A new study has revealed that the migratory red knot bird is getting smaller in size due to the increasing pressures of climate change, making it harder for them to find the best food.
The data reveals that chicks born under rapidly warming conditions miss the insect peak, which causes smaller beak sizes before migration starts. Furthermore, if they manage to reach their wintering grounds, shorter beak sizes makes it harder to find their favorite foods.
Although the shrinkage of animal body size is a phenomenon that has only recently been discovered, evidence thus far suggests that it is a universal response to climate change. This shrinkage occurs across a variety of animal taxa, and the current red knot study is more evidence that backs current theories.
"The red knot (Calidris canutus canutus) is one of the world's most northerly breeding birds and a well-known long-distance migrant," said Jan van Gils from the Royal Netherlands Institute for Sea Research (NIOZ) and lead author of the study. "Analysis of satellite images has shown that over the past 33 years, snow at the red knot's breeding grounds has progressively melted earlier, at a rate of half a day per year, so that's now more than two weeks."
"The retreat of the snow marks the start of the insect peak in the Arctic; the main food source of the chicks before they leave the Arctic," he added. "Juvenile red knots that we caught along the Baltic coast while on their way to West Africa were smaller and had shorter bills after warm Arctic summers."
Once the birds arrive in West Africa, the survival of the smallest of the birds is just half that of the larger young birds due to the detrimental effects of a short bill. The study revealed that only larger birds with long bills were able to reach their food, with shorter-billed birds forced to eat seagrass, a comparatively poor food source.
"The poor survival of shrunken first-year birds clearly contributes to the current population decline seen in red knots nowadays," van Gils said.
In addition to the changes in body size pushed by climate change, red knot body shapes are also changing. Long bills cause changes in body shape, and since natural selection favors against short-billed birds, survival rates of long-billed red knots are higher, and thus, their body type is more common.
"Changes in body size and shape, and the negative population dynamical consequences, will be widespread among other High-Arctic breeding species in the future," van Gills said. "This is a very serious ecological effect that requires our immediate attention."
The findings will be published in the May 13 issue of the journal Science.
