Jayasekara et al. /Journal of Tropical Forestry and Environment Vol. 9, No. 01 (2019) 59-68

Microhabitat Utilisation of Endemic Lizard Calotes nigrilabris in the

Grasslands of Horton Plains National Park, Sri Lanka

Jayasekara E.G.D.P., Prabhath M.C., Mahaulpatha W.A.D.*

Department of Zoology, University of Sri Jayewardenepura, Gangodawila, Nugegoda, Sri Lanka

Date Received: 20-02-2019 Date Accepted: 16-05-2019

Abstract

The endemic endangered agamid lizard Calotes nigrilabris inhabits the grasslands of Horton

Plains National Park (HPNP) and it is restricted to a few localities in the central highlands of Sri Lanka.

In this study, the microhabitat utilisation of Calotes nigrilabris was investigated utilising line transects

and quadrate method. The comparison of available microhabitat variables with occupied microhabitat

variables revealed that there was a significant difference between some of the variables (Man-Whiteney U

test, p<0.05) indicating that C. nigrilabris was selective in its microhabitat utilisation. Based on PCA

analysis, amount and type of vegetation was the main determining factor of microhabitat preference of

this species. Ulex sp. cover (PC1, 0.606) and Rhododendron sp. cover (PC2,-0.603) were significantly

affecting the occupied microhabitat structure. Microhabitat utilisation varied in the temporal and spatial

scales also indicating clear resource partitioning between different maturity stages. The results of this

study indicate that C. nigrilabris actively selects and utilises the most suitable grassland microhabitats of

HPNP and provide important insights for the conservation and management of the species as well as its

natural habitat.

Keywords: Black-cheeked lizard, grassland habitat, resource partitioning, Agamidae, Ulex europaeus

1. Introduction

A habitat can be defined as the sum of the specific resources that are needed by organisms

(Thomas, 1979) which include food, cover, water and special factors needed by a species for survival and

reproductive success (Leopold, 1933). Macrohabitat and microhabitat are two relatable terms which

depend on the scale of landscape and relate more to a specific animal being studied rather than to a type of

habitat (Krausman, 1999). According to Johnson (1980) microhabitat usually refers to finer scaled habitat

features which are at the lower levels of the hierarchical structure of habitats. Since lizards are

ectothermal animals, they tend to depend highly on smaller microhabitats for thermoregulation. However

microhabitat selection may also depend on morphology and behavioral preferences of the animal (Adolph,

1990). According to Arnold (1983) force of natural selection on specific aspects of morphology,

physiology and behaviour lead to differences in functional capabilities, which, in turn, are adaptive for the

differing demands of different environments (Schulte et al., 2004). Therefore, animal populations develop

certain traits which increase their fitness in the given habitat (Arnold, 1983) which is also reflected in

microhabitat utilisation (Adolph, 1990). The term microhabitat utilisation can be defined as the practical

and effective use of the available microhabitats by a species. Thus, understanding the microhabitat

requirements and the utilisation of those microhabitats by a species requires considering different life

history strategies, morphometry, behavioural characteristics as well as environmental parameters

(Krausman, 1999).

*Correspondence: mahaulpatha@sjp.ac.lk
Tel: +94 718251516

DOI: https://doi.org/10.31357/jtfe.v9i1.3952

Horton Plains National Park is home for three of Sri Lanka’s agamid lizards, all of which are

endemic to the island. Critically endangered (CR) Cophotis ceylanica and endangered (EN) Ceratophora

stoddarti occur in its montane cloud forests (De Silva, 2007). The association of endangered C.

nigrilabris with the grasslands of HPNP and surrounding areas has long been observed (Manamendra-

Arachchi and Liyanage, 1994; Bahir and Surasinghe, 2005; De Silva, 2007; Somaweera and Somaweera,

