Sea-bird chick survival rate reduced by moth parasites

18/08/2008 10:04:50

August 2007. Parasites contribute to the reduced breeding success of seabird populations in the North Sea because they reduce the ability of mothers to rear their sons, a new study shows. The experimental research, which was published online by the journal Science, was carried out on European shags breeding on the Isle of May, off the east coast of Scotland.

Male chicks suffer most
The research found that internal parasite infection negatively affects the foraging performance of mothers during the critical nestling period. This is a time when chicks most need food and as the males grow to be larger than their sisters, they tend to suffer more.

Isle of May
Seabird populations have been studied on the Isle of May for many years and while much is known about their breeding biology, their parasites have until now received little attention.

Lead author Dr Tom Reed, formerly of the University of Edinburgh's School of Biological Sciences, explains: "Parasites are ever-present in nature and are key players in ecosystems, but their ecological effects are often under-appreciated. Our work shows that parasites can have important repercussions for host populations, by affecting which sex mothers concentrate on rearing and the overall breeding success of infected parents."

Dr Reed continues: "It is not clear why mothers seem to be affected more than fathers, but previous studies of birds and mammals have found that maternal condition can be an important factor in the survival of male offspring. The novel twist here is that parasites might play a key role in this process, by compromising the condition of the mother and reducing the amount of energy she has to invest in her sons."

Shags
The study also found that parasite treatment was most beneficial for late-breeding shags. Like many birds, shags that breed later tend to have reduced success. Treatment could be more beneficial to late breeders because there are more parasites around in the environment at this time. It could also be due to them being less healthy birds who struggle to cope with the additional burden of parasites at a time when they are already pushed to their limit.

Dr. Francis Daunt from the Centre for Ecology & Hydrology who co-authored this paper and oversees the long term research of bird populations on the Isle of May commented: "I'm very excited about the findings, since they provide a potential explanation for some earlier work that showed that birds that lay early in the season contribute 10 times as many birds to subsequent generations, compared to pairs that breed later. The study raises a whole suite of new questions so it is vitally important that we continue to monitor the effects of parasites, in order to explore the possible impact on gender imbalance and population numbers."

The study was led by biologists from the University of Edinburgh and the Centre for Ecology & Hydrology, in collaboration with researchers from the University of Glasgow (now based at Exeter University), and the British Antarctic Survey.