The long-term European Storm-petrel ringing project

European Storm-petrel

A Rocha Portugal’s ongoing European Storm-petrel (Hydrobates pelagicus) ringing project was started in 1990. It uses tape-lures at night during June to attract migrating Storm-petrels onto land, where they are netted to study aspects of their migration behaviour.

Storm-petrels migrate annually between the coasts of southern Africa and the North Atlantic. Migrant birds must build up large fat reserves to fuel their journeys, but their ability to do this, and the level of fat reserves carried, depends on conditions along the migration route. One of the most striking results of A Rocha’s research on Storm-petrels is that the body weight of petrels migrating northwards past Portugal varies greatly between years. These changes represent very large differences in the level of fat reserves carried by these tiny seabirds on their long-distance migration journeys. Rather than varying erratically between years, body weight has fluctuated remarkably smoothly over the 16-year study period. Much of our recent Storm-petrel research has focused on how these fluctuations are caused by climate-driven changes in the marine environment.

Night-time mist-nests for ringing Storm-petrels

Migrating Storm-petrels are fatter in years when the seas are colder. But it is sea temperatures in the two to seven months before migration, when the birds are many hundreds of miles to the south, which explains the level of fat reserves. This time-lag suggests that sea temperature influences the bird’s food supply, which in turn causes changes in fat reserves, but a major problem in understanding these relationships is that it is not known what the birds are eating during migration. A Rocha Portugal is now investigating the bird’s diet and foraging behaviour using a variety of methods, including infra-red video monitoring of behaviour along the shoreline at night, and identifying prey DNA extracted from the gut contents of mist-netted birds.

Accurate monitoring of body mass variations requires a good number of birds to be captured in each year. As the dataset develops, each year’s data becomes more and more valuable, and it becomes increasingly important that an adequate sample of birds is ringed.

Over the 16 years of the project, the number of birds caught has varied greatly. Therefore, one of the major aims has been to establish the Storm-petrel project as a recurrently and independently funded, long-term annual monitoring project. In late 2003 A Rocha Portugal submitted a proposal for funding from the Earthwatch Institute, a global NGO. During 2004 it won funding for three 10-day teams of eight volunteers and two field staff to run the fieldwork.

The 2005 fieldwork therefore resulted in the improved total of 436 birds ringed, as well as providing for related research on the diet and foraging ecology of migrating Storm-petrels.

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Rob Thomas can be contacted at ThomasRJ@cardiff.ac.uk. A Rocha's Storm-petrel work is coordinated by Marcial Felgueiras who can be contacted at portugal@arocha.org.