1. History of the Mednyi arctic fox population:
Food habits of the arctic fox Alopex lagopus Semenovi Ognev, in the Mednyi Island O. G. Nanova^ , M.E.Goltsman, S.N. Sergeev ^Degree work Moscow State University Lomonosov M.V.
Foraging ecology of the Mednyi arctic fox was studied by means of diet analysis of individual families with the use of data on distribution of food resources scats from 19 families of tagged animals, 1007 food remains from 21 breeding dens, 700 hours of tagged foxes foraging behaviour observation were used. The Mednyi arctic fox is opportunistic in its food habits but pronounced selectivity in foraging behaviour was observed. Breeding colonies of sea birds were the main food resource examined in our study. Fur-seal rookeries were nearly unused by foxes despite there high productivity (placentas, carrion and newborn cubs). This finding contrasts previous data ( ) which showed that rookeries were an essential food resource at that time. Loss of foraging tradition of rookery utilization as a result of «bottleneck» ( ) and important role foraging conservatism is supposed.
The food resources on the Medniy Island are highly clumped and temporally predictable. There are two rookeries of fur-seals (fur-seal Callorhinus ursinus and sea-lion Eumetopias jubatus) and colonies of seabirds (fulmar Fulmarus glacialis is most numerous, storm petrel Oceanodroma furcata, O. leucorrchoa is numerous too, there are also Alcidae, Phalacrocoracidae, Larinae). Food resources on the Mednyi are more stable and predictable than lemming sources on mainland. Possibly, stable and predictable environment of the Mednyi Island creates necessary prerequisites for the development of foraging conservatism.
What has determined foraging behaviour of the Mednyi arctic fox? Foraging behaviour of individual families was studied.
Materials and methods
1719 scats from 19 families with tagged animals (it was collected at 1997, 2002, 2003, 2005 years) were analyzed. Relative frequency of occurrence F (%) of objects was recorded.
The origin of 1007 food remains from 21 breeding dens (1997, 2003, 2005 years) was determined.
700 hours of observations of tagged foxes from three families were obtained.
We have used personal communications of observers ( yeas).
Food availability was assessed by Goltsman M.E., Kruchenkova E.P., Sergeev S.N. (Fig. 2)
Statistical methods are indicated in the text.
Results
Sea birds were the main food resource analyzed in our study (Fig. 1, 3, 4). Fur-seal rookeries were nearly unused by foxes. Few families used rookeries. Dens of these families were located at a distance of less than 1 km from a rookery. Hence, only 18 families from 144 (from 1994 to 2005) could potentially use rookery resources. It is only 12 % of the all families. Families in immediate proximity to a rookery used it as an additional food resource only (Fig. 3), but never as the main one. Ration of these families consisted of sea birds in up to %.
An example: In the vicinities of the rookery «Urilie» colonies of birds are very poor. As a result, in 1997 cubs of the family living close to this rookery were starving. However, all the attempts to feed on rookery were made by cubs, but not the adults.
History of the Mednyi arctic fox population:
years. Regular hunts of arctic fox on newborn furseals cubs and scavenge on rookery are observed (Chelnokov, 1970; Smirin, Goltsman, Kruchenkova, Ovsyanikov, Safronov, 1979). Arctic foxes numbers on the Mednyi are about 600.
years. Epizootic happened. Only few fox families survived on the Mednyi Island.
years. There are no hunts on rookery. Rookeries are nearly unused. Arctic foxes numbers on the Mednyi are about 100.
Fig. 1 Mean ration for 19 families (contributions of families in the sample are equal)
Fig. 2 Study area: a) the distribution of Arctic fox breeding dens ( ) at which foraging behaviour of foxes was studied; b) the distribution of food resources along the seashore on the Mednyi Island study area
Fig. 3 Ration of families living near the rookery estimated from food remains at breeding dens (colors see Fig. 1)
Variation in individual foraging strategy
We found that adults from the same family can differ in their foraging strategies (results of behaviour observation).
In breeding dens «Drovyanie Stolbi» only male hunted on fulmars (during all summer 2005), but female did not. Female preyed only on storm petrels and small passerine birds.
In breeding dens near South-East rookery only male visited the rookery, but female never did so (Shienok, 2006).
Conclusion
Colonies of seabirds are the main food resource for the Mednyi arctic fox. Fur-seal rookeries were nearly unused by foxes despite their high productivity. This pattern is drastically different from the one reported in , when rookeries provided an essential part of ration in the Mednyi foxes.
The Mednyi arctic fox is opportunistic in his foraging behaviour and can feed on various objects (ranging from freshwater shrimps to fur-seal cubs). However, the Mednyi population is characterized by foraging conservatism. Foraging behaviour of Mednyi arctic fox is determined not solely by resource distribution, family’s foraging traditions are important too.
Both family's foraging traditions and individual food preferences have impact on foraging strategy of the Mednyi arctic foxes.
Methods of analysis of population diet spectrum should take into account the variation among families. Optimal sampling should be based on equal contribution of every family in the total sample.
Fig. 4 a) Detailed mean ration for 19 families. b,c) Example of rations for two different families (from the northern and central part of the studied territory, 2005) (dotted part in b,c corresponds to «other sources»)
Now, colonies of seabirds are the main food resources for the arctic fox from the Mednyi Island. All breeding dens are located in richest part of seabird’s colony. There is significant difference between families in ration (Fig. 4; chi-square-test, p<0.01) Main food resource for 78% of all families was fulmar. Main food resource for 11% of all families was storm petrel. 11% of all families use fulmar colonies and storm petrel colonies equally. We have not found significant correlation between resource distribution and resource consumption (R-rank, p>0.1).
We grateful for help of data collection to Bocharova N., Doronina L., Shienok A.