This shift means many fewer kelp forest fish for the eagles to eat. In response, the eagles have adjusted their foraging tactics. Anthony and his colleagues surveyed remains of bald eagle prey in their nests during 1993 and 1994, when otters were abundant and the kelp forests were healthy, and in 2000, 2001 and 2002, when otters were scarce and the kelp forests had collapsed. They found that when otters were abundant, eagle prey consisted of predominantly kelp-forest fish and sea otter pups. When the otters were rare, however, the proportion of marine birds in the eagles' diet was much higher.
Anthony explains that because the eagles defend territories in dense patches along the coastline and there are few terrestrial animals to eat, they must be flexible in what they hunt.
"These bald eagles are opportunistic foragers as a consequence of their evolutionary history," he says. "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."
Anthony and his colleagues also found that the eagles had more young on average during 2000-2002, a fact that 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 says. The propensity of the eagles to adapt quickly to a changing environment may have allowed them to flourish, but Anthony also cautions that adapting to this scenario might be difficult for more spe
|Contact: Christine Buckley|
Ecological Society of America