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Climate change pushing gannets to the limit

Climate change is pushing Northern Gannets to the limit, by forcing the large seabirds to search further and further afield for food for their young, according to new research. The work, which was funded by the EU and the UK's Joint Nature Conservation Committee (JNCC), is pu...

Climate change is pushing Northern Gannets to the limit, by forcing the large seabirds to search further and further afield for food for their young, according to new research. The work, which was funded by the EU and the UK's Joint Nature Conservation Committee (JNCC), is published in the journal Marine Ecology Progress Series. Northern Gannets are found across the North Atlantic, but two thirds of the world's population nests around the coast of the UK. The North Sea is one of the most heavily fished seas in the world. It is also affected by climate change, with increasing sea temperatures leading to lower fish stocks around the gannets' natural habitats. While these pressures have caused the populations of other seabirds to decline over recent years, the gannet population has remained relatively stable. However, as this new research shows, gannets may be reaching the limits of their capacity to adapt to these pressures. The scientists, led by Dr Keith Hamer of the University of Leeds, studied a population of gannets living on the Bass Rock, which lies just off the coast of south-east Scotland. Using satellite transmitters attached to the birds, the researchers were able to gather information on the birds' diet and foraging behaviour. They found that the adult gannets were extremely flexible in both species and sizes of prey and also in the duration, range and distance travelled during their foraging trips. This flexibility has undoubtedly contributed to the stability of the gannet population so far. However, the research also revealed that the gannets may be reaching their limits. Usually, while one parent goes out hunting, the other will stay with the chick to protect it from attacks from other gannets seeking to take over the nesting site. However, if the hunting parent stays at sea for too long, the other parent will leave the chick alone and go hunting. The scientists found that adult birds are embarking on ever longer journeys to find food, resulting in increasing numbers of chicks being left alone and vulnerable to attack. For distances up to 300km from the colony, the birds fly faster to get back to their nest as soon as possible. However, on journeys to the furthest feeding destinations, which were over 400km away, the birds simply did not have the energy to increase their flying speed. 'Gannets have been forced to travel as far as the Norwegian coast to find food - a round trip of over 1,000km,' 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.' 'These data suggest that while adults have so far been able to maintain high reproductive success in years of low prey availability, they may not be able to do so in future years if providing sufficient food for chicks entails any further increases in trip duration or foraging effort,' the researchers conclude. It takes forty days for a gannet egg to hatch, and a further ninety days for the chick 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,' warns Dr Hamer. The EU funding came from the IMPRESS (Interactions between the marine environment, predators, and prey: Implications for sustainable sandeel fisheries) project and a project entitled 'Modelling the Impact of Fisheries on Sea Birds'.