casque-butting in the Great Hornbill
By T. R. Shankar Raman
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
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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
Ali, S. and Ripley, S. D. (1987) Handbook
of the birds of India and Pakistan.
Oxford: Oxford University Press.
Cranbrook, Earl of, and Kemp, A. (1995) Aerial casque-butting by hornbills
(Bucerotidae): a correction and an expansion. Ibis
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,
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,
T. R. Shankar Raman, Nature