Browsing by Author "Rockwell, Robert F."
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Item Developmental abnormalities in wild populations of birds : examples from lesser snow geese (Chen caerulescens caerulescens). American Museum novitates ; no. 3400(New York, NY : American Museum of Natural History, 2003) Rockwell, Robert F.; Pezzanite, Barbara (Barbara M.); Matulonis, P. (Paul)Changes in the frequency of individuals with gross abnormalities can be used as an indicator of changes in the occurrence of biologically significant levels of developmental toxicants in the habitats of natural populations. The precise nature of the defects and their relative distribution can often provide clues as to the type of contamination. Such inferences clearly require baseline data on the frequency of such deformities, and that is the purpose of this paper. For Mid-continent lesser snow geese (Chen caerulescens caerulescens) nesting at La Pérouse Bay, the current rate of gross external abnormalities among embryos and near-hatch goslings at hatch is 3.937 x 10⁻⁴ per egg (95% confidence limits 1.7053 x 10⁻⁴ to 6.507 x 10⁻⁴) and is consistent with estimates made for other species in minimally or uncontaminated habitats. Among the abnormal specimens, however, the relative distribution of defects of the beak and eye is not consistent with rates of spontaneous abnormalities reported for chickens. If the higher relative frequency of beak defects persists in future or other geographic samples displaying overall levels of abnormalities higher than our benchmark, then contaminants acting as type 1 teratogens should be suspected. Of the compounds this increasingly agriculturally dependent species is exposed to, insecticides rather than herbicides would be the more likely class of candidates. We urge others who may have similar data on other species to make it more broadly available since such benchmarks are crucial for the use of birds as bioindicators of environmental conditions. To that end, we offer our web site as a place where data on and images of abnormal specimens can be posted and, within certain constraints, will curate submitted specimens.Item Polar bear foraging behavior during the ice-free period in western Hudson Bay : observations, origins, and potential significance. (American Museum novitates, no. 3885)(American Museum of Natural History., 2017-10-24) Gormezano, Linda J.; Ellis-Felege, Susan N.; Iles, David T.; Barnas, Andrew, 1991-; Rockwell, Robert F.During much of the year, polar bears in western Hudson Bay use energy-conserving hunting tactics, such as still-hunting and stalking, to capture seals from sea-ice platforms. Such hunting allows these bears to accumulate a majority of the annual fat reserves that sustain them on land through the ice-free season. As climate change has led to earlier spring sea-ice breakup in western Hudson Bay, polar bears have less time to hunt seals, especially seal pups in their spring birthing lairs. Concerns have been raised as to whether this will lead to a shortfall in the bears' annual energy budget. Research based on scat analyses indicates that over the past 40 years at least some of these polar bears eat a variety of food during the ice-free season and are opportunistically taking advantage of a changing and increasing terrestrial prey base. Whether this food will offset anticipated shortfalls and whether land-based foraging will spread throughout the population is not yet known, and full resolution of the issues requires detailed physiological and genetic research. For insight on these issues, we present detailed observations on polar bears hunting without an ice platform. We compare the hunting tactics to those of polar bears using an ice platform and to those of the closely related grizzly bear. We examine how the techniques are related and explore how they may have evolved. We also discuss how they may contribute to polar bear adaptability in the face of climate change projections.