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Catoptrophorus semipalmatuswillet

By Tanya Dewey

Geographic Range

Willets are widespread in the Americas, breeding and wintering in coastal areas and inland wetlands from the Canadian maritime provinces and northern California south to Venezuela, Brazil, and Uruguay. They are occasionally seen in Europe and the Hawaiian Islands. (Lowther and Douglas, 2001)

Habitat

Willets are found in a wide variety of coastal habitats in winter, during migration, and during breeding season, including sandy coastlines, mudflats, and rocky intertidal zones. Western willets breed in wetlands and grasslands near water and with sparse vegetation, including croplands. They are also found along lakeshores and on salt or alkali flats. Eastern willets breed in coastal marsh and wetland habitats, including salt marshes and beaches. (Lowther and Douglas, 2001)

  • Aquatic Biomes
  • temporary pools
  • coastal

Physical Description

Willets are large, long-legged shorebirds. Their plumage is grey or brown overall and they have a distinctive white rump and broad, white wing stripe visible when in flight. They are 33 to 41 cm long and from 200 to 330 grams. Sexes are similar in plumage pattern and color, but females are slightly larger overall. Basic plumage is plain gray, alternate plumage is darker, brownish, and barred or streaked. When willets are in flight,they display their distinctive, broad, white wing stripe set against the dark primary wing coverts. They also vocalize in flight. There are two distinct populations of willets that differ in distribution, ecology, and morphology: eastern willets (Catoptrophorus semipalmatus semipalmatus) and western willets (C. s. inornatus). Western willets are larger and paler, eastern willets are slightly smaller and darker overall. Their vocalizations and habitats differ as well. Their bill and legs are grayish, but vary from light to dark. The toes are slightly webbed. (Lowther and Douglas, 2001)

Willets may be confused with other, larger shorebirds that are found in the same range, such as whimbrels (Numenius phaeopus), Hudsonian godwits (Limosa haemastica), and greater yellowlegs (Tringa melanoleuca). Whimbrels are darker overall and have a distinctly curved bill, greater yellowlegs are smaller and have yellow legs, and Hudsonian godwits have an upcurved bill that is longer and a broad, black band on the tail. (Lowther and Douglas, 2001)

  • Sexual Dimorphism
  • female larger
  • Range mass
    200 to 330 g
    7.05 to 11.63 oz
  • Range length
    33 to 41 cm
    12.99 to 16.14 in

Reproduction

Willets are monogamous. There is no information on extra pair copulations, but males tend to guard mates and females continue to advertise, potentially for extra pair copulations. Populations may vary in the strength of the pair bond. In eastern populations mates may remain together for life. In western populations, mate relationships may dissolve more frequently, but mate fidelity is still high, up to 65%. Pairs reunite on breeding grounds. Males may begin to court a new female on the breeding grounds, but will re-establish a relationship with his previous mate if she shows up. Males display to attract female attention. They fly with their wings held high above their heads and flutter their primary feathers. Females fly to the male and hover beneath him while they sing to each other. They then slowly fly to the ground together. Once the pair bond has formed, they no longer display. Another display initiates copulation. Males approach female while making a "click click" sound and flap their wings high over their heads. Females then allow male to mount. Willets make a vocalization during copulation. (Lowther and Douglas, 2001)

Willets breed from May through July, with mating occurring in May and early June. Once pairs have formed, they begin to search for a nest site together. Males lead females to a spot and settle on an area of ground, followed by the female. Nests are simple scrapes that are then lined with grass or other plant material. They are generally near good foraging habitat, where possible, and on higher ground near wetlands. Willets have one brood yearly. Females lay 4, sometimes 3, olive-buff eggs over the course of 6 days. Incubation is 22 to 29 days, averaging 25. Young willets generally can fly about 4 weeks after hatching. There is little information on sexual maturity, but males and females breed as early as their 2nd year. (Lowther and Douglas, 2001)

  • Breeding interval
    Willets breed once yearly.
  • Breeding season
    Willets mate in May and June.
  • Range eggs per season
    3 (low)
  • Average eggs per season
    4
  • Range time to hatching
    22 to 29 days
  • Average time to hatching
    25 days
  • Average fledging age
    4 weeks
  • Average time to independence
    4 weeks
  • Range age at sexual or reproductive maturity (female)
    2 (low) years
  • Range age at sexual or reproductive maturity (male)
    2 (low) years

