Bird Conservation International, page 1 of 14. ª BirdLife International 2009
doi:10.1017/S0959270909008612
Population, distribution, habitat use and
breeding of Gurney’s Pitta Pitta gurneyi in
Myanmar and Thailand
PAUL F. DONALD, SIRIRAK ARATRAKORN, THURA WIN HTUN,
JONATHAN C. EAMES, HTIN HLA, SOMYING THUNHIKORN,
KRIANGSAK SRIBUA-ROD, PINYO TINUN, SEIN MYO AUNG,
SA MYO ZAW and GRAEME M. BUCHANAN
Summary
Gurney’s Pitta Pitta gurneyi was not seen in the wild for over 30 years before its rediscovery in
a small area in southern Thailand in 1986. In 2003, it was found over a much larger area in
southern Myanmar (Burma) after an even longer absence of records. This paper reports the results
of recent research on both populations. In Myanmar, birds were found in a high proportion of
visited sites, including sites up to 40 km further north than any previous records in the country.
Occupied forest sites had a higher density of seedlings, saplings, bamboo and rattan than
unoccupied forest sites, suggesting a preference for regenerating forest. There was no evidence of
a decline in the species’s likelihood of occurrence up to at least the highest visited altitude of 230 m.
Maximum entropy models suggested a potential range size of between 3,200 and 5,800 km2 and
the predicted range extended just over the border into Thailand, suggesting that birds might persist
there. Population estimates for southern Myanmar ranged from 9,300 to 35,000 territories, with
a mid-point estimate of 20,000 territories, based upon range sizes modelled from different
parameters and a range of territory densities estimated from Thailand. The population in southern
Thailand was estimated at between 15 and 20 territories in 2003, 2005 and 2007, and there was
a reduction in the historic rate of forest loss in the core range over the same period, suggesting that
long-term declines have been at least temporarily contained by recent conservation intervention.
However, nesting success in Thailand was very low, due to heavy nest predation by cat snakes
Boiga. Nests were usually built close to waterlogged areas and damp gullies, and nestlings were fed
almost exclusively on earthworms. Occupied sites in Thailand had a higher density of seedlings,
saplings, spiny palms and rattans, but sparser ground cover and a lower density of large trees and
bamboo, than forests in Myanmar, indicating their secondary nature. Occupied and unoccupied
sites in Myanmar were structurally more similar to each other than either was to occupied sites in
Thailand. The results suggest that the species might inhabit a wider range of altitudes, slopes and
forest types than previously thought, and so might persist in previously unsurveyed areas and
might survive or even benefit from a degree of forest disturbance. However, the species’s
conservation-dependent status in Thailand and accelerating forest clearance in Myanmar suggest
that forest protection measures are urgently needed to secure its long-term future.
Introduction
Gurney’s Pitta Pitta gurneyi is the only bird species endemic to peninsular Thailand and
Myanmar where it inhabits Sundaic lowland forests. Sundaic forest is perhaps the world’s most
threatened ecosystem (Lambert and Collar 2002). In Thailand and Myanmar, the greatest threat
P. F. Donald et al.
2
is clearance for oil palm, which supports few forest species and low biodiversity (Aratrakorn
et al. 2006).
First described from Burma (now Myanmar) in 1875, Gurney’s Pitta has a chequered
ornithological history. Early records suggest that it was common in semi-evergreen forests
between around 7oN and 12oN (Collar et al. 1986), within which range it was probably resident
(Round 1995). However, numbers must have declined rapidly prior to 1952, since it was not
recorded in the wild between that year and its rediscovery in a small area in southern Thailand in
1986 (Round and Treesucon 1986). At this site, around Khao Nor Chuchi in Krabi Province, the
population by 1989 was estimated at just 20–30 pairs and appeared to be heading to extinction
due to rapid forest loss (Gretton et al. 1993). The failure of several conservation efforts to do
more than slow the rate of decline led in 2002 to the formulation and agreement of a Gurney’s
Pitta Species Recovery Plan (GPSRP), adopted by representatives of the relevant Thai
authorities, national and international NGOs, and a range of local stakeholders. The GPSRP
included a range of measures, including research, which needed to be put in place to save the
population from extinction. The results presented in this paper make a contribution to the
technical actions agreed in the GPSRP.
