Status of birds in Agasthyamalai Hills, Western Ghats, Kerala, India

Madhumita Panigrahi 1 & V.J. Jins 2

 

1, 2 Sálim Ali Centre for Ornithology and Natural History (SACON), Anaikatty (Post), Coimbatore, Tamil Nadu 641108, India

1 madhumita.panigrahi7@gmail.com (corresponding author), 2 jinsvj@gmail.com

Introduction

Regional assessment of population status of any taxa is crucial for conservation planning of species and landscapes (Vetaas & Grytnes 2002). The mountain ranges of Western Ghats, are ranked high among the global biodiversity hotspots (Myers et al. 2000; Mittermeier et al. 2004). It is one of the 200 most important global ecoregions (Olson & Dinerstein 1998), and endemic bird areas of the world (Stattersfield et al. 1998). The Western Ghats form one of the 10 biogeographic zones of India (Rodgers et al. 2002) and are known to harbour more than 500 species of birds (Ali & Ripley 1996).

Of the 504 species of birds occurring in southwestern India, 360 species are terrestrial (Daniels 1997). A total of 16 species are endemic and restricted to the Western Ghats (Sattersfield et al. 1998, 2005). The range boundaries of many of the bird species is largely influenced by the Palghat Gap, a 30km wide low-elevation mountain pass at 10.08330N latitude between Nilgiris in the north and Anaimalai Range in the south. Notably, the moist forests, particularly tropical montane evergreen rainforest in the southern Western Ghats, is a major habitat for over 100 species of birds, including 14 endemics (Mudappa & Raman 2008). In Kerala alone, 500 species of birds have been recorded belonging to 88 families and 22 orders, out of which 17 species are endemic to this region (Praveen 2015). In the light of new taxonomic revisions, 24 species are considered to be endemic to the Western Ghats (Rasmussen & Anderton 2012).

The present study was carried out in Agasthyamalai Biosphere Reserve (ABR), particularly in two wildlife sanctuaries namely, Neyyar and Peppara in Kerala State which have been listed among the Important Bird Areas (Birdlife international 2015; Rahmani & Zafar-Ul Islam 2004). Nair (1993) has recorded 172 bird species belonging to 39 families from Neyyar Wildlife Sanctuary (NWS) alone. A concise checklist by Sashikumar et al. (2011) has enlisted a total of 221 and 215 birds from Neyyar and Peppara respectively making a total list of 227 birds in this area. There are many studies conducted in the eastern slope of the mountain range, i.e., mostly covering Kalakad-Mundanthurai Tiger Reserve (Johnsingh & Joshua 1994; Venkatraman 2011; Ramachandran & Ganesh 2013). However, no long-term studies on forest bird community are available from the western slopes apart from a few checklists. In light of the above-mentioned gap in information, the present study highlights the status of forest birds in the western slope of Agasthyamalai Hills of Kerala.

Materials and Methods

Study area

The intensive study area (250km2) is along the western slope of Agasthyamalai Hills in Kerala 8.55N-77.10E & 8.7166N-77.250E, and includes the areas of Neyyar and Peppara wildlife sanctuaries and the Agasthyavanam Biological Park (ABP) (Fig. 1). The area has an elevation range between 100–1,866 m above mean sea level. The forest types of this region include southern hilltop evergreen forest, west coast tropical evergreen forest, west coast semi-evergreen forest, southern secondary moist mixed deciduous forest and reed brakes (Champion & Seth 1968). The lower elevations (<600m) are dominated by mixed deciduous and semi-evergreen forests, and the zone 600–1,200 m is characterized by tropical evergreen forest. Southern hilltop evergreen forests and reed brakes occur near and above 1,200m (Varghese & Balasubramanyan 1999; Kunhi & Sankar 2000). Higher elevations are marked by steep undulating terrains and the area receives 2,000–5,000 mm annual rainfall with only two-three dry months in a year. The mean temperature of the coldest month ranges from 13.50C to above 230C (Pascal 1982). Besides the natural vegetation, these hill ranges also have vast stretches of tea, cardamom and rubber plantations. In 2016, ABR was included in UNESCO’s World Network of Biosphere Reserves making it 10th Biosphere Reserve in the list, out of 18 from India. It falls within the Indo-Malayan realm and the Western Ghats biogeographic zone. This region is the traditional stronghold of ‘Kanis’, one of the oldest tribal groups living in the southern Western Ghats. This mountain peak is also of paramount spiritual and cultural significance for people in the states of both Tamil Nadu and Kerala and is an important pilgrim center.

