The global decline in seabird populations is of growing concern to ecologists, and now researchers have discovered a new cause – some may be becoming too stupid to survive. Climate change may be the root of the trouble. New environmental conditions lead fish to migrate, leaving the birds that feed on them malnourished. The new research shows that lack of a specific nutrient in red-legged kittiwakes damages their cognitive abilities and could leave them too daft to find food.
The sharp drop in the seabird numbers coincided with a climate shift that resulted in a reduced abundance of lipid-rich fish in the area, though other fish species remained available as food. The researchers theorised that chicks born at or after this time lacked the lipid-rich foods they needed for proper cognitive development, leaving them less likely to have the skills needed to survive as independent adults.
So Kitayski’s team set up an experiment with 20 kittiwake chicks from the Pribilof Islands that were hatched in captivity. For the first 14 days after hatching, all the chicks were fed a high lipid diet corresponding to adequate parental feeding. After that and until the age of 47 days – the average fledgling age – half the chicks were switched to a low-lipid diet of rainbow smelt, while the other 10 received lipid-rich silverside fish. During this time, the birds were given multivitamins and mineral supplements to ensure that lipids were the only nutrients being varied. Then for a final 10 days, all the kittiwakes were fed silverside.
The birds’ cognitive abilities were then tested with a series of learning tasks, such as discovering the link between the colour of a dish and the presence of food. Those raised on a poor lipid diet could not learn tasks that birds raised on lipid-rich diets learned almost to perfection. Such learning skills are believed to be important in finding food. “This is really fascinating research, and demonstrates a very complex mechanism driving a reduction in population,” says Mark Grantham, at the British Trust for Ornithology. “Climate change has had a noticeable effect on both the timing and success of breeding of many of our bird species, but this new study just shows how unpredictable such consequences can be.”
Norman Ratcliffe, seabird biologist for the UK’s Royal Society for the Protection of Bird, agrees that the experiment shows chick nutrition affects the ability of birds to find food after they fledge. But he says it remains unclear if this is the cause of the red-legged kittiwake decline: “The chicks fed poor quality diets are lighter as well as cognitively impaired and this could also contribute to their chances of post-fledging survival.” Weekly blood tests performed during the study also showed that the birds on the low-lipid diet had elevated levels of the stress hormone corticosterone. “Malnutrition imposed early in life is known to alter morphological, neuro-physical and functional aspects of the developing brain, which might affect learning and memory formation in mammals,” the researchers write. “A chronic elevation of corticosterone may also cause atrophy of the hippocampal processes and neuron loss in mammals.”
“This work may have implications for many migratory species that will have to deal with an increasingly changing environment and will need to be able to adapt rapidly,” Grantham told New Scientist. “It has been shown recently that brain size effects behaviour and can even influence population trends, so it would be expected that an increase in stupidity in some species would adversely affect their ability to perform their day-to-day activities.”
December 6, 2005
Original web page at New Scientist