Young birds support their parents in raising youngsters, defending the territory and keeping predators at bay. This social behaviour, exhibited by birds such as the mousebird, appear to contradict the prevailing theory of evolution: young birds even surrender their food to younger siblings. This is the result of a study conducted by Wageningen University & Research scientists in Swaziland.
The birds’ social behaviour may be largely attributed to the limited availability of territories. This causes young birds of some species to continue to ‘live with their parents’ and to delay own reproduction. ‘If a young bird actively contributes to the household and defending the nest of others, he is more likely to inherit a decent territory,’ says researcher Sjouke Kingma. ‘And, if one expects to inherit the family home, he is more likely to give the windowsills a fresh coat of paint, so to speak.’
The birds that are being studied, such as the mousebird and the white-crested helmet shrike, take their social behaviour to great lengths. Not only do they help in defending the territory and the nest from predators, but they also feed the young with their own food, if need be. Kingma: ‘This social behaviour offers advantages. If a bird inherits the territory, the animals he helped raise will take their turn in contributing to the household.’
The fascinating aspect of the research in the Mbuluzi Game Reserve in Swaziland is that it appears to contradict the prevailing theory of evolution: Animals are selfish by nature. The future-help theory offers a possible explanation. Another possible explanation for this selfless behaviour is the kin-selection theory: If an animal assists family members, it indirectly contributes to proliferating shared genes through future generations.
In Europe, there is a distinct short seasonal peak in food available to birds, and the seasons are fairly predictable. Swaziland, on the contrary, offers few potential territories, while food availability is also limited. Moreover, the climate in this country is very unpredictable, which means food is not predictably available in the spring. Currently, for example, the country faces an extended period of drought. ‘Under circumstances this poor, being social is worthwhile,’ says Kingma.
In the Mbuluzi game reserve Kingma and his colleagues from the Netherlands and the University of Swaziland search for bird nests in order to determine their exact number. They then ring the birds and mount cameras. This allows them to monitor and meticulously record the lives of almost every individual bird. Who belongs to what group, who helps whom and, do young birds remain to help? All these details should help solve the dilemma of the selfless, helpful behaviour.