Paying the bill for climate change
Shorebirds are finding it tough to obtain food. Along with a food shortage, it appears a beak shortage is also to blame. Researchers have found that red knots — and their beaks — are rapidly shrinking.
In the past, these Arctic breeders would hatch just before a brief burst in insect numbers, which provided an ideal opportunity for hatchlings to gorge and gain weight in preparation for their upcoming long-distance migration from the northernmost part of Russia to their tropical wintering ground in West Africa.
These days, warmer Arctic temperatures have thrown the red knots’ schedule out of whack. “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,” said Jan van Gils from the NIOZ Royal Netherlands Institute for Sea Research and first author of the study published in Science, in a press release.
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Retreating snow marks the start of the insect peak in the Arctic. Earlier snow melting means that by the time the red knots hatch, they have missed the insect explosion they once relied on. Juveniles must now search high and low to scrounge up whatever food they can before their migration, with many suffering malnutrition and hampered growth in the process.
Van Gils noted, “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."
For smaller juvenile birds that manage to complete the gruelling journey and arrive in West Africa, the real hardships have just begun. The researchers found that the small ones had much lower chances of survival than larger juveniles, even after reaching their wintering grounds, and the reason was strikingly apparent.
“Only larger birds with long bill were able to reach the relatively deeply burrowed bivalves at Banc d'Arguin [in West Africa],” said van Gils. “Shorter-billed birds were forced to live on seagrass, which is a poor food source for these birds.”
As the authors wrote, their findings show “that seasonal migrants can experience reduced fitness at one end of their range as a result of a changing climate at the other end.”
While the red knots are shrinking in body size due to rapidly advancing insect peaks in the Arctic, natural selection is beginning to favor relatively long beaks that enable the birds to feed on mollusks in West Africa. With these shifting proportions, red knots of the future might look very different than they do today.
The researchers warn that these sorts of changes in size and appearance, and their detrimental effects on population dynamics, are likely to hinder other species that breed in the High Arctic in the coming years.
“This is a very serious ecological effect that requires our immediate attention," said van Gils.
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