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Stephen H. Allen

Publications and source records attributed to Stephen H. Allen.

7 recordsLinked to original sources
USGS1995

Using known populations of pronghorn to evaluate sampling plans and estimators

Although sampling plans and estimators of abundance have good theoretical properties, their performance in real situations is rarely assessed because true population sizes are unknown. We evaluated widely used sampling plans and estimators of population size on 3 known clustered distributions of pronghorn ( Antilocapra americana ). Our criteria were accuracy of the estimate, coverage of 95% confidence intervals, and cost. Sampling plans were combinations of sampling intensities (16, 33, and 50%), sample selection (simple random sampling without replacement, systematic sampling, and probability proportional to size sampling with replacement), and stratification. We paired sampling plans with suitable estimators (simple, ratio, and probability proportional to size). We used area of the sampling unit as the auxiliary variable for the ratio and probability proportional to size estimators. All estimators were nearly unbiased, but precision was generally low (overall mean coefficient of variation [CV] = 29). Coverage of 95% confidence intervals was only 89% because of the highly skewed distribution of the pronghorn counts and small sample sizes, especially with stratification. Stratification combined with accurate estimates of optimal stratum sample sizes increased precision, reducing the mean CV from 33 without stratification to 25 with stratification; costs increased 23%. Precise results ( x̄ CV = 13) but poor confidence interval coverage (83%) were obtained with simple and ratio estimators when the allocation scheme included all sampling units in the stratum containing most pronghorn. Although areas of the sampling units varied, ratio estimators and probability proportional to size sampling did not increase precision, possibly because of the clumped distribution of pronghorn. Managers should be cautious in using sampling plans and estimators to estimate abundance of aggregated populations.

North Dakota↗
USGS1993

Dispersal patterns of red foxes relative to population density

Factors affecting red fox (Vulpes vulpes) dispersal patterns are poorly understood but warranted investigation because of the role of dispersal in rebuilding depleted populations and transmission of diseases. We examined dispersal patterns of red foxes in North Dakota based on recoveries of 363 of 854 foxes tagged as pups and relative to fox density. Foxes were recovered up to 8.6 years after tagging; 79% were trapped or shot. Straight-line distances between tagging and recovery locations ranged from 0 to 302 km. Mean recovery distances increased with age and were greater for males than females, but longest individual recovery distances were by females. Dispersal distances were not related to population density for males (P = 0.36) or females (P = 0.96). The proportion of males recovered that dispersed was inversely related to population density (r = -0.94; n = 5; P = 0.02), but not the proportion of females (r = -0.49; n = 5; P = 0.40). Dispersal directions were not uniform for either males (P = 0.003) or females (P = 0.006); littermates tended to disperse in similar directions (P = 0.09). A 4-lane interstate highway altered dispersal directions (P = 0.001). Dispersal is a strong innate behavior of red foxes (especially males) that results in many individuals of both sexes traveling far from natal areas. Because dispersal distance was unaffected by fox density, populations can be rebuilt and diseases transmitted long distances regardless of fox abundance.

Journal of Wildlife Management↗
USGS1987

Spatial relations between sympatric coyotes and red foxes in North Dakota

Spatial relations between coyotes ( Canis latrans ) and red foxes ( Vulpes vulpes ) on a 360-km2 area in North Dakota were studied during 1977-78. Coyote families occupied large (mean = 61.2 km2), relatively exclusive territories that encompassed about one-half of the study area. Fox families occupied much smaller (mean = 11.9 km2), relatively exclusive, territories that overlapped perimeters of coyote territories and/or encompassed area unoccupied by coyotes. No fox family lived totally within a coyote territory, but 3 fox families lived within the 153.6-km2 home range of an unattached yearling male coyote. Both coyotes and foxes, from families with overlapping territories, tended to use their overlap areas less than was expected by amount of overlap. Encounters between radio-equipped coyotes and foxes from families with overlapping territories occurred less often than was expected by chance. Foxes living near coyotes exhibited considerable tenacity to their territories, and no monitored fox was killed by coyotes during 2,518 fox-days of radio surveillance. A hypothesis for coyote-induced fox population declines, based largely on fox avoidance mechanisms, is presented.

