Bodil Elmhagen

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Abstract

From breeding pairs to fox towns: The social organisation of arctic fox populations with stable and fluctuating food availability

Food availability can impact group formation in Carnivora. Specifically, it has been suggested that temporal variation in food availability may allow a breeding pair to tolerate additional adults in their territory at times when food abundance is high. We investigate group occurrence and intraspecific tolerance during breeding in a socially flexible canid, the arctic fox (Vulpes lagopus). We compare Iceland and Sweden where resource conditions differ considerably. A breeding pair was the most common social unit in both populations, but as predicted, groups were more frequent where food abundance varied substantially between years (Sweden: 6%) than where food availability was stable (Iceland: ≤2%). Within Sweden, supplemental feeding increased group occurrence from 6% to 21%, but there was no effect of natural variation in lemming (Lemmus lemmus) availability since group formation was rare also at lemming highs. Thus, additional factors appeared to influence the trade-off between intraspecific territoriality and tolerance. We report two cases where related females showed enduring social relationships with good-neighbour strategies. Related females also engaged in alloparental behaviour in a ‘fox town’ with 31 foxes (4 adults, 3 litters). In contrast, when unrelated foxes bred close to each other, they moved or split their litters during summer, presumably because of territorial conflict. We suggest that fluctuating food availability is linked to group formation in this Arctic carnivore, but also when food availability increases, additional factors such as relatedness, alloparental benefits, competition and predator defence appear necessary to explain group formation.

Reference
Elmhagen B, Hersteinsson P, Norén K, Unnsteinsdottir ER, Angerbjörn A (2013) From breeding pairs to fox towns: The social organisation of arctic fox populations with stable and fluctuating food availability. Polar Biology 37: 111-122.

 
     
 
Fox pairs living under fluctuating resource conditions might adjust their territory size to the amount of resources available when food availability is low. If so, periods of high food availability would imply that their territory then provide them with more resources than they need. Under such circumstances, they might tolerate additional adults at their den. In this paper, we describe alloparental behaviour in a Swedish fox town with 31 foxes; an old female (left photo), her two 1-year old daughters, and their 3 litters with a total of 27 cubs (right photo: a few of the cubs). A 1-year old son of the old female was also present at the den.

 

 

Arctic fox hunting along the Icelandic coast, a habitat with stable resource availability.
 

Icelandic arctic fox barking.
In Iceland, fox density is high. It would be costly to defend a territory larger than necessary. This might force an adult pair to match the size of their territory exactly to their own needs, which is possible under stable resource conditions. However, it also means that there will not be enough resources to allow the pair to tolerate additional adults in their territory during breeding.