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We studied a population of Burrowing Owls whose eggs contained the or- ganochlorine compound p,p9DDE and traces of other organochlorine contaminants to de- termine if the levels of contamination were associated with survival or reproduction when nonanthropogenic environmental and biological variables were also considered. Demo- graphic data were collected in conjunction with sampling eggs for contaminants and an- alyzing pellets for dietary information. Levels of p,p9DDE in eggs varied over four orders of magnitude during the study but were not by themselves associated with reproductive failure. However, contaminant concentrations in combination with low rodent abundance in the diet were related to reduced productivity. The variation within and among years in egg contaminants suggests that patterns of egg contaminants are the result of immigrating owls from more contaminated sites, and to a lesser extent, to annual patterns in prey availability. Even low levels of chronic pesticide exposure may be detrimental when com- bined with other stressors, and documentation of the existence of a persistent pesticide in a biotic system is not enough to either infer the origin of the contamination or its potential

To assess the consequences of increased recreational activity in wilderness areas, we studied the effects of human activity on breeding behavior of Bald Eagles (Haliaeetus leucocephalus) in interior Alaska. Activity budgets of breeding eagles changed considerably when humans were camped for 24 h at a distance of 100 m from nests (treatment) compared to when they were camped 500 m from nests (control) (P = 0.0036). With humans near nests, adult eagles decreased the time they preened (percentage change from control to treatment = −53%), slept (−56%), maintained nests (−50%), and fed themselves and their nestlings (−30%) and increased the time they brooded nestlings (+14%). Further, overall activity (total number of behaviors performed by adults at nests per day) decreased by 27% with humans near nests, as did the amount of prey adults consumed (−26%) and fed to nestlings (−29%). In contrast, nest attendance did not change with humans near nests (percentage change = 0.3%, P = 0.9); however, the time adults w...

We assessed DNA repair and resistance to solar radiation in eggs of members of the western spotted frog complex (Rana pretiosa and R. luteiventris), species whose populations are suffering severe range reductions and declines. Specifically, we measured the activity of photoreactivating enzyme (photolyase) in oocytes of spotted frogs. In some species, photoreactivation is the most important mechanism for repair of UV-damaged DNA. Using field experiments, we also compared the hatching success of spotted frog embryos at natural oviposition sites at three elevations, where some embryos were subjected to ambient levels of UV-B radiation and others were shielded from UV-B radiation. Compared with other amphibians, photolyase activities in spotted frogs were relatively high. At all sites, hatching success was unaffected by UV-B. Our data support the interpretation that amphibian embryos with relatively high levels of photolyase are more resistant to UV-B radiation than those with lower levels of photolyase. At the embryonic stage, UV-B radiation does not presently seem to be contributing to the population declines of spotted frogs.

Along narrow rivers, spatial restriction of human use based on wildlife responses can effectively eliminate the entire river corridor from human use. Therefore, if river use by both wildlife and humans is a goal, an alternative management strategy is necessary. We measured flush response rate and flush distance of breeding and nonbreeding Bald Eagles (Haliaeetus leucocephalus) to recreational boating along the Gulkana River in interior Alaska from 1989 to 1992. Eagle responses to our nonmotorized boat were governed by the context within which human-eagle encounters occurred. Flush response rate of nonbreeding eagles decreased as perch height and its distance from the river's edge increased, increased as the season progressed and as eagle group size increased, was lower for juveniles (20%) than other age classes (49-65%), and varied with the existing level of human activity in a geographic location (P < 0.01 for all parameters). Flush distance of nonbreeding eagles increased as the distance a disturbance was first visible to a perched eagle increased, as perch height and its distance from the river's edge increased, and as the season progressed. In contrast to flush response, flush distance was strongly associated with age and was greatest for adults, least for juveniles, and intermediate for subadults. Breeding adults were much less likely to flush than nonbreeding adults, and flushed at lesser distances. We recommended that along narrow wilderness rivers, the impacts of human activity on Bald Eagle populations be regulated with temporal, rather than spatial, restrictions.