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dunlin

Calidris alpina

What do they look like?

Dunlins are fairly small birds, they are 16 to 22 cm (6.5 to 8.5 in) long, have a wingspan of 32 to 44 cm (12.5 to 17.5 in), and weigh 45 to 65 g (1.6 to 2.25 ounce). Males and females are the same color, although females are larger than males. In the non-breeding season, they have a dull, gray-brown head and back with a whitish-gray underside. Before the breeding season, dunlins complete a molt that results in red plumage on their back with a large black belly patch. Due to this coloring, dunlins are sometimes called red-backed sandpipers. Young dunlins have a similar coloration as non-breeding adults, but have some black and cream striping on their back and 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, which is black, points slightly downward, and is good for probing in the mud. (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

Where do they live?

Dunlins are migratory birds that breed in Arctic and Subarctic regions, but winter in many different areas depending on where they are from. For instance, dunlins from Iceland, the British Isles, the Baltic, and Southern Scandinavia tend to winter in Morocco, Mauritania, and the Mediterranean Basin. 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)

What kind of habitat do they need?

Dunlins are mostly found in the Arctic tundra during their summer breeding season. They prefer wet marshy and dry grassy areas for nesting, with nearby lakes, shallow ponds, or river channels. After breeding in tundra areas, dunlins move to coastal estuaries and inter-tidal regions to eat before migrating south. Their winter habitat is mostly 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 high areas. Dunlins have also been seen simply flying in a large flock for the entire high-tide period. (Holmes, 1966a; Holmes, 1971; Sibley, 2001)

  • These animals are found in the following types of habitat
  • temperate
  • polar

How do they reproduce?

Dunlins mostly breed in Arctic and Subarctic areas, with a few groups breeding in the British Isles and northern Europe. Dunlins arrive in their breeding grounds just as the snow 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 establishing boundaries by flying along the borders. Females arrive shortly after and pair bonding begins. Dunlins typically remain together for the breeding season. Dunlins that arrive late may already be in a bonded pair. They have usually established a pair bond and territory by about June 15th. (Gates, et al., 2013; Holmes, 1966a)

After finding a territory, courtship and bond pairing begin when male dunlins perform flight displays. They rise from the ground to about 50 feet, and then move in a slow, wide circle, moving between gliding and hovering flights with rapid wing beats. They also perform vocalizations, which include a series of short trills and ends in a more melodic song at the landing. The smaller body size of males may allow them to perform these displays for a longer period of time, which is very important for defending a territory and attracting a mate. Males continue to show territorial displays until the eggs have hatched. Other courtship behaviors include long in-flight chases between males and females, ground level chasing and posturing between males, and nest scraping. (Blomqvist, et al., 1997; Holmes, 1966a)

Dunlins choose nesting sites in well-drained upland tundra with wet marshy ponds, lakes, and river channels. They will sometimes nest in the marsh itself, but this is usually only when all of the best sites are already taken. There are usually about 19 nests per km² to 7 nests per 100 acres. Males begin building nests as part of their courtship behavior by scraping the ground with their feet and throwing pieces of grasses into the hole. The males make several of these scrape nests. Females eventually help by stepping in and out of the hole and tossing in a few more pieces of grass. At some point, the female chooses a nest and finishes the lining. Female dunlins normally lay a 4 egg clutch, usually one egg per day. Most eggs are laid from June 12 to 18, but can start as early as June 6 or as late as July 6. Both parents help incubate the eggs for 21 to 22 days, although females are slightly more involved. Most eggs hatch between July 4 and 10. The chicks 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 can have a second brood if they lose their first, which is usually due to predation. Because producing eggs takes a lot of energy, larger females are more likely to re-nest. If they do have a second nest, it usually only includes three small eggs. As the breeding season ends, dunlins end their pair bonds and start to re-flock. By the beginning of July, males and females begin to gather in small groups. From July 15 to 30, females group together and juveniles separate from adults. 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 without the juveniles. (Gates, et al., 2013; Holmes, 1966a; Jamieson, 2012)

  • How often does reproduction occur?
    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 about 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 lead them to areas that contain food, where the chicks already know how to feed themselves. (Jamieson, 2012)

How long do they live?

