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Waders or shorebirds are birds of the order Charadriiformes commonly found wikt:wade#Etymology 1, wading along shorelines and mudflats in order to foraging, forage for food crawling or burrowing in the mud and sand, usually small
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s such as
aquatic insect
Aquatic insects or water insects live some portion of their life cycle in the water. They feed in the same ways as other insects. Some ''diving'' insects, such as predatory diving beetles, can hunt for food underwater where land-living insects ca ...
s or
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
s. The term "wader" is used in Europe, while "shorebird" is used in North America, where "wader" may be used instead to refer to long-legged wading birds such as
storks and
heron
The herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 72 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genera ''Botaurus'' and ''Ixobrychu ...
s.
There are about 210
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
of wader, most of which live in wetland or coastal environments. Many species of Arctic and temperate regions are strongly
migratory, but
tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
birds are often resident, or move only in response to rainfall patterns. Some of the Arctic species, such as the
little stint, are amongst the longest distance migrants, spending the non-
breeding season
Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and ch ...
in the
southern hemisphere.
Many of the smaller species found in
coastal habitats, particularly but not exclusively the
calidrids, are often named as "sandpipers", but this term does not have a strict meaning, since the
upland sandpiper is a grassland species.
The smallest member of this group is the
least sandpiper, small adults of which can weigh as little as and measure just over . The largest species is believed to be the
Far Eastern curlew, at about and , although the
beach thick-knee
The beach stone-curlew (''Esacus magnirostris'') also known as beach thick-knee is a large, ground-dwelling bird that occurs in Australasia, the islands of South-east Asia. At and , it is one of the world's largest shorebirds. At a mean of in ...
is the heaviest at about .
Taxonomy
In the
Sibley-Ahlquist taxonomy, waders and many other groups are subsumed into a greatly enlarged order
Ciconiiformes. However, the classification of the Charadriiformes is one of the weakest points of the Sibley-Ahlquist taxonomy, as
DNA–DNA hybridization has turned out to be incapable of properly resolving the interrelationships of the group. Formerly, the waders were united in a single suborder ''Charadrii'', but this has turned out to be a "
wastebasket taxon", uniting no fewer than four charadriiform lineages in a
paraphyletic
In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
assemblage. However, it indicated that the
plains wanderer
The plains-wanderer (''Pedionomus torquatus'') is a bird, the only representative of family Pedionomidae and genus ''Pedionomus''. It is endemic to Australia. The majority of the remaining population is found in the Riverina region of New So ...
actually belonged into one of them. Following recent studies (Ericson et al., 2003; Paton et al., 2003; Thomas et al., 2004a, b; van Tuinen et al., 2004; Paton & Baker, 2006), the waders may be more accurately subdivided.
The waders are a group of two Charadriiformes
suborders which include 13
families. Species in the third Charadriiforme suborder,
Lari, are not considered as waders.
* Suborder Charadrii
** Family
Burhinidae – stone-curlews, thick-knees (10 species)
** Family
Pluvianellidae
The Magellanic plover (''Pluvianellus socialis'') is a rare wader found only in southernmost South America.
Taxonomy
It was long placed in with the other plovers in the family Charadriidae; however, behavioural evidence suggested they were disti ...
– Magellanic plover
** Family
Chionidae – sheathbills (2 species)
** Family
Pluvianidae – Egyptian plover
** Family
Charadriidae – plovers (68 species)
** Family
Recurvirostridae – stilts, avocets (10 species)
** Family
Ibidorhynchidae – ibisbill
** Family
Haematopodidae – oystercatchers (12 species)
* Suborder Scolopaci
** Family
Rostratulidae – painted-snipes (3 species)
** Family
Jacanidae – jacanas (8 species)
** Family
Pedionomidae – plains-wanderer
** Family
Thinocoridae – seedsnipes (4 species)
** Family
Scolopacidae
Sandpipers are a large family, Scolopacidae, of waders. They include many species called sandpipers, as well as those called by names such as curlew and snipe. The majority of these species eat small invertebrates picked out of the mud or soil ...
– sandpipers, snipes (98 species)
* Suborder Lari
** Family
Turnicidae
** Family
Dromadidae
The crab-plover or crab plover (''Dromas ardeola)'' is a bird related to the waders, but sufficiently distinctive to merit its own family Dromadidae. Its relationship within the Charadriiformes is unclear, some have considered it to be closely ...
** Family
Glareolidae
Characteristics
Shorebirds is a blanket term used to refer to multiple bird species that live in wet, coastal environments. Because most these species spend much of their time near bodies of water, many have long legs suitable for wading (hence the name ‘Waders’). Some species prefer locations with rocks or mud. Many shorebirds display migratory patterns and often migrate before breeding season. These behaviors explain the long wing lengths observed in species, and can also account for the efficient metabolisms that give the birds energy during long
migrations.
["Explore the World With Shorebirds." U.S. Fish and Wildlife Service, 1 Aug. 2004. Web.<http://www.fws.gov/alaska/external/education/pdf/Chap4.pdf>.]
The majority of species eat small
invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
s picked out of
mud or exposed soil. Different lengths of bills enable different species to feed in the same habitat, particularly on the coast, without direct competition for food. Many waders have sensitive nerve endings at the end of their bills which enable them to detect prey items hidden in mud or soft soil. Some larger species, particularly those adapted to drier habitats will take larger prey including
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...
s and small
reptiles.
Sexual dimorphism
Shorebirds, like many other animals, exhibit
phenotypic
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...
differences between males and females, also known as
sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
. In shorebirds, various sexual dimorphisms are seen, including, but not limited to, size (e.g. body size, bill size), color, and agility. In
polygynous species, where one male individual mates with multiple female partners over his lifetime, dimorphisms tend to be more diverse.
