嗯 這鳥看起來就蠻邪惡的 ：P
Cuckoos use mafia-style tactics to raise young
* 22:00 05 March 2007
* From New Scientist Print Edition
* Andy Coghlan
Marlon Brando eat your heart out. Around the world, parasitic birds such as cuckoos and cowbirds are displaying the same mixture of guile, ruthlessness and brutality as any self-respecting Godfather. Using a delicate mixture of intimidation and retribution, they "persuade" other birds to accept their eggs and raise their chicks.
Ten years ago, Anders Pape MÃ¸ller at Copenhagen University in Denmark and colleagues discovered that great spotted cuckoos (Clamator glandarius) run a mafia-style protection racket against magpies living in Andalucia, Spain.
If a magpie rejects a cuckoo egg laid in its nests, the cuckoo promptly returns to destroy the magpie's own eggs or kill its chicks.
Not to be outdone, American cowbirds, which are not related to cuckoos, employ an even more forceful racket against warblers. "The cowbird has much more sophisticated predatory behaviours than we thought," says James Hoover at the Illinois Natural History Survey in Champaign, US, who has been monitoring brown-headed cowbirds (Molothrus ater) for four years in the swamps of the Cache River in southern Illinois.
Wild warblers are very compliant with cowbirds, and are not known to recognise and eject cowbird eggs. But Hoover and Robinson wanted to find out what would happen if they did. To mimic this situation, they provided artificial nests for 180 pairs of prothonotary warblers (Protonotaria citrea), waited for the cowbirds to cuckold them, then selectively removed the cowbird eggs.
The cowbirds soon retaliated, returning to the nest to eat or destroy the remaining warbler eggs. What is more, warblers that had laid too early for the cowbirds to cuckold them suffered retribution too. Cowbirds would routinely eat or trash these more developed eggs to force the warblers to rebuild the nest elsewhere.
They would then spy on the warbler parents, find out where they were nesting anew, and sneak in to lay an egg at exactly the right time.
Better to comply
This process, which the researchers call "farming", enables the cowbirds to effectively manufacture a new breeding opportunity for themselves. On average, 20% of warbler nests were farmed in this way, and the cowbirds parasitised 85% of the rebuilt nests.
Hoover says the overall effect is that the cowbirds bully the warblers into "an evolutionary state of acceptance". It turns out to be more profitable for the warblers if they comply. On average, they raise three of their own chicks when they also support a cowbird chick. Yet they raise just one of their own if a cowbird egg has been rejected.
"This has been a controversial area, that cuckoos and cowbirds might have protection rackets to get their own eggs protected," says Becky Kilner, a researcher on cuckoos at the University of Cambridge, UK. She says that the study provides the best evidence yet that parasites destroy hosts' nests, and that hosts ultimately benefit by complying. Hoover is now tagging and filming wild cowbirds to see how they act in a natural environment unchanged by the researchers.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0609710104)