21 July 2020

Something is happening among nesting bald eagles in the James River watershed that may explain what we’re seeing among peregrines in western Pennsylvania. There are lots of eagles at the James River but less nesting success than in the past. The Center for Conservation Biology (CCB) in Williamsburg, Virginia has figured out why.

CCB has been conducting bald eagle nesting surveys every March since the 1970s. Seven years after DDT was banned they found only one pair of bald eagles in the watershed. This year there are 319 pairs.

Meanwhile, “eagle productivity has dropped as the population has grown and breeding density has increased.” The number of eaglets per nest peaked at 1.6+ in the mid 1990s but has dropped to only 1.05 today.

Lower nesting success is not a food problem, it’s a competition problem. CCB explains:

The mechanism causing the decline does not appear to be traditional resource competition where pairs scramble for their share of limited fish. Rather, the mechanism appears to be young marauding eagles that are disrupting territory holders and competing for a limited set of viable breeding territories.

Young bald eagles are harassing adult pairs in an attempt to gain a territory — so much so that some pairs fail to nest successfully.

This sounds like what happened at the Cathedral of Learning peregrine nest this year. In February a young male, Ecco, showed up at the Pitt nest and persistently vied for the site — so much so that Morela didn’t lay eggs until May and her eggs were never incubated. Hmmmm.

Young bald eagles are home wreckers. Maybe young peregrines are, too.

Read more about the James River bald eagle population at CCB’s James River Eagle Population Continues to Soar While Productivity Continues to Fall.

(photos by Steve Gosser)