Seychelles Warbler
Encyclopedia
The Seychelles Warbler (Acrocephalus sechellensis), also known as Seychelles Brush-warbler, is a small songbird
found on four 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 50 birds surviving on Cousin Island
in 1965. Due to conservation efforts there are more than 2500 of the species alive today with viable populations on Denis
, Cousine
and Aride Island
s, as well as Cousin Island.
(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 Swamp-warbler.
warbler, between 13 to 14 cm (5.1 to 5.5 in) in length and with a wingspan of 17 cm (6.7 in). 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, similar to a human whistle
. Its structure is simple and is composed of short song sequences delivered at a low frequency range. 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.
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. Most of the foraging occurs on Pisonia, Ficus
lutea
and Morinda citrifolia
. 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. The planting of Morinda on Cousin, and the associated improved foraging for the warbler, was an important part of the recovery of the species.
Passerine
A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...
found on four granitic and corraline islands in the Seychelles
Seychelles
Seychelles , officially the Republic of Seychelles , is an island country spanning an archipelago of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar....
. 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
Alloparenting
In biology and sociology, alloparenting is where individuals other than the actual parents act in a parental role.One common form of alloparenting is where grandparents adopt a parental role. This is sometimes named a "skipped generation household"...
; which means that the monogamous pair is assisted by nonbreeding female helpers
Helpers at the nest
Helpers at the nest is a term used in behavioural ecology and evolutionary biology to describe a social structure in which juveniles and sexually mature adolescents of either one or both sexes, remain in association with their parents and help them raise subsequent broods or litters, instead of...
.
A few decades ago the Seychelles Warbler was on the verge of extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
, with only 50 birds surviving on Cousin Island
Cousin Island
Cousin Island is a small granitic island of the Seychelles, lying 2 km SSW of Praslin. It is a nature reserve protected under Seychelles law as a Special Reserve and is run by Nature Seychelles, a national non-profit organization and Partner of BirdLife International .Until 1968, Cousin...
in 1965. Due to conservation efforts there are more than 2500 of the species alive today with viable populations on Denis
Denis Island
Denis Island is the second northeasternmost Island in the Seychelles. It is 60 miles north of Mahé and lies at the northern edge of the Seychelles bank, along with the nearby Bird Island, which is the northernmost Seychelles island. The 1.31 km² coral island was named after the French explorer...
, Cousine
Cousine Island
Cousine Island is a small granitic island in the Seychelles 6 km west of Praslin Island. It is a combination luxury resort and since 1992 a nature preserve....
and Aride Island
Aride Island
Aride Island is the northernmost granitic island in the Seychelles and is 10 km north of Praslin. It is 68 hectares in area and is a nature reserve. Aride is leased and managed by the Island Conservation Society of Seychelles. The only human inhabitants are the reserve's staff; currently four...
s, as well as Cousin Island.
Taxonomy and systematics
The Seychelles Warbler is closely related to the Rodrigues WarblerRodrigues Warbler
The Rodrigues Warbler is a species of Old World warbler in the Acrocephalidae family.It is found only on Rodrigues, which belongs to Mauritius....
(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
Nesillas
Nesillas is a genus of Old World warbler in the Acrocephalidae family.It contains the following species:* Grand Comoro Brush-Warbler * Lantz's Brush-Warbler...
. A 1997 study confirmed however that the two species were part of a clade of Afrotropical warblers within Acrocephalus
Acrocephalus
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...
that also includes the Madagascar Swamp-warbler
Madagascar Swamp-warbler
The Madagascar Swamp-warbler is a species of Old World warbler in the Acrocephalidae family.It is found only in Madagascar.Its natural habitat is swamps.-References:...
, the Greater Swamp-warbler
Greater Swamp-warbler
The Greater Swamp-warbler is a species of Old World warbler in the Acrocephalidae family.It is found in Angola, Botswana, Burundi, Cameroon, Central African Republic, Chad, Republic of the Congo, Democratic Republic of the Congo, Equatorial Guinea, Gabon, Ghana, Kenya, Mali, Mauritania, Namibia,...
, the Lesser Swamp-warbler
Lesser Swamp-warbler
The Lesser Swamp Warbler or Cape Reed Warbler, Acrocephalus gracilirostris, is an Old World warbler in the genus Acrocephalus. It is a resident breeder in Africa from the Democratic Republic of the Congo, the Chad and Ethiopia south to South Africa...
and the Cape Verde Swamp-warbler.
Description
The Seychelles Warbler is a small, plain AcrocephalusAcrocephalus
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...
warbler, between 13 to 14 cm (5.1 to 5.5 in) in length and with a wingspan of 17 cm (6.7 in). It has long grey-blue legs, a long horn coloured bill
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
, and a reddish eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
. Adults show no sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
in their plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...
, 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
Bird song
Bird vocalization includes both bird calls and bird songs. In non-technical use, bird songs are the bird sounds that are melodious to the human ear. In ornithology and birding, songs are distinguished by function from calls.-Definition:The distinction between songs and calls is based upon...
of the Seychelles Warbler is described as rich and melodious, similar to a human whistle
Whistle
A whistle or call is a simple aerophone, an instrument which produces sound from a stream of forced air. It may be mouth-operated, or powered by air pressure, steam, or other means...
. Its structure is simple and is composed of short song sequences delivered at a low frequency range. The lack of a wide frequency range sets it apart from other species in its genus, such as the Reed Warbler
Reed Warbler
The Eurasian Reed Warbler, or just Reed Warbler, Acrocephalus scirpaceus, is an Old World warbler in the genus Acrocephalus. It breeds across Europe into temperate western Asia. It is migratory, wintering in sub-Saharan Africa....
, its song is similar to its closest relatives in Africa such as the Greater Swamp Warbler.
Behaviour
The Seychelles Warbler naturally occur in dense shrublandShrubland
Shrubland, scrubland, scrub or brush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs, and geophytes. Shrubland may either occur naturally or be the result of human activity...
and in tall forests of Pisonia grandis
Pisonia grandis
Pisonia grandis is a species of flowering tree in the Bougainvillea family, Nyctaginaceae.-Description:The tree has broad, thin leaves, smooth bark and bears clusters of green sweet-smelling flowers that mature into sticky barbed seeds....
. It is almost exclusively an insectivore
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....
(99.8% of its diet is insects), and obtains 98% of its prey by gleaning
Gleaning (birds)
Gleaning is a term for a feeding strategy by birds in which they catch invertebrate prey, mainly arthropods, by plucking them from foliage or the ground, from crevices such as rock faces and under the eaves of houses, or even, as in the case of ticks and lice, from living animals. This behavior is...
small insects from the undersides of leaves. It does occasionally catch insects on the wing as well. Most of the foraging occurs on Pisonia, Ficus
Ficus
Ficus is a genus of about 850 species of woody trees, shrubs, vines, epiphytes, and hemiepiphyte in the family Moraceae. Collectively known as fig trees or figs, they are native throughout the tropics with a few species extending into the semi-warm temperate zone. The Common Fig Ficus is a genus of...
lutea
Ficus lutea
Ficus lutea is a tree in the Moraceae family. It is commonly known as the Giant-leaved Fig. These trees occur from the Eastern Cape of South Africa to Tropical Africa.- References :...
and Morinda citrifolia
Noni
Morinda citrifolia, commonly known as great morinda, Indian mulberry, nunaakai , dog dumpling , mengkudu , Kumudu , pace , beach mulberry, cheese fruit or noni is a tree in the coffee family, Rubiaceae...
. 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. The planting of Morinda on Cousin, and the associated improved foraging for the warbler, was an important part of the recovery of the species.