THE CONTROL OF POPULATION-DENSITY THROUGH SOCIAL BEHAVIOUR: A HYPOTHESIS

Any given species of animal generally occurs at a higher population-density where food is more plentiful, and vice versa ; quantitative evidence points to a rather close correlation between the two. Such density differences arise from the activities of the animals themselves, and this implies that population-density is subject to effective internal control, i.e., it is self-regulating.
A theory is put forward that, for each species, population-densities are limited at a safe level, which will protect the food-supply from long-term depletion and assure its renewal for the future. Instead of competing directly for food, animals compete for conventional substitutes, e.g. territory or social position, which are capable of imposing a ceiling density at the optimum level, and can prevent it from rising to the starvation level which would endanger future resources.
Such limitation by conventional means requires the existence of a social organisation. Forms of social competition supplant direct competition for food; their intensity is density-dependent and provides the animals with an index of population-density. This index serves as the "feed-back" for the machinery of density-adjustment, which operates, very broadly, through (1) direct movement (emigration/immigration), and (2) varying the birth and survival rates.     

COMPARISONS OF THE VOCALIZATIONS AND SOCIAL BEHAVIOUR OF SOUTHERN AFRICAN PYCNONOTUS BULBULS

Lloyd, P., Hulley, P.E. & Craig, A.J.F.K. 1996. Comparisons of the vocalizations and social behaviour of southern African Pycnonotus bulbuls. Ostrich 67: 118–125.

Vocalizations and associated behaviour of three Pycnonotus species are described, based on field observations and tape recordings from which sonagrams were produced. These species, which are locally sym-patric and hybridize, have similar vocalizations and displays; differences are most apparent in their contact calls and songs. Quantitative analysis of the songs showed that P. barbatus and P. capensis are easily distinguished, whereas the song characteristics of P. nigricans overlap those of both the other species. Playback experiments with territorial male P. barbatus in an area of allopatry showed similar responses to songs of conspecifics and of P. nigricans, but almost no response to the song of P. capensis.     

THE SOCIAL BEHAVIOUR OF THE WHITE WAGTAIL MOTACILLA ALBA ALBA WINTERING IN ISRAEL

White Wagtails Motacilla alba wintering in Israel are partly territorial, mostly around human habitations, and partly live in flocks around temporary food sources. Individual birds may spend part of the season (or the day) in the territory and the other part with a flock. Experiments with artificial distribution of food, in a natural habitat, brought about a change from flocking to territorial behaviour. Preliminary observations suggest that in the natural situation the pattern of food distribution may be the proximate factor which regulates the birds' behaviour, by determining whether they have to fight for their food. Pairs are formed on many territories, and may last for long or short periods. Pair formation is initiated by females, who when seeking food appease the territorial males and are able to stay with them on their territories. Females also manifest territorial behaviour. Although pairing in winter territories is similar, in the behaviour involved, to sexual pairing, it is very unlikely that winter pairing continues into, or influences, pairing for breeding. It is suggested that the function of winter pair formation is that it allows two birds to exploit one territory, and that the main advantage is to the female which is the subordinate bird of the pair. This kind of pair-formation may be analogous to non-breeding group territories reported in some other birds.     

OF MICE AND KIN: THE FUNCTIONAL SIGNIFICANCE OF KIN BIAS IN SOCIAL BEHAVIOUR

1. Sharing recent ancestry (kinship) increases the degree of genetic similarity between individuals, where genetic similarity could mean anything from sharing a particular allele to sharing an entire genome. 2. Genetic similarity can influence behavioural and other responses between individuals in a number of ways, discriminatory and non-discriminatory. All are likely to result in kin bias, because of the correlation between genetic similarity and kinship, but only some should be regarded as involving kin discrimination. 3. Non-discriminatory kin bias could arise through close relatives sharing, for instance, physical characteristics (such as those influencing competitive ability), thresholds of behavioural response or requirements for particular resources. 4. Discriminatory kin bias could arise through the direct perception of genetic similarity between individuals (direct similarity discrimination) or the use of cues likely to correlate with genetic similarity (indirect similarity discrimination--of which kin discrimination is one form). Alternatively, it could arise incidentally through mistaken identity or discrimination at some other level, such as species identification. 5. Experiments with laboratory and wild house mice have revealed kin bias in a number of contexts, including (a) parental and infanticidal behaviour, (b) sexual development and behaviour and (c) investigatory behaviour and passive body contact among juveniles and adults. 6. While kin bias in mice has been interpreted as evidence for kin discrimination, there are several problems with such an interpretation. These include (a) pronounced and complex effects of familiarity on discrimination, (b) a high risk of error-proneness in the indirect cues used in apparent kin discrimination and (c) weak and easily disrupted kin bias effects in certain contexts. 7. Consideration of social structure and discriminatory responses within populations of wild house mice leads to an alternative explanation for some kin bias in terms of incidental discrimination based on social group membership. 8. Several results from laboratory experiments suggest incidental discrimination is a more parsimonious explanation than kin discrimination for some intrasexual kin bias in behaviour. However, kin or direct similarity discrimination appears to be the most likely explanation for other aspects of intrasexual kin bias and for intersexual kin bias.     

