Seychelles warbler | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Passeriformes |
Family: | Acrocephalidae |
Genus: | Acrocephalus |
Species: | A. sechellensis |
Binomial name | |
Acrocephalus sechellensis (Oustalet, 1877) | |
Synonyms | |
Bebrornis sechellensis [2] |
The Seychelles warbler (Acrocephalus sechellensis), also known as Seychelles brush warbler, [2] is a small songbird found on five granitic and corraline islands in the Seychelles. It is a greenish-brown bird with long legs and a long slender bill. It is primarily found in forested areas on the islands. The Seychelles warbler is a rarity in that it exhibits cooperative breeding, or alloparenting, which means that the monogamous pair is assisted by nonbreeding female helpers.
A few decades ago the Seychelles warbler was on the verge of extinction, with only 26 birds surviving on Cousin Island in 1968. Due to conservation efforts there are more than 2500 of the species alive today with viable populations on Denis, Frégate, Cousine and Aride Islands, as well as Cousin Island. [3]
The Seychelles warbler is closely related to the Rodrigues warbler (Acrocephalus rodericanus) and the two species have sometimes been placed in their own genus, Bebrornis. The two species have also been considered allied to the Malagasy genus Nesillas . A 1997 study confirmed, however, that the two species were part of a clade of Afrotropical warblers within Acrocephalus that also includes the Madagascar swamp warbler, the greater swamp warbler, the lesser swamp warbler and the Cape Verde warbler. [4] [5] [6]
The Seychelles warbler is a small, plain Acrocephalus warbler, between 13 and 14 cm (5.1–5.5 in) in length and with a wingspan of 17 cm (6.7 in). [7] It has long grey-blue legs, a long horn-coloured bill, and a reddish eye. Adults show no sexual dimorphism in their plumage. The back, wings, flanks and head are greenish-brown and the belly and breast are dirty white. The throat is a stronger white and there is a pale supercilium in front of the eye. Juvenile birds are darker with a more bluish eye.
The voice of the Seychelles warbler is described as rich and melodious, [7] similar to a human whistle. Its structure is simple and is composed of short song sequences delivered at a low frequency range. [8] The lack of a wide frequency range sets it apart from other species in its genus, such as the reed warbler, its song is similar to its closest relatives in Africa such as the greater swamp warbler.
The Seychelles warbler naturally occurs in dense shrubland and in tall forests of Pisonia grandis . It is almost exclusively an insectivore (99.8% of its diet is insects), and obtains 98% of its prey by gleaning small insects from the undersides of leaves. It does occasionally catch insects on the wing as well. [9] Most of the foraging occurs on Pisonia, Ficus reflexa and Morinda citrifolia . [10] Studies of the foraging behaviour found that Seychelles warblers favour Morinda and spend more time foraging there than in other trees and shrubs; the same study found that insect abundance is highest under the leaves of that shrub. [11] The planting of Morinda on Cousin Island, and the associated improved foraging for the warbler, was an important part of the recovery of the species.
Seychelles warblers demonstrate cooperative breeding, a reproductive system in which adult male and female helpers assist the parents in providing care and feeding the young. [12] The helpers may also aid in territory defense, predator mobbing, nest building, and incubation (females only). [13] Breeding pairs with helpers have increased reproductive success and produced more offspring that survived per year than breeding pairs with the helpers removed. [14] Helpers only feed the young of their parents or close relatives and do not feed unrelated young. This is evidence for the kin-selected adaptation of providing food for the young. The indirect fitness benefits gained by helping close kin are greater than the direct fitness benefits gained as a breeder. This could be evidence for the kin-selected adaptation of providing food for the young.
On high-quality territories where there is more insect prey available, young birds were more likely to stay as helpers rather than moving to low-quality territories as breeders. [15] On low quality territories, having a helper is unfavorable because of increased resource competition. Females are more likely to become helpers, [16] which may explain the adaptive sex ratio bias seen in the Seychelles warblers. On high quality territories, females produce 90% daughters; on low quality territories, they produce 80% sons. Clutch sex ratio is skewed towards daughters overall. [17] When females are moved to higher quality territories, they produce two eggs in a clutch instead of a single egg, with both eggs skewed towards the production of females. This change suggests that Seychelles warblers may have pre-ovulation control of offspring sex ratio, although the exact mechanism is unknown.
