Channel Island eagles

A new study coming out in PNAS is interesting from a couple of standpoints. For one, reintroduced bald eagle populations on California's Channel Islands may have to use different food sources than their predecessors in the islands. Evidence indicates that eagles that lived in the islands 30,000 years ago fed primarily on seabirds. This remained the preferred diet until introduced sheep became a staple in the middle of the 19th Century. Then, the eagles were KO'd by DDT in the 1960s. The reintroduced birds, with the seabird population recovering but diminished and no sheep available, may be living it up on seal carcasses or the endangered island fox.

Interesting enough, but the techniques being employed are kinda cool too. The research, described here at Science Daily, is employing stable isotopes in bones and feathers to determine the source of the eagles' nutrition. Different prey types leave a different stable isotope signature, which may allow biologists to develop an understanding of eagle feeding habits that will help make their reintroduction efforts a success.

We're seeing more and more bald eagles in our local wilds every year, but our guys seem to prefer a fish diet. You'd think such prey would be available in abundance in the Channel Islands, but eagles are notoriously opportunistic. If there's abundant carrion, they'll take it. Ben Franklin was right.