Assessment of Avian Diversity in Gudalur Forest Division, the Nilgiris, Tamil Nadu

Introduction

Declining biodiversity is one of the most dramatic and irreversible aspects of anthropogenic global change and biological invasions are believed to be the second largest cause of current biodiversity loss after habitat destruction [1, 2, 3]. Avian community is an important component of forest ecosystem. Birds are playing a major role as pollinators, consumers, dispersers of plant seeds and predators of insects. Studies on bird community starting from MacArthur, et al. [4] have attracted wide attention. Investigations on the bird communities of the Western Ghats to plan for biodiversity friendly development are gaining significance [5]. The focus of community ecology is the study of the grouping of species, their distribution and the interactions between them and the physical and biological factors of their environment [6]. According to Cody, et al. [7] bird communities have direct relation with the structure of habitat and are indicators of environmental changes. Birds are one of the best indicators of environmental quality of any ecosystem [8]. Many other groups of animals such as [9], tiger beetle [10], birds [11] and mammals as well as plants [12] have been used to assess the habitat quality.

Majority of the studies on bird community were focused on understanding of the structure of a community based on the population [4, 7]. They attempted to explain the diversity, especially with respect to the forest structure or floristic diversity. The presence of a particular species in a type of forest was traditionally explained in terms of the availability of foraging substrates and vegetative layers. In recent years, the trend among community ecologists is to elucidate the function of a community focusing on habitat selection.

A number of environmental factors are known to influence the population of birds directly. Availability of food, detectability and capture, location of nesting sites, availability of nesting materials, presence of predators and competitors are the major factors influencing the foraging and breeding of birds and subsequently their population. One of the key aspects in community structure is the food habits of a species which is critical in understanding the pattern and process of community organization [6]. Population studies have been traditionally used to monitor long term changes in avian population and to assess both habitat quality and the responses of birds to both natural and human caused environmental changes [6].

Eight percent of bird species in India occur in Gudalur and adjacent Mudumalai Tiger Reserve. Among the 227 bird species found in this region, 110 species are insectivores, 62 are carnivores, 23 species are fishwives, 12 species are omnivores and 20 species are gramnivores. These include the unique  near threatened  Black-and-orange Flycatcher. Regional endemics include  Malabar trogon  and  Malabar grey hornbill. Some rare birds of prey like the  Rufous bellied hawk eagle  can occasionally be seen in this area. Other predatory birds include  crested hawk-eagle,  crested serpent eagle, Changeable Hawk Eagle, Black Eagle, Oriental Honey-buzzard,  Jerdon’s Baza,  Bonelli’s Eagle,  Crested Goshawk, Besra sparowhawk, Mottled Wood Owl and Brown Hawk Owl,  Minivet sp. There are also Hornbills, Golden Oriole,  Chloropsis,  Paradise flycatcher,  Golden-backed Woodpecker, Malabar Great Black Woodpecker,  Blue- winged Parakeet, Fairy bluebird, Jungle fowl, Racket-tailed Drongo,  Peacock,  Red Spurfowl,  Grey Francolin,  Painted Spurfowl, Painted Bush Quail, White-bellied Woodpecker, Lesser Yellownape, Golden Woodpecker, Streak- throated Woodpecker, Chestnut-headed Bee-eater, Emerald Dove, Green Imperial Pigeon, Pompadour Green Pigeon, Grey- bellied Cuckoo,  Indian Cuckoo,  Alpine Swift,  Black-hooded Oriole, Greater Racket-tailed Drongo, Black-headed Cuckooshrike, Grey-headed Bulbul, Forest Wagtail, Crimson- backed Sunbird and Loten’s Sunbird. It also holds the isolated southern population of the Striped Tit-babbler. The present survey was made to find out the avian diversity in the lantana dominated area of Gudalur Forest Division with an objective of study the avian diversity in prior to removal of invasive alien species Lantana camara of Gudalur Forest Division.

Methods

Line transect method [13] was applied for recording birdlife communities. Sometimes the transect might even gone beyond our physical target area. The care was taken that transects’ midpoint should cross on the target area. Survey was made to count the number of birds along with the transect. Using binocular bird species were identified from the transect. Grimmett, et al. [14] was referred for the identification of birds in the field. The diversity variables are collected to estimate encounter survey. For each sighting of the bird 1 m radius circle was laid at sighting location in order to record micro habitat utilization of the bird species.

Results and Discussion

A total of 33 species of birds were recorded during the survey conducted in three phases in Gudalur Forest Division (Table 1). Out of these species Red vented bulbul (25%), Malabar Parakeet (12%), Jungle myna (9%), House swift (7%) and Spotted dove (6%) were sighted dominantly, whereas the other species (41%) are sighted very few (Figure 1).

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The area is highly rich in avifauna. This high diversity may be attributed to the fact that this area supports good vegetation. Among the species identified, 26 are abundant and 7 are very abundant. The value of Simpson’s dominant index is very low (0.006) indicating co-dominance of species structure [15, 16]. The diversity index is rather fair (4.7267) which are almost similar to the bird diversity index of other luxuriant Western Ghat forests. The bird species were more or less evenly distributed in this area as indicated by the evenness value close to one (0.8416) (Table 2). The area is dominated with deciduous habitats provide good forage ground to bird diversity supports increased bird species diversity in this region.

The relative density of different bird species seen during the field work during pre monsoon, monsoon and post monsoon seasons are given in the Tables 3-5. Using birds as an indicator taxon, we assessed the consequence of invasion of lantana camara on the health of the ecosystem of the moist and dry deciduous forests of the division. Bird diversity was lower at high intensities of lantana in both the moist and dry deciduous forests but the species richness did not show a similar pattern. Various diversity parameters (such as species richness, Shannon diversity and abundance) were correlated with the average tree canopy cover and the average  lantana  cover. In the moist deciduous forest, bird species richness was positively correlated with average tree cover, but the Shannon index values were negatively correlated with the  lantana  cover. We stratified the birds into 4 guilds (Canopy, Understorey, Ground and Open Areas) based on their microhabitat preferences and analyzed the impact of lantana on these guilds. There was a decrease in canopy specialists as the density of  lantana  increased in both vegetation types, whereas under-storey species were low at low levels of lantana. The other guilds did not display any patterns over the range of  lantana sampled. We also stratified birds based on feeding habits and analysed their response to lantana. Insectivores and frugivores showed high species richness at moderate levels of lantana intensity in dry deciduous forests. Our results suggest that lantana does not affect the bird community as severely as it is believed to affect other components of the ecosystem.