This video from Brazil says about itself:
The red knot (Calidris canutus) (just knot in Europe) is a medium-sized shorebird which breeds in tundra and the Arctic Cordillera in the far north of Canada, Europe, and Russia. It is a large member of the Calidris sandpipers, second only to the great knot. Six subspecies are recognised.
Their diet varies according to season; arthropods and larvae are the preferred food items at the breeding grounds, while various hard-shelled molluscs are consumed at other feeding sites at other times. North American breeders migrate to coastal areas in Europe and South America, while the Eurasian populations winter in Africa, Papua New Guinea, Australia, and New Zealand. This species forms enormous flocks when not breeding.
Body shrinkage due to Arctic warming reduces red knot fitness in tropical wintering range
13 May 2016
Migratory animals have adapted to life in multiple, sometimes very different environments. Thus, they may show particularly complex responses as climates rapidly change. Van Gils et al. show that body size in red knot birds has been decreasing as their Arctic breeding ground warms (see the Perspective by Wikelski and Tertitski). However, the real toll of this change appears not in the rapidly changing northern part of their range but in the apparently more stable tropical wintering range. The resulting smaller, short-billed birds have difficulty reaching their major food source, deeply buried mollusks, which decreases the survival of birds born during particularly warm years.
Reductions in body size are increasingly being identified as a response to climate warming. Here we present evidence for a case of such body shrinkage, potentially due to malnutrition in early life. We show that an avian long-distance migrant (red knot, Calidris canutus canutus), which is experiencing globally unrivaled warming rates at its high-Arctic breeding grounds, produces smaller offspring with shorter bills during summers with early snowmelt. This has consequences half a world away at their tropical wintering grounds, where shorter-billed individuals have reduced survival rates. This is associated with these molluscivores eating fewer deeply buried bivalve prey and more shallowly buried seagrass rhizomes. We suggest that seasonal migrants can experience reduced fitness at one end of their range as a result of a changing climate at the other end.
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