Both males and females incubate eggs and protect the young. Young are precocial and able to walk and feed themselves within hours of hatching. Hatchlings generally leave the nest within a day of hatching. Females stay with the young for up to 2 weeks, males for 4 weeks or more. (Lowther and Douglas, 2001)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • protecting
      • male
      • female

Lifespan/Longevity

The oldest recorded willet in the wild was 10 years and 3 months old. Adult annual survival rates have been estimated at between 76 and 98%. Eggs and nestlings may be lost to predators, severe weather, or exceptionally high tides. Adults are preyed on and may collide with man-made objects, such as powerlines or windows. Avian botulism outbreaks result in mortality each year, although overall impact on populations is not well understood. (Lowther and Douglas, 2001)

  • Range lifespan
    Status: wild
    10.25 (high) years

Behavior

Willets can be active at any time of the day. Activity patterns vary with the availability of prey and are influenced by tidal patterns and the presence of moonlight. Willets use their long legs to run after prey. They generally fly relatively low, less than 150 m, and will occasionally swim. They are generally found in small groups, except during the breeding season. (Lowther and Douglas, 2001)

Willet populations vary in their migratory behavior. Some populations are resident year-round, such as those in the Antilles or in California. Other populations migrate short to long distances. Northern populations may migrate over the ocean on their way to wintering grounds, but many populations likely migrate along coastlines and waterways. Eastern willets migrate primarily along coastlines. Western willets migrate along the Mississippi River and over other inland areas. In the spring, willets migrate northwards between March and May, with the earliest recorded arrival on breeding grounds in late March. Spring migration is generally rapid and direct, whereas fall migration may be more leisurely. Willets migrate south from late July through October. Willets migrate at night in small groups. (Lowther and Douglas, 2001)

Home Range

Willets aggressively defend territories during the breeding season. Western willets generally defend territories that include nesting and foraging areas. Eastern willets more often defend separate nesting and foraging territories. In general, eastern territories are larger than western territories. These differences are influenced by available nesting and foraging habitat. In the west, nesting sites are abundant and prey is more abundant. In the east, nesting sites are limited and freshwater marshes are less productive than western saltwater marshes and wetlands. Willets do not seem to have strong fidelity to their nesting sites and few return close to the area of their hatching. Few studies have estimated home range, but a Florida study suggested that home range sizes were 0.26 to 5.90 square km. (Lowther and Douglas, 2001)

Communication and Perception

Willets are known for their distinctive "pill-will-willet" call. This call is used in agonistic interactions and when birds are alarmed, but most importantly is used in territorial defense and sexual displays. Eastern and western willets have distinctive calls, although the differences are subtle. However, eastern willet females distinguish males using their calls and prefer eastern willet males over western willet males. Willets use a repertoire of other calls, from high pitched squeaks of the young to appeasement calls (Kyah-yah), clicks, clucks, honks, and screams. Adults use vocalizations to direct their fledgling young as well. Vocalizations used during mating are sometimes accompanied by visual displays. (Lowther and Douglas, 2001)

Food Habits

Willets eat a wide variety of invertebrate prey, depending on local abundance and habitat. They eat insects, crustaceans, molluscs, polychaete worms, and occasional fish. Willets feed at all times of the day, also depending on local abundance of prey, tide patterns, and moonlight. They use several foraging strategies: chasing prey down visually and using their bills to probe for prey in substrates or turn over objects to find prey underneath. They may also walk through shallow water with their bills open and held in the water to hunt by touch for prey or swim on the water and pluck prey from the surface. They may defend foraging territories in their wintering range, or they may abandon territories and forage with others in areas of abundant prey. (Lowther and Douglas, 2001)

Prey recorded in western willets during breeding include water scavenger beetles (Hydrophilidae), diving beetles (Dytiscidae), snout beetles (Curculionidae), spiders (Araneae), and fish (Cypriniformes). In winter, western willets have been recorded eating shorecrabs (Hemigrapsus), brachyuran crabs (Uca princeps, Uca crenulata), crabs (Pachygrapsus), clams (Macoma, Gemma gemma), nereid worms (Neanthes), mussels (Mytilus), whelks (Nassariidae), and others. (Lowther and Douglas, 2001)

