Note:
This article was originally published in Forktail 13 (1998)
the journal of the Oriental
Bird Club (OBC) and was kindly submitted by T.
R. Shankar Raman
Recently,
Cranbrook and Kemp (1995) drew attention to the phenomenon of
aggressive interactions among Asian hornbills (Bucerotidae)
involving individuals (males) clashing their casques in mid-air
flight. Among the six genera and 31 species of Asian hornbills
now recognized (Poonswad and Kemp 1993, Kemp 1995), such aerial
casque-butting has been reliably reported only in a single species
of large hornbill, belonging to the genus Buceros. This is the
Helmeted Hornbill, Buceros (subgenus Rhinoplax) vigil, which
was only recently placed in this genus (Kemp 1955). A reference
to the existence of aerial casque-butting behaviour in the Great
(Pied) Hornbill, B. bicomis, was made in Poonswad and Kemp (1993,
p. 104); this was, however, later reported to be an error (Cranbrook
and Kemp 1995). All species of Buceros are territorial as adults
when breeding, and it is of much interest, particularly in the
face of cladistic changes in the taxonomy, to see which aspects
of behaviour are shared among the species.
Here, I report field observation of the rare aerial casque-butting
behaviour in the Great Hornbill. During a sixmonth study of
the impact of shifting cultivation on tropical rainforest bird
communities (Raman 1995), aerial casquebutting was observed
in this species in a rainforest region in northeast India. The
study area, Dampa Tiger Reserve (c. 500 km2, 23°20'-23°4TNand
92°15'-92°30'E), in western Mizoram state, contains
an extensive tract of tropical evergreen forest vegetation.
Two other species of hornbills, the Wreathed Hornbill, Rhyticeros
(= Aceros) undulatus and the Oriental Pied Hornbill Anthracoceros
albirostris (incorrectly called A. malabaricus in Ali and Ripley
1987) also occur in the study area and were seen on a regular
basis in the rainforest.
On 11 April 1995, while walking a transect in mature rainforest
in the Tuichar valley near the Chawrpialtlang range (altitude
c. 450 m), four Great Hornbills were spotted. Three of the birds
were males and were perched on an emergent Tetrameles nudiflora
tree. A female was also perched nearby. At 06h21, one of the
males took off from the branch where it was perched, flew out
just above another perched male, and while still in flight,
clashed its casque loudly with that of the perched male. Flying
past the perched male, it then settled on another branch. After
a few seconds, it took off from the perch and repeated the behaviour,
clashing its casque with the perched male. This performance
was repeated several times, until 06h30, when all the birds
took off and flew away in the same direction. To all appearances,
the other male and the female did not participate in the above
interaction. It also should be noted that this observation,
where one of the interacting males was perched, is different
from that reported for Helmeted Hornbills, where both individuals
clashed their casques in mid-air flight (Cranbrook and Kemp
1995).
The observed behaviour may have been a territorial interaction
among the hornbills, which had the enhanced yellow plumage colouration
developed during the breeding season (Ali and Ripley 1987, R.
Kannan pers. comm.). It is intriguing that the interaction was
seen between only two of the three males present. It is not
known, however, whether the other male joined in the interaction
after the hornbills disappeared from view (chased by one male?).
Could the male-male aggression have been a form of competition
or display for securing the female, as two of the males appeared
to be unpaired? Unfortunately, the exact breeding season of
Great Hornbills could not be determined during the study. Judging
from the observation of plumage and vocalizations, however,
it appeared that some initiation of breeding activity may have
occurred between late February and May and breeding may have
continued after the onset of the monsoon (mid-May to June) after
I left the study area. Ali and Ripley (1987) report April- May
as the (onset of?) breeding season of this species in the Himalayas.
Preliminary observations from Pakhui Wildlife Sanctuary in Arunachal
Pradesh also seem to indicate that breeding in the Great Hornbill
begins around April-May (A. Datta pers. comm). While more definitive
evidence is required, it seems likely that the observed behaviour
is thus a pre-breeding interaction between adults.
With regard to the recent placement of Helmeted Hornbills in
the same genus as the Great Hornbill, the fact that this rare
behaviour has so far been reported from only these two species
is significant. A notable difference between the two species
is, however, that the Helmeted Hornbill, unlike other Buceros,
has a solid casque (vs. hollow casque) that may be better suited
to withstand aggressive casquebutting interactions. It would
be interesting to discover if such aerial casque-butting behaviour
occurs in the other species of Buceros hornbills as well.
The study was supported by a fellowship from the Ministry of
Environment and Forests, Govt. of India, and by a grant from
Per Undeland through the Oriental Bird Club, U.K. I thank R.
Kannan, Suhel Quader, Madhusudan Katti, and an anonymous reviewer
for comments and the Mizoram Forest Department and severalofficials
and field staff for permissions and assistance.
Cranbrook, Earl of, and Kemp, A. (1995) Aerial casque-butting
by hornbills (Bucerotidae): a correction and an expansion.
Ibis137: 588-589.
Kemp, A. (1995) Birdfamilies ofthe world1. The hornbills:Bucerotijormes
Oxford: Oxford University Press.
Poonswad, P. and Kemp, A. C. eds. (1993) Manual to the conservation
of Asian hornbills. Hornbill Project. Bangkok: Faculty
of Science, Mahidol University.
Raman, T. R. S. (1995) Shifting cultivation and conservation
of tropical forest bird communities in Mizoram, northeast India.
Unpub!. M.Sc. dissertation, Dehradun: Wildlife Institute of
India (Saurashtra University, Rajkot).
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