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New method developed to study parasite numbers in wild seabirds

13 December 2012

European shag seabird (Phalacrocorax aristotelis) photo by Mark Newell, CEH
European shags are a member of the
cormorant family. Photo Mark Newell (CEH)

Scientists have developed a new method for studying parasite numbers in the stomachs of individual seabirds in the wild. The technique enables the recording of video footage of worms inside seabird stomachs and is an important step forward in understanding the impact of parasites on seabird populations.

The research, published today (13 December 2012) in the scientific journal Methods in Ecology and Evolution, was led by the Centre for Ecology & Hydrology (CEH) and is part of ongoing work into how different factors such as gut parasites might affect the breeding success or survival of seabirds.

The research team trialled the use of endoscopy, often used in human and veterinary medicine but rarely in field situations, to measure natural parasite loads, or burdens, of European shags, a member of the cormorant family. Shags have nematode worms in their stomachs, obtained from their fish diet. These worms feed directly on food obtained by the birds, reducing the food available to both parent and chicks.

The team was led by Dr Sarah Burthe of CEH and, as well as colleagues from CEH, involved scientists from the University of Edinburgh, Biomathematics and Statistics Scotland, Aarhus University in Denmark and the Natural History Museum, London. The study was carried out on the Isle of May NNR, an important seabird colony off the east coast of Scotland which has been intensively studied since the 1970s.

Dr Burthe explained, “Endoscopy is used routinely in veterinary and human medicine but to our knowledge has not been used to measure parasites in wild animals. Our new method using an endoscope is a rapid, reliable and repeatable way of looking at gut parasites in European shags which has no obvious adverse effects.”

The study found that all birds had parasites ranging from low burdens of several worms through to high burdens of more than 40 worms. Burdens were significantly higher in males and in late breeders. There was a slight seasonal decline in worm counts within individuals.

"Our method is a rapid, reliable and repeatable way of looking at gut parasites in European shags which has no obvious adverse effects."
Dr Sarah Burthe, CEH

One way to get an understanding of the impact of parasites on breeding success and survival is to treat birds with an anti-parasite drug to reduce or remove worm burdens and then compare to untreated birds. However, until now, the lack of a method to measure parasite numbers effectively has made it difficult to know whether such treatments have worked. The use of the endoscope enabled the researchers to conclude that, at a suitable dose, the anti-parasite drug completely removed nematode worms from the stomach of treated shags.

Study co-author Dr Francis Daunt, a population ecologist at CEH, said, “Being able to monitor individual parasite burdens is a major step forward in this field of research. We are hopeful this new technique could be applied to other wild animal systems, possibly including reptile, mammal and other bird hosts.”

Dr Burthe added, “Endoscopy opens up some interesting research questions, enabling us to more fully explore the role parasites play in impacting the breeding success and survival of seabirds, particularly how impacts may vary with changes in prey availability.”

Parasites are an important part of ecosystems, occurring in all wild animal species and playing an important part in the evolutionary process. Relatively few studies have focused on gut parasites in wild animals, in part because it is very difficult to measure parasite levels in hosts without resorting to examining animal carcasses or counting eggs in faeces, both of which can be unreliable measures.

The endoscopy method is rapid and well suited to species that routinely swallow large prey items or where chicks feed by inserting their heads into the parent's throat. Observations from this study confirmed that shags went straight back to their broods and their breeding success was as high as pairs that did not undergo an endoscopy.

Endoscopy is a licensed procedure and was undertaken under a Home Office Project Licence and conducted by trained personnel.

Additional information

CEH issued a press release for this story.

The research was published in Methods in Ecology and Evolution. The full paper reference is Sarah Burthe (1), Mark A. Newell (1), Gidona Goodman (2), Adam Butler (3), Thomas Bregnballe (4), Eileen Harris (5), Sarah Wanless (1), Emma J.A. Cunningham (2) and Francis Daunt (1) Endoscopy as a novel method for assessing endoparasite burdens in free-ranging European shags (Phalacrocorax aristotelis). doi: 10.1111/2041-210x.12015

(1) NERC Centre for Ecology & Hydrology, UK (2) University of Edinburgh, UK, (3) Biomathematics and Statistics Scotland, UK, (4) Aarhus University, Denmark, (5) Natural History Museum, UK

This work was funded by the CEH project QUIP (QUantifying the Impact of Parasites on seabirds). The Natural Environment Research Council and the Joint Nature Conservation Committee support CEH’s long-term seabird studies. Scottish Natural Heritage allow CEH scientists to carry out research on the Isle of May NNR.

Related CEH links

Isle of May Long-Term Study

Staff page of Dr Sarah Burthe

Staff page of Dr Francis Daunt