Calidris alpinadunlin

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Geographic Range

Dunlins are migratory birds with ten recognized sub-species that all breed in the circumpolar Arctic and Subarctic regions, but winter across a wide geographic range based on their population origin. A study based on mtDNA revealed five distinct population groups that demonstrated a highly structured preference for specific breeding grounds in terms of geography. Some of the most common winter migration patterns show populations from Iceland, the British Isles, the Baltic, and Southern Scandinavia tend to winter in Morocco, Mauritania, and the Mediterranean Basin, which represents the southern extreme for wintering grounds. Breeding populations from Central Siberia winter in the Arabian Gulf. The eastern Arctic and northern Alaska populations winter in Southeast Asia, while the western Alaska population migrates to the Pacific coast of the United States. Likewise, the Arctic Canadian population heads to the Atlantic and Gulf coasts of the United States. (Greenwood, 1984; Wenink, et al., 1993; Wennerberg, 2001)

Habitat

Dunlins are primarily found in the Arctic tundra during their summer breeding season. Dunlins prefer wet marshy areas with sedges and grasses interspersed with dry islands of vegetation for nesting. Nearby lakes, shallow ponds, and river channels are also desirable. After breeding in the tundra areas, dunlins move to coastal estuaries and inter-tidal regions to take advantage of abundant food sources before migrating south. Their winter habitat is primarily in the intertidal mud flats and estuaries on temperate coast lines. During high tide, their roosting sites include high beaches, barrier reefs, islands, cliffs, or other similar high areas. Dunlins have also been observed simply flying in a large flock for the entire high-tide period. (Holmes, 1966a; Holmes, 1971; Sibley, 2001)

Physical Description

Dunlins are relatively small birds with a body length of 16 to 22 cm (6.5 to 8.5 in), a wingspan of 32 to 44 cm (12.5 to 17.5 in), and a weight of 45 to 65 g (1.6 to 2.25 ounce). There is no sexual dimorphism in their plumage coloring, but females are distinctly larger than males. In the non-breeding season, they have a dull, gray-brown head and back with a whitish-gray underside. In preparation for the breeding season, dunlins complete a pre-alternate molt that results in distinctive red plumage on their back with a large black belly patch. Dunlins are sometimes referred to as red-backed sandpipers, in reference to their alternate plumage. Juvenile dunlins are similar in coloration to non-breeding adults, but have some black and cream striping on their back and prominent, thin white wing bars. Their legs are shorter than other related shorebirds and their feet are black with a short, elevated hind toe. Dunlins have a long, tapered bill suitable for probing in the mud, which is black in color and points slightly downward. (Sibley, 2003; Vuilleumier, 2009)

  • Sexual Dimorphism
  • female larger
  • Range mass
    45 to 65 g
    1.59 to 2.29 oz
  • Range length
    16 to 22 cm
    6.30 to 8.66 in
  • Range wingspan
    32 to 44 cm
    12.60 to 17.32 in

Reproduction

Dunlins are primarily Arctic and Subarctic breeders, with a few groups breeding in the British Isles and northern Europe. Dunlins arrive in their breeding grounds just as the snow cover is melting, usually during the last week of May or the first week of June. Male dunlins usually arrive first, choose a territory, and begin to establish boundaries by patrolling borders with territorial flights. Females arrive shortly after and pair bonding begins. Dunlins typically remain together for the duration of the breeding season. Late arriving dunlins may already be in a bonded pair. The transition from flocks to pair bonding and the establishment of territory is usually completed by approximately June 15th. (Gates, et al., 2013; Holmes, 1966a)

After securing a territory, courtship and bond pairing begin with male dunlins performing flight displays. They rise from the ground in a steep ascent up to an average of 50 feet, and then move in a slow, wide circle, alternating between a glide and a hovering flight with rapid wing beats. This display is accompanied by vocalizations that consist of a series of short trills, which ends in a more melodic song at landing. This aerial display may be associated with the reverse sexual size dimorphism, in which females are larger than males. There are some indications that the smaller male body size increases their ability to perform the display for a longer period of time. Increased display duration is important for vocal signaling and visual presence in defending a territory and attracting a mate. Territorial displays continue until the eggs have hatched. Other courtship behaviors include long aerial chases between males and females, ground level chasing and posturing between males, and ritualized nest scraping. (Blomqvist, et al., 1997; Holmes, 1966a)

