in the Status of Lophura Pheasants in Khao Yai National Park, Thailand:
A Response to Warming Climate?
By Philip D.
Round & George A. Gale
This article was originally published in BIOTROPICA 40 (2),
2008 and was kindly submitted by Philip D. Round.
Over the past 100 years, the global average temperature
has increased by approximately 0.6 degrees C and is expected to continue
to rise rapidly (Houghton et al. 2001). Although species
have responded to climatic changes on an evolutionary timescale, a
critical question for wild species is how they cope with the current
rate of change (Root et al. 2003). Among birds, climate change
is linked with earlier breeding (Crick et al. 1997, Forcchammer
et al. 1998, McCleery & Perrins 1998, Crick & Sparks
1999, Schaefer et al. 2006), earlier arrival dates, and later
departure dates in breeding visitors (Mason 1995, Butler 2003, Lehikoinen
et al. 2004, Beaumont et al. 2006, Jonz´en
et al. 2006). Poleward and altitudinal range expansions have
been documented in birds and in many other taxa (Thomas & Lennon
1999, Hickling et al. 2006). Typically, studies of responses
of birds and other species to climate change have focused on organisms
occurring in the temperate zone and climatic zones closer to the poles
(Root et al. 2003).However, since the mid- 1970s all tropical
rain forest regions have experienced a significant warming at a mean
rate of 0.26 ± 0.05 degrees C per decade, in synchrony with
the global increase (Malhi & Wright 2005). In one of the few tropical
studies on birds, Pounds et al. (1999) documented rapid change
in the avifauna (the colonization of montane habitats by nonmontane
species) linked to declining mist frequency (itself induced by rising
air temperatures) in cloud forest in Costa Rica.
Here, we investigate whether the incidence of two species of Lophura
pheasants that occur syntopically in a mid-elevation forest in Khao
Yai National Park, northeastern Thailand has changed in the past
two to three decades, and speculate on the possible causes.
The Silver Pheasant Lophura nycthemera and Siamese Fireback
L. diardi occur sympatrically over much of their SE Asian
ranges encompassing north and east Myanmar, northern and eastern Thailand,
and Indochina (King et al. 1975, Delacour 1977, Dickinson
2003). The race of Silver Pheasant occurring in northern Thailand,
south to Khao Yai, L. n. jonesi, is mainly montane and submontane
in distribution, inhabiting elevations of 700 m and above in Thailand,
though other races are occasionally found lower, down to 200 m in
some parts of Laos and Vietnam, (J. W. Duckworth, pers. comm., J.
C. Eames, pers. comm., R. Timmins, pers. comm.). The monotypic L.
diardi is a lowland species, in Thailand mainly inhabiting forest
in plains and foothills to a maximum elevation of 700–800 m
(King et al. 1975, Lekagul & Round 1991, Robson 2000),
though usually found below 500 m in Laos (J. W. Duckworth, pers. comm.).
Although there is substantial local variation in altitudinal range
in both species across their ranges, the two are only rarely found
alongside each other in Laos and Vietnam (J. W. Duckworth, pers. comm.,
J. C. Eames, pers. comm.). In their relatively wide zone of geographical
overlap, the two species are thus largely segregated by habitat and
AREA - Khao Yai is Thailand’s oldest park, established in
1962, and is occupied mainly by evergreen or semi-evergreen forest,
with small areas of mixed deciduous forest around the northern margins.
Much of this forest is tall and mature, with large trees, and is
roughly evenly divided between foothills (< 600 m) and submontane
elevations (600–1000 m). However, significant areas in the
foothills zone, such as along the southern access road from the
headquarters descending to the town of Prachinburi, have been logged.
were collected within a radius of 5 km of the park headquarters.Most
of the area was evergreen forest alternating with patches of Imperata-dominated
grassland, left over from former cultivation, the area having supported
a small human population before the park was established. Parts
of this grassland area are maintained as grazing habitat for large
herbivores by annual burning or mowing. The topography is an undulating
plateau, at elevations 600–890 m, with over 80 percent of
the area lying > 750 m. The plateau is transected by a major
stream, the Lam Takhong, and there are many smaller streams, most
of which dry up seasonally during February to April. The area has
been regarded as lying in an altitudinal transition zone between
lowland forest and hillslope (or even lower montane) forest (e.g.,
Smitinand 1968). The highest summit in the park, Khao Rom (1350
m), lies only 8.5 km SE of the study area.