 

 

 

Data collection

Sampling was carried out from October 2012 to December 2014. Variable circular-plot method was used to survey bird populations at each sampling plot (Reynolds et al. 1980; Bibby et al. 1998). Point count survey was carried out for a duration of 10 minutes on a clear day in the first three hours after sunrise (Ralph et al. 1995; Raman & Sukumar 2002; Raman 2003). Birds seen and heard up to a distance of 50m were recorded. Radial distance and perching height were recorded by the help of Nikon Forestry Pro laser range finder. Other parameters like group sizes, sex, and type of contact were also recorded. Primarily, sampling plots were placed on the basis of elevation and accessibility at each 100m elevation, except the elevation classes between 600–700 and 800–900 meters due to unapproachability. Transects of one kilometer length were laid in each elevation band mostly along the existing paths or animal trails. The transect was divided into each 250m and the permanent sampling point were taken perpendicular to the transect line at a distance of 50m on either side of transect to avoid habitat edges (Jones et al. 1995). A total of 122 point count stations were laid representing all possible habitat types and elevational ranges in the study area. Bird counts in each point were repeated with number of replications varying between 2–16 depending on accessibility and logistic support which resulted in 746 point count efforts in total. Sampling points were marked using colour paint and GPS coordinates were noted. We followed Praveen et al. (2016) for taxonomic classification and nomenclature. For subspecies identification we followed Rasmussen & Anderton (2012). Recent taxanomic changes for Kerala Laughingthrush Trochalopteron fairbanki meridionale (Ashambu Chilappan Montecincla meridionale) and white-bellied Shortwing Brachypteryx major (Ashambu Sholakili, Sholicola ashambuensis) have also been considered (Robin et al. 2017) although the old names have been maninated in the text.

Data analysis

For assessing the status of birds; in addition to our systematic sampling, opportunistic sightings of species were also included. IUCN criteria (IUCN 2015) were used to assign conservation status at a global level.

Density estimates were calculated using Distance 6.2 Release 1, for the overall bird population density for Agasthyamalai Hills and also density of 18 species of birds for which we had adequate number of detections, i.e. >28. For density estimates of specific species, select point count stations were included with suitable habitats based on prior knowledge of species biology. The best-fit model was examined using Akaike’s Information Criterion (AIC) value and goodness of fit tests (Thomas et al. 2010; Buckland et al. 2001). The best possible model with lowest AIC values was then selected. Variables like encounter rate, average probability of detection, cluster density were computed on the basis of priori estimator models namely uniform, half-normal, hazard-rate and negative exponential along with cosine adjustments. Depending on the outliers, the detection distances for each species were truncated to achieve the best-fitted model.

Relative density was calculated to evaluate the most dominant species in the landscape and in different elevational zones. Since sufficient numbers of detections for certain species in all elevational zones was not available for calculating absolute density, relative abundance was calculated as the number of individuals in proportion of the total number of individual of all species.

Results

The present study reports 197 bird species from 16 orders and 57 families from both Neyyar and Peppara Wildlife Sanctuaries (Appendix 1; Images 1–101). This list does not include many species of waterbirds, as the study focused on forest habitats. According to the IUCN criteria 5% (n = 9) species are under Near Threatened category including Black-and-orange Flycatcher Ficedula nigrorufa, Great Hornbill Buceros bicornis, Grey-headed Bulbul Brachypodius priocephalus, Grey-headed Fish Eagle Icthyophaga ichthyaetus, Kerala Laughingthrush Montecincla meridionale, Lesser Fish Eagle Icthyophaga humilis, Nilgiri Flycatcher Eumyias albicaudatus, Oriental Darter Anhinga melanogaster, and River Tern Sterna aurantia. The study recorded two Vulnerable species, i.e., Woolly-necked Stork Ciconia episcopus and Nilgiri Woodpigeon Columba elphinstonii, and one Endangered species i.e. White-bellied Shortwing (Ashambu Sholakili) Sholicola ashambuensis.

Other species though common in other areas are categorized as rare because of their limited sight records. Some interesting sightings from the study area where of: Milvus migrans Black Kite which have been observed in periphery of forest in Neyyar WLS but not recorded from interior forest. Lesser Fish-eagle Icthyophaga humilis was sighted only once in flight in Neyyar WLS, while the Grey-headed Fish-eagle Icthyophaga ichthyaetus is quite common site in Kaviyar river, Peppera WLS. A single individual of Pied Harrier Circus melanoleucos was sighted at an elevation of 1300 m among grassland and southern hilltop forest. Brown-headed Barbet Psilopogon zeylanicus has been often sighted from Peppara WLS.

