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Nesting habitat of the Great Hornbill (Buceros bicornis) in the Anaimalai Hills of southern India.

Article Excerpt
The Great Hornbill (Buceros bicornis) is the largest of the nine species of hornbills (Family Bucerotidae) occurring in India (All and Ripley 1968). Basic breeding biology and habitat information is available from southern India (Kannan 1994; Kannan and James 1997, 1998, 1999, 2007, 2008; James and Kannan 2007). It is an endangered species (CSE 1982), listed in Schedule I (most protected) of the Indian Wildlife (Protection) Act of 1972 (MOEF 2006) due to being affected by a variety of problems ranging from destruction of its wet forest habitat to poaching of adults and squabs from nests (Ali and Ripley 1968). The bird is ~120 cm long and ~3 kg in mass, and is believed to have the problem of finding large trees with natural cavities sufficiently large to accommodate the nesting female and young during their confinement. Large scale destruction of forests and selective commercial removal of large trees in peninsular India is suspected to have reduced the availability of optimal nesting sites (Ali and Ripley 1968).

Several authors have commented on the apparent highly specialized nesting requirements of the Great Hornbill. The species is widely believed to depend on tall, old growth trees for nesting. The literature is replete with anecdotal references to its dependence on mature forest vegetation (Hume 1890; Bingham 1897; Prater 1921; Baker 1927, 1934; Ali 1936; Ali and Ripley 1968; Kemp 1995). However, systematic studies have not been conducted concerning the bird's habitat. All conjecture concerning the nesting habitat of the species amount to an untested and unproven hypothesis. Some quantitative information on nesting habitat is available from Thailand (Poonswad 1995), but only a few environmental factors were considered in that study, and empirical procedures comparing nest sites to non-used forest sites were not performed. Comparison between used and non-used sites within the same general vegetation type is essential for identifying habitat features associated with forest nesting sites compared to surrounding forest stands (Conway and Martin 1991). One study, (Datta and Rawat 2004), repeated our earlier work (Kannan 1994) and incorporated unused sites but the results combined four species of hornbills.

Cavity-nesting birds often are affected by land management practices (Gysel 1961, Haapanen 1965, Hunter 1990, Conway and Martin 1991, Mudappa and Kannan 1997). Selective removal of large trees in the Western Ghats in India, our study area, could limit populations of large birds such as hornbills by diminishing nesting opportunities. A detailed description of the critical habitat is the first step in any attempts to ameliorate this situation. An examination of habitat factors using multivariate statistics is essential in describing the habitat-niche of an organism (James 1971) since habitat is an important component of the niche of an organism (Hutchinson 1957, Root 1967). Vegetation factors have been used in multivariate procedures to analyze niche-dimensions of birds (Cody 1968, James 1971, Shugart and Patten 1972, Posey 1974, White and James 1978, Rotenberry and Wiens 1980, James 1992).

The objectives of this study comparing nest sites with unused forest sites were to: (1) use multivariate statistics to test the hypothesis that Great Hornbills use the largest trees for nesting, (2) ascertain forest patch characteristics associated with nest sites, (3) identify nest tree species, (4) obtain information on nest cavity dimensions and related issues, and (5) investigate suitability of the overall forest for accommodating hornbill nests.

STUDY AREA

The study was conducted between 1991 and 1993 in the vicinity of the village of Top Slip (10[degrees] 25' N, 76[degrees] 50' E) in the Indira Gandhi Wildlife Sanctuary, Tamil Nadu State, in the Anaimalais, which are a part of the hills extending along the southwestern coast of peninsular India (the Western Ghats). The sanctuary has a variety of vegetation types ranging from bamboo (Bambusa arundinaceae) and open deciduous...

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