Stephen H. Allen

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)

Observed interactions between coyotes and red foxes

Etude des interactions entre Vulpes vulpes et Canis latrans. Des descriptions de rencontres entre individus de ces deux especes sont realisees pour comprendre les relations qui existent entre elles

Some Aspects of Reproductive Performance in Female Red Fox in North Dakota

Female age class and spring adult sex ratios were found to consistently affect ( P < 0.05) reproductive performance of North Dakota red fox ( Vulpes vulpes ). Reproductive performance was found to increase through 8 age classes. Increases ( P < 0.05) in ovulation rates, embryonic litter sizes, and declines in prenatal mortality were observed as a function of increasing female age. Body fat was found to increase in relation to female age class. An inverse relationship was noted between annual estimates of ovulation rates compared to March adult sex ratios and embryonic litter size compared to March adult sex ratios. A direct relationship was determined for annual estimates of prenatal mortality and March adult sex ratios. No consistent relationship was found between annual estimates of ovulation rates, embryonic litter sizes, or prenatal mortality when compared to annual spring population density.

Comparison of Red Fox Litter Sizes Determined from Counts of Embryos and Placental Scars

mining the annual reproductive performance of furbearers, because such data are needed for annual management decisions and population modeling. Counts of placental scars are often used to estimate litter size because large numbers of carcasses are easily obtained during harvest seasons. However, for many species, no data are available to assess the validity of litter-size estimates derived from placental-scar counts in relation to other procedures used for estimating productivity. Sanderson and Nalbandov (1973) found close agreement between numbers of embryos in individual captive raccoons (Procyon lotor) examined after 30 days or more gestation with numbers of individual placental scars identified for up to 10 months or more after parturition. They urged that caution be used to accurately distinguish scars representing live births of the most recent litter. Englund (1970) assessed placental-scar counts in red fox (Vulpes vulpes) and determined that only the 2 darkest shades of scars should be counted for litter-size estimates. However, Pils and Martin (1978) noted that some disagreement exists regarding determination of litter sizes of red fox from counts

Determination of Age and Whelping Dates of Live Red Fox pups

COWAN, W. F. 1973. Ecology and life history of the raccoon (Procyon lotor hirtus Nelson and Goldman) in the northern part of its range. Ph.D. Thesis. Univ. North Dakota, Grand Forks. 161pp. FRITZELL, E. K. 1978a. Habitat use by prairie raccoons during the waterfowl breeding season. J. Wildl. Manage. 42:118-127. . 1978b. Aspects of raccoon (Procyon lotor) social organization. Can. J. Zool. 56:260-271. GREENWOOD, R. J. 1979. Relating residue in raccoon feces to food consumed. Am. Midi. Nat. 102:191-193.

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 x 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 (x 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