Density Estimates: A total of 3151 individuals of birds were recorded in 1997 detections in overall Agasthyamalai range (Table 1). To estimate the density of birds ‘Half normal key’ function was selected as the best fit model based on its lowest AIC value. The cluster density was estimated to be 1137.9 clusters/km2 with a mean cluster size of 1.59 clusters/km2. The estimated density of individuals was 1643.6 individuals/km2 with a coefficient of variation of 10.97%, which accounts for a population range size from 334,030–412,530 birds in the entire region (intensive study area). The highest bird density was recorded at high elevations (2988.7 individuals/km2) followed by low elevations (1833.8 individuals/km2) and least in the middle elevation (1176.5 individuals/km2).

Density estimates of 18 species, which provided minimum possible detections to run the Distance program (Table 2), were calculated. The highest cluster density was of Black Bulbul Hypsipetes leucocephalus ganeesa (459.63 clusters/km2), followed by Plain Flowerpecker Dicaeum concolor (370.97 clusters/km2) and Crimson-backed Sunbird Leptocoma minima (358.72 clusters/km2). The highest density of 958.57 individuals/km2 was of Black Bulbul, followed by Yellow-browed Bulbul Acritillas indica 722.12 individuals/km2 and Crimson-backed Sunbird 506.74 (individuals/km2). The details of detection functions and density estimates for all 18 species are provided in Table 2.

Relative abundance: The highest relative abundance along all elevational bands was for Yellow-browed Bulbul (0.08), followed by Greenish Leaf warbler Seicercus trochiloides (0.066), and 0.06 each for Greater Racket-tailed Drongo Dicrurus paradiseus and Black Bulbul. In case of three different elevation classes, in lower elevation (100–700 m) Yellow-browed Bulbul had the highest relative abundance (0.08); Greater Racket-tailed Drongo (0.068) and Greenish Leaf Warbler is 0.065. In the middle elevation (701–1,200 m), the highest relative density was of Black Bulbul (0.123), Yellow-browed Bulbul (0.12); White-cheeked Barbet Psilopogon viridis is (0.06). In higher elevation (Above 1201m), Black Bulbul again dominated with a relative density of 0.18; Kerala Laughingthrush Montecincla meridionale (0.16) and Greenish Leaf Warbler (0.1).

Species account of threatened and endemic species in Agasthyamalai Hills are given below:

Great Hornbill: The species was mostly recorded in and around evergreen patches at 500–1,000 m elevation ranges. Seasonal movements were observed which could be influenced by the availability of fruits. Though we did not record its nesting during our study, but mating calls and sub-adult were seen in suitable localities.

Malabar Grey Hornbill Ocyceros griseus: Among the two hornbill species recorded from Neyyar and Peppara, this species was the most abundant. It was found in almost all habitat type, in accordance with other studies from the Western Ghats (Balasubramanian et al. 2004; Mudapppa & Raman 2008).

Malabar Pied Hornbill Anthracoceros coronatus: This species has not been recorded in the present study. Balasubramanian et al. (2004), however, have reported its rare presence from NWS and Thenmala Reserve Forest in Agasthyamalai Hills, which are considered as the southernmost distribution record for this species. Absence of this species in Neyyar during our study is of great concern as the species is Near Threatened under IUCN Red List of Threatened Species.

Nilgiri Wood Pigeon Columba elphinstonii: This species had a wider distribution across the elevation compared to other endemic bird species in the area. It has been sighted in almost all forest types except grasslands and fire prone areas. In particular, it was seen in higher numbers in high-elevation preferring hilltop forests where nesting has also been recorded. Few sightings were recorded from rubber plantations and adjoining highly disturbed forest patches in lower elevations.

Malabar Barbet Psilopogon malabaricus: This species was fairly common in comparison to Coppersmith Barbet. It was observed to be widespread from low elevational forest up to 1000m.

White-bellied Treepie Dendrocitta leucogastra: Observed mostly near semi-evergreen and evergreen forests from 500–1,100 m. Appeared to be locally common in suitable habitats.

White-bellied Blue Flycatcher Cyornis pallidipes: It was widely distributed from lower elevation to 1,200m and prefers well-wooded areas. Found to be fairly common in this region.

Nilgiri Flycatcher Eumyias albicaudatus: Restricted to the of hilltop evergreen patches between 1,100–1,860 m. Encountered commonly in undisturbed habitats mostly hilltop evergreen patches intermixed with grasslands and reeds compared to same kind of habitat in disturbed area.

Black-and-orange Flycatcher Ficedula nigrorufa: Restricted to hilltop evergreen patches and mostly sighted in the elevation belt of 1,100–1,860 m. This species shares same habitat as Nilgiri Flycatcher, but was always observed in lower abundance. This also appears to avoid disturbed areas.

Crimson-backed Sunbird Leptocoma minima: A widely distributed endemic species and has been recorded from lower elevation to 1,600m. We recorded a density of 506.74 individuals/km2 (Table 2). Found in almost all forest types and among the most abundant species in the study area.