OF LOPHURA PHEASANTS IN KHAO YAI. - Dickinson (1963) was the first
to record L. nycthemera in Khao Yai National Park, though
Deignan (1963) was presumably aware of its occurrence there, since
he listed the species ‘south as far as Nakhon Ratchasima,’
the province in which a major part of Khao Yai lies.McClure (1974)
listed both L. nycthemera and L. diardi for Khao
Yai but described both as rare, and his seasonal distribution table
provides only one monthly entry for each species, indicating that
he made, or knew of, very few sightings, perhaps as few as one of
each species, during the period of his coverage (1967–1973).
the scarcity of early records, both L. nycthemera and L.
diardi are now known to be relatively common, and are frequently
observed in the headquarters area of Khao Yai.
AND ANALYSES OF DATA.—Sightings of both Lophura pheasants
were usually reported in the written accounts of birdwatchers, filed
at the (now defunct) Association for the Conservation of Wildlife,
Bangkok, during 1978–1986, and at either the Center for Conservation
Biology,Mahidol University, Bangkok, or the Bird Conservation Society
of Thailand from 1986 onwards up to the present, and this constituted
our primary data source. Further, an appeal for all sightings of
either L. nycthemera or L. diardi in Khao Yai
was posted on the Oriental Birding Newsgroup in January 2000. The
data supplied were usually numbers and sexes of pheasants sighted,
date and duration of visits, and approximate location (by trail),
and were therefore amenable to analysis, even though the search
effort was not standardized. In addition, we incorporated all our
own sightings, made both while birdwatching in the park, and implementing
standardized surveys (below). The extensive trail and road network
allowedmore or less even access across the limited range of elevations
within the park headquarters area. We noted all records of Lophura
pheasants, and recorded search effort as number of days per trip,
regardless of the number of observers. Negative records were also
linear correlations were used to assess changes in pheasant encounter
rates and changes in rainfall and temperature through time. Distance
data from line transects conducted on a mapped 30-ha plot, the Mo-Singto
Long-term Biodiversity Study Plot, lying 800 m from the park headquarters,
during May 2003 to August 2005, analyzed using DISTANCE 5.0 software
(Thomas et al. 2004), were employed to estimate densities
and probability of detections of both species.
(not including those from transect sampling) of a total of 354 individual
pheasants were available for the period of analysis. This comprised
84 sightings (177 individuals) of L. diardi and 87 sightings
of 177 individuals of L. nycthemera. Eighty-six individuals
of both species combined were seen during the 15-yr period from
1979 to 1993 compared with 268 individuals during 1994–2004
inclusive (Fig. 1). The approximate detection rates for these two
periods, for both pheasants combined, were 0.21 pheasants per day
and 0.67 pheasants per day, respectively.
1: Numbers of Lophura pheasants detected in Khao
Yai National Park, ca 1978–2004.
proportions of sightings contributed by each species varied markedly
through time. Up to 1993, L. diardi contributed only 16
of 86 individual pheasants seen (18.6%) with only two sightings
of single individuals being made before 1987. In the period from
1994 to the present, L. diardi contributed more than half of all
pheasants observed (60.1%; 161 out of 268 observations). Lophura
diardi contributed a significantly higher proportion, and L.
nycthemera a significantly lower proportion, of pheasants observed
in the second period than in the first (?2 = 43.1; P < 0.01,
df = 1).
