For years, researchers believed that the population of red knots was declining due to changes in the migratory paths linked to increased human activity. While that may be the case, researchers have found that climate change is a big reason behind this. According to a study published in the journal Science, global warming is causing the birds to grow smaller with shorter bills – which is directly linked to their survivability rate.
Climate change causing body shrinkage
The shorebirds that migrate from Siberia to West Africa have been shrinking in size as temperatures rise at their Arctic breeding grounds. The red knots breed in the Arctic during summer and fly to their feeding grounds in West Africa in winter. Co-author of the study, Professor Marcel Klaassen of Deakin University said the Arctic was warming faster than any other place on the planet. In response to global warming, several species are adapting by shrinking their body sizes, said Pro Klaassen.
Scientists led by Dr Jan van Gils of the Royal Netherlands Institute for Sea Research studied the red knot Calidris canutus over 30 years. They found that the bird’s size and shape both have changed. Dr Jan van Gils said they had “strong evidence” that it was an effect of climate change. Using satellite data, they found that snow melt in the Arctic is starting earlier at a rate of about half-a-day every year. In the last 30 years, the date of snow melt in the high-Arctic breeding grounds of red knots had advanced by more than two weeks.
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The red knot breeding season in Siberia was timed such that the chicks would hatch when there was plenty of food (insects) available. The early onset of snow melt means the chicks hatch after the “peak food” period was over. Reduced availability of food affected their growth. The negative effects multiplied when the juvenile birds flew to their winter feeding grounds in Africa.
Red knots with shorter bills have only 40% survival chance
After flying about 9,000 kilometers, the birds with shorter bills were not able to delve into mudflats to detect and retrieve food. Scientists found that red knots with a 40mm bill had easy access to about 66% of mollusks (their primary food). But those with 30mm bills had access to only a third of mollusks. So, they were forced to consume less nutritious food.
Researchers had tagged 2,381 red knots between 2002 and 2013. Subsequent re-sightings of the birds suggested that juvenile red knots with shorter bills had only 40% chance of survival. By comparison, those with longer bills had 80% survival chance.