Arctic fox winter diet
Recently we finished the project: What are the foxes eating? The winter diet of the Icelandic arctic fox.
Full report (in Icelandic) is found here on the web page. The project was funded by the hunting-bounty grant on the behalf of The Icelandic Ministry for the Environment and Natural Resources.
Here is a short abstract:
The arctic fox (Vulpes lagopus) is a circumpolar species, adapted to climate and food resources dispersed around the arctic. A common prey of arctic foxes inhabiting the arctic tundra is small rodents (Lemmus, Mycrotus and Myodes spp.) Those fluctuate in numbers with regular 3-4 years cycles. The distribution of the arctic fox has reduced considerably during the last century and in Scandinavia, the population size is seriously low despite protection for over 80 years (P. Hersteinsson et sl. 1989). It has been suggested that indirect effects of warming climate in northern areas are the main causes of the species´ problems in Scandinavia and in other areas.
However, In Iceland, warming climate and milder weather during the past 30 decades has benefitted the Icelandic arctic fox. The population grew eightfold since estimation began in 1979 until it reached a peak of around 11.000 individuals in 2007. Actually, the population was historically small at the onset of the population estimates, around 1000 individuals, and had been declining since the 1950´s (P. Hersteinsson 2010). The reason for the increase is probably related to better conditions for various bird species inhabiting Iceland in accordance to milder weather. The arctic fox in Iceland feeds mainly on birds as there are no reliable rodent populations in Iceland.
One important limiting factor for the arctic fox population is food availability, both in quality and quantity. This is especially important for survival and breeding probabilities of females, even fertility (A. Angerbjörn o.fl. 1991). Because of this, it was interesting to see what the Icelandic foxes were eating during the winter.
We got stomachs from carcasses of legally hunted arctic foxes and looked into it to diagnose the food remains. We used 100 stomachs of winter hunted foxes, from the eastern and western part of Iceland. The methods were based on a former study by Hálfdán H. Helgason (2008). The identification on the stomach contents and analysis of the data took place at the laboratory of The Westfjords Natural History Institute in Bolungarvík (www.nave.is). Jónas Gunnlaugsson took care of the analysis and got help from the staff of NAVE. Ester Rut Unnsteinsdóttir and Þorvaldur Guðmundsson from The Icelandic Institute of Natural History (www.ni.is) also assisted Jónas.
Iceland can with respect to the arctic fox be divided roughly into two main habitat types, coastal and inland (Hersteinsson 1992a; Angerbjörn et al. 1994; Hersteinsson & Macdonald 1996). Western Iceland has a far higher proportion of productive seashores than northern, eastern and southern Iceland combined (Ingólfsson 1975). While western Iceland, as defined here comprises only a quarter of the total surface area of the country, productive seashores are twice as long there as in the rest of the country (3884 km versus 1985 km). The difference in surface area of productive seashores is even greater, 90% is in western Iceland (Ingólfsson 1975).
In the statistical analysis, Iceland was thus divided into two main parts, western and eastern.
The food items were divided into birds, eggs, mammals, fish, invertebrates, plants and other. Furthermore, birds were divided into alcids (guillemots, razorbills), gulls (various), fulmars, ducks, geese, waders and passerines. Mammals were either mice or larger mammals (sheep, horse, cow, and reindeer).
The main results were that alcids, fish and egg were only found in stomachs from the western part of Iceland. The eggs were probably from a fulmar and had been cached to be kept for later during last spring. Wood mice were found mostly in stomachs from the western part of the country. Geese and passerines were more commonly found in stomachs from the eastern part (together >50%). Ptarmigans were somewhat more common at the eastern part (28%) than the western (23%). Fulmars and gulls were more likely found in stomachs from western part (15%) than eastern (9%).
Invertebrates were found in considerable amounts in stomachs, especially at the eastern country. Among common types found were larva and pupae of Melanchra pisi but these are large items and full of nutritious proteins and calories.
In a wide range of the distribution of the arctic fox, competition with the larger and stronger red fox (Vulpes vulpes) is causing serious problems. These two fox species compete for food and habitats and in some cases, the arctic fox has become more specialized in food habits than the generalist red fox. As Icelandic arctic foxes are the only foxes in Iceland and here there are no lemmings or other cycling rodents, our foxes are generalist opportunists in food habits. Thus, in Iceland, arctic foxes can react quite fast on changes in food resources in time and space. Since variable food resources are important in sustaining viable populations, knowledge on the ecology of the Icelandic arctic fox can become useful in other areas, where the species is facing troubles due to competition, over-hunting and indirect climate effects (A. Angerbjörn o.fl. 1991; A. Angerbjörn og P. Hersteinsson 2004).
In a comparative study in two different habitat types within Iceland it was revealed that arctic foxes that live in coastal areas had quite a lot of mercury in their bodies, up to ten time higher amount than inland foxes in Iceland (N. Boahcarova o.fl. 2013). This mercury comes from marine based diet, mammals and birds. It is unknown what effects these chemicals have on the success of the foxes. According to this, the diet is quite different between inland (eastern) and coastal (western) foxes in Iceland.
Thus, it is important to continue monitoring both arctic foxes and their main prey species.
Population changes in time and space reflect variability in the ecosystems and predator-prey interactions are therefore an interesting study base.
Agnar Ingólfsson, 1975. Lífríki fjörunnar. Í: Votlendi (ritstj. Arnþór Garðarsson), Rit Landverndar 4, Landvernd, Reykjavík. Bls. 61-99. (In Icelandic).
Anders Angerbjörn, B. Arvidson, E. Norén og L. Strömgren, 1991. The effect of winter food on reproduction in the arctic fox, Alopex lagopus: a field experiment. The Journal of Animal Ecology, 705-714.
Anders Angerbjörn, P. Hersteinsson og M. Tannerfeldt, 2004. Arctic foxes: Consequences of resource predictability in the Arctic fox – two life history strategies. In Biology and Conservation of Wild Canids.
Hálfdán H. Helgason, 2008. Fæða refa (Vulpes lagopus) á hálendi Íslands að vetrarlagi. Rannsóknarverkefni (3 ein). Líffræðiskor Háskóla Íslands. (In Icelandic)
Natalia Bocharova, G. Treu, G. Czirják, O. Krone, V. Stefanski, G. Wibbelt, E. Unnsteinsdottir, P. Hersteinsson, G. Schares, L. Doronina, M. Goltsman og A.D. Greenwood, 2013. Correlates between feeding ecology and mercury levels in historical and modern arctic foxes (Vulpes lagopus). PloS one, 8(5), e60879.
Páll Hersteinsson, 1998. Spendýr á norðurslóðum Í: Undur veraldar: Greinasafn um raunvísindi fyrir almenning (ritstj. Þorsteinn Vilhjálmsson. Heimskringla, Reykjavík. Bls. 89-106. (In Icelandic)
Páll Hersteinsson, 1992. Demography of the arctic fox (Alopex lagopus) population in Iceland. In Wildlife 2001: Populations. D. R. McCullough, and R.H. Barrett (ritstj.). Elsevier, London. bls. 954-964.
Páll Hersteinsson, 2010. Tófan. Veiðidagbók Umhverfisstofnunar 2010. (In Icelandic).
Páll Hersteinsson, A. Angerbjörn, K. Frafjord og A. Kaikusalo, 1989. The arctic fox in Fennoscandia and Iceland: management problems. Biological Conservation, 49(1), 67-81.
Páll Hersteinsson og D.W. Macdonald, 1996. Diet of Arctic foxes (Alopex lagopus) in Iceland. J. Zool. Lond. 240:457-474.