Snowy plover
Snowy plover | |
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Male in breeding plumage on Morro Strand State Beach, California | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Charadriiformes |
Family: | Charadriidae |
Genus: | Anarhynchus |
Species: | A. nivosus
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Binomial name | |
Anarhynchus nivosus (Cassin, 1858)
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Breeding range Resident range Non-breeding range
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The snowy plover (Anarhynchus nivosus) is a small
Snowy plovers are pale brown above and white below, with a white band on the hind neck. During the breeding season, males have black patches behind the eye and on the side of the neck; the neck patches are separated from each other and do not form a continuous breast band as in many other plovers. Snowy plovers can also be distinguished from other plovers in having an all-black and slender bill, and gray to black legs. The typical call is a repeated "tu-wheet".
This plover inhabits open areas in which vegetation is absent or sparse, in particular coastal sand beaches and shores of salt or soda lakes, where it feeds on invertebrates such as crustaceans, worms, beetles, and flies. At the beginning of the breeding season, males excavate multiple nest scrapes that are advertised to females; one of these scrapes is later selected for breeding. Some females will desert their brood soon after the chicks hatch to re-mate with another male, while their first mate will continue to rear the chicks. Such polygamy is uncommon in birds, and is possibly a strategy to maximize breeding success. There are more males than females – 1.4 times as many in California – and the more pronounced this sex ratio imbalance is, the more females engage in polyandrous behavior.
The snowy plover is listed as
Taxonomy and systematics
The snowy plover was first described by John Cassin in 1858 as Aegialitis nivosa, based on a skin collected in 1854 by William P. Trowbridge in Presidio, which later became part of San Francisco.[2] This skin, the holotype of the species, was subsequently lost. Although originally part of the collection of the National Museum of Natural History, it was given to the collector Henry E. Dresser of England in 1872. In 1898, the Dresser collection was transferred to the Victoria University of Manchester, but the skin was apparently not part of this transfer. Joseph Grinnell, who attempted to locate the holotype in 1931, suggested that Dresser may have been unaware of the specimen's significance and may have given it elsewhere.[3]: 271–272 The snowy plover is one of the best-studied endemic shorebirds of the Americas, although most of this research was carried out on western North American populations, with few monitoring programs targeting the South American and eastern North American populations.[4]
The snowy plover appears to be most closely related to the Kentish, the white fronted, the Malaysian, the chestnut-banded, and the red-capped plover, as shown in a cladogram from a 2015 study:[8][11][12]
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The snowy plover is closely related, and visually similar, to the Kentish plover of
Subspecies
Two to three subspecies are commonly recognized:[8][9]
- Louisiana.[8]
- Anarhynchus nivosus tenuirostris (Lawrence, 1862): The Cuban snowy plover, found in North America east of Louisiana. The distinction of this subspecies from the nivosus subspecies is contested, but two genetic analyses in 2007 and 2020 have supported its separation.[15][4]
- Anarhynchus nivosus occidentalis (Cabanis, 1872): Found on the Pacific coast of South America. It is slightly larger than the nominate subspecies, the lore (the area between eye and beak) is white, and the black patch on the forehead is slightly broader.[8]
A 2020 study suggested that the snowy plover populations can be subdivided into four distinct demes (groups of individuals more genetically similar to each other than to other individuals): The western nivosus deme in western North America, the eastern nivosus deme in Florida, the tenuirostris deme on the Caribbean islands and Bermuda, and the occidentalis deme in South America. The study found little genetic exchange between these demes, except for a strong migration from the western to the eastern nivosus deme (but not vice versa).[4]
Description
The snowy plover is a plump shorebird with a large head, a short and slender bill, and short neck and tail. It is a small plover, with adults ranging from 15 to 17 cm (5.9 to 6.7 in) in length, from 34 to 43.2 cm (13.4 to 17.0 in) in wingspan, and from 40 to 43 g (1.4 to 1.5 oz) in weight. Its body is typically held horizontally.[16] Compared to other plovers, its legs are relatively long and its wings short.[17] The bill is black, the iris dark brown, and the legs gray to black.[8]
