Gurney’s Pitta (Hydrornis gurneyi): revise global status?

Gurney’s Pitta has a restricted distribution in extreme southern Myanmar (southern Tanintharyi Region, formerly Tenasserim) and perhaps adjacent Thailand; it also formerly occurred in the far south of Thailand in Khao Nor Chuchi (Krabi Province).

It is currently listed as Endangered under criterion A3c+4c, as a very rapid population reduction (50-79% in three generations) is anticipated to be occurring now and in the near future as a result of land clearance.

After its rediscovery in 1986 in Thailand, intensive surveys found it in at least five localities, although it disappeared from all but one of these, Khao Nor Chuchi. This population declined from 44-45 pairs in 1986 to just nine pairs in 1997. Detailed work in 2003-2007 recorded birds at 27 sites in Khao Nor Chuchi, and a further survey of the area in 2009 found 12 individuals responding to tape playback. Intensive surveys of the site in 2015 and 2016 recorded no individuals, until a single female was recorded in April 2016. It is now considered extinct (or at least functionally extinct) in the country.

Following its rediscovery in Myanmar, the population there was proposed to number 5,152-8,586 pairs (Eames et al. 2005), equating to c10,300-17,100 mature individuals, in 2000. This was based on densities of 3.6-6 pairs per km2 of suitable habitat extrapolated across the five largest remaining suitable forest patches, which covered a total area of 1,431 km2 in 2000.

Since then, the extent of suitable intact forest in Tanintharyi (between 7°N-12°N latitude, below 150 m above sea level and <10° slope), was found to have declined by 81%, from 3,395 to 656 km2, between 1999-2016 (Shwe et al. submitted).  During January-October 2016 Shwe et al. revisited 142 point locations out of 147 where the species was detected between 2003 to 2012 (Donald et al. 2014), and found it remaining in only in 41 of those locations (29%).

Assuming that a reduction in population has taken place in line with the reduction of total suitable habitat from 3,395 km2 in 2000 to 656 km2 in 2016, a revised 2016 population estimate could be in the order of 1,990-3,304 mature individuals, rounded to 2,000-3,300, if using the same methods as Eames et al. (2005). However, based on surveys in 2010-2016 it has been suggested that the population size may be considerably lower than this, at c.800-1,000 (T. D. Aung in litt. 2016).

This rapid loss of habitat and associated population reduction have led several species experts to raise the prospect that the species may once more qualify as Critically Endangered. At the very least, an update to the information in the Red List assessment and factsheet is now overdue. Here we attempt to gather the latest information and request further input as to whether a status change may be warranted.

 

Assessment against Red List Criteria

Criterion A – based on the estimates presented by Shwe et al. (submitted), the rate of habitat loss during three generations between 2003-2016 equated to 38.7%, with the rate of loss having slowed since initial extremely rapid loss between 1999-2003. Indeed, whilst forest loss continues, some major oil palm concessions in the region have recently been cancelled or postponed (P. Insua-Cao in litt. 2018). Nevertheless, the political change and social reform which has been ongoing since 2010 carries environmental risks including the potential for increased commercial access to previously restricted areas (Donald et al. 2015)

Note that Shwe et al. do not find any evidence that the species is being targeted by collectors or hunters, so this is not thought likely to be increasing the rate of decline above that driven by habitat loss.

Nevertheless, the index of population derived from the surveys in Shwe et al.  is worrying. That 142/147 previous confirmed locations were checked, and 101 had been cleared while the 41 that remained forest retained the species (i.e. where habitat remained the surveys detected the species) does indicate within this sample (which is pretty significant) that the population decline exceeded 70% during the three generation period between 2003-2016. This suggests that despite the apparent reduction in the rate of habitat loss, the rate of population decline still exceeds the threshold for listing as Endangered under criterion A. On this evidence however, it does not meet the threshold for listing as Critically Endangered under this criterion (which requires declines of 80% or more in three generations).

Criterion B – extent of occurrence, as measured according to IUCN guidelines based on a minimum convex polygon around the known range, is measured at 24,700 km2 and is therefore too large for the species to qualify for a threatened category based on this measure of range. However, the area of remaining suitable habitat was estimated at 656 km2 in 2016, suggesting that the area of occupancy is likely to be small. The potential category under this criterion depends how much of the remaining suitable habitat is occupied (and a resulting calculation of area of occupancy), and also on the degree of fragmentation and number of locations. Nevertheless, the highest possible category is Endangered since the area of occupancy is certainly greater than 10 km2.

Note that the difference between the BirdLife estimate of 24,700 km2 and Shwe et al.’s figure of 656 km2 is not a question of different modelling methods – we are measuring two different things. The first is the extent of occurrence (24,700 km2, based on a minimum convex polygon), while the latter is an estimate of extent of suitable habitat (which could approximate to a maximum possible area of occupancy).

Criterion C – The subpopulation structure is unclear, but there are almost certainly still >250 mature individuals in total and therefore the highest category the species could qualify for under this criterion is Endangered.

Criterion D – If we accept a population estimate of 800-1,000 individuals the species would qualify as Vulnerable under criterion D1.

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

In the absence of any further information Gurney’s Pitta appears to continue to warrant listing as Endangered, under criterion A2+3+4, as the population index suggests that declines likely fall within the range 50-79% in three generations. However we recognie that the species is certainly close to the threshold for listing as Critically Endangered and we welcome any further information to help refine population and trend estimates, as well as discussion of future threats and the likely future trend in the rate of loss of suitable habitat for the species.

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 relevant to the information that is sought, or about the species’ Red List status.

References

Donald, P. F.; Aratrakorn, S.; Thura Win Htun; Eames, J. C.; Htin Hla; Thunhikorn, S.; Sribua-Rod, K.; Pinyo Tinun; Sein Myo Aung; Sa Myo Zaw; Buchanan, G. M. 2009. Population, distribution, habitat use and breeding of Gurney’s Pitta Pitta gurneyi in Myanmar and Thailand. Bird Conservation International 19: 353-366.

Donald, P. F.; Hla, H.; Win, L.; Aung, T. D.; Moses, S.; Zaw, S. M.; Ag, T. T.; Oo, K. N.; Eames, J. C. 2014. The distribution and conservation of Gurney’s Pitta Pitta gurneyi in Myanmar. Bird Conservation International 24: 354-363.

Donald, P. F.; Round, P. D.; Aung, T. D. W.; Grindley, M.; Steinmetz, R.; Shwe, N. M.; Buchanan, G. M. 2015. Social reform and a growing crisis for southern Myanmar’s unique forests. Conservation Biology 29(5): 1485-1488.

Eames, J.C., Htin Hla, Leimgruber, P., Kelly, D.S., Sein Myo Aung, Moses, S. & U Saw Nyunt Tin. 2005. The rediscovery of Gurney’s Pitta Pitta gurneyi in Myanmar and an estimate of its population size based on remaining forest cover. Bird Conservation International 15: 3–26.

Erritzoe, J. & de Juana, E. (2018). Gurney’s Pitta (Hydrornis gurneyi). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/57560 on 15 February 2018).

Gurney’s Pitta Working Group. 2017. Gurney’s Pitta Strategic Plan and 2018 Annual Workplan: Goals and Actions to Protect the Tanintharyi Endemic Gurney’s Pitta and Its Habitat. Report 59 of the Tanintharyi Conservation Programme, a collaboration between the Myanmar Forest Department and Fauna & Flora International, FFI: Yangon.

Round, P. D. 2014. Gurney’s Pittas in Thailand – from rediscovery to extinction in just 28 years. Nat. Hist. Bull. Siam Soc. 60(1): 3–8.

Shwe, Nay Myo, Sukumal, N., Grindley, M., & Savini, T. submitted. Gurney’s Pitta on the brink of extinction!

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