Publications

Environmental factors have long been demonstrated to influence the toxicity of pollutants to vertebrates. The vast majority of data has been derived from studies on fish, highly inbred laboratory rodents, and man.1,2 The magnitude and significance of these factors on toxicity has almost exclusively been elucidated in controlled experiments conducted in a laboratory setting. The...

The California condor (Gymnogyps californianus) is a member of the vulture family. With a wingspan of about 3 m (9 ft) and weighing about 9 kg (20 lb), it spends much of its time in soaring flight visually seeking dead animals as food. The California condor has always been rare (Wilbur 1978; Pattee and Wilbur 1989). Although probably numbering in the thousands during the Pleistocene...

The dominant feature of point counts is that they do not census birds, but instead provide incomplete counts of individuals present within a survey plot. Considering a simple model for point count sampling, we demon-strate that use of these incomplete counts can bias estimators and testing procedures, leading to inappropriate conclusions. A large portion of the variability in point...

The North American Breeding Bird Survey comprises a network of regularly censussed, road-based survey routes and constitutes the most comprehensive set of data on the relative abundance and population trends of these birds during the summer months. Its value was highlighted in 1989, when the data were used to confirm suspected population declines in a number of species of neotropical...

No abstract available.

Conservation of biological diversity is dependent on sound scientific information about underlying ecological processes. Current knowledge of the composition, distribution, abundance and life cycles of most species of plants and animals is incomplete, insufficient, unreliable, or nonexistent. Contemporary managers are also confronted with additional levels of complexity related to...

Samples of bat guano, primarily from Mexican free-tailed bats (Tadarida brasiliensis), were collected at nine bat roosts in caves in northern and eastern Mexico and analysed for organochlorine residues. DDE, the most abundant residue found in each cave, was highest (0.99 p.p.m. dry weight) at Ojuela Cave, Durango. Other studies of DDE in bat guano indicate that this concentration is too...

No abstract available.

In many areas of the tropics, forests are being converted to agriculture and other uses at a rapid rate. Previous research has documented that forest-breeding migratory birds are distributed across a wide variety of habitat types during midwinter. However, to evaluate the relative importance of different habitat types to wintering birds, we need to examine habitat-specific estimates of...

We delineate bird populations using cluster analysis to group ringing sites based on pairwise comparisons of recoveries. Clustering provides a quantitative (but non-unique) grouping that can be used to examine the relationships of bird distributions at both local and regional geographic scales. Clustering is based on similarity matrices composed of pairwise comparisons of recovery...

During the summers 1994-1995, over 80 eyries were located on over 10,000 km of survey routes in Mongolia. Where possible, production and hatch dates were assessed when the eyries were found. For 75 nesting attempts, breeding success was found to be 92%. The average number of young per brood was 28 for 68 attempts. The number of young fledged per pair by year were 3.2 in 1994 and 2.6 in...

No abstract available.