Grey W. Pendleton

Fat scoring : sources of variability

Fat scoring is a widely used nondestructive method of assessing total body fat in birds. This method has not been rigorously investigated. We investigated interand intraobserver variability in scoring as well as the predictive ability of fat scoring using five species of passerines. Between-observer variation in scoring was variable and great at times. Observers did not consistently score species higher or lower relative to other observers nor did they always score birds with more total body fat higher. We found that within-observer variation was acceptable but was dependent on the species being scored. The precision of fat scoring was species-specific and for most species, fat scores accounted for less than 50% of the variation in true total body fat. Overall, we would describe fat scoring as a fairly precise method of indexing total body fat but with limited reliability among observers.

SPATIAL AND TEMPORAL VARIATION IN THE TIMING OF BIRTHS OF STELLER SEA LIONS

Abstract Throughout the range of the Steller sea lion (Eumetopias jubatus), nearly all births of full-term pups observed from 1968 to 1998 occurred between 15 May and 15 July. We found significant differences in timing of births between rookeries with the earliest mean date of birth (4 June) at Forrester Island, Alaska, and the latest (21 June) at Año Nuevo Island, California. Mean date of birth becomes progressively later both north and south of Forrester Island. Births at individual rookeries were synchronous, with 90% of pups born within a 25-day period. We hypothesize that timing of births at rookeries is determined through selection for time periods when weather conditions are generally favorable for pup survival and when adequate prey items are predictably available near rookeries for lactating females. Temporal differences also were found in mean date of birth at 4 rookeries, with a maximum difference between earliest and latest mean date of birth of 10.2 days at Año Nuevo Island. The most likely explanation for temporal variability at individual rookeries is variable nutritional status of reproductive females.

Cohort effects and spatial variation in age-specific survival of Steller sea lions from southeastern Alaska

Information concerning mechanistic processes underlying changes in vital rates and ultimately population growth rate is required to monitor impacts of environmental change on wildlife. We estimated age-specific survival and examined factors influencing survival for a threatened population of Steller sea lions (Eumetopias jubatus) in southeastern Alaska. We used mark-recapture models and data from 1,995 individuals marked at approximately one month of age at four of five rookeries in southeastern Alaska, and resighted from Oregon to the Bering Sea. Average annual survival probability for females was 0.64 for pups and 0.77 for yearlings, and increased from 0.91 to 0.96 from age 3–7 yrs. Annual survival probability of males averaged 0.60 for pups and 0.88 by 7 yrs, resulting in probability of survival to age 7, 33% lower for males compared to females. Pups from northern southeastern Alaska (including an area of low summer population size but rapid growth) were twice as likely to survive to age 7 compared to pups from southern rookeries (including a large, historical, stable rookery). Effects of early conditions on future fitness were observed as (1) environmental conditions in the birth year equally affected first- and second-year survival, and (2) effects of body mass at approximately one month of age were still apparent at 7 yrs. Survival from 0–2 yrs varied among five cohorts by a maximum absolute difference of 0.12. We observed survival costs for long-distance dispersal for males, particularly as juveniles. However, survival was higher for non-pups that dispersed to northern southeastern Alaska, suggesting that moving to an area with greater productivity, greater safety, or lower population size may alleviate a poor start and provide a mechanism for spatial structure for sea lion populations.

Survival rates of American woodcock wintering along the Atlantic coast

Because American woodcock (Scolopax minor) populations have been declining, we attached radio transmitters to woodcock at coastal plain sites to determine if survival during winter was involved in the decline. Sites were in Georgia (1982-84, 1989-92), South Carolina (1988-89), and Virginia (1991-92). Survival rotes were not different between age or sex classes. Survival rates differed (P = 0.003) among years. Daily survival rates were lowest (P = 0.030, S = 0.987) during 1982-83 in Georgia and highest (P = 0.004, S = 0.999) during 1990-91 in Georgia than in the other years and locations combined (S = 0.996). We attributed all mortality to raptors and mammals. Compared with other periods of the year, winter was a time of low survival for woodcock

