Foraging Behaviours and Population Dynamics of Arctic Foxes

Abstract

... The main objectives of my work are to examine (1) how arctic foxes use seasonally abundant foods and (2) how seasonal and annual fluctuations in food abundance affect foraging behaviours and population dynamics of arctic foxes. I am especially interested in how arctic foxes use geese and their eggs (i.e., seasonally abundant foods) and how this varies with fluctuations in small mammal abundance (i.e., foods that fluctuate annually). ... My work is done at Karrak Lake (67°14'N, 100°16'W) and surrounding areas in the Queen Maud Gulf Bird Sanctuary in Nunavut, Canada. ... Fieldwork for my project was done in the spring and summers of 2000-04, and data analyses are currently underway. I monitor population dynamics of arctic foxes in two goose nesting areas at Karrak Lake and two areas outside the influence of nesting geese, whereas I monitor foraging behaviours of arctic foxes in one section of the goose colony at Karrak Lake. ... I examine foraging behaviours of arctic foxes by observing individually marked foxes with spotting scopes .... Avoiding cache loss to competitors is a critical component for the evolution of caching .... I examine how nesting distribution of geese and dispersal of geese away from the colony affect cache loss by evaluating the survival rate of experimentally deployed caches .... I examine arctic fox diets by comparing isotope ratios (delta 13C and delta 15N) of fox tissues ... with those of food items collected in the field .... Fur is metabolically inactive, whereas blood is metabolized continuously ..., so by examining spring blood and winter fur I obtain information on both spring and fall diets. Geese are not present at Karrak Lake in either spring or fall, so goose signatures in this study represent foods cached in summer. I monitor population dynamics of arctic foxes ... through line-transect surveys, mark-recapture studies, and den inventories. ... Goose eggs (from both nests and existing caches) made up 91% of all foods taken by arctic foxes during goose-nesting at Karrak Lake. Foxes cached 96% of these eggs (i.e., most eggs from existing caches were moved to new locations) whereas other foods (i.e., small mammals, geese, and passerine eggs) were either consumed immediately or brought back to den sites. ... Age of cache sites and dispersal by geese away from the colony after hatch (when ca. 1 million geese and their offspring leave the colony in about 10 days) affected loss of experimental caches. These results suggest that both food abundance and strategies to prevent ageing of cache sites (e.g., cache site selection and moving of caches in poor condition) were important in affecting the arrangement of caches at our study site. Cached eggs constituted 30% to 40% of the arctic foxes' diet in autumn and 0% to 30% in spring. ... The abundance of arctic foxes was predominantly affected by abundance of geese ... whereas the density of breeding foxes and litter size were predominantly affected by small mammal abundance. ... This study will provide information on how seasonal and annual fluctuations in food abundance influence use of stored foods and population dynamics of arctic foxes. ... This study will also provide information on predator-prey interactions, which can be used for management and conservation of both arctic foxes and Arctic-nesting birds. ...