Choice nesting sites are located in well-drained upland tundra interspersed with wet marshy ponds, lakes, and tidal influenced river channels. Only rarely will a nesting site be located in the marsh itself, and this is most often due to high population densities, in which all prime sites are occupied. Competition for nesting sites is influenced by snow-free access to sites, arrival date, and availability of food resources. Nest densities range from 19 nests per km² to 7 nests per 100 acres. Nest construction begins with the nest scraping behavior of courtship. A male will scrape a hollow depression in the ground with his feet, rotate his breast against the bottom, and throw some token pieces of grass and sedge into the nest. Several of these depressions will be created. The female will eventually start participating by stepping in and out of the depressions and possibly tossing in a few more pieces of grass. At some point, a depression will be chosen and the female will finish the lining to complete a nest for egg laying and incubation. Female dunlins normally lay a 4 egg clutch, approximately one egg per day, with peak egg laying from June 12 to 18, with a range as early as June 6 or as late as July 6. Both parents participate in the 21 to 22-day incubation period, with the female slightly more involved. The peak hatching period is from July 4 to 10. The chicks are precocial and will leave the nest along with both parents within hours of hatching to move to wetland marshy areas for feeding, although they may stay in the nest an extra night if the weather is poor. Female dunlins are capable of a double brooding and can leave the first nest and produce a second, although this is unusual due to the very small window of suitable breeding time in the Arctic environment. Re-nesting is normally attributed to losing the first brood due to predation. Replacement clutches are highly dependent on when the loss takes place. Clutches lost within the first 5 days have an 82% to 95% replacement rate, versus a late loss at 13 days, with only a 35% to 50% replacement rate. Due to the high energy cost of producing eggs, a more important measure of potential re-nesting is the female’s body mass, where larger females are more likely to re-nest. Generally, only three eggs will be laid in a second nest and the overall egg size will be smaller. As the breeding season ends, dunlins begin to sever their pair bonds and start to re-flock. By the beginning of July, males and females that have lost either their nest or their broods begin to gather in small groups. From July 15 to 30, females begin to congregate and juveniles separate from adults shortly thereafter. Newly hatched juveniles flock together and head toward coastal areas to feed before winter migration begins in August and September. Adults tend to head to inland tundra areas to feed and migrate south independently of juveniles. (Gates, et al., 2013; Holmes, 1966a; Jamieson, 2012)

  • Breeding interval
    Dunlins breed once yearly and usually only produce one clutch.
  • Breeding season
    These birds breed from late May to mid-July.
  • Range eggs per season
    3 (low)
  • Average eggs per season
    4
  • Range time to hatching
    21 to 22 days
  • Average fledging age
    19 days
  • Range time to independence
    1 to 24 hours
  • Average age at sexual or reproductive maturity (female)
    1-2 years
  • Average age at sexual or reproductive maturity (male)
    1-2 years

Females usually leave the family group when the chicks are approximately five days old. Male dunlins take over the parenting and stay with the chicks until they fledge at about 19 days old. Dunlins do not bring food directly to the chicks, but instead lead them to areas that contain food. Chicks are precocial and know how to feed themselves. (Jamieson, 2012)

Lifespan/Longevity

Among wild individuals in the Calidris alpina schinzii subspecies, adult dunlins have an average lifespan of about 5.4 years. This varies between genders, where males have an average lifespan of 8.6 years and females average 3.9 years. However, maximum wild lifespan can be much greater, the oldest known individual survived at least 24 years. (Warnock and Gill, 1996)

  • Range lifespan
    Status: wild
    28 (high) years
  • Average lifespan
    Status: wild
    5.4 years
  • Average lifespan
    Status: wild
    5.4 years