Eastern willets eat primarily marine coastal prey, including fiddler crabs (Uca minax, Uca pugnax, Uca pugilator, Sesarma cinerea, Sesarma reticulatum), mole crabs (Emerita talpoida), amphipods (Corophium volutator), and other marine invertebrates. (Lowther and Douglas, 2001)

  • Animal Foods
  • insects
  • mollusks
  • aquatic or marine worms
  • aquatic crustaceans

Predation

Willets use vocalizations to warn others of the presence of a predator and they will gather to mob predators, especially after the young have hatched on the breeding grounds and during the winter season. During nesting, willet parents defend their young and will attack predators. In response to avian predators, willets sometimes crouch or hide, rather than taking flight. Most predation on willets is on eggs and young. Adults are mainly taken by raptors, or terrestrial predators when they are on a nest. Reported predators on eggs include northern harriers (Circus cyaneus), Cooper's hawks (Accipiter cooperii), red-shouldered hawks (Buteo lineatus), fish crows (Corvus ossifragus), common ravens (Corvus corax), American crows (Corvus brachyrhynchos), raccoons (Procyon lotor), red foxes (Vulpes vulpes), coyotes (Canis latrans), rat snakes (Pantherophis obsoletus), and feral dogs (Canis lupus familiaris). Fish crows and American crows hunt in groups of 3 for willet nests and cooperate to drive off adults while they take the eggs. Adults and young are taken by Swainson's hawks (Buteo swainsoni), northern harriers (Circus cyaneus), peregrine falcons (Falco peregrinus), red-tailed hawks (Buteo jamaicensis), Cooper's hawks (Accipiter cooperi), and herring gulls (Larus argentatus). There are many other potential predators, including other raptors, snakes, and terrestrial predators, such as mink, otters, and skunks. (Lowther and Douglas, 2001)

Ecosystem Roles

Willets compete directly for food with a wide variety of similarly-sized shorebirds and often interact aggressively over food and space. They have been recorded competing with long-billed curlews (Numenius americanus), least sandpipers (Calidris minutilla), common terns (Sterna hirundo), least terns (Sterna antillarum), American crows (Corvus brachyrhycnhos), Wilson's phalaropes (Phalaropus tricolor), greater yellowlegs (Tringa melanoleuca), killdeer (Charadrius vociferus), dowitchers (Limnodromus), Wilson's plovers (Charadrius wilsonia), fish crows (Corvus osifragus), marbled godwits (Limosa fedoa), and gulls (Larus). (Lowther and Douglas, 2001)

Willets are parasitized by a wide variety of internal parasites, including numerous species of flukes (Trematoda), tapeworms (Cestoda), roundworms (Nematoda), and spiny-headed worms (Acanthocephala). American dog ticks (Dermacentor variabilis) have been recorded as ectoparasites. They are also susceptible to avian botulism. New species of worms discovered in willets include Parvatrema borinquenae, Parvatrema bushi, and Paragymnophallus kinsellai. (Lowther and Douglas, 2001)

Mutualist Species
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Willets were once eaten and eggs and young were collected for markets. They are interesting and charismatic shorebirds.

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no adverse effects of willets on humans.

Conservation Status

Willets have a large geographic range and relatively large population sizes. There don't seem to be any significant declines in population recently. They are considered "least concern" by the IUCN and are protected by the U.S. Migratory Bird Act. However, the habitats they depend on for breeding, migration, and wintering are increasingly modified or destroyed and contaminated by pesticide accumulation and oil. Grassland habitats are especially imperiled worldwide, these are critical for breeding in western willets especially. Also, coastal marshes, important foraging habitats for willets, have been extensively destroyed and degraded. (Lowther and Douglas, 2001)

Other Comments

Recent genetic evidence suggests that willets fall within the genus Tringa. The American Ornithological Union has recognized willets as Tringa semipalmata rather than Catoptrophorus semipalmatus. (Lowther and Douglas, 2001)

Contributors

Tanya Dewey (author), Animal Diversity Web.

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

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

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.

crepuscular

active at dawn and dusk

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
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.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

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).

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.

nocturnal

active during the night

oviparous

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

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

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).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

Lowther, P., H. Douglas. 2001. Willet (Catoptrophorus semipalmatus). The Birds of North America Online, 579: 1-20. Accessed April 15, 2009 at http://bna.birds.cornell.edu.proxy.lib.umich.edu/bna/species/579.

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