The Cosa Nostra has nothing on the cowbird, a species that routinely lays eggs in other birds' nests. Like a mafia enforcer the bird uses violence to ensure co-operation.
US researchers involved in the study of the bird referred to it as "mafia behaviour" in a paper published today in the journal, Proceedings of the National Academy of Sciences.
The cuckoo is a typical "brood parasite" that lays its eggs in others' nests. The big question has been why the host birds willingly raise chicks that are obviously not their own.
Researchers from the Illinois Natural History Survey and the University of Florida now know why the brown-headed cowbird gets away with it.
Basically if it doesn't get the co-operation it wants from its warbler host, it will ransack the warbler's nest and destroy any eggs it finds.
The rough stuff was dished out in particular to "rejecter" warblers who resisted the interloper's presence. The researchers manipulated cowbird access to nests and made warbler "accepters" look instead like rejecters.
They found that the cowbirds ransacked only 6 per cent of accepter nests but 56 per cent of rejecter nests. Once the warblers got a taste of what was in store for rejecters their attitude changed markedly. After the warblers rebuilt their nests 85 per cent became accepters.
The research threw up another interesting result. Resisting the bullying tactics dished out by the cowbird was bad for reproductive success. Rejecter birds produced fewer offspring, showing that tolerating cowbird eggs may be a better evolutionary tactic.
The team also showed that the cowbirds often ransacked warbler nests even when they hadn't left eggs behind. The scientists put this behaviour down to the cowbird "farming" for new hosts.
Once the unsuspecting warblers experienced a taste of cowbird justice they rebuilt their nests and became accepters the next time around.
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