Líffræðifélag Íslands - biologia.is
Líffræðiráðstefnan 2021
Erindi/veggspjald / Talk/poster E38
Höfundar / Authors: Ester Rut Unnsteinsdóttir
Starfsvettvangur / Affiliations: Náttúrufræðistofnun Íslands
Kynnir / Presenter: Ester Rut Unnsteinsdóttir
The Arctic fox is the only native terrestrial mammal in Iceland and serves as a top predator in a bottom-up ecosystem with a twist of marine and inland input. It is a solitary species with a monogamous mating system. Mating takes place in late winter and most females give birth in mid-to late May. At first the male brings food to the female in the den but soon both parents forage and feed the fast-growing pups. Cubs begin eating solid food with their mother’s milk at 4 weeks of age and are weaned at 6-7 weeks of age. The quality of the territory is determined by a combination of food- and den availability and can vary in time and space. Arctic fox territories in Cliff Hornbjarg and nearby coastline of Hornstrandir nature reserve, northwest Iceland, have been monitored quite intensively during the past 12 years. In one of the territories, breeding has been poor or unsuccessful in the past decade. This territory is located at the ground level and food resources only come from the sea. It is oblong in shape, with a short coastline, cut by a river which marks the territory border. In the summer of 2021, four of six cubs of that territory survived the summer, and they were in good condition in August. When looking into how this year differed from the past years of breeding failure, two interesting observations were made. First, in late-June and early July, many fresh remains of wolffish heads (Anarhichas lupus) washed up to the shore. At least six full size heads (~700gr each) were found on the den in one day. The cubs, and their lactating mother, were seen feeding on these fish heads in the following two weeks. There is no doubt that this stochastic food availability made a big difference in the survival of the litter, at least during the first weeks of their life. Second, both the male and female of this territory were frequently seen swimming across the river, with and without food in their mouth. This behaviour is rare as the foxes usually avoid water but is not unseen either, but never with food. These individual foxes have mastered the skill of swimming and could therefore enlarge the foraging grounds of their territory to a large extent. In August, two of the cubs were already learning this behaviour from their mother. By this, the foxes have found a solution to increase the quality of their territory by beating a local stressor and swim across the river. With the addition of stochastic food supply, this territory switched from being the poorest, to amongst the richest and most successful in the summer of 2021.