There was a
significant increase in the detection rate of L. diardi during the
survey period, both as measured by the number of individuals per
day (r = 0.607; P = 0.002), and the number of sightings per day
(r=0.686; P<0.001; Fig. 2). In contrast, neither the number of
individuals detected nor the number of sightings per day increased
significantly in L. nycthemera (r = 0.164, P = 0.45 and
r = 0.265, P = 0.708, respectively). There was no significant increase
in flock size in either species during the study period (L.
nycthemera mean flock size: 1.98 ± SD 1.42; r = 0.095,
P = 0.669; L. diardi mean flock-size: 2.22 ± 1.44;
r = 0.376, P = 0.152).
Detection rates of Lophura pheasants, 1980–2004.
disparity between the detection patterns of L. nycthemera
and L. diardi was very striking. One of us (PDR) spent
many hours in 1982–1985 walking trails on the 30-ha Mo-Singto
study plot, with access routes to and from the plot probably adding
another 50 ha in total. Though L. nycthemera was seen eight
times during that period there were no sightings of L. diardi.
A colleague spent approximately 20 d/mo during the period November
1981 to March 1983 studying White-handed Gibbons Hylobates lar
on the same plot, encountering L. nycthemera at least six
times during that period, but never once seeing L. diardi (U.
Treesucon, pers. comm.).
At the present
time, the majority of pheasant encounters on and around the Mo-Singto
plot are with L. diardi. During 2001–2004 we recorded
23 sightings of 48 individual L. ycthemera, compared with
49 sightings of 84 L. diardi on, or in the immediate vicinity
of, the study plot. Camera-trapping, conducted beneath fruiting
Prunus trees during 2004 recorded ca. eight L. diardi
compared with only one L. nycthemera (W.Y. Brockelman, pers. comm.).
The latter observer, who has worked in the park for nearly 30 yr,
commented that L. nycthemera ‘used to be much more
common’ (W.Y. Brockelman, pers. obs.).
transect surveys, we recorded 13 sightings of 23 adult L. nycthemera
and 15 sightings of 34 adult L. diardi. Only six records
of L. nycthemera (46.1%) were on lower, flatter areas below
the 770-m contour, while the 11 of 15 L. diardi records
(73.3%) were below this contour. However this difference was not
statistically significant (?2 = 2.23, P = 0.142) and there was much
estimation, due to the small sample size, and as detection distances
between species appeared to be similar, data from both specieswere
pooled to generate a single detection function following Buckland
et al. (2001). The density estimate for L. diardi
was greater (10.0 groups or 22.8 individuals/km2, vs. 8.0 groups
or 14.7 individuals/km2) However, due to the small sample size,
the variances of the estimates were large (95% CI: 4.7–21.5
groups/km2 for L. diardi and 2.6–24.5 groups/km2 for L.
nycthemera) suggesting that the estimates should be treated
with caution (Buckland et al. 2001).
pheasants presently co-exist in the headquarters of Khao Yai, though
their relative abundance has changed markedly over the past two
decades. The proportion of sightings contributed by L. diardi
changed from 18.6 percent during 1980–1993 (all but two of
these sightings coming from 1987 to 1993) to 60.1 percent during
1994 to 2004. There was a significant increase in the rate of detections
(sightings/unit effort) of L. diardi throughout the study
period, whereas the detection rate of L. nycthemera remained
identified most sightings by trail, most sightings could not be
related to point locations.Data collection was not standardized,
though there was no bias toward data collection from higher or lower
elevations, or from differential spatial coverage during any period
of the study that could account for the observed change in incidence
of the two species through time. While it is likely that some of
the same individuals were observed in the same locations repeatedly
by different observers, the change in the relative proportion of
observations of one species to another would not be expected to
show a strong bias over time. Some of the increase in sightings
may have been due to pheasants becoming tamer and easier to observe
than formerly, following the cessation of hunting in the 40 yr since
the park was established. The improved skills and more detailed
knowledge of birdwatchers on where to find pheasants within the
park may also have contributed. Much less information was available
pre-1990. Neither increased habituation nor differences in coverage
can account for the changing proportions of the two species, however.