Mountain Goat Survival in Coastal Alaska: Effects of Age, Sex, and Climate

ABSTRACT Ecological theory predicts that individual survival should vary between sex and age categories due to differences in allocation of nutritional resources for growth and reproductive activities. During periods of environmental stress, such relationships may be exacerbated, and affect sex and age classes differently. We evaluated support for hypotheses about the relative roles of sex, age, and winter and summer climate on the probability of mountain goat (Oreamnos americanus) survival in coastal Alaska. Specifically, we used known-fates analyses (Program MARK) to model the effects of age, sex, and climatic variation on survival using data collected from 279 radio-marked mountain goats (118 M, 161 F) in 9 separate study areas during 1977–2008. Models including age, sex, winter snowfall, and average daily summer temperature (during Jul–Aug) best explained variation in survival probability of mountain goats. Specifically, our findings revealed that old animals (9+ yr) have lower survival than younger animals. In addition, males tended to have lower survival than females, though differences only existed among prime-aged adult (5–8 yr) and old (9+ yr) age classes. Winter climate exerted the strongest effects on mountain goat survival; summer climate, however, was significant and principally influenced survival during the following winter via indirect effects. Furthermore, old animals were more sensitive to the effects of winter conditions than young or prime-aged animals. These findings detail how climate interacts with sex and age characteristics to affect mountain goat survival. Critically, we provide baseline survival rate statistics across various age, sex, and climate scenarios. These data will assist conservation and management of mountain goats by enabling detailed, model-based demographic forecasting of human and/or climate-based population impacts.

Home range and movements of juvenile puerto rican parrots

We studied home range and movements of 15 radio-marked, juvenile Puerto Rican parrots (Amazona vittata) fledging from wild nest during summer and fall, 1985-87. When juvenile parrots remained in the nest valley, home ranges during 1986 (x=32±10 [SE] ha, n=4) were larger (P=0.0079) than during 1987 (x=13±6 ha, n=5). After radio-marked parrots integrated into adult flocks, home ranges during 1986 (x=1,075±135 ha, n=3) were similar (P=0.10) to 1987 (x=416±62 ha, n=2). Juvenile marrots restricted their movements to nest valleys an average of 58±29 days following fledging. After joining adult flocks, juvenile parrots routinely flew between the east and west slopes of the Luquillo Mountains but did not exhibit a seasonal pattern of movement

Inter-Population Movements of Steller Sea Lions in Alaska with Implications for Population Separation

Genetic studies and differing population trends support the separation of Steller sea lions (Eumetopias jubatus) into a western distinct population segment (WDPS) and an eastern DPS (EDPS) with the dividing line between populations at 144° W. Despite little exchange for thousands of years, the gap between the breeding ranges narrowed during the past 15–30 years with the formation of new rookeries near the DPS boundary. We analyzed >22,000 sightings of 4,172 sea lions branded as pups in each DPS from 2000–2010 to estimate probabilities of a sea lion born in one DPS being seen within the range of the other DPS (either ‘West’ or ‘East’). Males from both populations regularly traveled across the DPS boundary; probabilities were highest at ages 2–5 and for males born in Prince William Sound and southern Southeast Alaska. The probability of WDPS females being in the East at age 5 was 0.067 but 0 for EDPS females which rarely traveled to the West. Prince William Sound-born females had high probabilities of being in the East during breeding and non-breeding seasons. We present strong evidence that WDPS females have permanently emigrated to the East, reproducing at two ‘mixing zone’ rookeries. We documented breeding bulls that traveled >6,500 km round trip from their natal rookery in southern Alaska to the northern Bering Sea and central Aleutian Islands and back within one year. WDPS animals began moving East in the 1990s, following steep population declines in the central Gulf of Alaska. Results of our study, and others documenting high survival and rapid population growth in northern Southeast Alaska suggest that conditions in this mixing zone region have been optimal for sea lions. It is unclear whether eastward movement across the DPS boundary is due to less-optimal conditions in the West or a reflection of favorable conditions in the East.

