Foraging red knots in Mauritania are shown. This material relates to a paper that appeared in the May 13, 2016, issue of Science, published by AAAS. The paper, by J.A. van Gils at NIOZ Royal Netherlands Institute for Sea Research in Den Burg, Netherlands, and colleagues was titled, “Body shrinkage due to Arctic warming reduces red knot fitness in tropical wintering range”
Credit: Copyright Jan van de Kam
Red knot birds are becoming smaller as temperatures warm in their Arctic breeding grounds. But the migrating birds don’t pay the price for this climate-caused shrinkage until they arrive at the more stable climate of their tropical winter homes. Having analyzed the data collected for more than three decades, scientists managed to show that the effects of climate changes in the Arctic may come out on a completely different continent, a few thousand kilometers away from the Arctic ice.
One of the authors, Eldar Rahimberdiev, researcher at the Biological faculty of MSU, says that the work is unique, as earlier scholars did not consider these problems so complex.
This article considers a small bird of the suborder waders — red knot (Calidris canutus). This bright red in summer and almost white in winter bird is one of a record-breakers for distance flight, being able to cover about 5000 kilometers non-stop. Every year in the autumn it flies to winter at 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). And then the bird has another record, choosing the most northern and cold nesting latitudes. The arrival of the red knots to these severe lands was “calculated” by evolution so that the birth of the chicks happens just at the peak of abundance of insects, their main food.
But that was before the global warming has seriously changed the lives of the birds within a few decades. These changes are described in the new article. At the disposal of the researchers was a data archive for 33 years, which included complete measurement by Polish scientists on the morphology changes in 1990 juvenile birds who committed intermediate stops in Poland within this period, and satellite images of the Taimyr Peninsula and the results of the Dutch zoologists’ observations on the birds at the coasts of Mauritania.
During these 30 years the arrival of spring on the Taimyr Peninsula, and the peak of the insect population moved for almost two weeks earlier in time. If the snow on the peninsula disappeared by the middle of July in the past, it is gone now at the end of June. Arrival dates of birds stayed stable, but phenologically birds begin to nest later than 30 years ago, and miss the peak of insect abundance essential for juvenile growth. The lack of food has caused a decrease in the size of the young birds, which is impossible be compensated later in life. However, at first glance, the problems for birds did not increase: with the arrival of cold weather, young red knots still go to their long journey and still successfully get to Africa, preparing to spend the whole winter there, and fly back only in spring. But the real difficulties come further. During the winter in the Banc d’Arguin National Park in Mauritania, red knots eat bivalve mollusks hiding in the sediment, and they need quite a long bill for reaching this food. Birds with long beaks often diversify their diet with Loripes lucinalis, burrowing deep enough into the sand. Even though that shellfish produces a toxin in their body, in a birds’ diet its proportion may be up to 40%. Red knots with a shorter bill reach another food source — Dosinia isocardia, and those not lucky with the length of the beak are to be fed with plant food — small rhizomes of Zostera (Zostera noltii). Survival rate of the birds that are not able to get to mollusks Loripes was significantly lower than those which were not restricted in their diet.
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Dietary restrictions imposed on too short-beak birds particularly impact the young birds, most of them are unable to survive their first winter. Thus, the consequences of the problem that occurred in the Arctic act in a few months, and moreover — on another continent. If the knot still manages to fly back on the Taimyr Peninsula, a short break even helps — to hunt insects is much easier than with a long one. But, as practice shows, the birds hardly survive in Africa.
According to Eldar Rahimberdiev, researcher of the biological faculty of the Lomonosov MSU, the threat of extinction is more than real for red knots. Now populations of all northern waders greatly decreases, some subspecies are already on the edge of extinction. 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. Moreover, many birds of the population are already close to the critical point, when any random fluctuations of numbers can destroy the population.
The work of scientists is unique, as the authors have shown that the transfer of the appeared problem is possible only in time but also in space. Earlier the articles of such level did not appear in Science magazines, and scientists, according to Eldar Rahimberdiev, rarely paid attention to the whole annual cycle.
‘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.
- Jan A. Van Gils, Simeon Lisovski, Tamar Lok, Włodzimierz Meissner, Agnieszka Ożarowska, Jimmy De Fouw, Eldar Rakhimberdiev, Mikhail Y. Soloviev, Theunis Piersma, Marcel Klaassen. Body shrinkage due to Arctic warming reduces red knot fitness in tropical wintering range.Science, 2016 DOI: 10.1126/science.aad6351