Snowy plovers are pale brown above and white below, with a white band on the hind neck and a smudgy eyestripe (absent in the South American subspecies). Breeding males have black patches behind the eye ("ear patch"), on the sides of the neck, and on the forehead. In males, the crown may be reddish at the start of the breeding season. The breeding female is slightly duller, and typically one or more of the patches are partly or completely brown. The neck patches on each side are well separated and rarely joined at the front, giving the appearance of a "broken" breast band in contrast to the continuous breast band in many other plovers. Outside the breeding season, the neck and ear patches are pale and the forehead patch is absent, and plumages of males and females cannot be distinguished. Newly hatched chicks have pale upper sides with brown to black spots and are white below.[8][17]
Similar species within its range include the piping plover, the collared plover, the semipalmated plover, and Wilson's plover. Amongst other features, the snowy plover differs from these species in its slender and entirely black bill (shorter and thicker in piping plover and longer and thicker in Wilson's plover, and with orange base in piping and breeding semipalmated plover), in its gray to black legs (orange or yellow in piping, collared, and semipalmated plover), and the "broken" breast band (usually complete in semipalmated, Wilson's, and breeding collared plovers).[8][18]
Vocalizations
The typical call is a repeated "tu-wheet" given in a wide range of contexts.[8][16] In males, these include advertisement while standing in territories and courtship. In both sexes, the call may be given in situations of threat, aggression, distress, and alarm. This call differs between sexes, being shorter, quieter, and hoarser in the female. Other calls include a repeated "purrt" that is given during breeding season, for example while flying from nest sites or when other plovers intrude their territory. A single "churr" is mostly given by males while defending territory or offspring from other plovers. Outside the breeding season, a repeated "ti" is given when disturbed while resting, and is often followed by flight. Chicks make a "peep" call from up to two days before hatching while still in the egg, and until their first flight.[8]
Distribution and habitat
The snowy plover is distributed along the Pacific coast of North and South America, in areas inland of the US and Mexico, along the coast of the Gulf of Mexico, and on the Caribbean islands and Bermuda.[8][4] On the Pacific coast, it breeds from south Washington down to Oaxaca in Mexico, and non-breeding individuals can be found as far south as Panama. In South America, it breeds from south Ecuador to Chiloé Island in Chile. In the Caribbean, breeding occurs eastwards as far as the Virgin Islands and Margarita Island. The coastal populations consist of both migratory and residential birds; migration occurs over relatively short distances north- or southward along the coast. Inland breeding populations exist in the US eastward to the Great Plains of Kansas and Oklahoma, as well as in Mexico north of Mexico City. These populations are mostly migratory, with western populations migrating to the Pacific coast, and the Great Plains populations to the Gulf of Mexico coast. Breeding has been recorded at elevations up to 3,000 m (9,800 ft).[8]
The species inhabits open areas in which vegetation is absent or sparse, in particular coastal sand beaches and shores of salt or soda lakes. It also breeds on river bars that are located close to the coast, and adopts human-made habitats such as wastewater and salt evaporation ponds, dammed lakes, and dredge spoils. It requires the proximity of water, although it may breed on salt flats where only very little water remains.[8]
Behavior and ecology
Feeding
The species feeds on invertebrates such as
Territoriality and roosting
At the beginning of the breeding season, the male, while still unpaired, will establish and defend a territory, which is then advertised to a female by calling and excavating scrapes. A pair will continue to defend the territory. After the chicks hatch, the family will soon begin to move around, when the adults will defend the surrounding radius rather than a fixed territory. When defending a territory, males may attempt to intimidate intruders by using the "Upright Display" posture, in which the body is upright with erected breast feathers. They may also run or fly at, or fight with intruders. Fighting may involve jumping at each other breast-to-breast with flapping wings and mutual pecking and shoving. In some cases, combatants pull on each other's feathers, and may even pull out a tail feather. Fights with intermittent short breaks can last up to 1.5 hours. Territories are defended not only against other snowy plovers but also against some other bird species, including semipalmated plovers and whimbrels. Territories are probably not important for protecting food resources, as the plovers often feed in flocks up to 6 km (3.7 mi) away from their territories. In Kansas and Oklahoma, where the birds are more stationary, protection of feeding grounds could be more important. The size of territories is variable, and sizes between 0.1 and 1 ha (11,000 and 108,000 sq ft) have been reported.[8]
