Overview

Brief Summary

Biology

The Seychelles warbler feeds primarily on a variety of insects, including bugs and their eggs, beetles, bees and ants. It also feeds on spiders and, occasionally, small skins and geckos (2). It forages for its prey in trees, particularly Pisonia grandis, Morinda citrifolia (the Indian mulberry) and Ficus (fig) species, plucking insects from the undersides of leaves and twigs (2) (3) (5). Occasionally, aerial insects are plucked from the air whilst in flight and rarely the warbler will descend to the ground to feed (2) (3). Being a monogamous bird, male and female Seychelles warblers form pairs and together defend a territory which they will remain in until one of the pair dies (2) (3). The peak breeding period occurs between June and August, with a smaller peak of breeding attempts occurring between December and February. The timing of breeding throughout the year seems to be dependent on rainfall, however, breeding may occur at any time of the year if insects are sufficiently abundant (3). Seychelles warblers have a cooperative breeding system, meaning that helpers, usually the daughters from previous broods, assist with defending the territory, building the nest, incubating the eggs and feeding the young (6). Normally, a clutch of just one egg is laid each season, which is incubated for around 15 days, and the chick remains in the nest for a further 14 days (3). However, even after leaving the nest the young warbler will continue to solicit food from its parents and helpers for months afterwards (3).
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Description

The Seychelles warbler stands as an example of how, whilst humans may push a species to the verge of extinction, human intervention may also protect a species from this fate. Once believed to have just 26 individuals remaining on this planet, the Seychelles warbler, with its long, rather stout bill and long tail, is now thriving (2) (3). Its plumage is dull, yellowish olive-brown with a greenish wash, which fades to pale, faintly streaked, yellow on the underparts. The wing feathers are darker and browner and the tail feathers are also darker but with white tips (2). A whitish line runs above the eye, while an indistinct stripe extends from the bill to the reddish-brown eye and continues behind it. The Seychelles warbler's legs are grey-blue. Males and females are similar in appearance, while juveniles have grey-brown or grey-blue eyes (2). Seychelles warblers sing a short but rich and melodious song of simple whistled phrases, and they call in alarm with a brisk chatter (2).
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Distribution

Range Description

This specieswas present on several islands in the Seychelles until human disturbance in the 20th century reduced the species to one population on the tiny (0.3 km2) island of Cousin between 1920 and 1988 (Komdeur 2003). Prior to human colonisation it is thought that the species's range covered the inner granitic islands, with a population of approximately 20,000 individuals (Spurgin et al. 2014, D. S. Richardson in litt. 2015). It occurred historically on Marianne and Cousine(A. Skerrettin litt.1999), and there are unconfirmed reports from Felicit(Komdeur 1996b,Dijkstra 1997).The population on Cousin reached an all time low of less than 30 individuals in 1968, but it has recovered following favourable management and conservation policies (Richardson et al. 2006), and the species has since been translocated to the islands of Aride, Cousine and Denis (Bristol 2005,Richardson et al. 2006) and most recently Frgate in 2011 (Wright et al. 2014).

In 1997, its population on Cousin was 323 birds and stable, and on Cousine and Aride 137 and 1,600 birds respectively, and increasing (Komdeur et al. 1997). In September 2005, the population on Cousin stood at 371 individuals, including 322 independent birds, and in August 2005 the population on Denis was 75 birds and increasing (Richardson et al. 2006). In 2007, the total population probably numbered over 2,500 birds (G. Rocamora in litt. 2007). In 2015 the population was estimated at c. 3,000 adults (D. S. Richardson in litt. 2015). Most recent population estimates for the five islands are: 320 on Cousin (Brouwer et al. 2006); 210 on Cousine (Van de Crommenacker and Richardson 2007); 1,850 on Aride (Orchard 2004); c. 600 on Denis (D. S. Richardson in litt. 2015) and c. 200 on Frgate (D. S. Richardson in litt. 2015). It is predicted that the populations on Denis and Frgate may eventually exceed 2,000 and 2,500 individuals respectively (Hammers and Richardson 2011, D. S. Richardson in litt. 2015), increasing the overall population to c. >6,500 individuals (D. S. Richardson in litt. 2015).

