Population Dynamics of the Mackenzie Delta Reindeer Herd, 1938-1958

Analyzes fluctuations in the size of both government- and Eskimo-owned herds of Rangifer tarandus in the Reindeer Grazing Preserve of northern Mackenzie District. Each of the six Eskimo-owned herds increased in numbers for a few years, then declined and ultimately, except one, was returned to the nucleus, government herd. Annual variation in herd size is examined in relation to the birth, death, and dispersal rates. The last which represents losses by straying, approx. 17,000 since 1938, usually yearlings, is the most important, birth rate the least. Effects of herd size and composition (tabulated by age and sex) on the birth and dispersal rates are deemed negligible. Dispersal is apparently caused by factors extrinsic to the herd itself, e.g. insects, weather, man, and their interactions

Rats, Mice, and People: Rodent Biology and Management

Farm Management,

Beyond population regulation and limitation

Population regulati on and limit ationC. J. Krebsr Abstract. The study of population dynamics addresses three questions that are not always separated in discussions with empirical data. Two questions address population regulation. What stabilises population density is the first question, and, in spite of much theory, little progress has been made in answering this question empirically. The assumption of an equilibrium density is impossible to test and direct experimental tests to answer this question are rare. What prevents population growth is a second question, and is the classic question of population regulation. To answer this question requires an increasing population, and, with adequate experimental manipulations, the density-dependent factors preventing increase can be identified. Surprisingly, answering this question has provided little assistance in solving practical problems in population dynamics, possibly because most populations are rarely in the state of growth and show a limited range of densities. What limits population density in good and poor habitats is a third question, which addresses population limitation rather than regulation, and has been the most useful question for empirical ecologists to ask. Population limitation admits of little theory and no elegant models, and highlights the gap between theory and practice in much of ecology. Defining the question clearly and adopting an experimental approach with clear alternative hypotheses will be essential to avoiding the controversies of the past while building useful generalisations for the practical problems of population management

Field methods for rodent studies in Asia and the Indo-Pacific

Farm Management,

Some Observations of Short-eared Owl, Asio flammeus, Ecology on Arctic Tundra, Yukon, Canada

We investigated nesting behavior, food habits, and interspecific interactions of Short-eared Owls (Asio flammeus) within an arctic tundra raptor community on Herschel Island and Komakuk Beach, northern Yukon, Canada. Short-eared Owls were the least common nesting raptor. We found only three nests, all on Herschel Island. All nests were on relatively elevated sites with fairly substantial vegetative cover. All nests failed in the egg stage, from a combination of human disturbance and possible predation by Arctic Fox (Vulpes lagopus) or Red Fox (Vulpes vulpes). Short-eared Owls nested only in years when small rodent densities were at least 4 to 5 individuals per hectare in the spring. Short-eared Owls ate Northern Collared Lemmings (Dicrostonyx groenlandicus), Brown Lemmings (Lemmus trimucronatus), and Tundra Voles (Microtus oeconomus) almost exclusively, without clear selectivity. Peregrine Falcons (Falco peregrinus) killed two adult Short-eared Owls. In northern Yukon, the Short-eared Owl remains an uncommon summer resident and uses the region as a migration route. Spring rodent densities and interspecific predation are prominent limiting factors, and human disturbance also limits nesting success. We recommend restricting access to most tundra areas during periods when the birds are mating, initiating nesting, and incubating eggs. We recommend that human infrastructure be designed so that it cannot support novel nesting (and therefore local range expansion) by other nesting raptors that compete with and prey on Short-earned Owls

Evaluation of a Technique to Trap Lemmings Under the Snow

We attempted to live trap lemmings under the snow in their preferred winter habitat at two sites in the Canadian Arctic using chimney-like boxes. Lemmings used the boxes during winter, but we had very low trapping success in April and May. During spring trapping, in contrast to most of the winter, subnivean temperatures became colder than ambient air temperatures. We hypothesize that our low success in spring resulted from lemmings’ leaving the deeper snow areas where our boxes were located and moving to shallower snow or exposed tundra. We suggest that the trapping boxes could be successful if trapping occurred earlier during winter.Nous avons tenté de capturer des lemmings sous la neige dans leur habitat hivernal préféré en utilisant des boîtes en forme de cheminée à deux sites situés dans l’Arctique canadien. Les boîtes ont été utilisées par les lemmings durant l’hiver mais nous avons eu un très faible succès de capture en avril et mai. Contrairement à la majorité de l’hiver, les températures sous-nivales étaient plus froides que les températures de l’air pendant que nous avons trappé au printemps. Nous émettons l’hypothèse que notre faible succès au printemps est dû au déplacement des lemmings des sites de fort enneigement, où nos boîtes étaient installées, vers ceux de faible enneigement ou vers la toundra exposée. Nous suggérons que les boîtes de trappage pourraient être plus utiles si le trappage se faisait plus tôt au courant de l’hiver