William R. Gould

ESTIMATION OF TEMPORAL VARIABILITY OF SURVIVAL IN ANIMAL POPULATIONS

Temporal variation of demographic characteristics for animal populations is of interest to both ecologists and biological modelers. The standard deviation of a series of estimated parameter values (e.g., estimated population size) or some function thereof (e.g., log of the estimated parameters) is commonly used as a measure of temporal variability. These measures of temporal variation overestimate the true temporal variation by not accounting for sampling variability inherent to the estimation of unknown population parameters. Using a variance-components approach to partitioning the total variability of an estimated parameter, we demonstrate the ease with which sampling variation can be removed from the observed total variation of parameter estimates. Estimates of temporal variability of survival are given after removal of sampling variation for three bird species: the federally listed Roseate Tern (Sterna dougallii), Black-capped Chickadees (Parus atricapillus), and Mallard ducks (Anas platyrhynchos). Sampling variation accounted for the majority of the total variation in the survival estimates for nearly all of the populations studied. Substantial differences in observed significance levels were observed when testing for demographic differences in temporal variation using temporal variance estimates adjusted and unadjusted for sampling variance.

An Evaluation of Trout Passage through Six Highway Culverts in Montana

Abstract Combinations of water velocity and passage length in highway culverts were evaluated to determine conditions that enabled or prevented the passage of nonanadromous rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, cutthroat trout O. clarki, and brook trout Salvelinus fontinalis. Fish passage through six culverts 45–93 m long was determined by trapping and electrofishing. Water velocities were measured 5 cm above the bottom (bottom velocity) and at 0.6 ofthe water depth at intervals between rest sites throughout the lengths of the culverts. Nonlinear regression lines specific to species and state of sexual maturity were fit to the combinations of mean bottom velocity and passage length representing the most strenuous conditions that allowed the upstream passage of trout. Because of the similarity of the strenuous passage relations among species, the spawning rainbow trout relation could be used as the general criterion for passage of the trout studied. This relation indicated that fish ...

Estimating Occupancy in Large Landscapes: Evaluation of Amphibian Monitoring in the Greater Yellowstone Ecosystem

Monitoring of natural resources is crucial to ecosystem conservation, and yet it can pose many challenges. Annual surveys for amphibian breeding occupancy were conducted in Yellowstone and Grand Teton National Parks over a 4-year period (2006–2009) at two scales: catchments (portions of watersheds) and individual wetland sites. Catchments were selected in a stratified random sample with habitat quality and ease of access serving as strata. All known wetland sites with suitable habitat were surveyed within selected catchments. Changes in breeding occurrence of tiger salamanders, boreal chorus frogs, and Columbia-spotted frogs were assessed using multi-season occupancy estimation. Numerous a priori models were considered within an information theoretic framework including those with catchment and site-level covariates. Habitat quality was the most important predictor of occupancy. Boreal chorus frogs demonstrated the greatest increase in breeding occupancy at the catchment level. Larger changes for all 3 species were detected at the finer site-level scale. Connectivity of sites explained occupancy rates more than other covariates, and may improve understanding of the dynamic processes occurring among wetlands within this ecosystem. Our results suggest monitoring occupancy at two spatial scales within large study areas is feasible and informative.

Effects of Temperature, Photoperiod, and Myxobolus cerebralis Infection on Growth, Reproduction, and Survival of Tubifex tubifex Lineages

Abstract Tubifex tubifex is the definitive host for Myxobolus cerebralis, the causative agent of whirling disease in salmonid fish. Several mitochondrial lineages of T. tubifex exhibit resistance to M. cerebralis infection. Release of the triactinomyxon form of the parasite from T. tubifex varies with water temperature; however, little is known about the interactive effects of temperature and photoperiod on the susceptibility of T. tubifex lineages to M. cerebralis infection. In addition, the environmental effects on the growth, reproduction, and survival of T. tubifex lineages are unknown. Monocultures of lineages III and VI were subjected to infection (0 and 500 myxospores per worm), a range of temperatures (5, 17, and 27°C), and various diurnal photoperiods (12:12, 14:10, and 16:8 dark: light) over a 70-d period by using a split–split plot experimental design. Lineage VI resisted infection by M. cerebralis at all temperatures, whereas lineage III exhibited infection levels of 4.3% at 5°C, 3.3% at 17°C,...

Comparison of helicopter and ground surveys for North American elk Cervus elaphus and mule deer Odocoileus hemionus population composition

Both ground and helicopter surveys are commonly used to collect sex and age composition data for ungulates. Little attention has been paid, however, to whether data collected by each technique are similar. We compared helicopter and ground composition data for both elk Cervus elaphus and mule deer Odocoileus hemionus across a variety of habitats in the state of Washington, USA. We found that ground and helicopter counts differed (Ps < 0.002) consistently in male age structure estimates for elk, and that the two survey methods differed in estimates of adult sex ratios for mule deer (P = 0.023). Counts from helicopters provided larger sample sizes, tended to be more consistent annually in their results, and were corroborated by other demographic studies of the test populations. We conclude that helicopter and ground surveys differ for male age structure and perhaps male:female ratios, but are similar for young:female ratios. Managers should maintain a standardized technique using the same survey vehicle for trend analysis of composition data.