In
monogamous species, where male individuals mate with a single female partner, males typically do not have distinctive dimorphic characteristics such as colored feathers, but they still tend to be larger in size compared to females. The suborder Charadrii displays the widest range of sexual dimorphisms seen in the order Charadriiformes.
[Székely, Tamás, John D. Reynolds, and Jordi Figuerola. 2000. Sexual Size Dimorphism In Shorebirds, Gulls, And Alcids: The Influence Of Sexual And Natural Selection. 54(4): 1404-413]
However, cases of sexual monomorphism, where there are no distinguishing physical features besides external genitalia, are also seen in this order.
[Lindenfors, P., T. Szekely, and J. D. Reynolds. "Directional Changes in Sexual Size Dimorphism in Shorebirds, Gulls and Alcids." Journal of Evolutionary Biology J. Evolution Biol: 930-38. Print.]
Sexual selection
One of the biggest factors that leads to the development of sexual dimorphism in shorebirds is
sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (in ...
.
[Szekely, T., R. P. Freckleton, and J. D. Reynolds. "Sexual Selection Explains Rensch's Rule of Size Dimorphism in Shorebirds." ''Proceedings of the National Academy of Sciences'' (2004): 12224-2227. Print.] Males with ideal characteristics favored by females are more likely to reproduce and pass on their genetic information to their offspring better than the males who lack such characteristics. Mentioned earlier, male shorebirds are typically larger in size compared to their female counterparts. Competition between males tends to lead to sexual selection toward larger males and as a result, an increase in dimorphism. Bigger males tend to have greater access (and appeal) to female mates because their larger size aids them in defeating other competitors.
Likewise, if the species exhibits gender role reversal (where males take on roles traditionally done by females such as childcare and feeding), then males will select female mates based on traits that are the most appealing. In the
Jacana species, females compete with each other for access to male mates, so females are larger in size. Males choose female mates based on who presents herself as the strongest and who 'owns' the most territory.
Natural selection
Another factor that leads to the development of dimorphisms in species is
natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
. Natural selection focuses on traits and the environment's response to the traits in question; if the said trait increases the overall fitness of the individual possessing it, then it will be 'selected' and eventually become a permanent part of the population's gene pool. For example, depending on the food available in a shorebird specie's respective
niche
Niche may refer to:
Science
*Developmental niche, a concept for understanding the cultural context of child development
* Ecological niche, a term describing the relational position of an organism's species
*Niche differentiation, in ecology, the ...
, bigger bill sizes may be favored in all individuals.
This would essentially lead to monomorphism within the species but is subject to change once sexual selection acts on the trait. Sexual selection could give rise to males with relatively larger bills than females if males used their bills to compete with other males. If larger bill size assisted the male in gathering resources, it would also make him more attractive to female mates.
See also
*
Hybridisation in shorebirds
*
List of Charadriiformes by population
References
Sources
* Ericson, P. G. P.; Envall, I.; Irestedt, M.; & Norman, J. A. (2003). Inter-familial relationships of the shorebirds (Aves: Charadriiformes) based on nuclear DNA sequence data. ''
BMC Evol. Biol.'' 3: 16.
PDF fulltext*Pandiyan, J. and S. Asokan. 2015. Habitat use of pattern of tidal mud and sandflats by shorebirds (charadriiformes) Wintering in southern India. Coastal Conservation https://doi.org/10.1007/s11852-015-0413-9.
* Paton, Tara A.; & Baker, Allan J. (2006). Sequences from 14 mitochondrial genes provide a well-supported phylogeny of the Charadriiform birds congruent with the nuclear RAG-1 tree. ''Molecular Phylogenetics and Evolution'' 39(3): 657–667. (HTML abstract)
* Paton, T. A.; Baker, A. J.; Groth, J. G.; & Barrowclough, G. F. (2003). RAG-1 sequences resolve phylogenetic relationships within charadriiform birds. ''Molecular Phylogenetics and Evolution'' 29: 268–278. (HTML abstract)
* Thomas, Gavin H.; Wills, Matthew A. & Székely, Tamás (2004a). Phylogeny of shorebirds, gulls, and alcids (Aves: Charadrii) from the cytochrome-''b'' gene: parsimony, Bayesian inference, minimum evolution, and quartet puzzling. ''Molecular Phylogenetics and Evolution'' 30(3): 516–526. (HTML abstract)
* Thomas, Gavin H.; Wills, Matthew A.; & Székely, Tamás (2004b). A supertree approach to shorebird phylogeny. ''
BMC Evol. Biol.'' 4: 28.
PDF fulltextSupplementary Material
* van Tuinen, Marcel; Waterhouse, David; & Dyke, Gareth J. (2004). Avian molecular systematics on the rebound: a fresh look at modern shorebird phylogenetic relationships. ''Journal of Avian Biology'' 35(3): 191–194
PDF fulltext
* Explore the World With Shorebirds. (2004). U.S. Fish and Wildlife Service. Web. http://digitalmedia.fws.gov/cdm/ref/collection/document/id/1598
* Lindenfors, P.; Szekely, T.; and Reynolds, J. D. (2003). Directional Changes in Sexual Size Dimorphism in Shorebirds, Gulls and Alcids. Journal of Evolutionary Biology J Evolution Biol: 930–38. Print.
* Szekely, T.; Freckleton, R.; & Reynolds, J. (2004). Sexual selection explains Rensch's rule of size dimorphism in shorebirds. ''Proceedings of the National Academy of Sciences.'' 101(33): 12224–12227.
* Szekely, Tamas; John D. Reynolds; and Jordi Figuerola. (2000) Sexual Size Dimorphism in Shorebirds, Gulls, and Alcids: The Influence of Sexual and Natural Selection. Evolution 54(4): 1404–413.
External links
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Bird common names