Habitat quantification followed previous methods (James and Shugart 1970,
Kannan 1994, Mudappa and Kannan 1997), using a 15 m circular plot (0.07 ha)
with the nest-tree as the centre. The nest-tree species was noted, plus all trees
of GBH (girth at breast height) ≥ 25 cm. Canopy cover was quantified using a
densiometer, taking 10 readings every 5 m (steps) in the four cardinal directions
from the nest-tree. The altitude of the nest-site (using an altimeter) and distances
to the nearest road, human habitation and river were also noted.
The nest-tree and cavity parameters measured or estimated were: height of
nest-tree and of first branch; distance from and height of tallest other tree in plot;
extent of emergence of nest-tree; height of cavity from the ground; location (main
trunk, primary, secondary or tertiary branch), position (emergent, upper, middle
or lower canopy) and orientation of cavity; cavity width and length; girth of nesttree
above any buttress and at nest cavity. The possible mode of cavity formation
was also recorded, based on whether the cavity was on a protrusion of an old
broken branch or directly on the main trunk or branch, and on the shape of the
hole.