In 2003, the species was rediscovered in Tanintharyi Division in southern Myanmar in what
was assumed, because of the extent of apparently suitable forest, to be considerable numbers
(Eames et al. 2005). Based largely on observations in southern Thailand, it has been suggested
that Gurney’s Pitta is a species of level, lowland forest generally below 100 m a.s.l., possibly with
a preference for secondary or degraded forest (Collar et al. 1986, Round 1995, BirdLife International 2001). Because of this, preliminary surveys in Myanmar were restricted to flat,
lowland forest below 160 m a.s.l. and the resulting population estimate of around 5,000 to 8,500
pairs based upon the assumption that birds were restricted to this habitat (Eames et al. 2005). On
the basis of this estimate, the species’s IUCN Red List threat category was down-listed from
‘Critically Endangered’ to ‘Endangered’ in 2007 (BirdLife International 2008).
This paper presents the results of research on the distribution, habitat use and breeding ecology
of the species undertaken in Thailand from 2004 to 2008 and in Myanmar in 2007 and 2008.
Methods
Myanmar
Fieldwork teams visited the area from March to May 2007 and again from March to April 2008.
These periods coincided with the species’s main period of territorial activity (Gretton et al.
1993, Round 1995, Eames et al. 2005). Access into the forest was opportunistic and greatly
restricted by the small number of roads and tracks, the weather and the security situation, so
a systematic survey of the whole of the lowland forest area of southern Tanintharyi was not
possible (Figure 1). Point transects were used to estimate the distribution and habitat use of
Gurney’s Pitta, with observation points separated by at least 100 m. Observation periods began
without playback to collect unbiased data suitable for distance sampling estimation of density.
After 10 minutes of recording, playback was used to determine the species’ presence followed
by a further 10 minutes of recording, a period within which another pitta species, Pitta
nympha, in Taiwan usually responded when present (Lin et al. 2007a). Observations after
playback were not considered suitable for distance sampling because playback might draw birds
closer to the observer before they responded, leading to inflated density estimates. As too few
contacts were made during the pre-playback period to allow density estimation, the population
was assessed by modelling the distribution and applying the range of densities recorded in
Thailand to this distribution. This follows the approach of Eames et al. (2005), but the extent
of distribution differed from that used by those authors because the collection of more field
data allowed a better estimate of the latitudinal, altitudinal and environmental limits of the
species.
Gurney’s Pitta in Myanmar and Thailand
3
Figure 1. Location of focal area (insert) and extent of remaining lowland evergreen forest (in
green) in southern Myanmar, based on Stibig et al. 2007.
At each point visited in 2007, a number of habitat variables were collected (Table 1). In 2008,
vegetation data were collected only at points over 150 m (as these were under-represented in
2007) and so the sample sizes for analyses of habitat structure was smaller than the total number
of points visited.
P. F. Donald et al.
4
Table 1. Vegetation structure recorded in Myanmar (at sites occupied and not occupied by Gurney’s Pitta)
and Thailand (from inside the core range of the species). Mean values are given. Mean values of each variable
did not differ significantly (at P , 0.05) between sites sharing the same superscripted letter (ANOVA, post
hoc Tukey tests). All variables differed significantly between the site in Thailand and one or both of the
classes of site in Myanmar. dbh 5 diameter at breast height.
Myanmar (unoccupied sites)
Sample size
141
% Ground cover1
86.7a
Seedlings2
7.7a
Bamboo3
6.0a
Spiny palm4
0.39a
Rattan4
1.5a
Trees , 1 cm dbh4
2.7a
Trees 1–10 cm dbh4
10.6a
Trees 10–20 cm dbh4
9.9a
Trees . 20cm dbh4
9.7a
Myanmar (occupied sites) Thailand (occupied sites)
79
96.7b
10.7b
8.0b
0.33a
2.5a
2.0a
15.4b
12.9b
10.5a
44
40.8c
5.0c
0.0c
1.43b
5.0b
13.6b
20.0c
4.7c
3.2b
Collection of habitat variables:
1
Estimated by eye within three 1 m2 quadrats within 10 m of the point and averaged;
2
Average counted within three 1 m2 quadrats within 10 m of the point;
3
Number of clumps within 25 m of the point;
4
Number of trees within 25 m of the point.
