''Selenidera'' is a

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

containing six species of dichromatic toucanets in the

toucan Toucans (, ) are members of the Neotropical near passerine bird family Ramphastidae. The Ramphastidae are most closely related to the American barbets. They are brightly marked and have large, often colorful bills. The family includes five ge ...

family Ramphastidae. They are found in lowland

rainforest Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainfores ...

(below ) in tropical South America with one species in Central America. All the species have green upper-parts, red undertail-coverts and a patch of bare blue or blue-green skin around the eye. Unlike most other toucans, the sexes are different in colour (

sexually dichromatic 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 anim ...

; hence the name dichromatic toucanets). The males all have a black crown, nape, throat and breast and an orange/yellow auricular streak. The females of most species have the black sections in the male replaced by rich brown and a reduced/absent auricular streak, while the female of one species, the

Guianan toucanet The Guianan toucanet, or Guyana toucanet (''Selenidera piperivora'') is a near-passerine bird in the toucan family Ramphastidae. It is found in Brazil, French Guiana, Guyana, Suriname, and Venezuela.Remsen, J. V., Jr., J. I. Areta, E. Bonaccors ...

, has grey underparts and a rufous nuchal collar, and the female of another, the

yellow-eared toucanet The yellow-eared toucanet (''Selenidera spectabilis'') is a near-passerine bird in the toucan family Ramphastidae. It is found from Honduras to Ecuador.Clements, J. F., T. S. Schulenberg, M. J. Iliff, T. A. Fredericks, J. A. Gerbracht, D. Lepag ...

, resemble the male except for its brown crown and lack of an auricular streak. The calls are low-pitched and croaking. Most species are relatively small toucans with a total length of , but the yellow-eared toucanet typically has a total length of approx. . They tend to forage alone or in pairs, feeding mainly on fruit. They are fairly quiet and elusive birds which generally keep to dense cover. The

nest A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materia ...

is a cavity in a tree which the birds enlarge by excavating with their bills. The white eggs are incubated by both parents.

Taxonomy and systematics

The genus ''Selenidera'' has six species considered to belong to the genus:

Species

Speciation in ''Selenidera''

The genus ''Selenidera'' was used by the German biologist

Jürgen Haffer Jürgen Haffer (9 December 1932 in Berlin – 26 April 2010 in Essen) was a German ornithologist, biogeographer, and geologist. He is most remembered for his theory of Amazonian forest refugia during the Pleistocene that would have contributed t ...

as an example of the " refugia" hypothesis of

speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

. He suggested that the different species evolved from one common ancestor whose population was fragmented by the retreat of the rainforest into the wettest areas during periods of dry climate in the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

epoch. The single species developed into several species in these isolated refugia. When the forest expanded again during a wetter period, the ranges of the different species expanded until they came into contact with each other, forming a complementary pattern of distributions. The refugial hypothesis is somewhat disputed as there is little field data to support or reject it. In any case it is simply one of several competing hypotheses to explain Amazonian biodiversity, each of which may or may not provide a good explanation for the geographical pattern found in any one group of

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

. In the present case, the refugia hypothesis is probably correct, as the Amazonian ''Selenidera'' have distributions ''centered'' on major river systems; they might be considered a superspecies. Some other birds from the region, in contrast, have

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

that are ''separated'' by the major rivers, which thus apparently acted as natural barriers to

gene flow In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...

. Whether a refugia or a barrier model describes superspecies distribution in the Amazonian basin most appropriately thus seems to be a direct consequence of the animals' ability to cross major waterways. But even in the ''Selenidera'' toucanets which, though largely sedentary, are technically able to disperse widely, the

Amazon River The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America is the largest river by discharge volume of water in the world, and the disputed longest river system in the world in comparison to the Nile. The headwaters of t ...

forms a barrier that was simply too wide to cross in significant numbers as to inhibit speciation.

References

*Jürgen Haffer (1969) Speciation in Amazonian Forest Birds, ''Science'', 165:131-137 *Jorge R. Rodriguez Mata, Francisco Erize & Maurice Rumboll (2006) ''A Field Guide to the Birds of South America'', Collins, London * Christopher Perrins, ''ed.'' (2004) ''The New Encyclopedia of Birds'', Oxford University Press, Oxford {{Taxonbar, from=Q257205 Toucans Bird genera