Seychelles warblers are socially monogamous, whereby a male and female form a long-term pair bond and cooperate to raise their young. Occasionally, a male and female may break their pair bond, a phenomenon known as divorce. The percentage of bonded pairs which undergo divorce varies from 1% to 16% per year, with more divorces occurring in years with very low or very high rainfall. However, divorce rates do not appear to be associated with decreased reproductive success. It has been suggested that physiological stress from harsh environmental conditions may be the cause of the increased divorce rates, rather than changes in reproductive success. [18]
The bushtits or long-tailed tits are small passerine birds from the family Aegithalidae, containing 13 species in three genera, all but one of which (Psaltriparus) are found in Eurasia. Bushtits are active birds with long tails compared to their size, moving almost constantly while they forage for insects in shrubs and trees. During non-breeding season, birds live in flocks of up to 50 individuals. Several bushtit species display cooperative breeding behavior, also called helpers at the nest.
The Acrocephalus warblers are small, insectivorous passerine birds belonging to the genus Acrocephalus. Formerly in the paraphyletic Old World warbler assemblage, they are now separated as the namesake of the marsh and tree warbler family Acrocephalidae. They are sometimes called marsh warblers or reed warblers, but this invites confusion with marsh warbler and reed warbler.
The sedge warbler is an Old World warbler in the genus Acrocephalus. It is a medium-sized warbler with a brown, streaked back and wings and a distinct pale supercilium. Sedge warblers are migratory, crossing the Sahara to get from their European and Asian breeding grounds to spend winter in Africa. The male's song is composed of random chattering phrases and can include mimicry of other species. The sedge warbler is mostly insectivorous.
The marsh warbler is an Old World warbler currently classified in the family Acrocephalidae. It breeds in temperate Europe and the western Palearctic and winters mainly in southeast Africa. It is notable for incorporating striking imitations of a wide variety of other birds into its song.
The great reed warbler is a Eurasian bird in the passerine genus Acrocephalus.
The European pied flycatcher is a small passerine bird in the Old World flycatcher family. One of the four species of Western Palearctic black-and-white flycatchers, it hybridizes to a limited extent with the collared flycatcher. It breeds in most of Europe and across the Western Palearctic. It is migratory, wintering mainly in tropical Africa. It usually builds its nests in holes on oak trees. This species practices polygyny, usually bigamy, with the male travelling large distances to acquire a second mate. The male will mate with the secondary female and then return to the primary female in order to help with aspects of child rearing, such as feeding.
The black-throated blue warbler is a small passerine bird of the New World warbler family. Its breeding ranges are located in the interior of deciduous and mixed coniferous forests in eastern North America. Over the cooler months, it migrates to islands in the Caribbean and Central America. It is very rarely found in western Europe, where it is considered to be a non-indigenous species. The black-throated blue warbler is sexually dimorphic; the adult male has a black face and cheeks, deep blue upperparts and white underparts, while the adult female is olive-brown above and light yellow below.
The cerulean warbler is a small songbird in the family Parulidae. It is a long-distance migrant, breeding in eastern North American hardwood forests. In the non-breeding season, it winters on the eastern slope of the Andes in South America, preferring subtropical forests.
The superb fairywren is a passerine bird in the Australasian wren family, Maluridae, and is common and familiar across south-eastern Australia. It is a sedentary and territorial species, also exhibiting a high degree of sexual dimorphism; the male in breeding plumage has a striking bright blue forehead, ear coverts, mantle, and tail, with a black mask and black or dark blue throat. Non-breeding males, females and juveniles are predominantly grey-brown in colour; this gave the early impression that males were polygamous, as all dull-coloured birds were taken for females. Six subspecies groups are recognized: three larger and darker forms from Tasmania, Flinders and King Island respectively, and three smaller and paler forms from mainland Australia and Kangaroo Island.