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Range

Seychelles Islands (Cousin, Cousine, Aride).
  • Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2014. The eBird/Clements checklist of birds of the world: Version 6.9. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/

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Historic Range:
Indian Ocean_Seychelles Island

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Range

The Seychelles warbler currently occurs on the islands of Cousin, Cousine, Aride and Denis in the Seychelles (2) (3) (4). Historically, this species is believed to have also existed on Marianne, possibly Praslin, and there were also occasional reports from Mahé and Félicité (3).
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
It appears to require scrub habitat and tall, scrub-like vegetation dominated by large trees like Pisonia grandis and Ficus reflexa (G. Rocamora in litt. 2007). It is insectivorous, gleaning 98% of its insect food from leaves (Dijkstra 1997). Males and females form long-term breeding pairs and are highly territorial year-round (Dijkstra 1997), with a complex system of cooperative breeding and the ability to bias the sex ratio of offspring (Komdeur 1996a,Lloyd 1998). Although it can breed independently in its first year, some birds, mostly females, remain in their natal territory as subordinates and help to feed the young (Komdeur 2003). This system of cooperative breeding is thought to be a product of habitat saturation (Komdeur 1992). It usually has a one-egg clutch and high adult survival (Komdeur 1996b, Komdeur et al. 1997) (81% adult survival[Komdeur 2003]; average life expectancy at fledging 5.5 years [Komdeur and Daan 2005]). Pairs may reside in a territory for up to nine years (Komdeur 2003). The gender of the egg appears to be modified in reaction to territory quality and the need for new helpers (Komdeur 2003). The breeding success of pairs is highly dependent on the quality of territory (Komdeur 1992) as breeding sometimes continues year-round if insects are abundant(Komdeur 1996c,Dijkstra 1997).

Most birds on Cousin breed during the south-east monsoon season (April-September), when the quality (foliage cover and insect availability) of most territories peaks, whilst most birds in territories in the south-east of the island breed every six months, both during the South-east monsoon season, when their territories are very poor quality and the north-west monsoon season (October-March) when the quality of their territories increases slightly (Komdeur and Daan 2005). This results in a main breeding season in June-August and a minor breeding season in December-February (Richardson et al. 2006). These patterns suggest that food availability and weather conditions primarily influence the timing of breeding on Cousin, with periodicity being a secondary factor (Komdeur and Daan 2005). Inter-island dispersal by the species is extremely rare, with only two out of 1,924 ringed birds (0.1%) known to have flown between islands, despite the species's physical adaptations for such flights, the saturation of Cousin, and the potential for higher reproductive success elsewhere (Komdeur 2003,Komdeur et al. 2004). This is perhaps because all islands previously occupied by the species were once saturated and such dispersal behaviour was not favoured (Komdeur 2003,Komdeur et al. 2004).


Systems
  • Terrestrial
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Thick scrub and dense, tall woodland dominated by the tree Pisonia grandis are the Seychelles warbler's preferred habitats (3), but it also occurs in scrub in old coconut plantations, and swamps and mangroves (2).
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Life History and Behavior

Life Expectancy

Lifespan, longevity, and ageing

Maximum longevity: 14 years Observations: Although there are no detailed studies, these animals have been known to live over 14 years (Richardson et al. 2007). Evidence of reproductive senescence has been reported in females over 6 years of age (Komdeur 1996). Annual survival has been reported to be 84% for adults (Brouwer et al. 2006).
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
NT
Near Threatened

Red List Criteria

Version
3.1

Year Assessed
2015

Assessor/s
BirdLife International

Reviewer/s
Symes, A.

Contributor/s
Lucking, R., McCulloch, N., Parr, S., Rocamora, G., Shah, N., Skerrett, A. & Richardson, D.

Justification
This species has been downlisted to Near Threatened. It is found on five islands and its population size is increasing owing to translocations and habitat management; there are not thought to be any threats that could drive the species to Critically Endangered or Extinct in a very short time (it almost meets the requirements for listing as threatened under criterion D2).


History
  • 2012
    Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Threatened (T)
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