The Arctic fox (Alopex lagopus): Adaptations, Morphology and Behaviour
The Arctic fox is a relatively small fox, with reasonably short legs and a large fluffy tail. It has a circumpolar distribution of all the Arctic tundra habitats, through North American and Eurasian Arctic tundra to the alpine tundra of Fennoscandia. The Arctic fox also inhabits most Arctic islands.
There are two distinct colour morphs in the Arctic fox population. First there is the traditionally envisioned ???white??™ morph which is virtually pure white in winter, with a few dark hairs on the tip of the tail. In summer the white moults to brown with a grey-white underside. The other colour morph is ???blue??™ with the fur in winter being brown tinged with a blue sheen which in the summer moults to a darker chocolate brown. (Angerbjorn et. al, 2004a)
The proportion of blue colour morphs increase in coastal areas and on islands, the blue morph is advantageous in these areas as they are better able to blend in to the ice free shorelines, thus enabling them to hunt more effectively. The white colour morph is naturally better suited for the inland, snow covered areas as it acts effective camouflage in a snowscape .
The fox??™s winter fur is very thick and soft, with a dense underfur and long outer guard hairs. Out of all mammals the insulating properties of the fur is the best, this means that the Arctic fox has no need to increase its metabolic rate to maintain homoeothermy (Prestrud, 1991 cited in Angerbjorn et. al, 2004b).
In coastal areas the foxes have access to stable food resources such as cliffs with bird colonies and the sea shorelines. Inland foxes have greater difficulties foraging for food as these a typically area of low productivity. The exception to this occurs once every 3 to 5 years when there is a super abundance of lemmings and voles. In winter Arctic foxes in areas with a predictable abundance of food can produce a body fat content of up to 40% (Prestrud, 1992; Prestrud and Nilssen, 1995 cited in Angerbjorn et. al, 2004a). This high fat content will also help the fox to survive in the freezing Arctic winters. When there is an abundance of food available the Arctic fox will form a cache of food (Chesemore, 1975 cited in Angerbjorn et. al, 2004b) which can then be accessed later in leaner times. The Arctic fox is an opportunistic forager, or as Elmhagen et. al (2002) considered, it could more accurately be termed an opportunistic specialist. It specialises on feeding on the fluctuating number of rodents that cycle over a number of years, while at the same time is an opportunistic carnivore.
In the inland areas which have an unpredictable abundance of food, the excess energy garnered in a year with a superabundance of prey is channelled into reproduction. The females will produce as many offspring as is physically possible (litters numbering as many as 19 have been recorded) with the only constraints being the maximum size of the litter at the late stages of pregnancy and producing sufficient milk for the suckling litter (Angerbjorn et. al, 2004a).
To summarise: The Arctic fox has developed a number of physiological adaptations such as a coat that allows act to camouflage it in either snowscapes or shorelines which also has outstanding insulating properties and the ability to gain significant body fat reserves. It has also developed a number of feeding strategies to help survive the polar conditions such as the cashing of food and becoming a opportunistic specialist. And finally it has also developed a breeding strategy that allows it to take advantage of the irregular superabundance of prey, producing a greater number of cubs in a single litter than any other member of the Canidae family.
Angerbjorn, A., Hersteinsson, P. and Tannerfeldt, M. (2004a) Arctic foxes. In Macdonald, D.W. and Sillero-Zubiri, C. The Biology and Conservation of Wild Canids. Oxford. Oxford University Press.
Angerbjorn, A., Hersteinsson, P. and Tannerfeldt, M. (2004b) Arctic fox (Alopex lagopus). Pp. 117-123 In Sillero-Zubiri, C., Hoffmann, M. and Macdonald, D.W. (eds) Canids: Foxes, Wolves, Jackals and Dogs. Status Survey and Conservation Action Plan. IUCN/SSC Canid Specialist Group. Gland, Switzerland and Cambridge, UK
Chesemore, D.L. 1975. Ecology of the Arctic fox (Alopex lagopus) in North America ??“ a review. Pp 143??“163 in M.W. Fox, ed. The wild canids. Their systematics, behavioral ecology and evolution. Van Nostrand Rheinhold Co., New York, USA.
Elmhagen, B., Tannerfeldt, M., Verucci, P. and Angerbjorn, A. (2000) The arctic fox (Alopex lagopus): an opportunistic specialist. The Zoological Society of London, 251, 139-149.
Prestrud, P. (1991) Adaptations by the Arctic fox (Alopex lagopus) to the polar winter. Arctic, 44, 132-138.
Prestrud, P. and Nilssen, K. (1995). Growth, size, and sexual dimorphism in arctic foxes. Journal of Mammalogy, 76, 522-530