Decline in sea otters affecting eagles' diet
Friday, 03 Oct 2008 06:31
Alaskan sea otter numbers can alter the diet of bald eagles
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Alaskan sea otter numbers can alter the diet of bald eagles, a new report has claimed.
A study published in the journal Ecology today looked at the remains of the eagles' prey and found that when otters were in abundance, the eagles' diets were mainly made up of fish and otter pups but when the otters were scarce, their diets consisted much more of birds.
Sea otters are known to feed on urchins, which can defoliate kelp forests, and therefore keep marine ecosystems in balance.
Researchers found that bald eagles live in high densities along the Aleutian archipelago off the coast of Alaska and place their nests on islets, coastal cliffs and shoreline sea stacks.
Sea otters once also occupied a large range of coastal marine environments near these islands, but in recent years otter populations have declined in response to increasing killer whales.
As a result, the eagles have had to develop their foraging techniques.
"These bald eagles are opportunistic foragers as a consequence of their evolutionary history," lead author Robert Anthony said.
"They've developed foraging territories they defend against members of the same species along these coastlines, and the terrestrial environment provides very little for them. So they forage over the open water."
Today's report found that the eagles had more young on average during 2000-2000 when otters were scarce, a fact that Mr Anthony believes might be a result of a high caloric content in the eagles' increasingly seabird-dominated diet.
"Across the range of this species, their diet can be quite varied, but here it appears as though the change in diet had either a neutral or positive effect," he said.