Seabirds feed their young less as they reach an age to fly the nest, but it's hormones that actually control when the chicks leave home, according to new research from the University of Leeds.
The study published online in Behavioural Ecology today (05 July) aimed to pinpoint the main trigger which causes chicks to leave the nest and embark on an independent life, a process known as fledging.
While studying a colony of Manx Shearwaters (Puffinus puffinus), on the island of Skomer, researchers from the University's Faculty of Biological Sciences noticed that parent birds seemed to become increasingly insensitive to their chicks' demands for food as they grew close to fledging. At the same time the chicks showed a marked increase in levels of the hormone corticosterone. However, the team needed to know whether this increase was independent of, or caused by, the reduction in feeding.
They decided to trick the parent birds, by swapping chicks of different ages between nests which the birds make in burrows in the ground to see how this affected both parental care and the time chicks took to fledge.
"Manx Shearwaters don't recognise their own offspring, but will simply go back to the same nest after they've gathered food. They have one chick, which makes the interactions between parent and offspring easier to study," explains lead researcher, Dr Keith Hamer. "We swapped chicks which were between 10 days and two weeks apart in age, to see what impact it would have. We wanted to find out whether parents and chicks were responding to each other's behaviour, or whether each was acting independently."
The team discovered that adults reduced their food provisioning after about 60 days of raising a chick, regardless of the chick's stage of development. Although females more than males will adjust their feeding levels to how much their chicks beg for food, after around 60 days both parents start to ignore the
|Contact: Dr. Keith Hamer|
University of Leeds