Thailand
Complete surveys were undertaken in 2003, 2005 and 2007, during which all forest below 200 m
a.s.l. within the known range of the species in southern Thailand was visited. Forest patches were
identified from aerial photographs and satellite imagery and visited at least twice. Playback was
used to assess or confirm the presence of birds. In 2004 and 2006, surveys were restricted to a core
c. 130-km2 study area of Gretton et al. (1993). Nests were searched for from March to October in
each year. When active nests were found, a hide was erected around 20 m away and nests
guarded round the clock in 6-hour shifts. At night, the nest and surroundings areas were briefly
checked by torchlight at regular intervals and any predators intercepted. Detailed observations
were taken on chick diet and provisioning rates.
Soil moisture measurements were taken using an electronic soil moisture meter along 12
gullies, half of them used regularly by Gurney’s Pittas and the other half not used. Measurements were taken across 10 cross-sections of each gully. On each cross-section, a single measurement was taken at the top of each side, three measurements down each slope and a single
measurement at the bottom of the gully, giving 90 measurements for each gully.
In April 2008, the same observer who collected habitat measurements in Myanmar (TWH)
visited southern Thailand and collected habitat measurements using the same methods at
a number of sites where Gurney’s Pitta were recorded during recent fieldwork. The use of the
same observer ensured comparability between countries in the habitat data collected.
Data analysis
The potentially intercorrelated habitat structure variables (Table 1) were reduced to a smaller
number of uncorrelated axes using unconstrained ordination (Principal Components Analysis,
PCA; McGarigal et al. 2000). Standard parametric tests were used to compare PCA scores
between occupied and unoccupied sites in Myanmar and occupied sites in Thailand to assess
structural differences. Maximum entropy models were used to predict the distribution of
Gurney’s Pitta in Myanmar as a function of land cover, slope and altitude using Maxent 2.3
Gurney’s Pitta in Myanmar and Thailand
5
(Phillips et al. 2006). Land cover characteristics were derived from information collected by the
SPOT – Vegetation sensor. This covers the globe daily, and collects data at a 1-km resolution. The
maximal NDVI (Normalised Difference Vegetation Index) values over 10-day (dekad) periods
for 2005 were extracted from http://free.vgt.vito.be. The 36 images that cover the entire area in
2005 were reduced by using PCA (in Erdas Imagine 8.7), with the top four components being
used in further analysis. Topography data were derived from 90 m Shuttle Radar Topography
Mission SRTM (USGS 2004), 30 arc seconds (Global Land Cover Facility, University of
Maryland, College Park, Maryland, February 2000; www.landcover.org). These indicate spot
heights every 90 m, and were used to calculate average altitude and slope (using the slope
procedure in ArcMap) across 1-km squares throughout southern Myanmar south of 13o N. The
coordinates of all confirmed presences were used (recent surveys and data from Eames et al.
2005). This presented problems, as some 1-km squares (the unit of the analysis) contained
multiple point counts, and the likelihood of a bird being present in a 1-km square increases with
the number of points surveyed (v2 5 9.43, P , 0.005, n 5 104). However it was not possible to
correct for this in the software, and 1-km squares were recorded as occupied irrespective of
amount of observer effort. A map of potentially suitable habitat was produced using georeferenced occurrences and environmental data comparing the spatial environmental variables at
locations where birds were recorded against data from a random selection of other locations across
the focal area, which was the area of lowland forest in southern Myanmar shown in Figure 1.
The 47 1-km squares in which birds were recorded were compared to 10,000 random putative
absences. All non-terrestrial habitats were excluded from the analysis. All data layers were included in the analysis, but 15% of points were used as test data, not included in the model
building, to assess the efficacy of the model.
