Songbird Species Has "Babysitters" That Boost Offsprings of Older Birds

A new study reveals that young Seychelles warblers have better odds, thanks to "babysitter" birds assisting their parents.

Researchers from the University of East Anglia (UEA) and the University of Groningen have examined Seychelles warblers, which is a songbird species that does cooperative breeding. Living in small family groups, taking care of the young is a shared responsibility between their parents as well as younger helper birds.

Their paper, titled "Helpers compensate for age-related declines in parental care and offspring survival in a cooperatively breeding bird," is set to appear in the January 19, 2021 issue of Evolution Letters.

Insight for Social Species

The collaborative effort discovered among Seychelles warblers can compensate for the elderly parents to provide enough care by themselves. Additionally, this also fosters a more social behavior in family groups with older warbler parents.

For social beings, like humans, the behavior observed in Seychelles warblers can help explain why living in groups and working together to cooperate and raise their offspring.

Researchers conducted the study and gathered data from individual Seychelles warblers from Cousin Island in the East African nation of Seychelles over the last 30 years. Researchers from the UEA and the University of Groningen in the Netherlands led the effort, together with Nature Seychelles and the University of Sheffield.

"In many animal species, offspring from ageing parents do not survive as well as offspring from younger parents," said David S. Richardson, a professor from UEA's School of Biological Sciences and the senior author in the paper, in a news release from the university. He also explains that the cooperative nature found in Seychelles warblers means that caring for the young is a shared responsibility between the "dominant breeding pair and a variable number of adult subordinate helpers" that support in different child-rearing tasks such as providing food for the young.

Working Together Increases Survival Chances for Warblers

"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," Richardson added.

Also, the extra offspring care provided by these support birds reduces offspring mortality. While the chances of the offspring's survival decline with the age of its mother bird, the risks are mitigated thanks to these helpers. The survival chances improve because the helper birds provide more care to compensate for the lower provisioning of the group's older dominant females. Since female breeders recruit more helpers, they get more help in rearing their young.

"Such late-life fitness benefits of breeding cooperatively lead to the prediction that older parents should be more inclined to recruit helpers to improve their both their own survival and that of their offspring," explains Dr. Martijn Hammers, first author of the study from the University of Groningen.

For Seychelles warblers, female birds are more likely to become helpers compared to their male counterparts, and that likelihood increases together with the age of the dominant female. The observation suggests that older dominant females are more likely to produce more female offsprings, although researchers note that this remains to be tested.