Pinyon Jay Gymnorhinus cyanocephalus
Version: 2.0 — Published March 19, 2020
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Demography and Populations
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Measures of Breeding Activity
Ages of First Breeding; Intervals Between Breeding
Based on complete data for 63 males and 66 females (2), most birds do not breed until 2 years of age. However, some females breed when they are 1 yr old; 71% of all yearling breeders are female. A premium is apparently placed on yearling females of large mass because they have longer life spans. In northern Arizona, about 10% of all males and 3% of all females do not breed until 3 years of age (2). There is typically only 1 nesting per year if 1 or more young fledge.
Clutch size is 2 (rarely) to 5 eggs. Two-egg clutches are most often abandoned (151). For a flock of Pinyon Jays near Flagstaff, Arizona, mean clutch size ranged from 3.0 to 4.32 eggs (overall mean 3.70; n = 307 clutches). Based on 115 nests containing 474 eggs (records at WFVZ from throughout species' range), mean clutch size was 4.12 eggs (range 3–5 eggs; WFVZ); no geographic variation in clutch size was noted. See also Breeding: Eggs.
Annual and Lifetime Reproductive Success
In northern Arizona, from 1971 to 1987, the average clutch size was 3.7 eggs; 55% of eggs hatched; 56% of nestlings fledged; and 32% of fledglings survived the crèche stage. Of these, 51% survived their first winter, and only about 5% of all eggs became yearlings (2). In New Mexico, over 5 nesting periods between 1969 and 1977, nest success varied from 31% to 54% (4). Lifetime reproductive success (LRS) is directly related to how long a Pinyon Jay lives; long-lived birds produce more offspring than short-lived birds. Age of breeders, size of cone crop, late winter snowfall, predator pressure, and summer climate all contribute, in a complex manner, to the yearly variability in productivity (2).
In northern Arizona, a breeding male lived an average of 5.65 yr, bred during 4.19 of these, fledged 0.92 young/yr, of which 0.51 survived to ultimately produce 2.74 yearlings in an average life span. An average breeding female lived 5.20 yr, bred during 4.27 of these, and produced 1.04 fledglings/yr and 2.86 yearlings in a lifetime. The proportion of females rearing at least 1 brood to independence varied greatly among years. The average proportion of life spent breeding by males was 0.71, by females 0.82, a significant difference (P = 0.003).
Expected fecundity, calculated from a life table (the product of the proportion of birds surviving to a given age [lx] and their fecundity at that age [mx]), was highest for birds 2–4 years of age because at these ages, maximum numbers of birds are alive, but after this time many birds die, thus lowering the lx . Heavy birds of both sexes may be maximizing different components of lifetime reproductive success: heavy males produced many young that fledged, but few survivors; heavy females produced few fledglings with high survival (2). Birds from helper-family lineages had significantly higher lifetime reproductive success than those from lineages without helping (2).
Number of Broods Normally Reared per Season
One brood is reared per season. Only 2 second broods were observed over 18 years of observation (RPB), and both cases were probably due to artificial feeding by humans, similar to Florida Scrub-Jay (Aphelocoma coerulescens; 127).
Proportion of Total Females That Rear at Least One Brood to Nest-Leaving or Independence
Proportion of females that rear a brood to nest leaving or independence is highly variable among years.
Life Span and Survivorship
In northern Arizona, a breeding male lived an average of 5.65 yr and an average breeding female lived 5.20 yr. The longest-lived bird in the Town Flock was a male that lived to be at least 16 yr old and produced 10 yearlings. The oldest female died when she was 14. Each year, a male can expect to live about a year longer than a female. In captivity, one male lived to be at least 16, and another 15 (RPB).
In Flagstaff, Arizona, Town Flock, 708 color-banded jays were followed for 13 yr (2). Survivorship varied by age. On average, 41.3% of juveniles survived their first 9–10 months of life, and 62.1% of these survived the next year. For 2-yr-old birds, annual survivorship was about 74%. Average adult survivorship was 74% (125). Survivorship curves for adults are very constant throughout life, suggesting that senescence or general deterioration does not occur in Pinyon Jays, in contrast to the Florida Scrub-Jay (157).
Mean age and sex structure of the northern Arizona Town Flock over 14 yr was: 47% adult males, 28% adult females, 15% yearling males and 9% yearling females (129). In central New Mexico, flocks consisted of 49% adult males, 29% adult females, 12% yearling males, and 10% yearling females (13).
Disease and Body Parasites
West Nile virus has been detected in Pinyon Jays (West Nile virus in birds in the United States, 1999–2016). The hypotheses that West Nile virus or other diseases may contribute to the species’ population decline has not been investigated.
A few body parasites have been collected when individuals were dusted before entering laboratory (RPB). Pinyon Jay has been identified as a host for the chewing louse Philopterus phillipi (158). See also Breeding: Parental Care.
Causes of Mortality
The following is from Marzluff and Balda (2), except where noted. Most mortality occurs during spring and autumn, suggesting that breeding activities and seed harvest are stressful, or birds enter fall after a particularly trying breeding season. Adult mortality is highest during breeding season when both sexes sustain about 40% of their yearly mortality. Adult mortality is also a function of the size of the pinyon pine cone crop in autumn. Mortality is high when cone crops are low (as expected), but mortality is also high when cone crops are huge. The noisy and conspicuous behavior of birds concentrated for long periods of time in patches with high densities of pinyon cones may attract predators. Adult mortality is apparently not affected by the vagaries of weather. Yearling mortality is possibly highest in autumn, but it may be confounded by autumnal dispersal of this cohort, which is difficult to track. Juvenile survivorship is highest when young hatch after or during warm, wet springs, which are conducive to production of insects. Predation appears to be the major cause of mortality for all age groups and both sexes. Starvation is extremely rare.