If one or the
other species had been more adversely affected by, or less able
to rapidly recover from, predation, this might lead to differential
detectability though time. However, there is no evidence that either
was the case. Both species are equally targeted by hunters. Clutch
sizes are also similar (reported as 6–8 eggs for L. n. jonesi
and 4–8 eggs for L. diardi; A. Hennache, pers. comm. to P.
Garson) suggesting no major difference in intrinsic rates of increase.
Captive L. nycthemera maintained in (Thai) Department of National
Parks breeding stations produced slightly more eggs than did L.
diardi (average 19.4 ggs/female/yr in L. nycthemera compared
with 18.4 eggs in L. diardi (P. Sanpote, pers. comm.).
There are no data on juvenile survival, which is likely to be more
important than clutch size in affecting recruitment, but again is
unlikely to have created such an obvious change in detections.
There has been
no major change in habitat, such as the breakdown in a former physical
or vegetational barrier, which could account for a rapid colonization
of the headquarters area by a species that was formerly absent.
The southern parts of Khao Yai slope down gently from > 1000
m to the park boundary to ca 100 m, and in most of the area the
forest cover is unbroken. Although a northern access road into the
park road was constructed during the late 1950s and early 1960s,
and a connecting road to the southern park boundary was built in
1982, this low level of habitat perturbation would not have affected
the distribution of forest interior species such as pheasants. A
few open-country or deciduous woodland birds that have apparently
benefited, and have recently colonized the headquarters area of
the park (e.g., Asian koel Eudynamys scolopaceus, plaintive
cuckoo Cacomantis merulinus, red-wattled lapwing Vanellus
indicus, racket-tailed treepie Crypsirina temia, common
myna Acridotheres tristis and olive-backed sunbird Nectarinia
jugularis; Lynam et al. 2006) are all confined to
forest edge or grassland, and their numbers have remained small.
Nor is it likely that loss of habitat in the lowlands has displaced
L. diardi and causedmore individuals tomove upslope into
suboptimal habitat formerly occupied solely by L. nycthemera.
If this was the case, it would be likely that, after some initial
increase in numbers in that habitat, the population would gradually
dwindle as senescent birds, unable to sustain their numbers through
recruitment, died off.
LOPHURA PHEASANTS. - Why has L. diardi recently become
more detectable in relation to L. nycthemera? One should
first consider how usual is the co-existence of two Lophura
species in the same habitat.
In the few cases
where Lophura pheasants occur in sympatry, they are usually
ecologically segregated by habitat or elevation (Davison 1981; Thewlis
et al. 1998; BirdLife International 2000, 2001). The co-occurrence
of two Lophura in lowland mixed dipterocarp forest of Malaysia
(Davison 1981) occurs in the context of an exceedingly rich avifauna
and a high level of endemism at the Sunda subregional level. The
avifauna of Khao Yai, by contrast, is relatively species-poor. It
supports, for example, only ten species of babblers and laughingthrushes
(Timaliiinae and Garrulacinae) compared with roughly
25 species of babblers in lowland Sundaic rain forest (Wells 1985).
This makes it all the more surprising that two Lophura
pheasants should both be relatively common in the same habitat.
syntopy of two congeneric pheasants in Khao Yai’s relatively
depauperate avifauna is unlikely to reflect a stable situation,
but instead indicates a dynamic interaction, in which the lowland
species, L. diardi, is increasingly moving into the habitat
of the higher elevation species, L. nycthemera. Even thoughboth
species seemingly take a wide range of plant matter and invertebrates,
the two overlap greatly in feeding ecology, and an increase in one
species might be expected to affect the numbers of the other.
