Their mother's squawks competed with the din of morning-rush bridge traffic as Chris Nadareski, a wildlife biologist with the New York City Department of Environmental Protection, gently lifted the fluffy chicks out of their nestingbox and used pliers to fasten metal bands around their legs.
In the third phase of the experiment a male was placed in the cage over the box where the female had once been, and the amount of aggression towards this male from the nesting male was measured.