J. Ward Testa

Body Condition and Adjustments to Reproductive Effort in Female Moose (Alces alces)

We studied condition and reproduction of moose ( Alces alces ) in southcentral Alaska using ultrasonography to determine rump-fat thickness and numbers of corpora lutea and embryos in early gestation, and intensive radio-tracking of the same animals in spring to measure rates of calving and neonatal survival. Rump-fat thickness, pregnancy rate, and embryo size were less among female moose accompanied by a calf in autumn. Fifteen percent of ovulations failed to result in a detectable embryo, and additional reproductive losses occurred between early gestation and birth. Body condition in the autumn was correlated positively with pregnancy and calving rates and negatively with reproductive losses in both early and late gestation and neonatal mortality. Our study documents the extent to which body condition and prior reproductive success affect adjustments to reproductive effort made by female moose within a single reproductive cycle.

Habitat Selection and Home Ranges of River Otters in a Marine Environment: Effects of the Exxon Valdez Oil Spill

We studied habitat selection and home ranges of river otters ( Lutra canadensis ) living along the coastlines of Prince William Sound, Alaska, following the Exxon Valdez oil spill in late March 1989. Deposition of feces by otters at latrine sites that were heavily oiled was significantly less than for nonoiled sites in Herring Bay in June and July, but not during August 1989. Finer-scale measurements of habitat showed selection differed significantly on oiled (Herring Bay) and nonoiled (Esther Passage) study areas in 1990; otters selected steeper tidal slopes and sites with larger rocks on oiled than on nonoiled areas, based on characteristics of latrines and random sites. We believe otters avoided shallower slopes and protected areas with smaller rocks and gravel where oil persisted the longest. Thus, differences in habitat selection ostensibly were the result of a reduction in habitat availability caused by oil contamination. Otters on both study areas strongly selected old-growth forest; commercially logged areas in Esther Passage had no otter latrines. River otters on both areas also selected vegetated slopes (approaches to latrine sites) that were less steep. Home ranges of otters were about twice as large on the oiled area as on the nonoiled area, again suggesting that habitat for otters was reduced as a result of the oil spill. These outcomes were detected >1 year after the oil spill and suggest that there may be chronic effects of the oil spill on river otters.

POPULATION DYNAMICS OF WEDDELL SEALS (LEPTONYCHOTES WEDDELLI) IN McMURDO SOUND, ANTARCTICA'

Population dynamics of Weddell seals in McMurdo Sound, Antarctica, were studied from 1970 to 1984 using mark-recapture estimation, aerial surveys, age structure and magnitude of harvests, and direct counts of pup production. Similar data from earlier studies were used to reconstruct the history of the population during the period of human presence after 1956. Jolly-Seber estimates of population size indicated a general decline from 1970 to 1976, low numbers in 1976 and 1978, and relative stability from 1979 to 1984 at - 1500 adult seals. From 1970 to 1983, mean annual survival of adult female and male Weddell seals was estimated at 0.85 and 0.76. Counts made in aerial surveys in the summers of 1982/1983 and 1983/1984 were substantially below similar survey counts in the 1960s. Pup production in the breeding colonies also declined from 1967 to 1976, but has recovered and been stable since 1979. Collections spanning 28 yr indicated significant shifts in age structure characteristic of populations undergoing a rapid increase and then decline. The age structure of both sexes indicated a constant age of recruitment to the adult population at 5 yr, which corresponds closely with age of maturity in females. Generalized least squares and standard regression analyses failed to detect any correlation of adult survival or female reproductive estimates with population size or ice conditions, but there were significant trends in survival estimates from 1970 to 1983 that may be due to shifting age structure. The most plausible interpretation of these data is that heavy harvests of seals to feed dog teams in the mid-1950s severely depleted the resident population of adult Weddell seals. When population studies began in the early 1960s the population was expanding rapidly, probably as a result of immigration by juveniles. The population declined to low levels in 1976-1978 and has been fairly stable since 1979, probably at a level lower than before harvesting began. Survival and reproductive parameters of these Weddell seals are low relative to other pinnipeds, suggesting that the adult population is at an equilibrium with its environment.

POPULATION DYNAMICS AND LIFE HISTORY TRADE-OFFS OF MOOSE (ALCES ALCES) IN SOUTH-CENTRAL ALASKA

A common framework toward understanding the ecological forces affecting herbivore population dynamics is to partition those forces according to their origin higher (“top-down”) or lower (“bottom-up”) on the trophic chain. I employed that framework to describe phenotypic life history trade-offs in a large herbivore, moose (Alces alces). The relative importance of top-down and bottom-up ecological constraints to female moose in south-central Alaska was appraised at the population level by analyzing population size, growth, and winter habitat of moose, and the size and impact of their principal predator populations (wolves [Canis lupus] and brown bears [Ursus arctos]). At the individual level, longitudinal mortality and reproductive patterns of radio-collared individuals were studied to estimate vital rates and life history trade-offs that could be attributed to nutrition and predation, respectively. The population was essentially stable through the 1980s and early 1990s, and began declining in the period of...