Behavior

Dunlins are terrestrial birds that predominately walk but will occasionally run. They are noted for their tight, cohesive flying. These birds also turn as a flock using two distinct maneuvers. The first is when the entire flock changes course or direction seemingly in synchronization. The second is a rotation, in which each bird shifts along the axis from head to tail. This produces a flash of color change from light to dark. The mechanisms governing flock level flight control are not apparent. There does not seem to be a leader, nor is there any structured formation. Flight speed has been documented at 72 to 88 km per hour. Dunlins are highly social birds that live in large flocks. Aggression is almost always related to breeding behavior. (Davis, 1980; McCabe, 1942)

Dunlins engage in preening, head-scratching, and bathing. In one study, there was a notable increase in the amount of time spent bathing and grooming feathers during the prebasic molt. Dunlins complete a prebasic molt in their summer breeding grounds just after breeding, but before migrating to wintering grounds. In the more northern latitudes, 61⁰N or more, breeding and molting will overlap as an adaptive response to the short summer season. This overlap takes place near the end of the breeding effort, when nutritional demands of breeding are declining. In addition, molting tends to coincide with their movement from the tundra habitat to the coast, where more abundant food resources are available. The pre-alternate molt is an incomplete molt that begins in mid-February to early March and is completed by mid-April to early May, just before the spring migration north to the breeding grounds. (Handel and Gill, 1992; Holmes, 1966a; Holmes, 1966b)

Home Range

Dunlins only defend a territory during the nesting season. Territory sizes vary by subspecies and population density, but they can be as small as 0.25 ha and as large as 7.5 ha. Dunlins maintain these areas through territorial songs and flights. (Warnock and Gill, 1996)

Communication and Perception

Dunlins appear to signal extensively with loud, low-frequency sounds during aerial mating displays and when defending nesting territories in the Arctic tundra breeding grounds. These vocalizations may be especially suited for distance signaling in their open habitat. Vocalizations between parents and chicks have also been documented. Parent dunlins may emit a low-intensity purring sound as they lead their chicks to food sources. Although their chicks are precocial, they rely on their parents to lead them to food sources for the first few days of their life. Dunlins also call to their chicks during this same critical period to gather them for brooding. Dunlins are also known for tight flying flock formations in which the entire flock will turn in a coordinated motion. Two distinct types of course changes are used, one in which the flight course is altered and the other in which a body rotation is performed creating a flash of light and dark. This behavior seems to indicate some type of communication, but the exact mechanisms are not known. Dunlins appear to have good eyesight and hearing, comparable to most mammals. Unlike many other avian species, dunlins appear to have a well-developed sense of taste, with the ability to differentiate between sand that contained worms and sand that did not. Similar to other wading shore birds, dunlins use tactile foraging techniques that utilize the herbst corpuscles, a highly sensitive group of nerves located in the tip of their beaks. By probing into soft, wet sediment on the shore, they are able to detect subtle pressure differences in the water that indicate a solid object in the sand. However, they are not able to differentiate between stones and food, and accordingly do not forage on rocky beaches. (Baker, 1982; Blomqvist, et al., 1997; Davis, 1980; Gill, 2007; Piersma, et al., 1998; Van Heezik, et al., 1983)

Food Habits

Dunlins primarily consume freshwater, marine, or terrestrial invertebrates such as bivalves, worms, insect larvae, crustaceans, snails, slugs, and occasionally small fish. Dunlins sometimes feed in agricultural areas that are adjacent to estuaries. Adult females and juveniles have been documented eating the teeth and bones of lemmings. This may be a source of calcium, as female consumption coincides with egg laying. In their secondary habitat choices, such as marshes and estuaries that have become agricultural land, dunlins will subsidize their diets with agricultural products. (Brennan, et al., 1990; Colwell, 1993; Gill, 2007; Hobson, et al., 2013; Maclean, 1974; Shepherd and Lank, 2004; Van Heezik, et al., 1983; Vuilleumier, 2009; Warnock, 1989)

