The eggs "advertised" by the tree-nesters' begging calls were found bitten significantly more often than the eggs associated with the ground-nesters' calls.

人们发现，录音机在播放树上筑巢的鸣禽的乞食叫声时，比起在播放地面筑巢的鸣禽的乞食叫声时，鸟蛋被攻击的几率明显增大。