Because the maximum altitude visited during the field surveys was 226 m (see results), up to
which altitude there was no evidence of a reduction in the probability of recording the species,
three Maxent models were produced. The first was fitted with altitude (producing models that
predict the species’s distribution based upon the observed altitudes), the second with a binary
variable denoting above or below 500 m a.s.l. (to predict the distribution if the altitudinal limit
were 500 m) and the third fitted without altitude (producing models that predict the species’
distribution based solely on land cover). Within each of these three modelled distributions, we
applied territory densities of 2.8 km-2 and 6 km-2, being the extremes recorded within a 2.5 km2
forest study plot in southern Thailand shortly after the rediscovery of the species there (Gretton
et al. 1993).
Results
Myanmar
In total 391 points were visited, 207 along 21 transects in 2007 and 184 along 29 transects in 2008
(Figure 1). Of these, habitat data were collected at 220 points. Gurney’s Pitta was recorded at 101
(25.8%) points, either before playback (11% of first contacts) or after (89%). Too few contacts
were made before playback to allow density estimation using distance sampling.
There were significant differences in forest structure between points where birds were recorded
(before or after playback) and points where they were not recorded (Table 1). Logistic regression
with backward deletion retained four variables (number of bamboo stands, density of seedlings,
number of rattan trees and number of trees 1–10 cm dbh) which were uncorrelated and contributed
independent significant (all P , 0.02) explanatory power. All were positively related to the
likelihood of occurrence of Gurney’s Pitta and the final model correctly assigned 70.3% of points.
Altitude of visited points ranged from 5 m a.s.l. to 226 m a.s.l., with an average of 60.8 m.
There was no difference in altitude between occupied and unoccupied sites (F1,389 5 2.04, P .
0.1), though the highest altitude at which birds were recorded was 184 m (Figure 2). Similarly,
there was no association between the likelihood of occurrence and slope (v23 5 4.37, P . 0.2).
P. F. Donald et al.
6
Figure 2. Histogram of altitude (m a.s.l.) of points surveyed in Myanmar. The shaded portion
indicates points at which Gurney’s Pitta was recorded.
Gurney’s Pitta was recorded between 10o42’ N and 11o47’ N, the last some 20’ (approximately
36 km) north of the previous most northerly record in Myanmar at Lenya (Eames et al. 2005),
and at almost the same latitude as the most northerly historical location in Thailand at 11o50’ N
(BirdLife International 2001).
Maximum entropy models based upon land cover and topography (altitude and slope)
predicted a range of 3,320 km2 (Figure 3). Darker red colours indicate greater chance of
occurrence. The ROC value for the model was reasonably high (0.924), suggesting that the
model was appropriate for predicting distributions. For the 15% of data held back as test data, the
ROC was 0.851, which we consider satisfactory. The optimal cut-off for separating occupied and
apparently unoccupied areas was 0.30, which meant that 13% of the focal area was predicted to
be suitable, equating to approximately 3,320 km2. Most of the predicted range fell within the
GLC2000 land cover (Stibig et al. 2007) class ‘Lowland evergreen forest’, though some also fell
into squares classified as ‘Swamp forest/woodland’.
When altitude was fitted as a binary variable relating to above or below 500 m a.s.l., the
predicted range increased to 5,573 km2, and when altitude was removed from the models and the
range predicted solely from land cover, the predicted range was 5,908 km2. Much of this lies
within the known altitudinal range of Gurney’s Pitta (Figure 4), so even if the species’s
altitudinal limit is significantly higher than previously indicated, this might not result in a much
larger distribution.
When combined with the extreme range of territory densities recorded in Thailand, the estimated population was predicted to lie between 9,296 territories (assuming a range of 3,320 km2
and a density of 2.8 pairs km 2) and 3,5076 (assuming a range of 5,846 km2 and a population
density of 6.0 pairs km 2). If the true range size and population density fall towards the mid
point of the range of estimates, the population can be estimated at 20,165 territories.
Thailand – nesting
In Thailand, 24 nests were found, of which eight were found when active (at four of which
24-hour watches were established). Nests were built almost exclusively in spiny Calamus (rattan)
Gurney’s Pitta in Myanmar and Thailand
7
Figure 3. Modelled distribution (using maximum entropy) of potentially suitable Gurney’s
Pitta habitat in southern Myanmar, based on altitude, slope and SPOT – Vegetation data. Darker
red colours indicate greater modelled suitability. Green points show locations where birds were
recorded by current study and purple points are those where birds were recorded by Eames et al.
(2005).
P. F. Donald et al.
8
Figure 4. Relationship between the area of predicted suitable habitat in southern Myanmar
(from a model of distribution that includes land cover but excludes altitude) and the altitudinal
limit of Gurney’s Pitta, which is currently uncertain.
or Salacca palms (20 of 24 nests), with smaller numbers in climbers (n 5 2) and the canopy of
other trees (n 5 2). Nests were located 0.7–6.2 m above ground level (mean 5 3.2 m, SE 5 0.37,
n 5 24) and tended to be built close to streams, pools or flooded gullies (mean distance to
water 5 14.5 m, SE 5 3.3, n 5 24) and to trails (mean distance 5 20 m). Clutch sizes of two eggs
(n 5 1), three eggs (n 5 2) and four eggs (n 5 2) were recorded. The incubation period was
around 17 days. Of the 18 nests for which an outcome could be determined with any degree of
confidence, only four successfully produced fledged chicks, and three of these were nests that
were guarded around the clock. This might underestimate nest success, as damaged nests could
have been damaged following successful breeding. However, intensive nest guarding confirmed
the high predation rate, as during a total of 53 days and nights of observation at four nests, 11
snake attacks were observed and prevented. All attacks took place at night between 20h00 and
05h00. If it is assumed that each attack would have led to complete nest failure, this equates to
a daily Mayfield nest survival estimate (Mayfield 1975) during the chick stage of 0.792, giving an
estimate of overall nest survival rate over the 16 days the chicks are in the nest of just 2.4%.
Because of removal of snakes from the vicinity of the nest, three out of four protected nests
survived to produce at least one fledgling (the fourth failed when a snake was not detected in
time). All snakes were of the genus Boiga (cat snakes), a genus of generalist and adaptable
predators. The species identified in attacks on guarded nests included Mangrove Snake B.
dendrophila, Dog-toothed Cat Snake B. cynodon, Jasper Cat Snake B. jaspidea and Grey Cat
Snake B. ocellata.
After hatching, chicks remained in the nest for 13–15 days before leaving. Intensive
observations at four nests identified a range of food items but the diet of chicks was clearly
dominated by earthworms (Table 2).
Thailand – population and distribution
Accurate determination of the number of territories of Gurney’s Pitta in Thailand is extremely
difficult because of the frequent movements of calling birds. However, the plotting of near-
Gurney’s Pitta in Myanmar and Thailand
9
Table 2. Identity of items brought to nests by adult Gurney’s Pittas feeding chicks in southern Thailand.
Tabulated values are percentages of all items.
Nest 1 (Oct 2003)
Earthworm
Insect larva
Insect imago
Millipede
Centipede
Spider
Snail
Amphibian
Reptile
Fish
Unidentified
Total items
85.6
4.4
Nest 2 (Jun 2004)
83.8
3.6
0.9
0.5
0.5
0.7
0.5
2.2
Nest 3 (Jul 2004)
88.6
1.8
0.3
0.6
Nest 4 (Sept 2006)
70.7
1.9
0.2
0.4
0.5
0.2
0.6
0.1
7.1
411
9.3
802
0.2
8.0
651
26.8
477
simultaneous contacts suggested a population of 15–20 territories throughout the study period of
2003 to 2007. Minimum numbers of territories were estimated at 16 in 2003, 20 in 2005 and 15 in
2007. In each year, all birds were recorded in the Khao Nor Chuchi lowland forest, including 2–3
territories at Ao Tong in neighbouring Trang province. In total, birds were recorded at 27 sites
over the study period, more than half of them in the Bang Khram Reserved Forest, with the
remainder in the Khao Pra-Bang Khram Wildlife Sanctuary (Table 3). All records were below
100 m a.s.l. with the exception of a single male recorded in 2003 moving through forest at 180 m
a.s.l. (this bird was followed for over 500 m and was presumed to be moving between sites) and
a male at 153 m a.s.l. in 2005. The Thai population lies approximately 300 km due south of the
population in Myanmar.
