Monday, November 5, 2007

They've got better long-term planning skills than most people

Arctic foxes create larders of goose eggs to eat for when food gets scarce:
Arctic foxes create "nest eggs" each year to prepare for leaner times, according to a new study.

Like squirrels gathering nuts for the winter, the small foxes hoard bird eggs in case there's not enough of their favorite prey—the collard lemming—to go around in the spring.

The stored eggs can last for up to a year after being buried, thanks to the Arctic permafrost and natural preservatives inside the eggs.

"It appears as if cached eggs are used as a backup for unpredictable changes in lemming numbers," lead study author Gustaf Samelius of Grimsö Wildlife Research Station in Riddarhyttan, Sweden, said in an email.

"This is a neat adaptation in an environment where food abundance changes dramatically both among seasons and years."


Over the course of their four-year study, which appeared in last month's issue of the Journal of Animal Ecology, the team found that the foxes stored similar numbers of eggs each year.

But the degree to which the mammals relied on their caches varied with changes in lemming abundance.

Collard lemming populations fluctuate dramatically over three- to five-year cycles, Samelius said, and the changes are largely unpredictable.

When lemming numbers were high, the stored eggs made up less than 28 percent of the foxes' springtime diet.

When the rodents were scarce, the eggs accounted for up to 74 percent of the mammals' food.

For the foxes, the eggs are a reliable backup system because they are abundant during goose nesting season and are well suited to long-term storage.

"Eggs are protected by the egg shell, several membranes, as well as chemical properties of the albumen [egg white], preventing microbial activity," Samelius said.

The cold conditions of the Canadian Arctic also extend the shelf life of stored eggs, according to the study team.

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