OF CHANGING CLIMATE. - The most likely reason for an increase in
numbers of L. diardi is the operation of an environmental
factor that favors this species. We suggest that factors mediated
by changing climate are the most plausible explanation for the increased
frequency of sightings of L. diardi.
caused directly by rising temperature, or mediated through increased
evapotranspiration, would be expected to benefit plants and animals
of drier lowland habitats at the expense of montane species. Logically,
one might assume that animals would track vegetational changes.However,
changes in distributions might be detected more easily in animals
than in plants due to their greater conspicuousness.Moreover, animals
could be responding to minor vegetational changes such as those
demonstrated by Karr and Freemark (1983) in the understory of a
Panamanian forest including changes in leaf litter depth, soil humidity
or other microclimatic features.
of the forest tree flora on the Mo-Singto permanent plot, carried
out over several years (Brockelman et al. 2002), provides
indications that changes in seedling recruitment among forest trees
are taking place. Seedlings of the third most common tree on the
plot (Nephelium melliferum Fam. Sapindaceae) are
failing to survive on south and west-facing slopes, while adult
trees are distributed throughout the plot. This has tentatively
been attributed to rising temperatures (Brockelman et al.
The direct evidence
for temperature change at Khao Yai is equivocal, however. Temperature
graphs for the two largest provinces abutting Khao Yai, Nakhon Ratchasima
to the north and Prachinburi to the south, show a significant rising
trend in two of three measurements. The mean minimum and mean temperature
for Nakhon Ratchasima, (r = 0.855, P < 0.001 and r = 0.840, P
< 0.001, respectively) and the mean minimum and mean maximum
for Prachinburi (r = 0.713, P < 0.001 and r = 0.706, P<0.001,
respectively) increased by 1.5–2.0?C over a 50-yr period (data
supplied by Meteorology Department, Bangkok). Although the trends
differ between the two stations for mean maximum and mean temperatures,
the trend of increase for mean minimum temperature was very similar
in both. However, the rise documented (~2?C) was larger than has
been recorded elsewhere where the climate is warming, and the effects
of increased urbanization or other ‘heat-island’ effects
around the recording stations have almost certainly contributed.
Temperature records from a recording station in Sakaerat Biosphere
Reserve, which lies to the north-east of Khao Yai, at ca 400 m elevation,
do not show any increase over the past 35 yr, however (data supplied
by Sakaerat Environmental Research Station). Rainfall also showed
no consistent pattern among the stations. There was a statistically
significant decrease in rainfall at Sakaerat during the years 1969–2004
(mean annual rainfall 1059 mm ± SD 239 mm; r = 0.706; P <
0.0001) and for Prachinburi during 1951–2003 (mean annual
rainfall 1929 mm ± SD 297; r = 0.321; P = 0.019). However,
the annual rainfall at third site, Pak Chong, to the north of the
park, showed no significant trend (mean annual rainfall during 1972–2004:
1113mm±SD 178; r= 0.173; P = 0.337). Temperatures elsewhere
in the region (southwestern China) have significantly increased,
while rainfall has significantly declined or increased depending on the station. In particular, temperatures
most notably increased and rainfall decreased in the lower reaches
of the Lancang (Mekong) river (Yunling & Yiping 2005).
FUTURE WORK. - The most plausible explanation is that there has
been a real increase in the size and viability of the L. diardi
population in the park headquarters area in response to changes
in an environmental variable. Lophura nycthemera, in contrast,
has not increased, and, allowing for likely increased detectability
in both pheasant species, may have actually declined during the
study period. The most plausible explanation for the observed trend
is climate change.
change may not be the only factor implicated, however. Khao Yai
was formerly part of a much larger area of surrounding forest, most
of which has since been cleared for farmland. Forest cover in the
provinces surrounding Khao Yai was reduced by 25–50 percent during 1973–1995 (Kermel-Torr`es 2004).
Fragmentation and associated edge effects such as reported in Pasoh,
Malaysia, can negatively affect a wide range of wildlife, including
insects, birds, and mammals (Okuda et al. 2003). The more
than 2000 km2 area of Khao Yai is a relatively large fragment. However,
the impact of large-scale deforestation on regional climate has
been demonstrated for Amazonia where, during the dry season, higher
temperatures and higher rainfall were observed over deforested areas
compared to forested areas (Negri et al. 2004). Loss of
forest from areas surrounding Khao Yai might be expected to induce
drying and increased temperatures in the forest interior that might
also benefit lowland species.
