Not much is known about what specific vocalizations are used in any given situation, but individuals will frequently give a soft quer-wer or knut sound. During breeding season, males give a high pitched mating call that increases rapidly closer to copulation. Also during mating season, males will perform agnostic song flights and an aerial display called v-wing flight (which is similar to a low song flight) and aerial chases in order to claim and defend territory. This has been observed to start on the first day of arrival to the breeding grounds.
Red knots have a large number of sensory pits in the tip of their beaks which contain many Herbst corpuscles (nerve endings) which are thought to be able to detect a change in pressure when probing the sand for bivalves. Like all birds, red knots perceive their environment through visual, auditory, tactile and chemical stimuli.
Communication Channels: visual ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
According to the United States Fish and Wildlife Service C. c. rufa is a candidate for the endangered species list, where they have rated the listing priority as “High.” The U.S. Shorebird Conservation Plan has listed the red knot as “A Species of High Concern”. As North American migratory birds, they are protected under the U.S. migratory bird act. This subspecies of red knots is not evaluated specifically by the IUCN Red List, but Calidris canutus is listed as "least concern".
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
During red knots' migration and stop-over period along the East Coast, horseshoe crab harvesting is banned in an effort to allow young juveniles and newly matured females to reproduce. This time period is crucial for knots because it is when the crabs move to the shore to mate and lay eggs. Shorebirds, including red knots, are heavily blamed by fishermen for low horseshoe crab egg harvests.
Shorebird migration brings many birders to the shores of Delaware Bay which generated nearly $36 million in New Jersey. C. c. rufa is hunted in South America as sport and food. Though this may bring money to the people of the area it may have drastic effects on population size.
Positive Impacts: food ; ecotourism
Red knots rely heavily on horseshoe crab eggs that are laid on the beaches of Delaware Bay during spring migration in order to refuel for the remainder of the migration. Because of this reliance, they have played a major role in indicating the population decline of horseshoe crabs that use Delaware Bay as a reproduction site. The decline in the crab population is due to over harvesting by fishermen who use the crab (especially egg laden females) as bait for conch and eels.
Red knots are mainly molluscivores, feeding largely on bivalves which are swallowed whole. During the spring migration stop-over around Delaware Bay, red knots feed exclusively on horseshoe crab eggs. The eggs are soft and jelly-like (unlike the mussels they usually prey on) and are the only thing their depleted bodies can digest after their non-stop northward flight from the south tip of South America. The eggs are high in protein and fat which helps the birds quickly gain enough weight to survive the remaining flight to the Arctic. During the breeding season their diet consists of terrestrial invertebrates and some plant material. They exhibit three main habits when foraging for food: pecking, plowing and probing. Pecking is used when eating small mussels and horseshoe crab eggs which are found mainly on or just below the surface of intertidal or mud flats and beaches. Plowing and probing are used to detect bivalves that are buried within the sand.
Animal Foods: eggs; insects; terrestrial non-insect arthropods; mollusks
Plant Foods: leaves
Primary Diet: carnivore (Molluscivore )
Calidris canutus rufa, one of six subspecies of red knots, breeds in the middle and high-Arctic areas of northern Canada. During the non-breeding season, C. c. rufa is found wintering in three main Neotropical regions. The largest wintering population is in Bahía Lomas, Chile, on the north coast of Tierra del Fuego. Smaller, but significant populations are found wintering on coastlines of Bahía San Sebastián and Río Grande in the Province of Tierra del Fuego of Argentina, and along the coast of Maranhão, Brazil. During migration, the Delaware Bay in the Eastern United States becomes the most important staging area for this subspecies, but C. c. rufa also appears along the coastlines of New Jersey, New York and Massachusetts.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
Red knots' breeding habitat consists of slightly vegetated land in the tundra where it is sunny and windy. The nests are built about 50 km off shore and less than 150 m above sea level near wetlands. Wintering and migration habitats consist of large, sandy tidal flats and coastlines near inlets of bays and estuaries that have remained undeveloped.
Average elevation: <150 m.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: tundra
Aquatic Biomes: coastal
Other Habitat Features: estuarine
The oldest C. c.rufa on record was banded as a juvenile in 1987 and recaptured in 2003 in Tierra del Fuego, making the bird a minimum of 16 years old. The annual survival rates of adults is about 80% while juvenile survival rates are only 40%. Given these rates few birds will live more than seven years.
Range lifespan
Status: wild: 16 (high) years.
Average lifespan
Status: wild: 7 years.
