heat of battle” (145), it was later noted that these calls stimulated nestlings to jump from the nest, where they may have a better chance of eluding nest predators.
Flock members respond to Rackas and Multiple Racks by immediately flying into trees, sitting silently, and searching for predators. If flocking associates, such as Hairy Woodpecker (Dryobates villosus) and Downy Woodpecker (D. pubescens), Northern Flicker (Colaptes auratus), Clark's Nutcracker, or European Starling (94), are with the flock, they respond similarly. When seeking an approaching predator, Pinyon Jays often assume a stoic pose with body perpendicular to the branch, legs flexed, neck retracted slightly, bill held out straight, wings held tightly to body, and tail folded. When located, a predator is mobbed vigorously by most members of the flock; they dive at it swiftly, hover in front of it, peck at it, or walk up to it on the ground.
During foraging, usually 4–12 birds are perched at high vantage points around the periphery of the flock. These birds are quick to give alarm calls in the presence of potential danger. These birds may be “sentries” (146) or birds that have finished their foraging but must wait for slower members of the flock to finish before moving on (2).