2009; Amarasinghe et al., 2011; Somaweera et al., 2012). C. nigrilabris is usually considered a diurnal

sub-arboreal species (Das and De Silva, 2005) that prefer low shrubs and ferns. This species is restricted

to montane forests above 1300 m elevation (Erdelen, 1984) and it is the only agamid species to occur in

the tropical high altitude grasslands of the island (Bahir and Surasinghe, 2005). Even though some

qualitative information regarding the habitat utilization of C. nigrilabris is available in the published

literature (De Silva, 2007; Somaweera and Somaweera, 2009; Amarasinghe et al., 2011) no quantitative

studies have been done, especially regarding the microhabitat utilisation, except for the study conducted

by Somaweera et al. (2012) to find the effect of Ulex europaeus on habitat selection of C. nigrilbris. In

this research we focused on the ecological aspects of C. nigrilabris with reference to microhabitat

utilisation to provide relevant information to bridge the gaps in data availability to help the conservation

and management. Therefore, the objectives of this study were to identify the microhabitat requirements,

microhabitat preferences and utilisation of those microhabitats by this species.

2. Methodology

2.1 Study site

We conducted the study for a period of one year from January to December 2016 in Horton Plains

National Park. It is located on the southern plateau of the central highlands of tropical island Sri Lanka

(6°47'-6*50'N, 80°46'-80°50'E) (Green, 1990; DWC, 2007). This is a unique national park in Sri Lanka

with discrete weather patterns and climatic conditions which harbors a large number of flora and fauna

with a high percentage of endemism (Pethiyagoda, 2012).

2.2 Grassland Habitat

We conducted sampling in the grassland (wet patana) habitat which makes up an area of 776 ha

(25.8%) of HPNP. Grasses generally known as ‘tussock grass” (Chrysopogon nodulibarbis, Andropogon

polyptychos and Garnotiaex aristata) are the more dominant plants in this habitat (DWC, 2007). “Maha

ratmal” (Rhododendron arboreum) and “european gorse” (Ulexe uropaeus) are commonly found scattered

throughout these grasslands. Invasive Ulex europaeus sometimes grows as impenetrable stands

threatening the native flora. Abandoned potato terraces have been colonized by carpet grass (Axonopus

fissifolius) which gives the appearance of a lawn (DWC, 2007).

2.3 Sampling

We carried out our sampling work utilising visual encounter surveys (Doan, 2003) along 200 m

line-transects (Garcia, 2008) in the grassland habitat. We recorded only the lizards we could observe

within 2 m on either side of transect and up to a height of 4 m to reduce any possible bias caused by the

variation in visibility. The maturity stage of each lizard (adult male, adult female, sub-adult male, sub-

adult female and juvenile) was also determined based on morphometrics (mainly relative estimation of

SVL) (Jayasekara et al., 2017) and secondary sexual characteristics when needed. We considered both

sub-adult male and sub-adult female under one category called “sub-adult” in the data analysis.

Transect surveys were carried out by two people one day per month (for a period of one year)

from 08.00 h to 17.00 h in three time periods; morning (08:00 h-11:00 h), midday (11:00 h-14.00 h) and

evening (14:00 h-17:00 h), with a sampling effort of 216 person-hours and a total of 108 transects. We did

observations by walking along transects at a very low speed (3-4 m/min) in order to carefully observe

both sides of transect without disturbing the natural behavior of lizards (Chandramouli, 2009).

Jayasekara et al. /Journal of Tropical Forestry and Environment Vol. 9, No. 01 (2019) 59-68

2.4 Microhabitat availability

Microhabitat availability was measured by putting five 1x1 m quadrates randomly along each

transect using a random number table (Díaz et al. 2006). At each quadrate we recorded percentage cover

of each plant species, rocks, leaf litter and bare soil. Ambient temperature and relative humidity at chest

height (Blair, 2009) were measured using Kestrel 4,000 pocket weather meter, USA.

We also measured soil characteristics like soil penetration (using soil penetrometer-Land

penetrometer INC.), soil pH and moisture content (using soil pH meter [Kelway soil acidity (pH) and

moisture tester]). A metal ruler was used to measure the leaf litter depth. We recorded the percentage

cover of each plant species, rocks, leaf litter and bare soil within each quadrate. In occasions where lizards

were occupying random quadrates, we considered them as occupied quadrates and did not consider them

under available microhabitats. A total of 320 unoccupied quadrates were sampled during the study period.

