Red knots are an amazing bird species that migrate more than 5’000 km each season. From their breeding grounds on the Taimyr Peninsula in Russian Siberia they fly down south as far as Mauretania and even Australia and New Zealand. Due to the warming of the Arctic, the birds are becoming smaller. A new study now shows that the price for this shrinkage is not due until they arrive at their winter homes in the south.

Red knots are rather small wading birds that usually breed in the high latitudes and spend the winter several thousand kilometers further south. They display a high degree of plasticity in order to achieve their record flights. Credit: Hans Hillewaert
Red knots are rather small wading birds that usually breed in the high latitudes and spend the winter several thousand kilometers further south. They display a high degree of plasticity in order to achieve their record flights. Credit: Hans Hillewaert

Red knots (Calidris canutus) are one of a record-breakers for distance flight, being able to cover about 5000 kilometers non-stop. Every year in the autumn this bird flies to the coast of Mauritania (or, depending on the subspecies, Australia or South America), and in the spring returns to breed on Taimyr peninsula -- the northernmost mainland of Eurasia (or, again, depending on the subspecies, Greenland, Alaska and the Canadian Arctic archipelago). The main reason for this long-distance flights is the enormous food abundance of insects in the north and in evolution, the birds managed to birth of the chicks coincides with the peak of insect abundance.

The various subspecies of red knots have different migration routes. Yet, four of the six subspecies spend their winters in the far south and thus have long migration routes. These birds can fly up to 5,000 km nonstop. Picture: D. Buehler on en.wikipedia
The various subspecies of red knots have different migration routes. Yet, four of the six subspecies spend their winters in the far south and thus have long migration routes. These birds can fly up to 5,000 km nonstop. Picture: D. Buehler on en.wikipedia

However, over the last 30 years, spring and the peak of insect populations have come earlier and earlier and is now almost two weeks earlier on average. But the arrival date of the birds has stayed stable and thus there is a smaller food abundance for chicks, which would be essential. The lack of food has caused a decrease in size of young birds, which is impossible to compensate later in life. An international group of scientists investigated the effect of this change on the survival of red knots. From their results, they concluded that the real difficulties for the birds occur only later in their winter grounds in Mauretania. There, the birds with their long beaks usually prey on mollusks and bivalves buried deep in the sandy shorelines. However, the beaks of young birds is not long enough to reach this energy source and the birds have to move to less energy rich sources like sea grass rhizomes or other bivalves. According to the results of the researchers, the survival rate of these birds was significantly lower than those with no diet restrictions due to beak length. The results of their study was recently published in the renowned journal Science.

The birds mainly feed on mollusks and bivalves found in the sand with their long beaks. Younger birds have shorter beaks and thus need to feed on different and less nutritious prey. This seriously impairs their chances of survival.
The birds mainly feed on mollusks and bivalves found in the sand with their long beaks. Younger birds have shorter beaks and thus need to feed on different and less nutritious prey. This seriously impairs their chances of survival.

According to Eldar Rahimberdiev, researcher of the biological faculty of the Lomonosov MSU, the threat of extinction is more than real for red knots. If the bird's bill is reduced to such an extent that they will not manage at all to get shellfish, the species will simply disappear. 'When I was a student and worked with the same species, we were always arguing with foreign colleagues, who said that the birds die because the problems occur during migration. We thought that the problem was at the breeding grounds. And those who worked on the wintering grounds in Africa, argued that there is no problem in Africa. Now it becomes clear that all these parts are interconnected and a sharp change in any part leads to unexpected consequences,' the scientist says.

The work of scientists is unique, as the authors have shown that the transfer of the appeared problem is possible not only in time but also in space.

Source: Lomonosov Moscow State University