Two other species-pairs
that might respond similarly to any habitat changes, whose habitat
relations are apparently similar to those of the pheasants and whose
numbers might be more easily tracked, are orange-breasted trogon
Harpactes oreskios (lowland) and red-headed trogon H.
erythrocephalus (submontane/montane); and Hainan blue flycatcher
Cyornis hainanus (lowland) and hill blue flycatcher C.
banyumas (submontane/montane). Both trogons occur on the Mo-Singto
permanent plot, in roughly similar numbers (there were 198 orange-breasted
trogons detections during May 2003–August 2005 compared with
243 red-headed trogon detections; Khao Yai Avian Diversity Project,
unpub. data). They are presumably ecologically segregated, and their
co-existence is not surprising, given that as many as four Harpactes
spp. may co-exist in lowland Sundaic rain forest (Wells 1999). We
have a strong suspicion that C. hainanus has become more common
in the past couple of decades. While both C. hainanus and
C. banyumas were previously known from the headquarters
area of Khao Yai, C. hainanus was usually found in the
lower-lying areas, 600–700 m. Only C. banyumas was
present on the Mo-Singto Plot during 1982–1983, and again
during 2000–2002, when intensive observations were recommenced
there. However, at least two C. hainanus appeared on the
plot for the first time during 2003. This is too little information
on which to base any conclusions, especially as C. hainanus
may tend to favor, and move into, small natural clearings and tangles
occasioned by treefalls, but it suggests that further monitoring
of these species-pairs, in addition to the Lophura pheasants,
might be instructive.
We cannot yet
prove that L. nycthemera has declined as L. diardi
has increased in numbers. If climate change is inducing vegetational
or other changes that favor the lowland species (L. diardi),
this is likely to be at the expense of the upland species, (L.
nycthemera) and we should eventually be able to demonstrate
an increase in the altitudinal range occupied by L. diardi,
and an upslope retreat of L. nycthemera. Up to now, though,
there have been few surveys outside of the narrow elevational range
around the Khao Yai headquarters in which our studies were conducted.
In addition to investigating the detailed ecology and interactions
between the two pheasants, future studies should concentrate upon
conducting standardized sampling of a wider range of bird species,
including, but not limited to, the other species-pairs mentioned,
along altitudinal gradients in the park. It would also be necessary
to increase the number of meteorological stations in and around
the park in order to monitor climatic changes.
areas in the tropics are small fragments of former large expanses
of forest. It may take many decades before the full effects of isolation
and fragmentation, and edge effects on the communities of plants
and animals that livewithin their boundaries, become fully evident.
However, the deleterious impacts of these factors are likely to
be exacerbated due to climate change. There is an urgent need for
more widespread monitoring of population trends among potentially
sensitive species, and also for the monitoring of habitat change
in tropical forest fragments.
We thank the many observers who submitted many of the records on which
this paper is based (see also Acknowledgments S1). K. Tokue and K.
Pobprasert assisted in compiling records. P. Sanpote, Director, Captive
Propagation Division, Department of National Parks (Bangkok), P.Garson,
and A.Hennache provided information on captive birds. W. Brockelman,
J. W. Duckworth, J. C. Eames, D. Hilbert, T. Savini, D. Wells, and
D. Westcott commented on versions of this manuscript. This analysis
was conducted while the authors were working on project BRT R_346004
(‘The Khao Yai Avian Diversity Project’) supported by
the Biodiversity Research and Training Programme, Thailand. PDR would
additionally like to thank The Wetland Trust (UK) for support.
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Round, Department of Biology, Faculty of Science, Mahidol University,
Rama 6 Road, Bangkok 10400, Thailand. Email: email@example.com
Gale, King Mongkut’s University of Technology Thonburi, School
of Bioresources & Technology, 83 Mu 8 Thakham, Bangkhuntien,
Bangkok 10150, Thailand.