The availability of cavities in this study was estimated at 2.3/ha, compared with
10 cavities/ha reported for the Malabar Gray Hornbill (Mudappa and Kannan
1997). The availability of the two most important nest-tree species was 1.3/ha
even though the nesting density was only 1 pair/km2. Cavity and nesting
density compares well with just less than 1 pair/km2 for four sympatric species
in Thailand (Poonswad et al. 1987), but is lower than the 5.6 cavities/km2
for Black-and-white Casqued Hornbills Ceratogymna subcylindricus in Uganda
(Kalina 1988) and the nesting densities of the Narcondam Hornbill Aceros
narcondami (2.8 pairs/km2, Ravi Sankaran pers. comm.) and Sulawesi Redknobbed
Hornbill Aceros cassidix (10 pairs/km2, Kinnaird et al. 1996).
The high degree of overlap among hornbill species and the importance of a
single tree species for nests suggest that availability of nest-sites may be a limiting
factor, exacerbated by competition from monitor lizards, flying squirrels,
wasps, bees, snakes and several other hole-nesting birds. However, the low
nesting density relative to cavity and tree species availability suggests that nests
are not limiting, although estimates are from a small sample size.