Piovanello maggiore

Tassonomia

Nome scientifico

Calidris canutus

Autorità

(Linnaeus, 1758)

Ordine

Caradriformi

Famiglia

Scolopacidi

Genere

Calidris

Areale e habitat

In the breeding season, the red knot has a circumpolar distribution in the high Arctic, then migrates to coasts around the world from 50° N to 58° S. The red knot has one of the longest migrations of any bird. Every year it travels more than 9,000 mi (14,000 km) from the Arctic to the southern tip of South America and repeats the trip in reverse. The exact migration routes and wintering grounds of individual subspecies are still somewhat uncertain. The nominate race C. c. canutus breeds in the Taymyr Peninsula and possibly Yakutia and migrates to Western Europe and then down to western and southern Africa. C. c. rogersi breeds in the Chukchi Peninsula in eastern Siberia, and winters in eastern Australia and New Zealand. Small and declining numbers of rogersi (but possibly of the later described piersmai) winter in the mudflats in the Gulf of Mannar and on the eastern coast of India. The recently split race C. c. piersmai breeds in the New Siberian Islands and winters in north-western Australia. C. c. roselaari breeds in Wrangel Island in Siberia and north-western Alaska, and it apparently winters in Florida, Panama and Venezuela. C. c. rufa breeds in the Canadian low Arctic, and winters South America, and C. c. islandica breeds in the Canadian high Arctic as well as Greenland, and winters in Western Europe.<p>Birds wintering in west Africa were found to restrict their daily foraging to a range of just 2–16 km2 (0.77–6.18 sq mi) of intertidal area and roosted a single site for several months. In temperate regions such as the Wadden Sea they have been found to change roost sites each week and their feeding range may be as much as 800 km2 (310 sq mi) during the course of a week.<p>B95, also known as Moonbird, is a noted individual of the subspecies C. c. rufa. A male, he has become famous amongst conservationists for his extreme longevity — he was aged at least 20 as of his last sighting in May 2014.

Areale riproduttivo

NA, PAL : patchily in high Arctic (mainly) tundra of Holarctic: nw, e Greenland, nc Siberia, islands n of nc and ne Siberia, and n Chukotskiy Pen. (ne Siberia)

Areale non riproduttivo

SA, Europe, AF, AU : coasts worldwide from temperate zone to tropics; in Indian Ocean mainly w Australia, and in Pacific in New Zealand but rare on other remote islands

Migrazione

Complete migrants

Comportamento

On the breeding grounds, knots eat mostly spiders, arthropods, larvae, and some plant material obtained by surface pecking, and on the wintering and migratory grounds they eat a variety of hard-shelled prey such as bivalves (including mussels), gastropods and small crabs that are ingested whole and crushed by a muscular stomach.<p>While feeding in mudflats during the winter and migration red knots are tactile feeders, probing for unseen prey in the mud. Their feeding techniques include the use of shallow probes into the mud while pacing along the shore. When the tide is ebbing, they tend to peck at the surface and in soft mud they may probe and plough forward with the bill inserted to about 1 cm (0.39 in) in depth. The bivalved mollusc Macoma is their preferred prey on European coasts, swallowing them whole and breaking them up in their gizzard. In Delaware Bay, they feed in large numbers on the eggs of horseshoe crabs, a rich, easily digestible food source, which spawn just as the birds arrive in spring. They are able to detect molluscs buried under wet sand from changes in the pressure of water that they sense using Herbst corpuscles in their bill. Unlike many tactile feeders their visual field is not panoramic (allowing for an almost 360 degree field of view), as during the short breeding season they switch to being visual hunters of mobile, unconcealed prey, which are obtained by pecking. Pecking is also used to obtain some surface foods in the wintering and migratory feeding grounds, such as the eggs of horseshoe crabs.<p>The red knot is territorial and seasonally monogamous; it is unknown if pairs remain together from season to season. Males and females breeding in Russia have been shown to exhibit site fidelity towards their breeding locales from year to year, but there is no evidence as to whether they exhibit territorial fidelity. Males arrive before females after migration and begin defending territories. As soon as males arrive, they begin displaying, and aggressively defending their territory from other males.<p>The red knot nests on the ground, near water, and usually inland. The nest is a shallow scrape lined with leaves, lichens and moss. Males construct three to five nest scrapes in their territories prior to the arrival of the females. The female lays three or more usually four eggs, apparently laid over the course of six days. The eggs measure 43 mm × 30 mm (1.7 in × 1.2 in) in size and are ground coloured, light olive to deep olive buff, with a slight gloss. Both parents incubate the eggs, sharing the duties equally. The off duty parent forages in flocks with others of the same species. The incubation period lasting around 22 days. At early stages of incubation the adults are easily flushed from the nest by the presence of humans near the nest, and may not return for several hours after being flushed. However, in later stages of incubation they will stay fast on the eggs. Hatching of the clutch is usually synchronised. The chicks are precocial at hatching, covered in downy cryptic feathers. The chicks and the parents move away from the nest within a day of hatching and begin foraging with their parents. The female leaves before the young fledge while the males stay on. After the young have fledged, the male begins his migration south and the young make their first migration on their own.

Conservazione

In 2003, scientists projected that at its current rate of decline the American subspecies, rufa, might become extinct as early as 2010, but as of April 2011 the subspecies is still extant. In New Jersey, state and local agencies are taking steps to protect these birds by limiting horseshoe crab harvesting and restricting beach access. In Delaware, a two-year ban on the harvesting of horseshoe crabs was enacted but struck down by a judge who cited insufficient evidence to justify the potential disruption to the fishing industry but a male-only harvest has been in place in recent years.<p>Late in the fall of 2014, the red knot rufa was listed as a federally threatened species under the United States Endangered Species Act – the second most critical status that can be awarded to a subspecies. This followed a decade of intensive petitioning by environmental groups and a lawsuit against the Department of the Interior for alleged negligence in the protection of endangered species through failure to evaluate and list them. The reasons for the red knot rufa's listing were varied; habitat degradation, loss of key food supplies, and threats posed by climate change and sea level rise were all listed as factors that were considered when the red knot rufa was listed.

Tendenza della popolazione

declining