2.5 Microhabitat use of C. nigrilabris

We broadly classified the perch types where we sighted C. nigrilabris as ground, leaf litter, shrub,

tree trunk, tree-branch and tree-leaf. We recorded the perch type where we first sighted each C.

nigrilabris. To study the preferred microhabitat 1x1 m quadrates were put along each transect having the

point of each lizard sighting as the center. A number of different parameters at the center of each occupied

quadrate were recorded as follows.

We categorised and recorded perch light to lizard’s location as full sun light (75% or greater

sunlight) filtered sun light (25% to 75% sunlight) and shade (less than 25% sunlight) (Angert et al., 2002).

Photo analysis was assisted in determining the light percentage. Perching plant species of lizards were

identified and the percentage cover of each plant species within the quadrate was determined by visual

estimation. We recorded percentage cover of each plant species, rocks, leaf litter and bare soil, ambient

temperature, relative humidity, soil penetration, soil pH and moisture content, leaf litter depth, percentage

cover of rocks, leaf litter and bare soil within each quadrate were also measured. A total of 303 occupied

quadrates were sampled.

2.6 Data analysis

Minitab version 17 statistical software package and Microsoft Excel were used for statistical

analysis and graphical representation of results. Principal components analysis (PCA) together with Eigen

analysis was performed to find out important microhabitat variables of occupied quadrates. Non

parametric Mann-Whitney U-test at significance level (p=0.05) was conducted to compare the

microhabitat variables between occupied and unoccupied quadrates of C. nigrilabris. Sample data were

checked for normality and other assumptions of parametric tests when required. One way ANOVA

(Analysis of Variance) was used to examine variations in perch height between different age classes of C.

nigrilabris. Non parametric Kruskal-Wallis test was performed when assumptions for parametric tests

were not met. Kruskal-Wallis analysis was used to examine significant differences in perch plant

preference.

3. Results

3.1 Microhabitat preference of C. nigrilabris

Characteristics of microhabitats occupied by C. nigrilabris were different from the available

random unoccupied quadrate characteristics. Variables that significantly differed include; Ulex sp. cover,

Rhododendron sp. cover, Tussock grass cover, fern (Pteridium sp.) cover, other plant cover, bare soil

percentage, temperature (ambient), relative humidity and soil moisture percentage. Therefore, those

variables correlated with microhabitat occupancy of C. nigrilabris (Table 1).

Table 1: Characteristics of available habitat variables vs. occupied microhabitats (Mean±SD).

Variable
Random unoccupied

quadrate (n=320)

Occupied quadrate

(n=303)

Mann-Whitney U-test

p value

Ulex sp. cover (%) 12.77±13.00 28.58±32.19 0.0001*

Rhododendron sp. cover (%) 13.58±20.41 25.59±30.23 0.0001*

Tussock grass cover (%) 28.41±17.25 14.109±14.91 0.0001*

Fern(Pteridium sp.) cover (%) 8.75±13.01 12.112±14.66 0.0000*

Dwarf bamboo cover (%) 3.45±7.48 3.564±9.81 0.0787

Other plant cover (%) 14.75±11.58 7.574±7.67 0.0001*

Cover of rocks (%) 1.606±3.40 1.436±3.66 0.0644

Bare soil (%) 6.33±6.12 7.079±15.57 0.0000*

Leaf Litter depth (cm) 4.403±2.41 4.607±5.55 0.0711

Leaf Litter cover (%) 11.53±8.31 11.271±10.39 0.2172

Temperature (ambient) 23.823±4.27 21.445±3.75 0.0000*

Relative Humidity (%) 76.60±11.79 73.002±14.37 0.0133*

Soil penetration (MPa) 11.71±2.32 12.041±2.61 0.3644

Soil pH 6.73±0.07 6.7282±0.07 0.4097

Soil moisture (%) 10.97±7.81 14.439±5.35 0.0001*

*Significantly different variables marked with “*” and in bold.