Estimating Populations of Marine River Otters in Prince William Sound, Alaska, Using Radiotracer Implants

One year after the spillage of oil from the Exxon Valdez in spring 1989, we used radiotransmitters and radiotracer labels to mark river otters ( Lutra canadensis ) at Knight Island (oiled) and Esther Passage (unoiled) in Prince William Sound, Alaska. Feces recovered from latrines of animals were used as “recaptures” in mark-recapture experiments to estimate the density of river otters in the two coastal study areas. Our methods were evaluated for sources of bias in estimating and comparing population sizes. There was no evidence that densities of river otters at Knight Island (oiled) were less than those at Esther Passage (unoiled) in summer 1990 or that density of river otters at Knight Island was declining. Estimates of river otters in Prince William Sound ranged from 0.28 to 0.80 animals per km of coastline. Our estimates are similar to those for marine river otters in southeastern Alaska, but bias in the different methods should be considered.

Differences in Blood Haptoglobin and Length–Mass Relationships in River Otters (Lutra canadensis) from Oiled and Nonoiled Areas of Prince William Sound, Alaska

Significant differences in levels of blood haptoglobin occurred between river otters (Lutra canadensis) inhabiting oiled x̄ = 361 mg/100 ml, SD = 38, n = 6) and nonoiled x̄ = 306 mg/100 ml, SD = 87, n = 8) areas of Prince William Sound, Alaska (USA) following the Exxon Valdez oil spill in 1989. Additionally, male river otters from oiled areas had significantly lower body mass (1.13 kg) than male otters from nonoiled areas. We propose oil-related causes for these differences.

BEHAVIORAL AND ECOLOGIC EFFECTS OF DIFFERENTIAL PREDATION PRESSURE ON MOOSE IN ALASKA

Abstract We studied behavioral and ecologic effects of differential predation pressure on moose (Alces alces gigas) in the eastern Talkeetna Mountains, Alaska, during 1996–1998. Annual mortality from grizzly bear (Ursus arctos) and wolf (Canis lupus) predation was higher for solitary yearling moose than for dependent yearlings (those with adults) and solitary adults. We tested hypotheses that solitary yearlings have heightened levels of vigilance and greater variation in vigilance responses and spend more time near protective cover than do dependent yearlings or adults. Proportion of time spent vigilant did not differ between solitary and dependent yearlings, and no differences were found between solitary yearlings and adults. However, variation in vigilance increased with distance to protective cover for yearlings but not for adults. Only at distances ≥20 m from protective cover did variation in vigilance differ between solitary yearlings and adults. Increased variation in vigilance at distances far from protective cover, locations where putative vulnerability to predators is greatest, may account for increased mortality among solitary yearlings. Mean distance to protective cover was not different between solitary and dependent yearlings or between solitary yearlings and adults. Because hypotheses regarding differences in vigilance and use of protective cover between age and social status categories generally were not supported, other factors may be involved in promoting high vulnerability of independent yearlings to predation. Smaller body size and maternal defense are unexplored alternatives for explaining differential mortality between yearlings with and without mothers.

Exploring Linkages between Abiotic Oceanographic Processes and a Top-trophic Predator in an Antarctic Ecosystem

Climatic variation affects the physical and biological components of ecosystems, and global-climate models predict enhanced sensitivity in polar regions, raising concern for Antarctic animal populations that may show direct responses to changes in sea-ice distribution and extent, or indirect responses to changes in prey distribution and abundance. Here, we show that over a 30-year period in the Ross Sea, average weaning masses of Weddell seals, Leptonychotes weddellii, varied strongly among years and were correlated to large-scale climatic and oceanographic variations. Foraging success of pregnant seals (reflected by weaning mass the following pupping season) increased during summers characterized by reduced sea-ice cover and positive phases of the southern oscillation. These results demonstrate a correlation between environmental variation and an important life history characteristic (weaning mass) of an Antarctic marine mammal. Understanding the mechanisms that link climatic variation and animal life history characteristics will contribute to understanding both population dynamics and global climatic processes. For the world’s most southerly distributed mammal species, the projected trend of increasing global climate change raises concern because increasing sea-ice trends in the Ross Sea sector of Antarctica will likely reduce populations due to reduced access to prey as expressed through declines in body condition and reproductive performance.

Evidence for Recovery of Body Mass and Haptoglobin Values of River Otters Following the Exxon Valdez Oil Spill

Levels of blood haptoglobin (Hp) and interleukin-6 immunoreactive protein (IL-6 ir) were significantly elevated in river otters (Lutra canadensis) inhabiting oiled areas of Prince William Sound, Alaska (USA) following the Exxon Valdez oil spill in 1989. By May and June 1992, however, such differences were not apparent. Mean body mass of otters, adjusted for sex, age-class, and total length with analysis of covariance, differed between oiled and non-oiled areas from 1990 to 1992, but were nearly identical by May and June 1992. We propose that river otters may be recovering from chronic effects that we observed in 1990 and 1991 following the 1989 Exxon Valdez oil spill, but further research is necessary to test this hypothesis.

DOES PREDATION ON NEONATES INHERENTLY SELECT FOR EARLIER BIRTHS

Abstract I hypothesize that predation on newborn young represents a seasonal analog to time-lagged predator–prey cycles and can cause directional selection against late birthing. Newborn offspring represent an irruption of vulnerable prey to which predators can respond by adapting their search efforts to find and capture these prey. Those born early would be the 1st to achieve the size or mobility necessary to escape predators. Simple models of predation on moose calves were used to demonstrate how changes in predator efficiency as newborns appear, combined with a short period of offspring vulnerability, would produce selection against late birthing. Of the 9 published studies of mammals, 6 showed evidence of selection against late-born young that could be driven by predation on neonates. If true, this hypothesis has consequences for the way we interpret evidence for “predator swamping” and optimal birthing periods in mammals and other taxa with synchronous reproduction.