Researchers at the University of Leeds have warned that global warming is a major threat to the gannet, a species known for its stable populations and constant breeding success.
In a paper published in Marine Ecology Progress Series, Dr Keith Hamer of the University’s Faculty of Biological Sciences reports that diminishing fish stocks around gannets’ natural habitats – caused partly by an increase in sea temperature – are forcing birds to search further afield in search of food for their young.
“Usually, one parent will stay with a chick while the other goes out hunting, says Dr Hamer. “But if left for long enough, it will eventually leave the nest itself to find food. This leaves the chick alone and vulnerable to attack - mainly from other gannets seeking prime nesting space, which is fiercely contested within colonies.”
Two thirds of the world’s gannets nest in the UK, with the largest northern gannet colony found in the Scottish islands of St Kilda. Dr Hamer’s research group has been studying birds nesting at Bass Rock off the Northumbrian coast, using satellite transmitters attached to the birds, to gather information about their movements.
“Gannets have been forced to travel as far as the Norwegian coast to find food – a round trip of over 1000km,” said Dr Hamer. “They compensate by flying faster to make sure they don’t leave their nests for too long, but our research shows they’ve hit their limit. They just physically can’t increase their speed any further.”
Until now, gannets have bucked the trend in the North Sea, their breeding success remaining stable while other seabirds were in decline. However, as sea temperatures continue to rise and fish stocks diminish, gannets are being forced further afield and are away from their nests for longer. The Leeds researchers are already seeing the numbers of unprotected chicks rise and fear it can only get worse.
Gannets pair for life and breed annually, occupying the same nest each year. It takes forty days for an incubated egg to hatch and a further ninety days for chicks to fledge. “There’s only time for each gannet pairing to raise one chick each year, so with an increasing number losing their chicks and their nesting sites we may start to see a decline in overall numbers,” says Dr Hamer.
This work was published in a paper entitled: Annual variation in diets, feeding locations and foraging behaviour of gannets in the North Sea: flexibility, consistency and constraint in Marine Ecology Progress Series on 24 May 2007.
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