7 August, 2008

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 with input from scientists at British Antarctic Survey (BAS), is published online by the journal Science this week, and 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 BAS.

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.”


Notes to Editors

The paper ‘Parasite treatment affects maternal investment in sons’, authored by Reed,T.E., Daunt,F., Hall,M.E., Phillips,R.A., Wanless, S. and Cunningham,E.J.A is published in this week’s issue of the journal Science.

Shags frequently suffer from heavy infections of nematode worms, which live in their guts. While these parasites usually do not kill the host, they compete with it for nutrients and trigger costly immune responses, which can compromise a bird’s physical condition and therefore its ability to rear chicks.

In the study researchers treated a group of both mother and father shags against parasites just before their eggs were due to hatch. They then compared the survival of these parents’ chicks to that of a control group, in which parents suffered from natural levels of parasite infection.

In this seabird species, males are bigger than females by about 20%. The size difference is already apparent at the nestling stage – male chicks grow faster than female chicks and are heavier by the time they leave the nest. Parents must feed their chicks several times a day for seven weeks in order to ensure nestlings make it through this critical period of dependency, when the chances of dying are higher than at other stages later in life.

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 at

About the Centre of Ecology & Hydrology: The Centre for Ecology & Hydrology (CEH) is the UK’s Centre of Excellence for research in the land and freshwater environmental sciences. CEH is a wholly-owned research centre of the Natural Environment Research Council and employs around 500 staff at six major sites in England, Scotland and Wales with an overall budget of about £35m. CEH science covers three core areas of expertise: Biodiversity, Water and Biogeochemistry with a major cross-cutting activity focusing on Environmental Information. CEH tackles complex environmental challenges through integrated research, aiming to deliver practicable solutions to help preserve the environment for future generations. www.ceh.ac.uk

About British Antarctic Survey: The Cambridge-based British Antarctic Survey (BAS) is a world leader in research into global environmental issues. With an annual budget of around £45 million, five Antarctic Research Stations, two Royal Research Ships and five aircraft BAS undertakes an interdisciplinary research programme and plays an active and influential role in Antarctic affairs. BAS has joint research projects with over 40 UK universities and has more than 120 national and international collaborations. It is a component of the Natural Environment Research Council.