Males have higher survivorship than females. This appears to be related to time of first breeding, as yearling females are more likely to breed than yearling males, and these yearling females have high mortality during their first nesting attempt. Movement of females between flocks may also contribute to their higher mortality.
Birds with broken legs are uncommon but regular in the flock. These birds may eventually die from this infirmity, but some successfully breed (N. Stotz, personal communication).
In Flagstaff, Arizona, rubbish generated and placed in open containers attracts American Crow (Corvus brachyrhynchos) and Common Raven (C. corax) into the area. Each spring, these corvids take eggs and nestlings of Pinyon Jay, as do local human residents with air guns.
Population Spatial Metrics
All attempts by R. P. Balda and associates to measure individual distance among Pinyon Jays failed. At feeding stations, salt licks, roosting sites, and other clumped resources, birds may feed, drink, or sleep while touching each other, with no aggressive actions between them. Sometimes an individual lands on the back of another bird when attempting to obtain a clumped resource. In these situations, some supplanting occurs, but a bird often yields its position to the intruder, especially a young bird.
Territoriality is not observed in this species except over nesting material, which pairs vigorously defend once it is in place. Pinyon Jays nest colonially on traditional breeding areas that may be up 100 ha in size and used every year (89). Across New Mexico from 2007–2019, nesting colonies averaged much smaller than 100 ha, perhaps due to population declines over the intervening 40 years between the two studies, or possibly due to differences in methods of measuring colony areas. The mean area of minimum complex polygons around 14 nesting colonies was 17 ha (range 2.67–60.32) (KJ).
Home Range Size
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). 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).
In New Mexico, breeding season home ranges of two nesting colonies, determined by radio-telemetry, were 2,638 and 1,776 ha, with the combined year-round home range 4,305 ha, including members of both nesting colonies (67). At White Sands Missile Range, New Mexico, the breeding season home range of one nesting colony was 2,551 ha, its non-breeding home range 2,721 ha, and combined range (April until October) was 3,487 ha (67). At another site near Farmington, New Mexico, the home range of one flock from April through October was 4,033 ha (68). The New Mexico ranges are within the range of those reported above for Arizona.
Pinyon Jay populations are difficult to survey because this species occurs in flocks that move widely over large home ranges. The only long-term survey data are those of the North American Breeding Bird Survey (BBS) (Figure 8; 159). Using BBS data, the mean annual population for the United States was estimated at 690,000 individuals for the period from 2005 and 2014 (160). However, BBS and other standardized surveys of breeding birds (e.g., Integrated Monitoring of Bird Conservation Regions, IMBCR) typically occur 2 months after the peak nesting period of the Pinyon Jay. Although the BBS likely provides reliable long-term population trends, assessments of local populations may be most effective using annual monitoring of nesting birds at colony sites (115), followed by radio tracking. A statistically rigorous method based on the principles of occupancy modeling would be desirable for this species, but to date no such modification has been developed or thoroughly assessed.
In the Flagstaff, Arizona, region, the Town Flock varied in number from about 160 birds when a study was started in 1973 to a high of about 300 birds in 1978 to a low of 150 birds when the study terminated in 1985 (2). Most of these fluctuations can be attributed to the production and/or immigration of young. This flock may have declined since then due to local human activities. Traditional breeding grounds and caching areas of the Town Flock are being developed (as housing developments, schools, hospitals, shopping malls, etc.), thus pushing the jays out of town. Nearby flocks censused on an irregular basis had average densities as follows: 27, 36, 77, 148, 210, and 280 (2).
Effective population size was calculated using data on dispersal from the Town Flock. Dispersal depends on the sex ratio of adjacent flocks that could serve as sink or source. Results indicate that a single flock plus neighboring or adjacent ones (totaling about 7 flocks) form an effective population. Depending on quality of habitat, effective population size was between 220 and 370 birds.
Breeding Bird Surveys (BBS) over the past 50 years indicate that Pinyon Jay populations have experienced steeper and more sustained population declines than any other songbird associated with pinyon–juniper woodlands (75). BBS data for the survey-wide region showed a significant decline of 3.3% per year (n = 301 BBS routes; 95% CI: -4.48, -2.25) from 1968 to 2017 (Figure 4; 159) and a 2.5% annual decline (95% CI: -4.64, -0.05) over the last 10 years (2008 to 2017) for the survey-wide region (159). Declines appeared largest where the species is most abundant, Nevada’s Great Basin and west-central New Mexico; no BBS region showed a significant positive trend (159).
Over a 45-year period (1970–2014), BBS data indicated that the range-wide population has decreased by an estimated 85% (160). However, these results should be viewed with caution because BBS surveys do not effectively sample.
Data on population regulation are limited to the Flagstaff, Arizona, Town Flock, with a home range at the interface of an urban/rural area on the southern edge of the species' range. This population had several important sources of mortality. A major source of mortality occurred when fledglings were in the crèche just after leaving the nest. Predation was heavy on these rather helpless young birds and continued to be high during their first year of life. A portion of this mortality may have occurred when young dispersed. Because females disperse more readily than males, this source of differential mortality is one likely cause of the skewed sex-ratio. A second cause of mortality is predation on eggs and nestlings, but this is much lower than that on young birds. Two lesser mortality factors include loss of eggs due to snow and cold weather and death of 6-yr-old birds. Survivorship of young birds is the most critical factor influencing dynamics and size of Pinyon Jay flocks (see Life Span and Survivorship).