Alloparenting is a term for any form of parental care provided by an individual towards young that are not its own direct offspring. These are often called "non-descendant" young, even though grandchildren can be among them. Among humans, alloparenting is often performed by a child's grandparents and older siblings. Individuals providing this care are called by the neutral term "alloparent".
Cousin Island is a small granitic island of the Seychelles, lying 2 km (1.2 mi) west of Praslin. It is a nature reserve protected under Seychelles law as a Special Reserve. It is managed by Nature Seychelles, a national nonprofit organization and Partner of BirdLife International, by which it has been identified as an Important Bird Area.
Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derives from the Greek roots philo, "liking, loving" and patra, "fatherland", although in recent years the term has been applied to more than just the animal's birthplace. Recent usage refers to animals returning to the same area to breed despite not being born there, and migratory species that demonstrate site fidelity: reusing stopovers, staging points, and wintering grounds.
The Australian reed warbler is an Old World warbler in the genus Acrocephalus and is the only Acrocephalus species native to Australia. It has also been observed in Papua New Guinea and nearby islands. The name Acrocephalus refers to the peaked crown found on reed warblers in this genus and can be translated to mean "topmost head" in Greek. The species name australis is translated to mean "southern" in Latin, and refers to the species range, Australia. In its western range the Australian reed warbler is also known as "Koordjikotji" in the local Aboriginal language of Perth and its surrounds.
Sex allocation is the allocation of resources to male versus female reproduction in sexual species. Sex allocation theory tries to explain why many species produce equal number of males and females.
Cousine Island is a small granitic island 30 ha in the Seychelles 6 km (4 mi) west of Praslin Island. It is a combination luxury resort and since 1992 a nature preserve.
Cooperative breeding is a social system characterized by alloparental care: offspring receive care not only from their parents, but also from additional group members, often called helpers. Cooperative breeding encompasses a wide variety of group structures, from a breeding pair with helpers that are offspring from a previous season, to groups with multiple breeding males and females (polygynandry) and helpers that are the adult offspring of some but not all of the breeders in the group, to groups in which helpers sometimes achieve co-breeding status by producing their own offspring as part of the group's brood. Cooperative breeding occurs across taxonomic groups including birds, mammals, fish, and insects.
The white-winged fairywren is a species of passerine bird in the Australasian wren family, Maluridae. It lives in the drier parts of Central Australia; from central Queensland and South Australia across to Western Australia. Like other fairywrens, this species displays marked sexual dimorphism and one or more males of a social group grow brightly coloured plumage during the breeding season. The female is sandy-brown with light-blue tail feathers; it is smaller than the male, which, in breeding plumage, has a bright-blue body, black bill, and white wings. Younger sexually mature males are almost indistinguishable from females and are often the breeding males. In spring and summer, a troop of white-winged fairywrens has a brightly coloured older male accompanied by small, inconspicuous brown birds, many of which are also male. Three subspecies are recognised. Apart from the mainland subspecies, one is found on Dirk Hartog Island, and another on Barrow Island off the coast of Western Australia. Males from these islands have black rather than blue breeding plumage.
The green warbler-finch is a species of bird, one of Darwin's finches in the tanager family Thraupidae. Sometimes classified in the family Emberizidae, more recent studies have shown it to belong in the tanager family.
Polygyny is a mating system in which one male lives and mates with multiple females but each female only mates with a few males. Systems where several females mate with several males are defined either as promiscuity or polygynandry. Lek mating is frequently regarded as a form of polygyny, because one male mates with many females, but lek-based mating systems differ in that the male has no attachment to the females with whom he mates, and that mating females lack attachment to one another.
Sexual selection in birds concerns how birds have evolved a variety of mating behaviors, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and color differences are energetically costly attributes that signal competitive breeding situations. Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signaling adaptations ensure that sexually selected ornaments such as plumage coloration and courtship behavior are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviors.