Archived 2011-2012 topics: Gabela Bush-shrike (Laniarius amboimensis): downlist to Vulnerable?

Initial deadline for comments: 31 January 2012 [note that this has been moved back by about two months].

BirdLife species factsheet for Gabela Bush-shrike

Gabela Bush-shrike Laniarius amboimensis is endemic to the Angolan escarpment, formerly known only from the vicinity of Gabela, where it inhabits the undergrowth of evergreen forest, overgrown coffee plantations and thickets of secondary growth. It is currently listed as Endangered on the basis that it was thought to have a very small range, with an Extent of Occurrence (EOO) estimated at 310 km2, in which it was known from only one location, with on-going declines in the EOO, Area of Occupancy (AOO), area, extent and/or quality of habitat and number of mature individuals, driven by the clearance of habitat primarily for subsistence agriculture.

Records of this species recently published by Mills (2010) indicate that its range is larger than previously thought. Remapping of its range by BirdLife has resulted in a new EOO of c.2,900 km2, which still meets the range size threshold for Endangered under criterion B1. However, the recent paper by Mills (2010) indicates that the species has been recorded at more than five locations since 1974. An additional record from the Sumbe-Gabela Road indicates that it has been recorded from at least seven locations in recent decades. This, coupled with the fact that the species’s habitat cannot be considered severely fragmented (i.e. more than 50% in patches too small to support viable populations) because of its tolerance of moderate habitat degradation and disturbance (Mills 2010), means that the species may no longer qualify as Endangered under criterion B1.

Updated BirdLife range map for Gabela Bush-shrike (click on map to see larger version)

The new estimate for this species’s EOO also suggests that its population size should be re-estimated. The population is currently estimated to fall in the band 250-999 individuals based on the density range of 2.5-7 individuals/km2 from the upper to the lower quartile of nine estimates for seven congeners, extrapolated to 45% of the EOO, giving an estimate of 350-980 for an EOO of 310 km2. Using the same method, the incorporation of the new EOO estimate (45% = 1,305 km2) gives a population estimate of c.3,260-9,140 individuals, suggesting that it should now be placed in the band 2,500-9,999 individuals. This might be supported by the observation that the species can be fairly common in its range (Mills 2010).

It is proposed that this species be downlisted to Vulnerable, for which it would qualify under criteria B1a+b(ii,iii); C2a(ii). This listing would be based on an EOO estimated at less than 20,000 km2 in which it is known from fewer than 11 locations, with on-going declines in the AOO and area, extent and/or quality of habitat, and a population estimated to number fewer than 10,000 individuals, in one sub-population, and suspected to be in decline owing to on-going habitat loss.

Comments are invited on this proposed category change, with input particularly requested on the new EOO estimate, new population estimate, number of locations and population structure (number of sub-populations and, if more than one, the size of the largest sub-population).

In relation to the IUCN criteria, a location is defined as a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the species present. The size of the location depends on the area covered by the threatening event and may include part of one or many sub-populations, whilst sub-populations are defined as geographically or otherwise distinct groups in the population between which there is little exchange (typically one successful migrant individual or gamete per year or less).

Reference:

Mills, M. S. L. (2010) Angola’s central scarp forests: patterns of bird diversity and conservation threats. Biodivers. Conserv. 19: 1883-1903.

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4 Responses to Archived 2011-2012 topics: Gabela Bush-shrike (Laniarius amboimensis): downlist to Vulnerable?

  1. Fabio Olmos says:

    The situation of the second-growth forests and derelict shade coffee plantations used by the species is not good at all. Everywhere we visited they were being replaced by maize and manioc, which obviously make poor habitat for this species. Actual usable habitat in the EOO may well be half than you estimated, and what remains is fragmented in small patches

  2. I fully agree with the text and reasoning to downlist the species to Vulnerable. I suspect that the EOO and population densities are not smaller than newest estimates presented, althoug it is quite true that those secondary forests are under a lot of pressure, and being transformed into agricultural fields at alarming pace. I wouldn’t be surprised if in a few years down the road, we will find objective reasons to propose uplisting again to endangered status…

  3. Michael Mills says:

    I spent a month conducting bird surveys (point counts) at Kumbira forest during September/October 2010, and was surprised to find as few Gabela Bushshrike as I did. I recorded Gabela Bushshrike within 50 m of only six of just over 200 sample points, and this was with playback of vocalisations to maximise detectability! I think we have overestimated the local abundances of the species. The calls could be heard from > 250 m away. Given that they are such vocal birds, one can walk a distance of more than 500 m (if you are watching birds this could take an hour) and hear the same birds, continually. This has given us an overinflated estimate of their local abundance, and I think we need to proceed with care before we downlist. Its habitats are disappearing alarmingly quickly, and given that there are so few birds actually at Kumbira, thought to be the stronghold for this species, there may be significantly fewer birds than the estimates above. Furthermore, the possibility of actually getting some of its habitat protected within the next five years are very uncertain.

  4. In spite of what I stated on an earlier comment, I must confess that I’m not so sure anymore. In fact, I had assumed that Michael Mills had been the one proposing to downlist the species, and knowing that he had conducted countless bird surveys in the region I fully trusted (and still do) his judgement on this one. The truth is that personally, I have never found the Gabela bush shrike to be common and easy to find, nor have I ever found it outside the secondary forests near Kumbira forest. I apologise for my unprofessioal and careless comment earlier.
    Putting now everything in perspective, I think Mills is right and we should proceed with caution before downlisting this species.

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