North Dakota↗
USGS1984

Red fox predation on breeding ducks in midcontinent North America

Red fox ( Vulpes vulpes ) predation on nesting ducks was assessed by examining 1,857 adult duck remains found at 1,432 fox rearing dens from 1968 to 1973. Dabbling ducks were much more vulnerable to foxes than diving ducks. Dabbling ducks (1,798) found at dens consisted of 27% blue-winged teals ( Anas discors ), 23% mallards ( A. platyrhynchos ), 20% northern pintails (A. acuta), 9% northern shovelers ( Spatula clypeata ), 8% gadwalls ( A. strepera ), 3% green-winged teals ( A. crecca ), 2% American wigeons ( A. americana ), and 10% unidentified. Relative abundance of individual species and nesting chronology were the most important factors affecting composition of ducks taken by foxes. Seventy-six percent of 1,376 adult dabbling ducks and 40% of 30 adult diving ducks for which sex was determined were hens. In western North Dakota and western South Dakota, 65% of mallard and northern pintail remains found at dens were hens compared with 76% in eastern North Dakota and eastern South Dakota ( P < 0.05). Percentage hens varied among the 5 most common dabbling ducks found at dens. In eastern North Dakota and eastern South Dakota, where predation on ducks was greatest, an average of 64% of gadwall, 73% of northern pintail, 81% of blue-winged teal, 81% of mallard, and 90% of northern shoveler remains found at dens were hens. Percentage hens among duck remains found at dens increased as the duck nesting season progressed. Numbers of adult ducks found at individual dens ranged from 0 to 67. The average number of ducks found in and around den entrances was used as an index of fox predation rates on ducks. Predation rate indices ranged from 0.01 duck/den in Iowa to 1.80 ducks/den in eastern North Dakota. Average annual predation rate indices for dabbling ducks in a 3-county intensive study area in eastern North Dakota were closely correlated with May pond numbers ( r = 0.874, P < 0.10) and duck population size ( r = 0.930, P < 0.05), but all species were not affected in the same manner or to the same degree. Drought had least effect on populations and predation rate indices of mallards and gadwalls and had greatest effect on those of northern pintails and northern shovelers. Hens of early nesting species were more vulnerable to foxes than hens of late nesting species. Predation rate indices were expanded to estimate total numbers of ducks taken by fox families during the denning season. Estimated numbers of dabbling ducks taken annually by individual fox families in 2 physiographic regions comprising the intensive study area ranged from 16.1 to 65.9. Predation was highest during wet years and lowest during dry years and averaged lower, but was more variable, in the region where tillage was greatest and wetland water levels were least stable. Predation in the intensive study area averaged 2.97 adult dabbling ducks/ km 2 /year and represented an estimated average annual loss of 13.5% of hen and 4.5% of drake populations in that area. Of 5,402 individual food items found at dens in the intensive study area, 24% were adult ducks. Ducks made up an estimated maximum average of 16% of the prey biomass required by fox families during the denning season. The average annual take of adult ducks by foxes in the midcontinent area was estimated to be about 900,000. This estimate included both scavenged and fox-killed ducks, as well as ducks taken after the denning season. Fox impact on midcontinent ducks was greatest in eastern North Dakota where both fox and duck densities were relatively high. Predation in that area was likely increased by environmental factors, especially intensive agriculture that concentrated nesting and reduced prey abundance. Predation by red foxes and other predators severely reduces duck production in the midcontinent area. Effective management to increase waterfowl production will necessitate coping with or reducing high levels of predation.

Iowa, Manitoba, Minnesota, Nebraska, North Dakota,↗