Soil moisture in gullies used by Gurney’s Pittas was significantly lower along the tops (F1,233 5
16.8, P , 0.0001) and sides (F1,702 5 21.4, P , 0.0001) than gullies not used by birds, but
significantly higher at the bottom of gullies (F1,108 5 14.9, P , 0.0001), where birds preferentially fed.
There was evidence of a decline in the rate of loss of forest within the core area of the species in
southern Thailand after 2000 (Figure 5), suggesting that recent conservation efforts may have
had some success.
Comparing habitats in Thailand and Myanmar
All measures of the structure of occupied forest in Thailand differed significantly from those in
both occupied and unoccupied sites in Myanmar (Table 1), the Thai sites having in particular
Table 3. Number of confirmed Gurney’s Pitta territories recorded in the Khao Pra-Bang Kram Wildlife
Sanctuary and the Khao Nor Chuchi National Reserved Forest, southern Thailand.
Year
KP-BK Wildlife Sanctuary
KNC National Reserved Forest
2003
2004*
2005
2006*
2007
5
2
4
4
7
10
3
16
2
8
*Surveys only undertaken in the core area of Gretton et al. (1993), which included parts of both the Wildlife
Sanctuary and the National Reserved Forest.
P. F. Donald et al.
10
Figure 5. Changes in forest area in the core Gurney’s Pitta area in southern Thailand, estimated
from Landsat and ASTER remote imagery. Values show the percentage cover by forest (primary,
secondary and regenerating) within the 133 km2 area shown in Figure 5 of Gretton et al. 1993 in
four years. This area held most of the Gurney’s Pittas recorded in southern Thailand in each
year. There is evidence of a recent decline in the rate of forest loss, though the estimate from
2007 is subject to some doubt because of cloud cover during the satellite overpass.
a higher density of saplings and small trees, spiny palms and rattan and a lower density of
bamboo and large trees. There was consequently very little overlap between forest in Thailand
and Myanmar in ordination space (Figure 6). Occupied sites in Myanmar were more similar in
forest structure to unoccupied forests in Myanmar than they were to occupied sites in Thailand
(Figure 6).
Figure 6. Scatterplot of scores of the first two principal components of an ordination of point
locations by vegetation variables. Black circles: unoccupied sites in Myanmar, red squares:
occupied sites in Myanmar; green diamonds: occupied sites in Thailand.
Gurney’s Pitta in Myanmar and Thailand
11
Discussion
All results must be interpreted in the light of the extreme difficulty of surveying this species.
Without tape luring, encounters with the species are infrequent even in core areas during the
main calling season. Even using tape luring it is difficult to estimate encounter probability. The
recorded absence of birds from any area must therefore not be taken to indicate certain absence
and the species is likely to be under-recorded where it occurs. However, the fact that the
vegetation measurements in Myanmar varied non-randomly with respect to the recorded
presence or absence of the species suggests that, within the lowland forest biome, birds do
exhibit some measure of habitat selection. The Maxent models also suggest that not all lowland
evergreen forest in southern Myanmar is suitable for the species, and indeed there is a considerable difference between forested areas in southern Myanmar (Figure 1) and the predicted
distribution of the species (Figure 3). Although the forest structure of sites where the species was
recorded in Myanmar differed greatly from that at sites in Thailand (Figure 6), it was interesting
to note that occupied sites in Myanmar held a significantly higher density of seedlings and
saplings and more rattans than unoccupied sites, reflecting perhaps a preference for disturbed or
regenerating forest. In Thailand, sites occupied by Gurney’s Pitta are largely secondary forest of
less than 50 years old, regenerating from previous pastures. The use of secondary forest in
Thailand has previously been assumed to reflect the almost complete loss of primary forest on
low, flat land, forcing the remaining population into sub-optimal alternatives, but the results
from Myanmar provide some support for a preference for disturbed or secondary habitats. The
greatly differing habitat structures recorded in occupied sites in Thailand and Myanmar suggest
that Gurney’s Pitta can occupy a range of forest types and might be able to tolerate a significant
