Climate Change Reduces Red Knot Birds' Body Shape And Bill Size As Well As Survival Rates

Climate changes are hitting even smaller species. The migratory red knot bird is shrinking in size, which makes it difficult for the species to find food.

When it is the peak insect season, chicks born under warm conditions tend to develop smaller beak sizes before migration, which makes it difficult for them to search for their favourite food after reaching their wintering grounds.

Climate change leads to smaller animal body sizes, suggests recent evidence. It is a phenomenon that has been noticed across a variety of animals as a response to climate change. The current red knot study gives evidence to back the 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."

After landing in West Africa, the smallest of the birds survived in just half the numbers compared to the larger ones. Only birds with longer beaks are able to forage for their favourite insects while the shorter-billed birds are forced to eat the comparatively poorer source of food in seagrass.

"The poor survival of shrunken first-year birds clearly contributes to the current population decline seen in red knots nowadays," van Gils said.

Moreover, the shortening of the bills changes even their body shapes.

"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.