Pinyon Jay Gymnorhinus cyanocephalus
Version: 2.0 — Published March 19, 2020
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The Pinyon Jay breeds in Upper Sonoran and Lower Transition zone habitat types in foothills and mid-elevations throughout its range. Pinyon–juniper woodland is used most extensively, but flocks may also breed in sagebrush (Artemesia spp.), scrub oak (Quercus spp.) and chaparral communities. In parts of its range (central Arizona, southern California), it inhabits ponderosa and Jeffrey pine (Pinus jeffreyi) woodlands (63, 64, 65, 18, 46).
Year-round home ranges in New Mexico can comprise several thousand hectares (66) and include various vegetation types, mainly pinyon pine woodland, dense pinyon–juniper woodland, sparse pinyon–juniper woodland, juniper woodland and savanna, sagebrush shrubland, and ponderosa pine (P. ponderosa) woodland (67, 68). Lower-elevation juniper woodlands, juniper savanna, and grasslands are used more commonly in the nonbreeding season, whereas pinyon woodlands and pinyon–juniper woodlands are favored in the breeding season (67, 66). Within pinyon–juniper woodlands, caching of pinyon seeds occurs in openings such as burned areas; gently sloping, open juniper scrub; or lower-elevation grassland (69). Caching areas are often sparsely vegetated, well drained, and free of snow in winter (2).
Pinyon Jays nest primarily in pinyon–juniper woodlands. Tree species in these woodlands vary geographically, with Colorado pinyon (Pinus edulis) the dominant pinyon tree in the Southwest (Arizona, Colorado, New Mexico, Utah) and single-needle pinyon (P. monophylla) dominating in California and the Great Basin (northwest Utah and Nevada (6). Junipers in New Mexico and from central Colorado to central Arizona are mainly one-seed juniper (Juniperus monosperma), while Utah juniper (J. osteosperma) dominates in Utah, Nevada, and northern Arizona (6). Alligator juniper (J. deppeana) overlaps the southern part of the Pinyon Jay range in Arizona and New Mexico, while Rocky Mountain juniper (J. scopulorum) may replace one-seed juniper at higher elevations in Arizona, Colorado, and northern New Mexico (70). In northern Arizona, Pinyon Jays nested in a ponderosa pine monoculture, an unusual habitat for them (2), where they placed nests in taller trees with denser foliage (71).
In northwestern New Mexico, nesting colonies occurred in areas with relatively low heat load and gentle slope (mainly northeast-facing); in large, dense patches of pinyon–juniper woodland; and closer to surface water but farther from gas wells than random sites (72). Associated with lowered winter precipitation, jays moved their nests from areas with declining tree vigor to areas with healthier trees (8).
A study of 9 colonies in persistent pinyon–juniper woodlands (see Romme et al.  for definitions of pinyon–juniper types) of New Mexico found that Pinyon Jays placed nests in taller trees and larger diameter trees, on plots with higher canopy cover around the nest and higher tree density than non-nest sites (74). In that study, nest habitat models from one site were not always effective when applied to another site, suggesting that management of Pinyon Jay nesting habitat should occur on a single-site basis when local nesting information is available.
In the Great Basin, Pinyon Jays are most closely associated with pinyon–juniper woodlands, but they also use shrublands for seed caching and foraging (75). In three large study areas in the Great Basin, the majority of Pinyon Jay flock activities during nesting and fall seasons were concentrated in or near the pinyon–sagebrush ecotone, where elevation and slope tended to be lower than in unoccupied woodland sites. Specific Pinyon Jay activities were further apportioned within this occupied zone. Caching sites tended to occur in the lowest elevations with low tree cover, but high woody plant density (including shrubs). Nesting sites were found in areas with higher tree cover and high woody plant density at multiple horizontal levels. Foraging sites showed no clear patterns, but encompassed the characteristics and range of caching and nesting sites. Data on roost sites were limited, but those identified were relatively close (< 500 m) to nesting sites and similar in vegetation structure (J. Boone and E. Ammon, unpublished data).
In southeastern Idaho, Brody (76) found Pinyon Jays using a home range comprising only junipers with no pinyon pines present; thus all nests were in junipers (n = 64). Another flock utilized a site with both pinyon pines and junipers, yet 12 of 13 nests were placed in junipers.
Pinyon Jay–Pinyon Pine Mutualism
The mutualism between Pinyon Jays and pinyon pines must have co-evolved. The ancestors of pinyon pines and Pinyon Jays can be traced to an ancient plant community on the Mexican Plateau encompassing northern Mexico and the southwestern United States called the Madro-Tertiary Flora (77, 78). Due to ideal growing conditions, this area was believed to support a highly diverse group of recently evolved plant species. About 30 million years ago, the climate gradually shifted from mild-moist to hot-dry. Progenitors of the modern pinyon pines were able to withstand and possibly thrive under these changes by developing a relatively slow spring growth pattern, short needles, and most significantly, large seeds that could germinate and produce seedlings under harsh growing conditions.
These highly nutritious seeds, the largest of any southwestern conifer (79), would be highly prized by seed predators, as they are conspicuous and easy to harvest. Thus, any tree producing a few large seeds every year would most likely have its entire seed crop consumed by insects, birds, and mammals. In contrast, when large crops of seeds are present at irregular intervals, seed numbers swamp the seed eaters, preventing consumption of the entire crop.
The ancestral corvid that evolved in association with and consumed the seeds of the ancestral pines likely had four characteristics still present in Pinyon Jays today:
(1) Relatively Large Size. Larger birds have metabolic flexibility in scheduling their daily time budget, compared to small birds which must spend the majority of their waking hours foraging for food to supply their immediate high energetic demands.
(2) Omnivorous Feeding Habits. An omnivorous feeding habit allows birds the opportunity to switch foods when seed crops were small or absent.
(3) Inquisitiveness. Most corvids spend considerable time exploring, probing, and visually inspecting many areas, ensuring they detect a crop of seeds.
(4) Strong Flight. Powerful flight allows birds to explore large areas in search of food that is frequently patchily distributed.
When ancestral corvids detected multiple seeds in cones, several seeds were probably extracted from cones and carried off in the mouth and bill to a suitable perch where they were opened and eaten. The entire cone may have been removed from the branch and carried to an above-ground perch for opening. Once birds were processing multiple seeds, they needed to protect for later use those not being eaten. This could be accomplished by placing the seeds in knots, cracks, and crevices in bark, needle clusters, etc., where they could later be retrieved. Thus, uneaten seeds were probably stored, albeit in an exposed location.
If foraging birds placed seeds in concealed or partly concealed locations, return visits might find the hidden seeds still intact. Many individual Pinyon Jays do employ area-specific, systematic search patterns, repeatedly returning to specific locations (RPB). Jays attempting to hammer open seeds on a soft substrate may push them into the soil, burying them from view (N. G. Stotz, personal communication). This behavior may have served as the precursor of caching behavior. If these seeds were not retrieved, they could germinate, establishing an ancestral mutualism between bird and pine. All the behaviors outlined above have been observed in Pinyon Jays (80, 81, RPB).
The key to success for the pinyon pines may have been their large, high energy-content seed (6), which allowed the pines to germinate and grow in areas and soil types where small-seeded forms could not survive. This large seed also attracted seed-eating birds, including a scrub-jay/Mexican Jay ancestor (82) and the ancestor of the Pinyon Jays. Once seed-hiding behavior was established, the Aphelocoma jays became the agent of local dispersal, while Pinyon Jays carried seeds on their strong wings into new areas, promoting swift colonization (6, 83, 84, 2, 85, 86).