degree of forest disturbance. It also appears that the species occupies a greater altitudinal range
than previously supposed, as there was no evidence of a decline in encounter probability up to the
highest visited altitude of 226 m in Myanmar. It has been suggested that this wider altitudinal
range might reflect a lack of competition with Banded Pitta Pitta guajana, a species which is
apparently absent from southern Myanmar but which might compete with Gurney’s Pitta in
southern Thailand (P. D. Round in litt). The modelled distribution of the species in Myanmar
suggests an extent of occurrence of at least 3,320 km2, rising to nearly 6,000 km2 if the
altitudinal limit is higher than currently thought. The model suggests that populations might
occur as far north as 12o20’ N, some 60 km north of the most northerly sightings made during
the present study, and as far south as 10o35’ N. Further, it indicates that some areas within
western Thailand may still hold suitable habitat, despite being distant from the known occupied
areas within this country. In addition to validating these distribution maps, further work needs to
be undertaken in Myanmar to clarify the altitudinal and latitudinal limits of the species, as this
will allow much more precise estimation of the species’ distribution and population. Forests in
Thailand that are currently considered too high for the species might actually hold birds.
The range of population estimates from Myanmar must be treated with caution since they are
based upon territory densities from Thailand, where the results show the forest structure to differ
significantly. It may be therefore that the average territory density in Myanmar falls outside the
extremes recorded in Thailand. However, the range of territory densities of 10 other species of
pitta given in Lambert & Woodcock (1996) fell within or above the range of estimates used to
estimate the population in Myanmar, suggesting that the estimates from Myanmar are unlikely
to be overestimates.
A heavy reliance on earthworms in the diet of nestlings, and possibly adults, appears to be
a common feature of the genus, as they were found to be the most important item in the diet of
nestling Fairy Pittas Pitta nympha (Lin et al. 2007b) and of adult and nestling Rainbow Pittas
Pitta iris (Zimmerman & Noske 2003). The selection by Gurney’s Pittas in southern Thailand of
wetter than average gullies and the siting of nest sites close to water sources might reflect
a reliance of damp habitats rich in earthworms. This suggests that reforestation efforts currently
underway through the GPSRP should be focused on naturally damper areas.
P. F. Donald et al.
12
Extremely heavy snake predation appears to lead to the loss of a very high proportion of nests
in Thailand. The prevention of no fewer than 11 separate snake attacks at four guarded nests
indicates the severity of this problem, and of only four nests thought to have produced chicks out
of the 24 nests found during the study, three were heavily guarded by 24-hour wardening. Snakes
are perhaps the most important predators of bird nests in the tropics (Weatherhead and BlouinDemers 2004) and their access to nests is facilitated by the interconnectivity of tree canopies
(Koenig et al. 2007). The secondary nature of the forest used by Gurney’s Pitta in southern
Thailand means that canopy connectivity is very high, and the strong selection by nesting
Gurney’s Pittas in Thailand for palms of the genera Calamus and Salacca, which are protected
by sharp spines, might reflect an attempt to reduce predation. The snake species recorded
attacking nests in southern Thailand all belonged to the genus Boiga, which is known to be
highly invasive and to cause high nest predation elsewhere (Wiles et al. 2003). Although the
species involved in attacks of Gurney’s Pitta nests were all native, their densities might have
been inflated by the highly fragmented nature of the forest patches occupied by the bird (e.g.
Chalfoun et al. 2002). Tests using electrical barriers have proved successful in reducing snake
predation of the nests of rare birds (Aguon et al. 2002) and might be useful in the conservation
of Gurney’s Pitta in southern Thailand.
The apparent stabilisation of the population and its lowland forest habitat in Thailand suggest
that recent conservation efforts have had some success in containing previous declines in both.
