Territory and Territorial Behaviour of the Grey-faced Buzzard-eagle Butastur indicus

Abstract

(1) Territory and territorial behaviour of the Grey-faced Buzzard-eagle Butastur indicus was studied in the vicinity of Kawachinagano City, Osaka Prefecture, Japan. Three pairs (A, B, C) were intensively investigated during the breeding season from 1 April to 20 July 1979. The totals of days (hours) spent for observations were as follows: 46 days (458.72 hr) for pair-A, 18 days (40.17 hr) for pair-B, and 11 days (18.08 hr) for pair-C. (2) The movements of each pair were plotted on a map of 1/5, 000 in scale. The outermost points at which the birds were sighted are connected by straight lines to form a convex polygon, and the area is defined as range. A polygonal area formed by connecting the outermost points of trees which were used for is designated as perching area. The movements of the chaser and the chased individuals were traced on the map, and the area formed by joining the outermost points at which the territory owner stopped chasing the intruders is referred to as territory. (3) The average size of home ranges was 191.63 ha for males (181.96-201.67ha, N=3) and 152.37 ha for females (117.21-180.97ha, N=4) respectively. Home ranges were overlapped to a large extent between both sexes of each pair and between neighbouring pairs. (4) Seasonal changes in the shape and size of home range and area of pair-A were studied. The shape and size of home range and area of the male were relatively stable throughout the breeding season in comparison with those of the female. As the breeding progressed, the home range and area of the female have become overlapped and coincided with those of the male.(5) Both intra- and inter-specific encounters between territory owners and other individuals were recorded during the breeding season. An encounter in which the intruder provoked no or an response by a territory owner is designated as admissive encounter. An encounter in which the intruder provoked an response by a territory owner is designated as aggressive encounter. Seven types of behaviour by the territory owner were observed: threat, soaring with calls, wing-flapped circling display, dive, aerial chase, displace, and attack with kicks. These behaviour were described. (6) The percentage of encounters to all encounters is defined as The responses of the territory owner to the intruder were analysed quantitatively on the basis of the admission ratio. The degree of aggressiveness of the territory owner varied with the sex, age (in conspecifics) and species of the intruder. Males were most toward conspecific adults (both males and females), less toward conspecific yearlings, and to non-conspecifics. Females were, as a rule, more to the intruders, both conspecifics and non-conspecifics, than males. But females showed an intensive aggressiveness toward conspecific adults of the same sex, almost equivalent to that of the males against other conspecific adults. (7) The territory owner generally behaved admissively to the intruders flying at a height of 300 m or more above the ground. On the other hand, the territory owner behaved aggressively to the intruders flying at a height of less than 300 m above the ground or perched on a tree. These results show a three-dimensional structure of the territory, which may permit the apparent overlap of home ranges among neighbouring pairs. (8) Aggressive encounters were 83.5% for males, and 48.9% for females, of all intra-specific encounters observed. The first behaviour was normally a threat or a chase. The sequence of behaviour of the territory owner appeared to be determined by the responses of the intruder.(9) Similar to the intra-specific encounters, the first behaviour of the territory owner in inter-specific encounters was usually a threat or a chase.