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Co-operative birds motivated by family ties

7 July 2014, by Alex Peel

Extraordinary co-operation by sociable weavers, which work together to build the largest nests in the world, is motivated by family ties, say scientists.

Sociable weaver birds

New research, published in Ecology Letters, says the birds, which are found throughout southern Africa, are more likely to maintain the communal part of the nest if they have relatives living nearby.

Dr Rene van Dijk from the University of Sheffield, one of the study's authors, compares the scenario to having lodgers to stay in the family home.

'If the lodger isn't related to the family, he or she may pay rent, but they will not care too much about the upkeep of the house,' he says.

'However, if the lodger is a known family member, then you would expect them to maintain the house which he or she may stay in for a longer period and possibly inherit. It may seem like a small difference, but it tips the balance towards a more co-operative society.'

Examples of co-operation can be seen throughout nature, no more so than in our own species. But understanding the evolutionary causes of this behaviour remains a major challenge to scientists.

While the interests of a group might be best served by working together, individuals within that group can often further their own cause by behaving selfishly, which creates a strong temptation to defect.

One potential explanation is that individuals contribute to communal activities to benefit their close family members and indirectly boost the survival chances of their own genetic material.

To test this hypothesis, the team led by Professor Ben Hatchwell closely monitored 23 colonies of sociable weavers at the Benfontein Nature Reserve in Kimberley, South Africa.

Sociable weaver bird and nest

Sociable weaver bird and nest.

Their enormous nests can weigh several tonnes and exist for decades. Each can house up to 300 birds in individual nest chambers. The chambers are embedded within a communal thatch, which helps to regulate the temperature inside the nest and provides extra protection from predators.

The communal thatch requires separate building and maintenance to the chambers, which is mostly done by the males. But the birds do not contribute equally.

A genetic analysis revealed that the weavers tend to cluster in family groups within the nest. Those males with family living close by are more likely to contribute to building the communal area, whereas those living away from family are more likely to be freeloaders.

'Our research reveals one mechanism through which co-operation between individuals for communal tasks is achieved,' says van Dijk. 'But there may be other solutions to the same problem.'

In some cases, co-operative behaviour may be enforced by social conventions or laws, he explains. Failure to follow these can lead to a so-called 'tragedy of the commons', where society collapses because too many individuals are seeking to further their own interests.

'In terms of humans, global fish stocks are an example of a communal resource that depends on co-operation,' says van Dijk. 'If fishermen and their governments don't work together to agree on policies that are enforced, then global fish stocks will be exhausted and the industry will collapse.'

Rene van Dijk, Jennifer C. Kaden, Araceli Arguelles-Tic, Deborah A. Dawson, Terry Burke, and Ben J. Hatchwell, 'Cooperative investment in public goods is kin directed in communal nests of social birds', Ecology Letters, 2014.

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Your comments

It's nice to get a scientific confirmation that even small animals such as these birds are very bright and hold close family bonds. Many people understand this, but many don't


Mary, San Jose
Wednesday, 16 July 2014 - 03:58


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