Brown-headed Cowbird
Molothrus ater

A part of me wants to protect the phoebes from cowbird eggs each year. But cowbirds are native and protected by law. The Nestwatch link below provides options for deterring them.

I think the environment should be put in the category of our national security. Defense of our resources is just as important as defense abroad. Otherwise what is there to defend?
Robert Redford
Yosemite National Park dedication, 1985