SOCIAL BEHAVIOUR OF BREEDING WESTERN SANDPIPERS CALIDRIS MAURI

The behavioural interactions among breeding Western Sandpipers ( Calidris mauri ) are described, and interpreted in terms of their adaptive characteristics.
Upon arrival in early spring, males disperse onto territories through mutual antagonism. Territorial advertisement and maintenance is accomplished through display flights low over the ground, which are accompanied by soft buzzy vocalisations. These characteristics of display are related to the fact that this species occurs in dense, localised breeding populations, where longdistance communication is unnecessary.
Because densities are high and feeding often occurs in communal areas off territory, violations of territorial boundaries are frequent. The result is an extremely high intensity of interactions among individuals. Chasing and physical combat between males is frequent and generally un-stereotyped. Birds nesting on territories away from the feeding sites often fly high above the other territories, and in doing so avoid being chased.
Western Sandpipers form monogamous pair-bonds which are maintained until the young are ready to fly. The initial association of the pair is facilitated by a strong tendency to return to the previous site and by the advertisement of the males in which a specific vocalisation is given. Once the female is present on a male's territory, she is courted persistently by him and gradually begins to participate in his scraping displays. Pair-bonds are re-enforced by the close association of the pair during the pre-nesting period and through a simultaneous preening display.
An hypothesis is developed that the participation of both sexes in incubation serves primarily as a means of pair-bond maintenance, acting to keep both parents present until after the young hatch. At this time, their presence is needed to provide protection for the precocial young against predators.     

THE EMERGENCE OF BEHAVIOUR

When King Solomon the Wise used those famous words Go to the ant, thou sluggard! he couldn't have known how lazy ants really are, but he was plainly recommending the study of insect behaviour and letting it be known he was a bit of a student himself, nearly 3,000 years ago. Man's interest in the behaviour of insects is indeed ancient and from the scientific point of view, that is a mixed blessing. For it has the corollary that behaviour is something that everyone, the entomologist included, has tended to take in his stride; something fascinating and even baffling at times, but still a study more like play than work, that did not seem to demand the sort of critical, analytical labour, or rigorous evidence demanded by, say, taxonomy or toxicology.     

THE BEHAVIOUR OF THE HOTTENTOT TEAL

Following recovery and successful rehabilitation, a young Steppe Eagle Aquila nipalensis was tagged with a 45 g GPS satellite transmitter to track its migration and identify potential wintering and summering areas of the species passing through the United Arab Emirates (UAE). The study is part of a larger study on understanding migration of important birds of prey species from the UAE. The satellite-tagged Steppe Eagle was released near the town of Al Ain, UAE on 5 January 2009 and was tracked until 6 November 2010. Two complete spring and autumn migrations were tracked in addition to its onward autumn migration from the UAE. The tagged eagle continued its autumn migration from its release site and reached Yemen after stopovers in Saudi Arabia. Unlike other Steppe Eagles, the bird did not cross the strait of Bab-al-Mandeb and wintered in the area before undertaking its first spring migration. In the second spring migration in 2010, the bird migrated along the Suez–Eilat route and demonstrated a loop migration. The bird spent the summer on the steppes in Kazakhstan, with marked differences in the home ranges between 2009 and 2010, whereas wintering areas used in 2009 and 2010 in Tanzania were overlapping.     

ASPECTS OF THE FORAGING BEHAVIOUR OF THE SHOEBILL

Guillet, A. 1979. Aspects of the foraging behaviour of the Shoebill. Ostrich 50:252-255.

The foraging behaviour of the Shoebill Balaeniceps rex. in relation to the bird's habitat and morphology, is described. The Shoebill preys on fish in shallow water, and uses platforms of floating vegetation as fishing sites. The Shoebill's behaviour in stalking, detecting and capturing prey is compared with foraging techniques used by herons and storks. The Shoebill uses a peculiar and complicated technique, called “collapsing”, for capturing prey.     

THE DISTRACTION BEHAVIOUR OF THE ARCTIC SKUA

Distraction displays of the Arctic Skua Stercorarius parasiticus were studied in the Faeroe Islands in colonial nesters and a solitary pair. There are aggressive and passive forms.
The aggressive flight against human intruders is common throughout the nesting cycle in the colony, but absent from the behaviour of solitary pairs. It is suggested that its development is correlated with an internal rhythm which requires a certain level of mutual stimulation not attainable by solitary or widely-scattered pairs. A highly formalized version of the attacking flight was employed against a sheep, in which the pair showed a marked tendency to coordinate their movements.
The lure display when eggs are fresh is markedly different from that employed nearer the hatching-period and afterwards. A courtship posture appears as a substitute activity in the early period, but only in the presence of the mate.
In the solitary pair development of the normal lure display was gradual, reaching its peak towards the hatching-period: there is a marked tendency for the pair to perform together, deriving mutual stimulation. It is suggested that this factor is important in the colony, where several perform together in scattered groups, in ensuring the earlier development (and therefore increased survival value) of the lure display. The birds' movements emphasize contrasts in the plumage coloration, and therefore the pattern may have greater biological advantage for colonies of predominantly light-phase birds in areas of fox predation.
The various patterns are described, and also variations incorporating false-brooding and drinking motions. The main components of the patterns are probably derived from the primitive food-begging of the chick, and elaborated with actions from courtship display.