2006-7 annual report - Nature Conservation Foundation

Table 1. Long-term monitoring (1998-2006) of hornbill nests in Pakke: total nest trees, number monitored, active nests and
successful nests and nest tree loss/takeovers. Data for 1997 is not shown as only two nests were monitored in that year.
1998 1999 2000 2003 2004 2005 2006
Known trees 19 21 22 23 34 40 46
Monitored 19 16 17 9 29 36 46
Active 16 8 11 6 22 21 32
% Active 84 50 65 67 76 58 70
Success 13 8 11 6 NM 13 28
% Success 81 100 100 100 NM 62 87.5
Trees cut/fallen 3 2 0 0 1 0 2
Nest takeover 0 0 0 0 1 0 3
4 of Wreathed hornbill and 1 Oriental Pied hornbill) in
the 2006 breeding season. The percentage of nests that
were active was high in most years (65-84%), except
for 1999 and 2005 when nesting was initiated in only
50-58% of nest trees (Table 1). There was poor nonfig
fruit availability in the breeding season of 1999 that
may have resulted in lower nesting. Phenological data is
currently not available; therefore the reasons for lower
nesting in 2005 cannot be elucidated.
Roost sites
Hornbills in the area roost communally, although the
phenomenon is more pronounced in the non-breeding
season. The Great hornbills (60+) roost communally
only in the non-breeding season. The Wreathed hornbills
are seen in the largest numbers (100+) and roost
communally throughout the year. Both single species
roosts and mixed-species communal roosts are seen.
Mixed species roosts have only been seen in the nonbreeding
season. Counts have been made at dusk at 5-6
roost sites over the last 7 years. A particular roost site
may be used only for a few days at a time or up to 3
months.
One of the roosting sites (mainly of the Wreathed
hornbill) is on the Assam side of the inter-state boundary.
They use this roost site every year in August-November
and sporadically in much smaller numbers at other
times. Floods and erosion have caused loss of crucial
roost trees and there is increased human disturbance.
However, the site is still being used by Wreathed hornbills.
In 2005, we made recommendations to the Assam
Forest Department on measures to protect this crucial
roosting site. The known hornbill roosts continued to
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annual
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be in use despite increased human disturbance at some
roost sites, although the Great hornbill has not been observed
using one roost site since 1999.
Hornbills (mainly the Wreathed hornbill) arriving
at the roost can be classified according to age and
sex. Immediately after the end of the breeding season in
August-September, this enables an estimation of population
recruitment as juveniles accompany the parent
birds to roost sites. Based on roost counts over 3 years,
it appears that at least 13-23% of the population is of
juvenile/subadult birds. On a single day roost count, at
least 32-37 juvenile birds were seen every year immediately
after the breeding season.
Hornbill population monitoring
We compared the encounter rates for hornbills with
data from a study in 1995-96 that used several of the
same trails in the sanctuary. There appears to be a marginal
decline in encounter rates for all the three hornbill
species in 2005-06. Although rigorous comparisons
cannot be made, Great Hornbill abundance was relatively
higher (0.5/km) in 1995-96, while Wreathed and
Oriental Pied Hornbill encounter rates remain similar
after 10 years. Great Hornbill numbers may have possibly
declined in the area due to the considerable loss of
nesting habitat in the foothill forests in the last 5 years.
We also examined whether there was any variation
in hornbill abundance over the months in the area.
Monthly monitoring of hornbill abundance over 2 years
has shown considerable local fluctuations in abundance
possibly related to seasonal variations in fruit availability.
Overall hornbill abundance peaks in the area at the