First five axes of the PCA analysis of microhabitat variables which were significantly different

from available habitat characteristics accounted for 75.3% of the total variance according to the Eigen

analysis of the Correlation Matrix. The first principal component (PC1) correlated positively with Ulex

sp. (PC1, 0.606) cover having the highest impact on PC1. It correlated negatively with Tussock cover.

Hence an increase in Ulex sp. cover will lead to a decrease in Tussock cover. The second component

(PC2) gave high scores to sites with high values of Rhododendron sp. cover (PC2, -0.603). PC3 correlated

negatively with Rhododendron sp. (PC3, -0.513) cover and positively with bare soil cover (PC3, 0.577).

Soil moisture percentage, other plant cover and relative humidity were significant respectively in PC4 and

PC5. The overall PCA result indicated that availability of different plant species (vegetation) is important

in deciding the preferred microhabitat of C. nigrilabris (Table 2).

Table 2: Factor loadings for the first five principal component (PC) axes of occupied microhabitat

variables.

Variable PC1 PC2 PC3 PC4 PC5

(OQ) Ulex sp. cover 0.606 0.379 0.163 -0.073 0.029

(OQ)Rhododendron sp. cover -0.097 -0.603 -0.513 0.032 0.074

(OQ) Tussock cover -0.51 0.325 -0.062 0.043 -0.282

(OQ)Fern (Pteridium sp.) cover -0.472 0.414 0.004 -0.113 -0.039

(OQ) Other plant cover -0.342 -0.033 0.265 0.128 0.615

(OQ) Bare soil -0.017 -0.251 0.577 0.131 -0.153

(OQ) Temperature (a) -0.105 -0.247 0.473 -0.143 0.27

(OQ) Soil moisture 0.003 -0.044 0.109 0.872 -0.291

(OQ)Relative Humidity 0.108 0.296 -0.261 0.405 0.595

*Significant variables of each axis are in bold.

3.2 Microhabitat variables in occupied quadrates

C. nigrilabris preferred microhabitats with high percentages of larger grassland plant species like

Ulex sp. (28.58±32.19)% and Rhododendron sp. (25.59±30.23)%. The percentages of Tussock grass

(14.11±14.9)% and other plants (7.57±7.67)% were relatively low in occupied microhabitats of C.

nigrilabris when compared to random sites. Average percentage of Fern (Pteridium sp.) cover was

12.11±14.66%. Average ambient temperature and substrate temperatures of the preferred microhabitats

were (21.45±3.75)o C and (20.22±4.00)o C respectively. Bare soil percentage cover (7.08±15.57)% and

Jayasekara et al. /Journal of Tropical Forestry and Environment Vol. 9, No. 01 (2019) 59-68

soil moisture percentage (14.44±5.35)% recorded high average values. Average value for relative

humidity was (73.00±14.37)% within microhabitats (Table 3).

Table 3: Microhabitat variables in occupied quadrates.

Variable Mean±SD n=330 Minimum Maximum

Ulex sp. cover (%) 28.58±32.19 0 60

Rhododendron sp. cover (%) 25.59±30.23 0 80

Tussock grass cover (%) 14.11±14.91 5 60

Fern (Pteridium sp.) cover (%) 12.11±14.66 0 40

Other plant cover (%) 7.57±7.67 5 40

Bare soil (%) 7.08±15.57 0 25

Ambient Temperature (ºC) 21.45±3.75 2 30.9

Substrate Temperature (ºC) 20.22±4.00 11 31.2

Relative Humidity 73.00±14.37 61 98.2

Soil moisture (%) 14.44±5.35 5 40

3.3 Perch type preference of C. nigrilabris

We observed the highest average percentage of individuals perching on branches (55.12±11.97)%.

Second most preferred perch type of C. nigrilabris was leaves (35.84±14.23)%. Relatively low

percentages of lizards were perching on shrubs (3.33±5.53)% and ground (5.49±8.3)%. Very low

percentage of lizards (0.22±0.76)% used tree trunks for perching. (Figure 1A).