The foraging habitats of dunlins vary based on whether they are at the summer breeding grounds in the Arctic or the wintering grounds along more southern coastlines. In addition to the coastal estuaries and mudflats, the Arctic tundra also has hummocks, wet marshes, and lake edges that are suitable for foraging. Their primary winter foraging habitats are intertidal mud flats. Dunlins are particular about the substrate in which they feed, preferring to forage in well to moderately sorted sand and in wetter areas with several centimeters of water cover. Dunlins do not appear to feed on rocky beaches, even if prey is available. They are both diurnal and nocturnal foragers, using different techniques for day versus night feeding. During daylight hours, dunlins find their prey largely through visual cues and taste buds, being able to distinguish the difference between sand that contains worms and sand that does not. Daytime feeding utilizes a stitch feeding, or pecking motion. Stitch feeding is described as a series of rapid probes into the mud in which the bill remains in contact with the substrate and little locomotion takes place. During the night, they rely more on tactile feeding, using a deep probing motion that detects changes in water surface tension, indicating the presence of prey. The probe-feeding technique involves a single rapid probe into the mud separated by several steps, during which the bill is withdrawn. Several reasons for nocturnal feeding have been proposed. It may compensate for insufficient energy intake during the day, there may be increased availability of prey, or it may reduce the risk of predation. Behavioral differences between day and night feeding in non-breeding grounds have been observed and may support predator avoidance. During the day, predators are avoided by the entire flock, taking to the air and fleeing. Nocturnally feeding dunlins are more silent, with reduced vocalizations. In the presence of a predator, only about 60% took flight. Those that remained would freeze and lower their body to the ground. This seems to indicate that for some birds, there was a greater benefit to feeding than avoiding predators. (Holmes, 1966a; Kelsey and Hassall, 1989; Mouritsen, 1992; Mouritsen, 1994; Page, et al., 1979; Van Heezik, et al., 1983)

  • Animal Foods
  • insects
  • mollusks
  • aquatic or marine worms
  • aquatic crustaceans
  • Plant Foods
  • seeds, grains, and nuts

Predation

Predation during the summer breeding season is largely centered on nest predation and destruction of clutches. Predators vary based on specific locations, but generally include short-tailed weasels, least weasels, Arctic foxes, polar bears, and avian species such as parasitic jaegers, long-tailed jaegers, pomarine jaegers, glaucous gulls, and common ravens. Predation in southern wintering grounds is related to their exposure on the mud flats while they forage. The most common predators in this area are marsh harriers, hen harriers, Montagu's harriers, peregrine falcons, merlins, kestrels, eagle owls, long-eared owls, and short-eared owls. (Gates, et al., 2013; Mouritsen, 1992)

Ecosystem Roles

Dunlins are a predator and a prey species. They are one of many species that contribute to the overall diversity of life that is essential to the habitats of the tundra, coastal mudflats, and estuaries.

Economic Importance for Humans: Positive

During the 1800’s, dunlins were commonly hunted and some populations may still be hunted in parts of China. They have no other commercial value to humans. They are listed as an indicator species for Holarctic ecosystems by the Conservation of Arctic Flora and Fauna. They are also an indicator of a healthy wetland or estuary ecosystem. (Warnock and Gill, 1996)

Economic Importance for Humans: Negative

There are no known negative effects of dunlins to human populations.

Conservation Status

The IUCN Red List indicates a “Least Concern” status for dunlins. They do have an overall declining population trend, but because of their large geographic range, large population counts, and no immediate habitat threats they are not considered threatened. Some potential conservation concerns do exist but have not been extensively studied. Dunlins have been losing their wintering habitat due to the disappearance of estuaries, especially in the British Isles and Baltic Sea areas. DDE, selenium, and mercury have been found in various levels in their habitat in the sediments and in their food sources. The effects of these chemicals are currently unknown. (Ferns and Anderson, 1994; Warnock and Gill, 1996)

Contributors

Laurie Karpinen (author), Northern Michigan University, Alec Lindsay (editor), Northern Michigan University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

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