Publications

Because habitat degradation has led to the loss of submerged vegetation in Chesapeake Bay, wintering canvasbacks (Aythya valisineria) have shifted from a plant diet of American wildcelery (Vallisneria americana) to an animal diet of Baltic clams (Macoma balthica). We conducted experiments with pen-reared canvasbacks (n = 32, 1990; n = 32, 1991) to assess the effect of this diet change on...

A pack of two to eight adult wolves (Canis lupus arctos) and their pups was observed during ten summers (1986-95) on Ellesmere Island, Northwest Territories, Canada. The author habituated the wolf pack to his presence in the first summer and reinforced the habituation each summer thereafter. The first alpha female produced four to six pups each year between 1986 and 1989. However, her...

Comparative demographic studies of terrestrial vertebrates have included few samples of species from tropical forests. We analyzed 9 yr of mark—recapture data and estimated demographic parameters for 25 species of birds inhabiting lowland forests in central Panama. These species were all songbirds (Order Passeriformes) ranging in mass from 7 to 57 g. Using Jolly—Seber stochastic models...

The production, consumption, and applications of fluorspar are reviewed. In 1994, the U.S. exported about 45 kt of fluorspar, but, according to the U.S. Bureau of the Census, 493 kt were imported during the same period. Consumption, according to preliminary figures from the U.S. Bureau of Mines, was about 473 kt. China continued to be the main supplier of imports to the U.S. with 61...

California gulls (Larus californicus) of known age and sex were censused on their breeding colony in 1979, 1980 and 1984 through 1993. Ages of 235 males and 196 females ranged from 4 to 27 years. Age classes used in the analysis were limited to 17, 4 through 19, and 20 or more as a final age category because data on gulls over 20 were sparse. Survival declined with age in a way that was

Comparisons of bird abundances among years or among habitats assume that the rates at which birds are detected and counted are constant within species. We use point count data collected in forests of the Mid-Atlantic states to estimate detection probabilities for Neotropical migrant bird species as a function of count length. For some species, significant differences existed among years...

Concentrations of DDE (a metabolite of DDT) in birds decreased during recent years in most areas of the continental United States. Organochlorine pesticides were widely used in agriculture in Texas from the early 1950s to the 1970s. I used previously published data to determine whether concentrations of DDE and polychlorinated biphenyls (PCBs) in birds from Texas have followed a...

No abstract available.

No abstract available.

No abstract available.

To examine sample size requirements and optimum allocation of effort in point count sampling of bottomland hardwood forests, we computed minimum sample sizes from variation recorded during 82 point counts (May 7-May 16, 1992) from three localities containing three habitat types across three regions of the Mississippi Alluvial Valley (MAV). Also, we estimated the effect of increasing the...

No abstract available.