Forest Thrush (Turdus lherminieri) | Text

Forest Thrush Turdus lherminieri

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Justification

Justification of Red List category
Human-induced deforestation, introduced predators and severe habitat loss from volcanic eruptions on Montserrat in 1995-1997 produced rapid population declines. On Montserrat, the population has increased markedly since 1997 and recent monitoring indicates that the species is both common and stable. The majority of the global population occurs on Guadeloupe, where the species is declining at most slowly. The smaller populations on Dominica and St Lucia are potentially in rapid decline. Overall, it is assumed that the rate of population decline has slowed down and no longer meets the threshold for listing as threatened. The species has therefore been downlisted to Near Threatened.

Population justification
Point counts on Montserrat found c.1,200 individuals at 88 stations in the Centre Hills in 2016 (Bambini et al. 2017). As these stations covered only 20-40% of the available forest habitat (Oppel et al. 2014), the population on Montserrat could be between 1,500 - 10,000 individuals (1,000-7,000 mature individuals). A recent study based on surveys and habitat mapping on Guadeloupe has suggested that previous population estimates have been substantial underestimates, with the Guadeloupe population estimated at 46,900 – 49,500 pairs (93,800 – 99,000 mature individuals; Eraud et al. 2012). However, the estimate was based on distance sampling which can be highly inaccurate in dense tropical forests given that most Forest Thrush detections are aural. The sizes of the populations on Dominica and St Lucia are unknown, although the latter is assumed to be very small, if not zero. The total population is therefore placed in the band 100,000-499,999 mature individuals.

Trend justification
The species underwent a significant population reduction over recent decades, particularly during 1995-1997, when the range on Montserrat was reduced by two-thirds by the effects of volcanic eruptions and ash fall (G. Hilton in litt. 2000). However, more recent data has suggested that the species’s population may no longer be declining. In December 1999, the population on Montserrat was estimated at 3,100 birds (Arendt et al. 1999), representing an increase of c.50% since December 1997, with further increases up until 2004, followed by a period of stability and further increased between 2011 and 2016 (Parashuram 2013, S. Oppel in litt. 2016, Bambini et al. 2017, S. Oppel in litt. 2019). Montserrat thus holds a small proportion of the global population, which is stable or slowly increasing. On St Lucia, there has been just one recent record (at Des Chassin in 2007), but it was considered numerous in the late 19^th century, indicating a serious long-term decline, if not extirpation (Keith 1997, B. Ibene in litt. 2014, L. John in litt. 2016, S. Oppel in litt. 2019). Little is known about population trend on Dominica, but the population size is likely low. As a consequence of hurricane Maria, which hit the island in 2017, the population may likely have declined further, though it is still observed there (see recent records on eBird; eBird 2018). The majority of the population is found on Guadeloupe (Eraud et al. 2012), and all evidence suggests only a very slow decline. Precautionarily, it is assumed that the historic decline on St Lucia, the potentially large declines on Dominica and the very slow declines on Guadeloupe sum up to such a magnitude that the species’s global population is currently in decline at a rate approaching 30% over three generations.

Distribution and population

Turdus lherminieri is endemic to the Lesser Antilles, where it is uncommon on Montserrat (to U.K.), Dominica and Guadeloupe (to France), and rare on St Lucia. It appears to have declined significantly throughout its range in the past (Raffaele et al. 1998). The range on Montserrat was reduced by two-thirds in 1995-1997 by the effects of volcanic eruptions (G. Hilton in litt. 2000). However, in December 1999, the population was estimated at 3,100 birds (Arendt et al. 1999), representing an increase of c.50% since December 1997, with further increases until 2016 (Bambini et al. 2017). The reasons for these increases are not known, but Forest Thrush is by now the third most abundant bird species in rainforests of Montserrat and improved monitoring between 2011 and 2016 indicated a stable or slowly increasing population (Bambini et al. 2017). On St Lucia, it was considered numerous in the late 19^th century, but is now very rare with just one recent record (at Des Chassin in 2007), indicating a serious decline (Keith 1997, L. John in litt. 2016). On Guadeloupe, the species is considered abundant on Basse-Terre, which also holds the largest population, while it occurs at lower densities on Grande-Terre (Arnoux 2012, Eraud et al. 2012). Birds on Basse-Terre were found to be significantly larger than on Grande-Terre (Arnoux et al. 2013), indicating that the species may show a significant population structure on a small geographic scale. On Dominica, the species also occurs at low densities, and has been observed in suitable habitat in the northern, western, central, south-eastern and southern regions (J. Arlington in litt. 2007).

