Long-legged Thicketbird (Megalurulus rufus): revise global status?

Endemic to Fiji, the Long-legged Thicketbird (Megalurulus rufus) has only been recorded from the islands of Viti Levu and Vanua Levu. Historically, the species was only known from one specimen on Vanua Levu, and four old specimens and a handful of sightings on Viti Levu (Kinsky 1975). The lack of sightings led to fears that the species could be extinct. However, survey work between 2002-2005 and in 2012 found the species at several sites on Viti Levu, and although not found when conducting surveys on Vanua Levu, its call was described by villagers at Valovoni (Dutson and Masibalavu 2004, Masibalavu and Dutson 2006, G. Dutson and V. Masibalavu in litt. 2006, V. Masibalavu in litt. 2007, 2012).

It is suspected to be at risk of predation by introduced mammals such as Black Rats Rattus rattus and the Small Indian Mongoose Herpestes auropunctatus, but these predators are present in Wabu Forest Reserve and the Thicketbird successfully breeds there alongside them. Additionally, some logging of montane forest occurs in Fiji, but it is not thought to severely affect the species’ preferred habitat (BirdLife International 2006). Therefore, in the absence of evidence for any declines or noticeably severe threats the population has been considered to be stable. The overall population size is, however, thought to be very small. Currently it is placed in the range 50-249 mature individuals (and as such it is currently listed as Endangered [BirdLife International 2017]), but it has been suggested that this may be an under-estimate and based on field observations the population size may instead be best placed in the range 250-999 mature individuals (G. Dutson in litt. 2016). Therefore, taking into account this potentially higher population size estimate we have re-assessed the species here against all criteria.

 

Criterion A – The population trend is considered to be stable. Therefore, it does not warrant listing under this criterion.

 

Criterion B – This species has an Extent of Occurrence (EOO) of 17,900km2, and is currently assessed as occurring at only 2-5 locations*. To warrant listing as Vulnerable under this criterion would still require at least one more condition to be met, though, and the species is not known to undergo any extreme fluctuations and so it would not meet the conditions for subcriterion c).

There is currently no evidence for a decline in the number of locations, the EOO or AOO of the species; and the population is considered to be stable. There is some evidence for some logging of montane forest on the islands where Long-legged Thicketbird occurs, however, this is thought to probably not be affecting the species’ preferred habitat (BirdLife International 2006). Therefore, it would also not meet the conditions for listing as Vulnerable under subcriterion b); and so the highest category of threat that may be warranted under Criterion B is Near Threatened under criterion B1ab(iii). Its Area of Occupancy (AOO) has not been directly estimated, and so it cannot be assessed against criterion B2.

 

Criterion C – Despite having a small population size, the population trend is considered to be stable, and as such the species does not warrant listing under this criterion.

 

Criterion D – In the most recent assessment the population size was placed in the range 50-249 mature individuals. However, it has been suggested that the range 250-999 mature individuals may be more appropriate based on field observations (G. Dutson in litt. 2016). This updated population size figure would mean the species qualifies as Vulnerable under criterion D1. While it does have a restricted range, there is not thought to be a severe enough threat to mean that the species also qualifies as Vulnerable under criterion D2.

 

Criterion E – To the best of our knowledge there has been no quantitative analysis of extinction risk conducted for this species. Therefore, it cannot be assessed against this criterion.

 

Therefore, it is proposed that Long-legged Thicketbird be listed as Vulnerable under criterion D1. Comments are welcome but please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are about the proposed listing.

 

*The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).

 

References

BirdLife International. 2006. Distribution of albatrosses and petrels in the Atlantic Ocean and overlap with ICCAT longline fisheries. International Commission for the Conservation of Atlantic Tunas Collective Volume of Scientific Papers 59: 1003-1013.

BirdLife International. 2017. Species factsheet: Megalurulus rufus. Downloaded from http://www.birdlife.org on 19/12/2017.

Duston, G.; Masibalavu, V. 2004. Fiji’s long-legged warbler seen again after 109 years. Oryx 38: 131.

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. Available at: www.iucnredlist.org/technical-documents/categories-and-criteria.

Kinsky, F. C. 1975. A new subspecies of the Long-legged Warbler Trichocichla rufa Reichenow, from Vanua Levu, Fiji. Bulletin of the British Ornithologists’ Club 95: 98-101.

Masibalavu, V. T.; Dutson, G. 2006. Important bird areas in Fiji: conserving Fiji’s natural heritage. BirdLife International Pacific Partnership Secretariat, Suva.

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