Bald eagle (Haliaeetus leucocephalus) population increases in Placentia Bay, Newfoundland: evidence for habitat saturation?

Across North America, Bald Eagle (Haliaeetus leucocephalus) populations appear to be recovering following bans of DDT. A limited number of studies from across North America have recorded a surplus of nonbreeding adult Bald Eagles in dense populations when optimal habitat and food become limited. Placentia Bay, Newfoundland is one of these. The area has one of the highest densities of Bald Eagles in eastern North America, and has recently experienced an increase in the proportion of nonbreeding adults within the population. We tested whether the observed Bald Eagle population trends in Placentia Bay, Newfoundland during the breeding seasons 1990-2009 are due to habitat saturation. We found no significant differences in habitat or food resource characteristics between occupied territories and pseudo-absence data or between nest sites with high vs. low nest activity/occupancy rates. Therefore there is no evidence for habitat saturation for Bald Eagles in Placentia Bay and alternative hypotheses for the high proportion of nonbreeding adults should be considered. The Newfoundland population provides an interesting case for examination because it did not historically appear to be affected by pollution. An understanding of Bald Eagle population dynamics in a relatively pristine area with a high density can be informative for restoration and conservation of Bald Eagle populations elsewhere.

Flight Paths of Migrating Golden Eagles and the Risk Associated with Wind Energy Development in the Rocky Mountains

In recent years, the eastern foothills of the Rocky Mountains in northeastern British Columbia have received interest as a site of industrial wind energy development but, simultaneously, have been the subject of concern about wind development coinciding with a known migratory corridor of Golden Eagles (Aquila chrysaetos). We tracked and quantified eagle flights that crossed or followed ridgelines slated for one such wind development. We found that hourly passage rates during fall migration peaked at midday and increased by 17% with each 1 km/h increase in wind speed and by 11% with each 1°C increase in temperature. The propensity to cross the ridge tops where turbines would be situated differed between age classes, with juvenile eagles almost twice as likely to traverse the ridge-top area as adults or subadults. During fall migration, Golden Eagles were more likely to cross ridges at turbine heights (risk zone, < 150 m above ground) under headwinds or tailwinds, but this likelihood decreased with increasing temperature. Conversely, during spring migration, eagles were more likely to move within the ridge-top area under eastern crosswinds. Identifying Golden Eagle flight routes and altitudes with respect to major weather systems and local topography in the Rockies may help identify scenarios in which the potential for collisions is greatest at this and other installations.