Charadriiformes


Charadriiformes is a diverse order of small to medium-large birds. It includes about 390 species and has members in all parts of the world. Most charadriiform birds live near water and eat invertebrates or other small animals; however, some are pelagic, others frequent deserts, and a few are found in dense forest. Members of this group can also collectively be referred to as shorebirds.

Taxonomy, systematics and evolution

The order was formerly divided into three suborders:
  • The waders : typical shorebirds, most of which feed by probing in the mud or picking items off the surface in both coastal and freshwater environments.
  • The gulls and their allies : these are generally larger species which take fish from the sea. Several gulls and skuas will also take food items from beaches, or rob smaller species, and some have become adapted to inland environments.
  • The auks are coastal species which nest on sea cliffs and "fly" underwater to catch fish.
The Sibley-Ahlquist taxonomy lumps all the Charadriiformes together with other seabirds and birds of prey into a greatly enlarged order Ciconiiformes. However, the resolution of the DNA-DNA hybridization technique used by Sibley & Ahlquist was not sufficient to properly resolve the relationships in this group, and indeed it appears as if the Charadriiformes constitute a single large and very distinctive lineage of modern birds of their own.
The auks, usually considered distinct because of their peculiar morphology, are more likely related to gulls, the "distinctness" being a result of adaptation for diving.

Families

The order Charadriiformes contains 3 suborders, 19 families and 391 species.

Evolutionary history

That the Charadriiformes are an ancient group is also borne out by the fossil record. Alongside the Anseriformes, the Charadriiformes are the only other order of modern bird to have an established fossil record within the late Cretaceous, alongside the other dinosaurs. Much of the Neornithes' fossil record around the Cretaceous–Paleogene extinction event is made up of bits and pieces of birds which resemble this order. In many, this is probably due to convergent evolution brought about by semiaquatic habits. Specimen VI 9901 is probably a basal charadriiform somewhat reminiscent of a thick-knee. However, more complete remains of undisputed charadriiformes are known only from the mid-Paleogene onwards. Present-day orders emerged around the Eocene-Oligocene boundary, roughly 35–30 mya. Basal or unresolved charadriiformes are:
  • "Morsoravis" - a nomen nudum?
  • Jiliniornis - charadriid?
  • Boutersemia - glareolid? jacanid?
  • Turnipax - turnicid?
  • Elorius
  • "Larus" desnoyersii - larid? stercorarid?
  • "Larus" pristinus - larid?
  • Charadriiformes gen. et sp. indet. - charadriid? scolopacid?
  • Charadriiformes gen. et sp. indet. - charadriid? scolopacid?
  • Charadriiformes gen. et sp. indet. - larid?
  • Charadriiformes gen. et sp. indet. - scolopacid? larid?
The "transitional shorebirds" are a generally Mesozoic form taxon formerly believed to constitute the common ancestors of charadriiforms, waterfowl and flamingos. They are now assumed to be mostly basal taxa of the charadriiforms and/or "higher waterbirds", which probably were two distinct lineages 65 mya already, and few if any are still believed to be related to the well-distinct waterfowl. Taxa formerly considered graculavids are:
Other wader- or gull-like birds incertae sedis, which may or may not be Charadriiformes, are:Ceramornis "Cimolopteryx" Palintropus Torotix Volgavis Eupterornis

Evolution of parental care in Charadriiformes

Shorebirds pursue a larger diversity of parental care strategies than do most other avian orders. They therefore present an attractive set of examples to support the understanding of the evolution of parental care in avians generally. The ancestral avian most likely had a female parental care system. The shorebird ancestor specifically evolved from a bi-parental care system, yet the species within the clade Scolopacidae evolved from a male parental care system. These transitions might have occurred for several reasons. Brooding density is correlated with male parental care. Male care systems in birds are shown to have a very low breeding density while female care systems in birds have a high breeding density.. Certain rates of male and female mortality, male and female egg maturation rate, and egg death rate have been associated with particular systems as well. It has also been shown that sex role reversal is motivated by the male-biased adult sex ratio. The reason for such diversity in shorebirds, compared to other birds, has yet to be understood.