Outside the breeding season, snowy plovers will often roost in groups of several to more than 300 birds. Roosting places are typically on the ground, often in depressions such as footprints (including those of humans) and vehicle tracks or behind objects such as driftwood.[8]
Breeding
Snowy plovers are facultatively polygamous, with females, and less frequently males, often abandoning their mate soon after the chicks have hatched. The deserting female will then pair with a new male and renest, sometimes a few hundred kilometers away from its first brood, while the male will continue to rear the chicks.[8] A 2021 study of a population at Ceuta , Mexico, found that females are more likely to abandon their broods when the chicks are likely to survive even in their absence, or when the chicks have a low probability of survival. The polygamy in this species could therefore be a strategy to maximize breeding success.[19] Polygamy is most pronounced where the breeding season is long, when birds may start two, and sometimes three, broods per season. On the other hand, birds do generally not brood twice in the Great Plains, where the breeding season is short. A biased sex ratio also appears to favor polygamy: males are generally more common than females, with one study reporting that males were 1.4 times more common than females in California. The causes for such pronounced sex ratios are unknown. Rarely, males breed with two females at the same time. Pairs can also be reestablished in the next breeding season, which occurred in 32 to 45% of cases in central California, or within the same season in the third breeding attempt of the female.[8] The polygamous mating system of the snowy plover is uncommon in birds, but the closely related Kentish plover shows a similar behavior.[5]
Snowy plovers nest in nest scrapes that are excavated by the male as an important part of the courtship ritual. In the coastal areas of California, males excavated an average of 5.6 scrapes per territory. A scrape may be constructed within a few minutes, often near conspicuous landmarks such as rocks and grass patches. One of these scrapes is later selected by the pair for nesting, commonly the scrape where most copulations took place. Both before and during incubation, the adults continue to line the nest with small objects such as stones and shell pieces. Where the ground is too hard to construct scrapes, other depressions such as animal and vehicle tracks are chosen.[8]
The species lays three eggs on average, but clutch size ranges from two to six eggs. When only a single egg is produced, the clutch is usually abandoned. Eggs are oval or asymmetric in shape and have a matte and smooth surface. In coastal California, they average at 31 mm (1.2 in) in length, 23 mm (0.91 in) in width, and 8.5 grams (0.30 oz) in weight, which accounts for 20% of the body weight of the female. Egg color is brownish-yellow, with dark brown or black speckles that become more numerous towards the blunt end of the egg. The female lays one egg every 47 to 118 hours until the clutch is complete. The time interval between egg laying and hatching varies geographically and seasonally, ranging between 23 and 49 days. Continuous incubation starts upon clutch completion; while still incomplete, males and females spend only about a quarter of the daytime incubating. In coastal areas of California, females tend to incubate during the day, while males incubate at night. The reason for this pattern is unclear, and hypotheses include a need of the female to feed at night to regain energy lost from egg laying and the need of the male to defend the territory during daytime. Under hot conditions greater 40 °C (104 °F), the male and female take turns at least once per hour.[8]
A day before hatching, chicks and parents begin to communicate by calling. After hatching, the parents will carry eggshells away from the nest. The chicks are
Predators and mortality
Adults are preyed upon by
Common diseases include
Status and conservation
The snowy plover is among the rarest
Causes of decline