An apparent reduction in the rate of loss of lowland forest coincides with efforts to reduce illegal
forest clearance through improved forest protection patrols, awareness-raising in the local
community and other actions set out in the GPSRP. A tree nursery has been established, local
staff trained in forest restoration and reforestation plots established. Due to its secondary nature,
it has been estimated that habitat suitable for Gurney’s Pitta could be recreated from confiscated
oil palm plantations within as little as 10–15 years (S. Elliott, pers comm.). However, the complex
political and socioeconomic problems besetting efforts to save the Thai population of Gurney’s
Pitta, described by Gretton et al. (1993) and BirdLife International (2001), have been reduced
rather than removed, and Gurney’s Pitta in Thailand can be regarded as conservation dependent.
As well as being threatened by forest loss, Gurney’s Pittas appear to be very susceptible to
disturbance during the breeding season, leading the local authorities to close the trail system in
the core area during the breeding period. Unfortunately, this ban is ignored by both local people
and visiting birdwatchers. In Myanmar, the population may be considerably higher than
the 5,000 to 8,500 territories estimated by Eames et al. (2005) and forest loss in southern
Tanintharyi was relatively low between 1990 and 2000 (Leimgruber et al. 2005). As a result, the
IUCN threat category for Gurney’s Pitta might merit downlisting to ‘Vulnerable’ (under
category B1) or even ‘Near Threatened’. However, forest loss in Myanmar is likely to accelerate
through state policies to support oil palm plantations and level lowland forest cannot be
regarded as safe anywhere in southeast Asia. Although the species appears able to tolerate
a degree of forest disturbance, and might survive or even benefit from some forest disturbance,
the main threat remains clear-felling for oil palm plantations. The future of this species in both
Myanmar and Thailand will depend on adequate and sustainable forest protection and
management.
Acknowledgements
This work was largely funded by the Darwin Initiative of the UK Government’s Department of
the Environment, Farming and Rural Affairs (DEFRA). Additional funding was provided by the
British Bird Fair. For constructive comments on earlier drafts we thank Stuart Marsden, Anthony
Sebastian, Phil Round and an anonymous referee. For help in many ways during this programme
of research we thank Isorn Sawaddiparp, Pitak Kaeoploy, Phil Round, Kritsana Kaewplang,
U Uga, Petch Manopawitr, Brian and Margaret Sykes, Budsabong Kanchanasaka, Gawin Chutima,
Gurney’s Pitta in Myanmar and Thailand
13
Ian Barber, Yotin Meekaeo, Uthai Treesucon, Stephen Elliott, Steve Parr, John Parr, Debbie Pain,
Dieter Hoffman, Tim Melling, Jeremy Lindsell, Gary Woodburn, Malcolm and Sheena Davies,
Andrew Owen, Somchai Prempanitnukul, Wasun Klomjinda, Prasan Prempree and Somprat
Phonchu.
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PAUL F. DONALD*, GRAEME M. BUCHANAN
RSPB, The Lodge, Sandy, Bedfordshire SG19 2DL, U.K.
SIRIRAK ARATRAKORN
Bird Conservation Society of Thailand, 43 Vipawadi 16/43, Vipawadi-Rangsit Rd., Sam sen nok,
Din Daeng, Bangkok 10400, Thailand.
THURA WIN HTUN, HTIN HLA, SEIN MYO AUNG, SA MYO ZAW
Biodiversity and Nature Conservation Association, 14A Bawga Lane, 9th Mile, Mayangon
Township, A/6-2 Anawrahtar Housing, Hledan, Ward No.2, Kamayut Township, Yangon,
Myanmar.
JONATHAN C. EAMES
BirdLife International in Indochina, No6/2+3, Lane 25, Lang Ha Street, Hanoi, Vietnam.
SOMYING THUNHIKORN, KRIANGSAK SRIBUA-ROD, PINYO TINUN
National Park, Wildlife and Plant Conservation Department, 61 Phahonyothin Road, Ladyaow,
Jatuchak, Bangkok 10900, Thailand.
*Author for correspondence; email: paul.donald@rspb.org.uk
Received 1 September 2008; revision accepted 30 November 2008