3.4 Preferred perch plant of different maturity stages

There was a significant difference in preferred perch plant within maturity stages of C. nigrilabris

adult male, adult female, sub-adult and juvenile [Kruskal-Wallis, p<0.05]. Highest percentage of adult

males was recorded perching on Rhododendron sp. (75.27±17.25) % (Figure 3A). Most preferred perch

plant of adult females was Ulex sp. (70.88±14.29) % (Figure 3B). A high percentage of sub-adults were

observed perching on Ulex sp. (35.05±30.72) % while their second most preferred plant species was

Rhododendron sp. (Figure 3E). There was no significant difference in average percentage of juveniles

observed in different plant species [Kruskal-Wallis, p=0.071, p>0.05]. However, juveniles most preferred

Rhododendron sp. and fern–Pteridium sp. (Figure 1B).

3.5 Diurnal perch light preference

In the morning time period highest percentage (78.47%) of C. nigrilabris were perching in full sun

light. Filtered sun light and shaded perches were used by 10.42% and 11.11% of lizards respectively in

the morning. During mid day time period lizards used all three perch types in approximately equal

amounts (31.88%, 30.43 % and 37.68 %). Most used perch light condition in the evening time period was

shade (82.02 %). (Figure 2A).

3.6 Diurnal Perch height variation in maturity stages

Perch height varied significantly between different maturity stages of C. nigrilabris [ANOVA,

F=21.93, p<0.05]. Average perch heights of adult males (103.60±63.48) cm and females (93.28±54.04)

cm were significantly higher than sub-adults (67.40±42.07) cm and juveniles (26.03±36.58) cm. Average

perch height juveniles was the lowest and it was significantly different from the average perch height of

sub-adults and the two adult maturity stages. There was no significant difference in the observed average

perch height in the three time periods (ANOVA, p>0.05). However, average perch height increased from

morning to mid day. We observed a decrease in the average perch height in the evening time period in all

four maturity stage categories (Figure 2b).

Figure 1: a-Perch type preference of C. nigrilabris; b-Perch plants of different maturity stages.

Figure 2: a-Diurnal perch light preference of C. nigrilabris; b-Diurnal Perch height variation of

different maturity stages (AF-Adult female, J-Juvenile, AM-Adult male, SA-Sub-adult).

Figure 3: a=C. nigrilabris adult male; b=C. nigrilabris adult female preying near the flowers

of Ulex europeus; c=Arial view of an adult male C. nigrilabris being camouflaged among the

Rhododendron sp. Leaves; d=Acrobatic movement of female C. nigrilabris between thorny

Ulex sp. Branches; e=A sub-adult female on the leaves of Rhododendron sp.; f-A juvenile on

the leaves of fern (Pteridium sp.).

a b

b a

Jayasekara et al. /Journal of Tropical Forestry and Environment Vol. 9, No. 01 (2019) 59-68

4. Discussion

C. nigrilabris was selective in its use of microhabitats. Most of the observed variables within

occupied microhabitats of C. nigrilabris were significantly different from the variables that were available

in random unoccupied sites. Therefore, variables such as Ulex sp. cover, Rhododendron sp. cover,

Tussock grass cover, fern (Pteridium sp.) cover, other plant cover, bare soil percentage, temperature

(ambient), relative humidity and soil moisture percentage were the determining factors of the microhabitat

of C. nigrilabris. According to the PCA results, Ulex sp. cover, Rhododendron sp. cover, Tussock grass

cover, and other plant cover were significantly affecting the microhabitat conditions. Therefore it can be

concluded that available vegetation type directly affects the microhabitat utilisation of C. nigrilabris.

High percentages of larger grassland plant species like Ulex sp. (28.58±32.19%) and Rhododendron sp.

