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A new study has found that parasites contribute to reduced breeding success of seabird populations in the North Sea because they reduce the ability of mothers to rear their sons. The experimental research, which will be published online by the journal Science this week, was carried out on European shags breeding on the Isle of May, off the east coast of Scotland.
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.
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.
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 from the University of Edinburgh, 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.”
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."
Additional information
The Centre for Ecology & Hydrology (CEH) has been carrying out research on seabirds on the Isle of May since 1973. IMLOTS (the Isle of May long-term study) is now one of the most data-rich and comprehensive studies of its type in Europe. IMLOTS forms part of CEH's network of long-term monitoring sites for detecting effects of environmental change. Further details can be found here.
Media enquiries about this work should be directed to the Centre for Ecology & Hydrology press office.
