Quantitative and Functional Variations of Certain Behaviour Patterns in Male Thomson's Gazelle of Different Social Status

Abstract

This paper gives information on quantitative differences and functional variations of certain behaviour patterns (marking with preorbital glands, urination/defecation, object aggression, horn threat, fight, grazing ritual, chasing a ♂, chasing a ♀, neck-stretch, nose-up, flehmen, laufschlag, mounting, and copulation) in adult ♂ ♂ of Thomson's gazelle of different social status (ten territorial ♂ ♂, ten bachelors in stationary all-♂ ♂ groups, ten migratory ♂ ♂ in mixed herds during 121/2 hour periods) in the Serengeti National Park (Tanzania). Most of the behaviour patterns under discussion, at least occasionally occur, in ♂ ♂ of all three classes. The exceptions are advanced mating rituals (beyond the flehmen caesura) and copulations which were exclusively observed in territorial ♂ ♂. On the other hand, most of these behaviour patterns are significantly more frequent (in a very few cases, at least, equally frequent) in territorial ♂ ♂, as compared to non-territorial — stationary or migratory — ♂ ♂. The single exception are the horn threats which are significantly more frequent in the ♂ ♂ in the herds than in the territorial ♂ ♂. Quite a number of the corresponding behaviour patterns occur about as often (or in some cases, better: as infrequently) in stationary bachelors as in migr atory ♂ ♂ (urination/defecation, object aggression, horn threat, grazing ritual, chasing a ♂, flehmen, laufschlag, and copulation - fights were found to be somewhat more numerous in the stationary bachelors). The other behaviour patterns (marking with preorbital glands, chasing a ♀, neck-stretch, nose-up and mounting) are significantly more frequent in the migratory ♂ ♂. Marking activities (marking with preorbital gland secretion, urination/defecation, and possibly also object aggression) are increased in the territorial ♂ ♂, as compared to the non-territorial ♂ ♂, since they create a marking system within their territories (which, apparently, is more important as a means of orientation to the owner than for repelling strangers). Since the production of preorbital secretion goes on all the time, the non-territorial adult ♂ ♂ also have to get rid of it and mark relatively frequently. Certain observations as well as the increase of preorbital gland marking in migratory ♂ ♂ (as compared to the stationary bachelors) seem to indicate that the non-territorial ♂ ♂ possibly may mark their trails. The encounters between territorial neighbours are characterized by reciprocal horn threats, fights, and grazing rituals. Non-territorial ♂ ♂ are expelled from the territories by one-sided horn threats and chases. Thus, all these forms of aggression serve to establish and to maintain the territorial boundaries, and all of them are well-pronounced and quite frequent in territorial ♂ ♂. Grazing rituals are even so exceptional in non-territorial individuals that usually, their occurrence can safely be taken as an indication of the territorial status of a ♂. Among non-territorial adult ♂ the major function of aggressive behaviour is the coordination and synchronization of group activities (mainly, the speeding up of activity changes and "pushing" during moves). The horn threat appears to be the most suitable form of aggression for these purposes. This explains its numerical preponderance in the non-territorial ♂ ♂ in the herds, as compared to the territorial ♂ ♂. Reproduction occurs only in territorial tommy ♂ ♂. Therefore, advanced mating rituals characterized by mating march with laufschlag (withous nose-up), mounting phase, and copulation (only one per mating ritual), occur only in territorial individuals. Neck-stretch and nose-up display (with or without laufschlag), which belong to the early phases of a mating ritual, are more frequent than any other "sexual" behaviour patterns since the territorial ♂ ♂ use them not only in mating rituals in the strict sense, but also for soliciting urine from ♂ ♂ (which leads to flehnten. in the ♂ ♂), and for herding the ♀ ♀ in the territories. In stationary bachelors, neck-stretch and nose-up are rather infrequent, but they are significantly more frequent in the migratory ♂ ♂ in the mixed herds. With the exception of the chase, the behavioural inventory of adult tommy ♂ ♂ in encounters among each other is different from that toward ♀ ♀, and the migratory ♂ ♂ use the neck-stretch and the nose-up toward ♀ ♀ in the same situations (activity changes, "pushing" during moves), in which they use horn threats toward other ♂ ♂. Thus, these "courtship" displays are functionally equivalent to threats in these situations, and the adult ♂ ♂ in the mixed herds — with their horn threats among each other and their neck-stretch and nose-up displays toward ♀ ♀ — are the "motors of migration" in this species.