A team of scientists led by the University of East Anglia has discovered the existence of grandparent helpers in the Seychelles warbler the first time this behaviour, which rarely occurs except in humans, has been observed in birds.
Research carried out over more than 20 years on a population on Cousin Island in the Seychelles has revealed that, as in humans, older adults that no longer breed themselves often help their children to raise grandchildren.
The concept is of evolutionary importance as it provides another route to co-operative breeding - where adult individuals appear to act altruistically by helping the dominant pair in the group to rear offspring.
Co-operative breeding is known to take place in birds, mammals and in some fish. But the helpers are usually offspring from previous years who, because of a lack of breeding opportunities elsewhere, stay within the territory and become subordinates who help their parents rear more young.
In the case of the Seychelles warbler, co-operative breeding occurs because the island is full and many birds cannot find suitable habitat in which to breed, so they instead become helpers.
For more than 10 years Dr David Richardson from UEAs School of Biological Sciences has been studying the Seychelles warbler, once one of the worlds rarest birds. He explained that the existence of what he terms grandparent helpers has, until now, been largely overlooked outside humans. The results of the research are published in the journal Evolution (Vol 61, issue 12, December 2007).
Older, often postreproductive adults have occasionally been found to engage in similar behaviour in a very small number of mammal species, such as pilot whales and some monkeys, but there is little documented evidence.
The study found that dominant females can be deposed from their breeding position by younger relatives. While some deposed females may then leave to live out a solitary life
|Contact: Cat Bartman|
University of East Anglia