Young Seychelles warblers have better health outcomes when their elderly parents have help raising them, according to a new study from the University of East Anglia (UEA). These songbirds live in small family groups, and parents have helpers who participate in incubating the eggs and providing food for the chicks.
The researchers found that this cooperation can help compensate for a decline in the ability of elderly parents to provide sufficient care for their offspring. Getting help at the nest means that the mothers will live longer, and also promotes social behavior in family groups with older parents.
The findings help explain why humans and other social species are often more successful when they cooperate in groups.
The team analyzed data collected on individual Seychelles warblers that had been observed on a tiny island in the Seychelles over the last 30 years.
“In many animal species, offspring from aging parents do not survive as well as offspring from younger parents,” said study senior author Professor David S. Richardson.
“The cooperative nature of Seychelles warblers means care for offspring is often shared between the dominant breeding pair and a variable number of adult subordinate helpers that help with various aspects of rearing, including providing food for the offspring.”
“The amount of care that dominant breeders provide is reduced when they are assisted by helpers and this lower parental investment can improve the parents own survival and future reproductive output.”
In addition, the extra help from other group members helps to reduce offspring mortality. The chances of survival for young birds progressively declines as the age of the mother bird increases. These declines, however, are mitigated when helpers are present.
According to the researchers, individual helpers do not simply provide more care in response to the lower provisioning of older birds, but are actually recruited by the older female breeders.
“Such late-life fitness benefits of breeding cooperatively lead to the prediction that older parents should be more inclined to recruit helpers to improve both their own survival and that of their offspring,” explained study first author Dr. Martijn Hammers from the University of Groningen.
Female Seychelles warblers are more likely to assist with caretaking than males. Furthermore, the likelihood that subordinate females will be entrusted as helpers increases sharply with the age of the dominant female. As a result, older dominant females may produce more female offspring, but this theory has not yet been tested.
The study is published in the journal Evolution Letters.