Sex- and age-specific survival of harbor seals (Phoca vitulina) from Tugidak Island, Alaska

Abstract We estimated sex- and age-specific apparent survival of harbor seals (Phoca vitulina richardii) born at Tugidak Island, Alaska, from 2000 to 2007 using mark–recapture models and photographs of ventral pelage markings to identify individuals. Estimates of annual apparent survival (1 − (mortality + emigration)) of females were from 0.05 to 0.10 higher than those of males and were 0.820 for weaning (∼1 month) to 1 year, 0.865 for 1–3 years, and 0.929 at 3–7 years. Annual survival of males was 0.717, 0.782, and 0.879 for the same ages. Highest mortality occurred preweaning, with cumulative mortality to 4 weeks of age of 0.259, indicating this is the most vulnerable period for Tugidak harbor seals. Estimates of survival, not biased by misidentification, required that an individual had at least 2 good-quality, matching photographs in the photograph library. The number of photographs available for matching improved resighting probabilities from 0.43 for seals with 2 photographs to 0.69 for seals with 8 photographs, but this heterogeneity did not affect survival estimates. Survival estimates based on photograph-identification data were nearly identical to those based on resightings of flipper-tagged seals using mark–recapture models with a preliminary double-tag–loss estimate of 2.5% per year. Photograph identification of natural pelage markings provides a viable method for estimating vital rates of harbor seals even at large haul-outs (>1,000 animals) and may be useful for populations of conservation concern that require low disturbance of animals or where capturing sufficient numbers of seals for artificial marking is not feasible.

Effects of Snow on Sitka Black‐Tailed Deer Browse Availability and Nutritional Carrying Capacity in Southeastern Alaska

Abstract Snow affects the nutritional ecology of northern ungulates during winter through burial of important winter forages. We used nonlinear regression analyses to model snow-burial dynamics of blueberry (Vaccinium spp.) browse biomass, a key winter food item of Sitka black-tailed deer (Odocoileus hemionus sitchensis) in southeastern Alaska, USA. During November 2003–March 2004 we collected data from 546 individually marked twigs located on 100 plants of differing sizes and architectures across a range of snow depths. In general, browse biomass became buried and unavailable to deer at snow depths substantially lower than prewinter twig heights. Plant architecture and plant height were related to the probability of a twig being buried. Probability of twig burial was higher on plants with lateral than on those with erect architectures. Twig height also affected the probability of burial by snow but the relationship was complex. For twigs located on erect plants, probability of burial was greatest for twigs near the bottom and top of the plant due to ground-up burial and bending of flexible apex stems, respectively. We used estimated nonlinear equations to model blueberry browse availability in a simulated upland old-growth habitat patch subject to a range of snow depths. We then compared subsequent estimates of deer winter nutritional carrying capacity for this habitat patch to findings derived using an alternative, simple linear (ground-up) model of winter-browse burial by snow. Comparisons indicated that ground-up models of browse burial overestimated browse availability and nutritional carrying capacity for most snow depths. Our findings demonstrate the importance of applying detailed snow-burial models when characterizing nutritional landscape of northern ungulates during winter.

Habitat Characteristics of American Woodcock Nest Sites on a Managed Area in Maine

We measured characteristics of habitat near 89 nests of American woodcock (Scolopax minor) and 100 randomly selected points on Moosehorn National Wildlife Refuge, Calais, Maine, an area managed for woodcock. At nest sites, basal area was lower (P 0.05) or between sites of successful nests and nests destroyed by predators, although the large variances of the variables reduced our power to detect differences. Habitat around sites of renests differed from sites of first nests. Sites around first nests had lower basal area of dead trees (P = 0.05) and higher stem densities of aspen (P = 0.03) and cherry saplings (Prunus spp.) (P = 0.001), and viburnum (Viburnum spp.) (P = 0.05), while renest sites had taller trees (P = 0.02). The change from nest sites in areas dominated by alders and tree-size gray birch used in 1977-80 to sites dominated by sapling trees, especially aspen, used during 1987-90 suggests that woodcock in the expanding population at the refuge are selecting nest sites created by habitat management since 1979.