Within at least one subspecies, wild adult dunlins have an average lifespan of about 5.4 years, although males have an average lifespan of 8.6 years and females average 3.9 years. However, the oldest known individual lived to be at least 24 years old. (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

How do they behave?

Dunlins are terrestrial birds that mostly walk but will sometimes run. When they fly, they stay close together in a group. They turn together in a flock by either turning at the exact same time or by shifting along the axis from head to tail, which creates a flash of color from light to dark. There does not seem to be a leader in the flock. Dunlins can fly 72 to 88 km per hour. They are very social birds that live in large flocks. Aggression is almost always related to breeding behavior. (Davis, 1980; McCabe, 1942)

Dunlins participate in preening, head-scratching, and bathing. They may increase the amount of time they spend bathing and grooming during their 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 areas, breeding and molting overlap due to the short summer season. Molting tends to happen at the same time as their movement from the tundra habitat to the coast, where the most food is 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. The sizes of their territory vary based on their subspecies and the number of individuals in a population, 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)

How do they communicate with each other?

Dunlins signal with loud, low-frequency sounds during mating displays and when defending nesting areas in the Arctic tundra breeding grounds. These vocalizations are especially useful for distance signaling in their open habitat. Parents vocalize with their young as they lead them to food sources using a low-intensity purring sound. Although their chicks are very independent, parents must lead them to food for the first few days of their life. Dunlins also call to their chicks to gather them for brooding. These birds are known for tight flying flock formations in which the entire flock will turn in a coordinated motion. This is probably due to some form of communication, although the exact type is unknown. Dunlins seem to have good eyesight and hearing, comparable to most mammals. Unlike many other bird species, dunlins have a well-developed sense of taste. Similar to other wading shore birds, dunlins forage using their sense of touch with a group of nerves at the tip of their beaks. By probing into soft, wet sand, they are able to find pressure differences in the water that can indicate a solid object. Unfortunately, they are not able to tell the difference between stones and food, and 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)

What do they eat?

Dunlins mostly eat freshwater, marine, or terrestrial invertebrates such as bivalves, worms, insect larvae, crustaceans, snails, slugs, and sometimes small fish. These birds occasionally feed in agricultural areas that are near estuaries. Adult females and juveniles sometimes eat the teeth and bones of lemmings. This may be a source of calcium, as females usually eat them when they are laying eggs. In less ideal habitats like marshes and estuaries that have become agricultural land, dunlins will also eat plants. (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)

Their foraging habitats vary based on whether they are at their summer breeding grounds in the Arctic or their 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 good for foraging. Their main winter foraging habitats are in intertidal mud flats. Dunlins prefer to forage in sorted sand and in wetter areas with several centimeters of water cover. Dunlins do not feed on rocky beaches, even if prey is available. They forage during the day and at night, but use different foraging techniques based on the time of day. In the daytime, dunlins find their prey using their vision and taste buds, using a stitch feed method, where they rapidly probing into the mud with their bill. During the night, they rely more on their sense of touch, using a probing motion that senses changes in water surface tension to tell if prey are present. There may be several reasons why they forage at night such as not receiving enough food during the day, the availability of more food at night, or the lower risk of predation at night. During the day, the entire flock avoids predators by flying away. Dunlins that eat at night are quieter and when they do see predators, they lower their body to the ground. (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

What eats them and how do they avoid being eaten?

During the summer, predators mostly prey on nests. Their predators vary based on their specific locations, but 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. In their southern wintering grounds, dunlins are often preyed on while they forage in open mud flats. 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)

What roles do they have in the ecosystem?

Dunlins are both predators and prey species. They are one of many species that contribute to the overall diversity of life in the tundra, coastal mudflats, and estuaries.

