Wednesday, 08 Oct, 2008 Environment

Bald Eagles Suggest a New Diet


A new research has found that bald eagles in Alaska started eating other birds instead of fish. Such a surprising diet was caused by the alterations in food chains. As scientists observed, these changes affected not only eagles, but also sea otters, urchins and kelp forests. The extinction of sea otters from the Aleutian Islands provided favorable conditions for fast reproduction of sea urchins which served as nutrition for otters.

As a consequence, the expansion of urchin population caused the consumption of underwater kelp forests. The forests gradually disappeared, making nearshore zone uninhabitable for kelp-consuming fish that was basically eaten by bald eagles.

According to the journal Ecology, the bald eagles went on a new diet eating mostly seabirds. Robert Anthony and his colleagues, who carried out the research, began gathering information about bald eagles inhabiting the Aleutian Islands in the early 1990s. At that time the number of sea otters was rather high. However, in the early 2000s their number decreased dramatically leaving just 10% of the population.  

Studying food remains in the birds’ nests the researchers observed that bald eagles prefered seabirds to fish, although some eagles still ate fish. These changes can be considered positive for bald eagles. Nevertheless, the researchers still don’t know what caused the decline of sea otters. One of the existing theories suggests that otter hunted by killer whales should be considered the main reason of their collapse.

It’s known that killer whales mainly hunt fish, but some of them hunt such mammals as sperm whales, humpbacks and fin whales. However, in the 20th century these food sources almost disappeared, forcing killer whales to hunt smaller species such as otters. 

This research shows how interrelated ecosystem links are and how easy it is to offset the balance.

Source: National Geographic
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Posted by sharaeff

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