Samplings: November 2007

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Arctic fox snatches an egg from a goose nest.

Gustaf Samelius

In a good summer, an Arctic fox living near a goose colony on the Canadian tundra can steal as many as 2,000 eggs. Foxes bury most of their loot for future consumption, and they don’t bother to stamp an expiration date on it. A year later the eggs are still edible, a new study shows. During four consecutive springs, just before snow geese arrived on the tundra to breed, Gustaf Samelius, then a graduate student, and three colleagues at the University of Saskatchewan in Saskatoon collected blood from wild foxes. By analyzing the proportions of the isotopes carbon-13 and nitrogen-15 in the blood samples, the team established that goose eggs were an important part of the foxes’ diet even eleven months after being cached by the carnivores. Freezing undoubtedly preserves the eggs through the winter; in the fall and spring, rot-causing bacteria seem to be inhibited in intact eggs by the shell and membrane and by protective proteins in the white. The researchers also discovered that in years when collared lemmings were abundant, the foxes ate fewer eggs. Cached eggs, it seems, are merely a standby in case the foxes’ preferred food—lemming—is in short supply. (Journal of Animal Ecology)