Do they cause problems?

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

How do they interact with us?

During the 1800’s, dunlins were often hunted and some populations may still be hunted in parts of China. They are considered to be an indicator of a healthy wetland or estuary ecosystem. (Warnock and Gill, 1996)

Are they endangered?

Dunlins are considered a species of "Least Concern". Overall, their population is declining, however, they have a large geographic range with no immediate habitat threats. Dunlins have been losing their wintering habitat as estuaries continue to disappear, 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.

References

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Blomqvist, D., O. Johansson, U. Unger, M. Larsson, L. Flodin. 1997. Male aerial displayand reversed sexual size dimorphism in the dunlin. Animal Behavior, 54: 1291-1299. Accessed January 22, 2014 at http://www.sciencedirect.com/science/article/pii/S0003347297905327.

Brennan, L., J. Finger, C. Buchanan, Schick, S. Herman. 1990. Stomach contents of dunlins collected in western Washington.. Northwest Nat., 71: 99-102.

Colwell, M. 1993. Shorebird community patterns in a seasonally dynamic estuary. The Condor, 95: 104-114.

Davis, J. 1980. The coordinated aerobatics of dunlin flocks. Animal Behaviour, 28: 668-673. Accessed March 19, 2014 at http://www.sciencedirect.com/science/article/pii/S0003347280801278.

Ferns, P., J. Anderson. 1994. Cadmium in the diet and body tissues of dunlins Calidris alpina, from the Bristol channel, UK. Environmental Pollution, 86: 225-231. Accessed January 22, 2014 at http://www.sciencedirect.com/science/article/pii/0269749194901945.

Gates, H., R. Lanctot, A. Powell. 2013. High Renesting Rates in Arctic-Breeding Dunlin (Calidris alpina): A Clutch-Removal Experiment. The Auk, 130: 372-380. Accessed March 12, 2014 at http://www.bioone.org/doi/abs/10.1525/auk.2013.12052.

Gill, F. 2007. Ornithology. New York, New York: W.H. Freeman and Company.

Greenwood, J. 1983. Post-nuptial primary moult in dunlin Calidris alpina. Ibis, 125: 223-228. Accessed January 22, 2014 at http://onlinelibrary.wiley.com/doi/10.1111/j.1474-919X.1983.tb03102.x/abstract.

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Hobson, K., G. Slater, D. Lank, R. Milner, R. Gardiner. 2013. Agricultural Lands Subsidize Winter Diet of the Dunlin at Two Major Estuaries. The Condor, 115: 515-524. Accessed March 12, 2014 at http://www.bioone.org/doi/abs/10.1525/cond.2013.120118.

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Warnock, N. 1989. Piracy by ring-billed gulls on dunlins. Wilson Bull, 101: 96-97.

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Wenink, P., A. Baker, M. Tilanus. 1993. Hypervariable-control-region sequences reveal global population structuring in a long-distant migrant shorebird, the Dunlin 9 (Calidris alpina). Proceedings of the National Academy of Science USA, 90: 94-98.

Wenink, P., A. Baker, H. Rosner, M. Tilanus. 1996. Global mitochondrial DNA phylogeography of holarctic breeding dunlins (Calidris alpina). Evolution, Vol. 50, No. 1: 318-330. Accessed January 22, 2014 at http://www.jstor.org/stable/2410803.

Wennerberg, L. 2001. Breeding origin and migration pattern of dunlin (Calidris alpina) revealed by mitochondrial DNA analysis. Molecular Ecology, 10: 1111-1120. Accessed January 22, 2014 at http://onlinelibrary.wiley.com/doi/10.1046/j.1365-294X.2001.01256.x/abstract.

 
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Karpinen, L. 2014. "Calidris alpina" (On-line), Animal Diversity Web. Accessed November 15, 2018 at http://www.biokids.umich.edu/accounts/Calidris_alpina/

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