Ecology

It mostly inhabits the undergrowth and edge of mid-altitude and high-altitude primary and secondary moist forest, but can be exceedingly shy where hunted (Bond 1979, Keith 1997, Raffaele et al. 1998). However on Montserrat, although it occurs at all altitudes, the species is most common in mesic mid-elevation forest under closed canopies (Parashuram et al. 2015). Pairs feed on insects and berries from ground-level to the forest canopy (Raffaele et al. 1998). On St Lucia, it previously gathered in large numbers in autumn to feed on berries (Keith 1997). Breeding has been recorded between March and August. The nest is made of dry leaves, twigs and moss, placed 3-10 m above the ground, in forks of large trees or on epiphytes. A clutch typically contains 2-3 blue-green eggs. The incubation period is approximately two weeks and a brood patch is present in both sexes. Chicks stay in the nest for 16-17 days. It is common for this species to nest twice in a year, where it does not build a new nest, but instead rearranges the one used for the first brood (Bénito-Espinal and Hautcastel 2003).

Threats

Habitat loss has occurred throughout the species's range, but has been particularly acute on Montserrat. Volcanic activity was much reduced during 1998-1999 (G. Hilton in litt. 2000), but a further major volcanic eruption in 2001 caused heavy ash falls across large areas of the remaining habitat. Threats on other islands include brood-parasitism by Shiny Cowbird Molothrus bonariensis, competition with Bare-eyed Thrush Turdus nudigenis, which are increasing on Guadeloupe (A. Levesque and B. Ibene in litt. 2007), and predation by mongooses and other introduced mammals (Raffaele et al. 1998). It is still legally hunted on Guadeloupe (P. Feldmann and P. Villard in litt. 1998), and illegal hunting for food continues on other islands (Raffaele et al. 1998). Forest loss represents a further threat to the species, though the area covered by forest within the range has only declined by 1.5% between 2000 and 2012 (Tracewski et al. 2016).

Conservation actions

Conservation Actions Underway

It occurs in Morne Diablotin and Morne Trois national parks, as well as the Northern and Central forest reserves on Dominica (J. Arlington in litt. 2007), Guadeloupe National Park on Guadeloupe and various forest reserves including Edmond on St Lucia.On Montserrat, remaining habitat in the Centre Hills area is protected and unlikely to suffer any further anthropogenic habitat destruction (Oppel et al. 2015). The species is monitored annually in the Centre Hills, and a stable population has been recorded since improved monitoring started in 2011 (Parashuram 2013, Bambini et al. 2017).

Conservation Actions Proposed

Survey to assess the status and seasonal requirements of the species on each island. Implement a specific hunting ban. Conduct an awareness campaign to limit hunting.

Identification

25-27 cm. Medium-sized thrush. All dark brown upperparts. Brownish below with white spots on breast, flanks and upper belly, and white lower belly. Yellow legs, bill and bare skin around eye. Similar spp. On St Lucia, distinguished from Bare-eyed Robin Turdus nudigenis by scaled underparts. Pearly-eyed Thrasher Margarops fuscatus is greyer and has white spots in tail. Voice Soft musical song. Hints Best located by song given from concealed perch.

Acknowledgements

Text account compilers
Pople, R., Sharpe, C.J., Wheatley, H., Stringer, C., Wege, D., Khwaja, N., Hermes, C., Mahood, S., Isherwood, I.

Contributors
Arlington, J., Arnoux, E., Feldmann, P., Hilton, G., Ibene, B., John, L., Levesque, A., Morton, M., Oppel, S., Parashuram, D. & Villard, P.

Recommended citation
BirdLife International (2024) Species factsheet: Forest Thrush Turdus lherminieri. Downloaded from https://datazone.birdlife.org/species/factsheet/forest-thrush-turdus-lherminieri on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org/species/search on 23/12/2024.