Polar Bears In Depth
Research Needs
Page 4 of 5
Understanding Reproduction. Delayed implantation is known mainly from animals that are tractable in the laboratory. How it works in ursids and how they use it to their advantage in highly variable environments is poorly understood. The timing of implantation, and hence that of birth, appears to vary geographically and also among individual females. It is likely dependent on body condition of the female, which in turn depends on a variety of environmental factors. The interaction between environmental and physiological factors that controls timing of birth and onset of lactation is simply not understood. Further research is necessary to understand how global warming and other broad-scale changes in Arctic conditions may affect reproductive processes.
Estimating Survival. Because polar bears are harvested in most areas and also increasingly exposed to other human perturbations, understanding the processes of reproduction and survival is essential. Estimating the numbers of cubs produced in polar bear populations can be logistically difficult, but is technically straightforward. Estimating survival, on the other hand, is both logistically and technically challenging. Making reasonable estimates of survival continues to provide a stumbling block for researchers and managers alike. Although estimates of survival derived from radiotelemetry studies are consistent with ecological theory (Amstrup and Durner 1995; Eberhardt 1985), the lack of concordance among estimates derived by different methods is troubling. The best estimates derived without the aid of telemetry (Derocher and Stirling 1995a; Lunn et al. 1997) are not in the range thought to be necessary to sustain populations (Eberhardt 1985). Also, telemetry estimates can be derived only for females because male polar bears will not retain radio-collars. As management needs intensify, precise estimates of survival of independent juvenile polar bears as well as adult males will need to be developed while survival patterns of females and dependent young are reevaluated.
Estimating Survival. Because polar bears are harvested in most areas and also increasingly exposed to other human perturbations, understanding the processes of reproduction and survival is essential. Estimating the numbers of cubs produced in polar bear populations can be logistically difficult, but is technically straightforward. Estimating survival, on the other hand, is both logistically and technically challenging. Making reasonable estimates of survival continues to provide a stumbling block for researchers and managers alike. Although estimates of survival derived from radiotelemetry studies are consistent with ecological theory (Amstrup and Durner 1995; Eberhardt 1985), the lack of concordance among estimates derived by different methods is troubling. The best estimates derived without the aid of telemetry (Derocher and Stirling 1995a; Lunn et al. 1997) are not in the range thought to be necessary to sustain populations (Eberhardt 1985). Also, telemetry estimates can be derived only for females because male polar bears will not retain radio-collars. As management needs intensify, precise estimates of survival of independent juvenile polar bears as well as adult males will need to be developed while survival patterns of females and dependent young are reevaluated.