(25.59±30.23%) were present within the occupied microhabitats. Both of these plants were utilised by C.

nigrilabris for a number of different behaviours. Lizards tend to bask on leaves or branches of these two

plant species in the morning sun light. They perch near the flowers of either Ulex sp. or Rhodhodendron

sp. to catch the prey that is attracted to the nectar of these flowers. They also used these plants for resting

and sleeping. We observed courtship behaviour on Rhodhodendron sp. leaves which are broad and

relatively rigid. Thorny Ulex sp. plant also provides good refuge from the possible predators of C.

nigrilabris. Somaweera et al. (2012) also suggested this type of a relationship between Ulex sp. (European

Gorse) and C. nigrilabris. These two plants are also the only species that grow several meters taller than

the dominant grasses of the grassland habitat. PCA results indicate that increase in percentage cover of

these two species leads to the decrease in the cover of tussock grasses within microhabitats. Hence, mean

percentage cover of tussock grass (14.11±14.91%) and other plants (7.57±7.67%) were relatively low in

occupied sites than random sites. Fern (Pteridium sp.) was another frequently occurring plant within

preferred microhabitats but in rather low percentages (12.11±14.66%).

Ambient temperature and substrate temperatures of occupied microhabitats were significantly

different from the random unoccupied. This result can be attributed to the thermoregulatory behaviour of

C. nigrilabris and lizards as a whole. Since lizards are ectothermic animals, the environmental

temperature has a high impact on their body temperature. Therefore, they tend to utilise microhabitats

which provide them suitable temperature conditions. Hence, C. nigrilabris was selective in microhabitats

with such conditions. Bare soil percentage cover (7.08±15.57%) and soil moisture percentage

(14.44±5.35%) were another two variables that were significantly higher in occupied microhabitats. These

two factors increased the presence of egg laying females providing suitable conditions for them, which in

turn increased the number of individuals of other maturity like newly hatched juveniles and mate seeking

adult males in the nearby microhabitats.

Dwarf bamboo cover, leaf litter depth, leaf litter cover, soil penetration and soil pH did not vary

significantly between occupied microhabitats and unoccupied random sites. Therefore, we can consider

those factors less important and not having a high impact on microhabitat selection and utilisation of C.

nigrilabris. Furthermore, leaf litter amount was relatively low within the grassland habitat in general since

not many woody plants were occurring. However, top soil layer was a thick humus layer within most of

the grassland habitat which is considered slightly acidic as Person (1899) mentioned (Pethiyagoda, 2012)

and results of the present study go in accordance with that.

From the available perch types within their microhabitat, C. nigrilabris mostly used plant leaves

and branches for perching indicating that it is an arboreal species as Somaweera and Somaweera (2009)

and Amarasinghe et al. (2011) described. A lower percentage of individuals were perching on tree trunks.

This result may be related to the greenish body colour of this species which is easily camouflaged with

leaves and leafy branches rather than darker tree trunks. They were also found on low shrubs and on the

ground as well. We observed ground foraging during sunny mornings where they fed on small

invertebrates. Therefore, C. nigrilabris can be considered as a sub-arboreal species in concordance with

Karunarathna et al. (2011).

Since C. nigrilabris is largely arboreal and their microhabitat preference was highly determined by

the vegetative cover. Therefore, it was interesting to study the perch plant preferences of this species. The

most preferred perching plants of C. nigrilabris were Rhododendron sp. and Ulex sp. However there was

a significant difference between preferred perch plant of different age classes. Adult males (Figure 3A)

mostly preferred Rhododendron sp. whereas adult females preferred Ulex sp. (Figure 3B, D). We can

attribute this result to the body colour difference between the two genders. Adult males with relatively

darker green body colour were better adapted to utilize Rhododendron sp. which also has leaves with a

darker shade of green. The triangular heads of matured males with black bands on the upper lips which

easily merge with Rhododendron sp. leaves makes it difficult for the aerial predators to spot them.

Sometimes even the dorsal scales of the head region were also occupied with blackish edges resembling

the venation of leaf blades making them better camouflaged (Figure 3c).