Calidris canutus rufa is one of six subspecies of red knots, which are distinguished by differences in geographical range, morphological traits, and annual cycles. C. c. rufa is similar in appearance to the subspecies C. c. roselaari but they both differ from other subspecies in their overall lighter plumage and longer bills. Differences between these two similar subspecies can be seen through genetic analysis.
Calidris canutus rufa is a sandpiper-like shorebird with a round body, long legs, a small head and tiny eyes. The beak tapers and is not much longer than its head. Males and females vary slightly in size and color. Adult females on wintering grounds weigh on average 124.2 g while males weigh, on average, 115.7 g and are more brightly colored in the face and chest. Females also have a slightly longer beak than males. Both sexes average 27 cm in length. Although the breeding plumage of C. c. rufa is the dullest of all red knot subspecies, the face, chest and belly are still a striking rufous color. The head is a dark gray and the eye stripe, back and rump are rust colored while the rear belly is white. The wing feathers are grey with a pale edging and oblong rust colored centers.
In non-breeding plumage the head, back and tail are a plain gray with a white eye stripe, while the face, chest and belly are a dingy white. The upper chest has dark streaking that may extend down the flanks.
In juveniles there is no distinction between male and female. Juveniles of both sexes have a dark gray head with a white eye stripe. The back and tail are gray with distinct white outlines on the feathers giving each feather a predominate shape. The chest and belly are white with light streaking.
Range mass: 115 to 124 g.
Average length: 27 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: female larger; male more colorful
On wintering grounds peregrine falcons, harriers and short-eared owls are the main predators of red knots. While on breeding grounds, long-tailed jaegers, Arctic foxes and herring gulls are known to pick off chicks and eggs. Like many shorebirds, the primarily brown-ish coloration (more-so in females and hatchlings) camouflages individuals to avoid predation.
Known Predators:
Anti-predator Adaptations: cryptic
Though little is understood about the reproduction habits of C. c. rufa., it is thought that they are annually monogamous. Males have many behaviors during breeding season that are applied to territoriality and advertisement. As soon as males arrive on the breeding habitat they begin a song flight which they perform all throughout the season. They also use a v-wing flight display which is similar to the song flight, but closer to the ground and also aerial chases that are performed by males to protect their territory. On the ground they perform a “tail-up” display before copulation or by a pair that has been reunited after a separation. After the clutch has been completed this display is no longer used.
Mating is initiated by the male who follows the female while performing the “tail-up” display and rapidly pecking at her back and making a fast, high-pitched call. If the female is receptive, the male mounts her back and flaps his wings rapidly. The female then drops her wings and lifts her tail to reveal her rump. The male then lowers his tail under hers and makes cloacal contact which lasts about a minute. The male then falls off holding the females head, neck or nape feathers in his beak for up to 30 seconds. This series of activities will occur many times in a day during the fertile period.
Mating System: monogamous
The age of reproduction is not known, but individuals are thought to reach reproductive maturity at about two years of age since this is the common age for first reproduction for related bird species. The males and females arrive to the breeding grounds in the Arctic region of northern Canada in late May to early June. Females lay on average a clutch of 4 eggs over a 4 to 6 day period. The incubation period is 22 days from the last egg laid to the last egg hatched. The young are precocial and fairly independent from the first day; they may move as far as 300 m from the nest within 24 hours of hatching. Shortly after hatching, the young are abandoned by the female and rely on only the male for protection. Young generally move from the higher nest site toward low wetland areas to forage. Approximately 21 days after hatching the chicks become fledged and no longer rely on the father for protection.
Breeding interval: Red knots breed once annually.
Breeding season: Red knots breed between late May and early June.
Range eggs per season: 3 to 4.
Average eggs per season: 4.
Average time to hatching: 22 days.
Average fledging age: 21 days.
Range age at sexual or reproductive maturity (female): 1 to 2 years.
Range age at sexual or reproductive maturity (male): 1 to 2 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Both the male and female take part in incubation. If a clutch is lost, the pair will not replace it. Within 24 hours of hatching the relatively precocial chicks leave the nest and the group heads from high nesting terrain to low wetlands. After this move the female leaves the group, and the male is the sole provider of care for the young. Young fledge at 18 to 25 days of age when the male no longer protects the chicks. The age of independence is not quite understood because the male never feeds his young, but they forage from birth.
Parental Investment: precocial ; male parental care ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Male, Female, Protecting: Male, Female); pre-weaning/fledging (Protecting: Male); pre-independence (Protecting: Male)