Mark-resight superpopulation estimation of a wintering elk Cervus elaphus canadensis herd

Abstract We executed four mark-resight helicopter surveys during the winter months January–February for each of the three years 1999–2001 at 7–10 day intervals to estimate population size of a wintering elk Cervus elaphus canadensis herd in northern New Mexico. We counted numbers of radio-collared and uncollared elk on a simple random sample of quadrats from the study area. Because we were unable to survey the entire study area, we adopted a superpopulation approach to estimating population size, in which the total number of collared animals within and proximate to the entire study area was determined from an independent fixed-wing aircraft. The total number of collared animals available on the quadrats surveyed was also determined and facilitated detectability estimation. We executed superpopulation estimation via the joint hypergeometric estimator using the ratio of marked elk counted to the known number extant as an estimate of effective detectability. Superpopulation size estimates were approximately four times larger than previously suspected in the vicinity of the study area. Despite consistent survey methodology, actual detection rates varied within winter periods, indicating that multiple resight flights are important for improved estimator performance. Variable detectability also suggests that reliance on mere counts of observed individuals in our area may not accurately reflect abundance.

CAN SELECTION BY AN ECTOPARASITE DRIVE A POPULATION OF RED CROSSBILLS FROM ITS ADAPTIVE PEAK

Abstract The bill structures of different call types of red crossbills (Loxia curvirostra complex) in western North America usually approximate the predicted optima for foraging on single species of conifers. One clear exception is the call type in the South Hills, Idaho, that is coevolving in an evolutionary arms race with Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia). Although South Hills crossbills forage only on the cones of these lodgepole pines, their average bill depth is smaller than that predicted to be optimal. Because preliminary data showed that large‐billed males were more likely to exhibit symptoms of ectoparasitic mite (Knemidokoptes jamaicensis) infestation, the goal of our study was to further quantify the incidence of mite infestation and determine whether selection by mites may have favored smaller‐billed crossbills and thus driven crossbills away from the foraging optimum. We estimated annual survival of both infected and uninfected South Hills crossbills using program MARK, which allows for auxiliary variables such as bill size and sex to be included in survival analyses. Mite infestation depressed crossbill survival and, especially for males, caused directional selection against larger‐billed individuals. Such selection may explain why South Hills crossbills have smaller bills than the optimum and why average bill size for males has decreased from 1998 to 2003. This selection may also explain why the degree of sexual size dimorphism has decreased by nearly 50% since 1998.

Effects of Depleted Uranium on Survival, Growth, and Metamorphosis in the African Clawed Frog (Xenopus laevis)

Embryos (stage 8–47, Nieuwkoop and Faber) of the African clawed frog (Xenopus laevis) were subjected to water-borne depleted uranium (DU) concentrations that ranged from 4.8 to 77.7 mg/L using an acute 96-h frog embryo teratogenesis assay–Xenopus (FETAX). In a chronic 64-d assay, X. laevis (from embryo through metamorphosis; stages 8–66) were subjected to concentrations of DU that ranged from 6.2 to 54.3 mg/L. Our results indicate DU is a non teratogenic metal. No effects on mortality, malformations, or growth were observed in the 96-h FETAX with concentrations of DU that ranged from 4.8 to 77.7 mg/L. From stage 8 to stage 47, X. laevis tadpoles do not actively feed and the gills are not well developed. Thus, uptake of DU was reduced despite exposure to elevated concentrations. The 64-d assay resulted in no concentration response for either mortality or malformations; however, a delay in metamorphosis was observed in tadpoles subjected to elevated DU concentrations (from 13.1 to 54.3 mg/L) compared to tadpoles in both the well-water control and reference. The delay in metamorphosis was likely due to increasing body burden of DU that ranged from 0.98 to 2.82 mg/kg.

Density and roost site characteristics of spotted owls in the Sierra Madre Occidental, Chihuahua, Mexico

We estimated density and characterized roosting habitat of Mexican Spotted Owls (Strix occidentalis lucida) in the Sierra Madre Occidental in southwestern Chihuahua, Mexico. Mean Spotted Owl density in Chihuahua (0.089 owls km -2 ) was approximately half that reported for Arizona and New Mexico. Owls were primarily (70%) roosting in medium-sized trees, which likely resulted from a paucity of mature and old-growth forest on our study area. Spotted Owl roosts had steeper slopes, more canopy layers, greater canopy closure, and greater live tree basal area than random sites. Management objectives should promote increasing canopy closure and understory diversity to improve habitats for Mexican Spotted Owls in northern Mexico.

CATCH-EFFORT ESTIMATION OF POPULATION PARAMETERS UNDER THE ROBUST DESIGN

Catch-effort models, as well as models for many other animal abundance estimation techniques, are distinctly divided in their application to either closed or open populations. Pollock (1982, Journal of Wildlife Management 46, 752-757) first attempted combining open-population and closed-population models in the capture-recapture literature and constructed what is now known as the robust design. In light of the advantages of the capture-recapture robust design, a similar sampling scheme is of interest in the catch-effort estimation framework. Here a description of the robust design for catch-effort methods is provided, complete with explicit maximum likelihood estimators for a range of open models. The presence of mortality and recruitment are handled in the model development sequentially. Monte Carlo simulations were used to evaluate the performance of maximum likelihood estimators under the robust design in comparison with a previously defined regression estimator. The robust design provided for greater model flexibility and in almost all circumstances produced maximum likelihood estimators that were superior to those estimated by regression methods. The advantages of the robust design are discussed for a variety of modeling scenarios.