In contrast adult females with relatively lighter body colour preferred Ulex sp. which has a similar

shade of green. Thorny branches of Ulex sp. provide them protection while making up a rich microhabitat

with high abundance of nectaring insect species as food sources. Relatively smaller bodied females were

able to move around the Ulex sp. bushes with ease than larger bodied males further separating the two

genders into these two plant species. However there were shifts in usual perching plants of these maturity

stages in specific behaviours. We observed adult males preying for insects on Ulex sp. during periods

with high insect densities around Ulex sp. flowers. During heavy ground frost conditions both males and

females were resting and sleeping under the broad leaf blades of Rhododendron sp. In all courtship

behaviours observed females moved on to Rhododendron sp. plants where males were perching. Sub-

adults (Figure 3e) used both these plant types. However percentage of individuals that used Ulex sp. for

perching was slightly higher. Juveniles mostly preferred young Rhododendron sp. plants that were close

to the ground. Another important result was high percentage of juveniles that used to perch on leaves of

fern-Pteridium sp. Juveniles which have the lightest shade of green among the five maturity stages were

benefited by perching on these fern leaves (Figure 3f) which were also light green in colour during young

stage.

Diurnal perch light preference of C. nigrilabris varied in different time periods of the day. To cope

with the temporal variation in the thermal environment, lizards need precise thermoregulation strategies

which involve flexible use of structural habitat (Porter et al., 1973; Adolph, 1990). According to Bennett

(1980) many lizard species have a relatively narrow range of preferred body temperatures and it in turn

corresponds to various physiological optima. Because of the spatial variation of thermal microclimates,

thermal biology and habitat use are interrelated (Roughgarden et al., 1981; Waldschmidt, and Tracy,

1983; Grant and Dunham, 1988; Adolph 1990). During the morning time period C. nigrilabris spent most

of the time in full sunlight which provide them required thermal energy for their activities. To maintain

optimal body temperatures they were utilising more filtered sun light and shaded perches in the mid day

and evening time periods.

There was a significant difference between average perch height of different age classes. Adult

males were occupying the highest perches closely followed by adult females. Average perch heights of

sub-adults and juveniles were significantly lower than adults. Juveniles were perching at the lowest level

more close to the ground. This result indicates a clear resource partitioning between the four age classes.

This behaviour would help them to utilise their microhabitat more effectively by sharing the resources

between maturity stages. Even though average perch height of any of the age classes did not vary

significantly in temporal scale, we could observe some variation in average perch height between the

three time periods considered. Perch height gradually increased from morning to mid day to reach a peak

height for each age class. This result indicates that C. nigrilabris start from lower sleeping perches to

Jayasekara et al. /Journal of Tropical Forestry and Environment Vol. 9, No. 01 (2019) 59-68

reach thermally suitable perches to help their activity. They used high perches for basking and feeding

during morning and mid day time periods. In all maturity stages perch height gradually decreased from

mid day to evening. A similar behaviour has been observed by De Silva (2007) and Somaweera and

Somaweera (2009). This is because C. nigrilabris descend down to sleep in more thermally preferable

lower shrubs and grasses during colder late evenings and nights.

5. Conclusions

C. nigrilabris in the grasslands of HPNP was actively selecting its microhabitats. We can conclude

that Ulex sp., Rhododendron sp. and fern (Pteridum sp.) are the most important plants for the survival of

this species in the grasslands habitat. However, it is not applicable to the areas outside the park where the

habitat composition is different. Most importantly Ulex sp. and Pteridium sp. are considered as invasive

species. Therefore, eradication programs (which are currently in operation) of these plant species should

be re-evaluated to ensure that it would not negatively affect the survival of this grassland adapted

endangered lizard. Furthermore, clear resource partitioning in microhabitat selection and microhabitat

utilisation between different maturity stages of C. nigrilabris has allowed it to thrive in the grasslands and

to be the only agamid to do so. Present study in the grasslands habitat of HPNP generated important data

regarding the microhabitat utilisation of C. nigrilabris. This may aid in present and future conservation

(in-situ and ex-situ) and management of this unique endangered endemic lizard species as well as the

grassland habitat as a whole.

Acknowledgement

We acknowledge the generous corporation of the Horton Plains National Park staff, Department of

Wildlife Conservation for granting permission (Permit no. WL/3/2/9/16) to conduct this research,

University of Sri Jayewardenepura and Department of Zoology, for the facilities granted to conduct this

research, IDEA WILD for providing us field instruments which were of great value during field

excursions.

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