Malabar Parakeet Psittacula columboides: Though one of the common endemics of the lower reaches of Western Ghats, was rarely observed in present study. A few records were made from semi-evergreen and moist-deciduous forests near Bonacaud tea estate at an elevation of 700–750 m.

Grey-headed Bulbul Brachypodius priocephalus: Locally common, encountered from low elevation up to 1,000m preferably in patches dominated by reed bamboo (Ochlandra sp.).

White-bellied Shortwing Sholicola ashambuensis: Rarely seen and restricted to above 1,000m and evergreen biotope.

Broad-tailed Grassbird Schoenicola platyurus: Though said to be breeding in areas of Pandipath and Ponmudi by local bird watchers; we did not record this generally rare species in the present study.

Kerala Laughingthrush Montecincla meridionale: Locally common, restricted to altitude above 1,100m in high elevation evergreen forest. It was one of the most common birds encountered at higher altitude. Often found feeding on the offerings left behind by visitors. The subspecies found here is having a very restricted distribution and reported to be sensitive to habitat alterations (Praveen & Nameer 2012).

Wayanad Laughingthrush Garrulax delesserti: Flocks were recorded near the forest edges and tea plantation prefers semi-evergreen forest. Found to be locally common.

Rufous Babbler Argya subrufa: Mostly encountered in area intermixed with grasses along the forest edges and abandoned tea plantations above 400m.

Nilgiri Thrush Zoothera dauma neilgherriensis: A sulking species, found in the areas having some undergrowth and good litter cover. It has been recorded from 500m up to the top of the hill. May be under-reported due to its sulking behaviour.

Discussion

Despite the fact that many bird species are broadly distributed, most of the endemic species occur or breed only in restricted elevation ranges, i.e., above 1,200m dominated by southern hilltop evergreen forest. Though higher elevation had few species (27) compared to medium (47) and lower elevation (87), it showed highest density of 2988.7 individuals/km2. This higher density of birds at higher elevations may be due to several reasons. Firstly number of detections is less compared to other elevations with 20.14% CV with a very high % CI (2017.4–4427.7). More detection might have improved the density estimates. The geographic area at higher elevations is significantly less (9.71km2) compared to medium (35.51km2) and lower altitudes (206.95km2) thereby augmenting the density in a smaller area. Besides, several Western Ghats endemics like Kerala Laughingthrush, Black-and-orange Flycatcher, and Nilgiri Flycatcher are only found in higher elevations and other species that have widest elevational amplitude further augment the density. Black Bulbul having the highest density (958.57 individuals/km2) among all the bird species was mostly recorded in large groups at higher elevation. These may be some of the reasons for the inflation in density at higher elevation. Since much of the bird detection where through calls, calculating absolute density may not give very good results. Density estimates of 18 species in table 2, shows that despite having low CV in 11 species, a higher value of 95% CI was obtained. Hence absolute density measures should be used carefully.

Present study reported 1643.6 birds/km2 compared to 1122 birds/km2 in the Silent Valley in Nilgiris (Jayson & Mathew 2000). Mudappa & Raman (2008) have reported White-cheeked Barbet and Crimson-backed Sunbird to be widely distributed in a study conducted in the selective places in Western Ghats from Goa to Tamil Nadu. In the current study, Yellow-browed Bulbul, Crimson-backed Sunbird and White-cheeked Barbet were found to be widely distributed in Agasthyamalai landscape.

In a hill range, species are often restricted or distributed across particular elevation bands, as their distribution may be governed by bioclimatic or vegetation attributes; since these environmental parameters are vulnerable to climate change and habitat alteration, montane species are at greater risk of extinction in the long run (White & Bennett 2015). Apart from this, the number of endemics found in specific habitats has to be taken as important criterion for landscape level conservation actions (Aliabadian et al. 2008). Impacts of human factors on the montane ecosystem with respect to the distribution and population status of endemic species are well documented (Vijayan & Balakrishnan 2005; Vijayan et al. 2005). Agasthyamalai and specifically Agasthyarkoodam attract a lot of pilgrims from both Tamil Nadu and Kerala and the trend is increasing every year especially during January to April. The visitation has increased from 5,490 visitors in 2007 to 7,055 visitors in 2011. (Management Plan 2012–2013 to 2021–2022). Increased and unchecked pilgrimage activity may have a detrimental effect not only on the endemic birds but on other fauna as well. Generally, it was observed that areas with least disturbance hold a good number of endemic species compared to same kind of forest type in areas frequented by visitors. Among the six forest types, the southern hilltop evergreen forest appears to the most important habitat for the endemic birds (Robin & Nandini 2012) which are currently under pilgrimage pressure in the Agasthyamalai Hills. An urgent management intervention is needed to regulate the flow of the tourist and pilgrims in this area before it severely affects these biodiversity rich high altitude forests.

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