Habitat degradation is a major cause for the declines in both coastal and inland populations in the US. Many coastal beaches have been developed for recreational use. Periodic raking of beaches to remove garbage and natural debris such as kelp causes plovers to abandon breeding areas, and reduces biodiversity and biomass of the invertebrates the plovers feed on. Dune habitat was lost to the
On US beaches, disturbance by humans and dogs is another significant cause for the abandonment of areas. One 2001 study found that at a public beach at
Several additional threats have been documented. Predation on chicks and eggs by crows, ravens, skunks, and invasive red foxes has intensified in some areas. Crows and ravens may be attracted to plover breeding areas by human food sources.[20][8][25] Several instances have been documented where environmental pollution affected populations. Oil spills have been a repeated threat, such as the New Carissa spill of 1999 that is known to have killed a minimum of 45 plovers. At Point Reyes National Seashore, mercury contamination has been identified as the cause for a high proportion of unhatched eggs. A 2018 study found that 98% of analyzed plovers in the Southern Great Plains had blood selenium levels exceeding the toxicity threshold.[21] Discarded monofilament fishing lines are a known threat, but their impact on populations is unknown.[8] In the future, effects of climate change, such as droughts and habitat loss due to sea level rise, are likely to become significant threats.[1][26]
Conservation measures
In 1993, the Pacific coast population of the US was listed as a "threatened" under the
Even though the global population is declining, conservation efforts have led to local increases in plover populations. In central Chile, protection of a small stretch of beach against human disturbance resulted in an increase of the local population, as was reported in 2001.[27][24] The first instance of snowy plovers reoccupying a breeding area following its protection from human disturbance was documented in 2006 at Sands Beach, Santa Barbara County, where barriers are in use since 2001.[24] As of March 2023, conservation efforts have been particularly successful in Oregon, where numbers increased to 483 birds, from just 55 birds in 1993. This increase was possible due to roping off 40–50 mi (64–80 km) of dry sand on beaches, as well as the removal of invasive grasses. In California, the population is estimated at 1,830 birds as of March 2023.[25]
References
- ^ . Retrieved 22 July 2023.
- ^ Baird, S.F.; Cassin, J.; Lawrence, G.N. (1858). Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean. Vol. 9. United States War Department. p. 696. Archived from the original on 19 November 2023. Retrieved 19 November 2023.
- ^ Grinnell, J. (1932). "Type localities of birds described from California" (PDF). University of California Publications in Zoology. 38 (3): 243–324. Archived (PDF) from the original on 18 June 2022. Retrieved 19 November 2023.
- ^ S2CID 211554642.
- ^ S2CID 186943645.
- from the original on 11 October 2023. Retrieved 10 October 2023.
- PMID 24205094.
- ^ from the original on 11 October 2023. Retrieved 17 November 2023.
- ^ Rasmussen, Pamela (eds.). "IOC World Bird List 14.1"(xlsx). Retrieved 20 December 2023.
- OCLC 1040808348.
- ^ S2CID 187918372.
- PMID 25916188.
- ^ S2CID 42282029.
- (PDF) from the original on 14 December 2023. Retrieved 19 November 2023.
- from the original on 14 December 2023. Retrieved 3 November 2023.
- ^ a b c "Snowy Plover Identification, All About Birds, Cornell Lab of Ornithology". www.allaboutbirds.org. Archived from the original on 4 September 2020. Retrieved 30 September 2020.
- ^ ISBN 978-0-593-53610-0.
- ISBN 978-0-547-15270-7.
- from the original on 14 December 2023. Retrieved 12 November 2023.
- ^ a b c d e Stinson, D.W. (2016). "Periodic status review for the Snowy Plover (2022)" (PDF). wdfw.wa.gov. Washington Department of Fish & Wildlife. Archived (PDF) from the original on 31 October 2023. Retrieved 31 October 2023.
- ^ from the original on 14 December 2023. Retrieved 12 November 2023.
- ^ ISSN 0006-3207.
- from the original on 31 October 2023. Retrieved 31 October 2023.
- ^ from the original on 14 December 2023. Retrieved 12 November 2023.
- ^ a b Urness, Z. (20 March 2023). "Western snowy plovers go from near extinction to expanded growth on Oregon Coast". Salem Statesman Journal. Archived from the original on 14 December 2023. Retrieved 3 August 2023.
- S2CID 86135649.
- from the original on 14 December 2023. Retrieved 13 November 2023.
External links
- Western Snowy Plover - Tools and Resources for Recovery
- "Charadrius nivosus". Integrated Taxonomic Information System.
- BirdLife species factsheet for Charadrius nivosus
- "Charadrius nivosus". Avibase.
- Snowy plover photo gallery at VIREO (Drexel University)
- Charadrius nivosus in Field Guide: Birds of the World on Flickr