THE COMPOSITION AND BEHAVIOUR OF SOME MIXED-SPECIES BIRD FLOCKS IN SARAWAK

Mixed-species flocks of birds feeding on insects were observed mainly in forest in Sarawak at a time of year when insect availability is known to be near its annual minimum. The approximate individual and specific composition of most flocks were noted. Twenty-six species occurring in 25% of flocks were regarded as occasional members, 15 species occurring in 40% of flocks being classed as regular members. Recording species' feeding behaviour was the main priority and few observations of inter- and intra-specific interactions within the flock, horizontal distribution or vertical stratification were made, although the last proved to be of potential significance. From the analysis of feeding behaviour two groups of species were distinguished. The larger group contained those usually having an exclusive common feeding pattern and showing very little overlap with the other such species. Fewer species used a wide range of feeding methods, all of which were shared with other species, but the least overlap was with other members of the same category. The observed composition of these flocks, in terms of regular members, might be interpreted as ensuring a low level of inter-specific competition and it is suggested that the less specialized foragers may occur in the flocks by utilizing the ‘gaps’ between, and absences of, specialists. The possible advantages of membership of mixed-species flocks are briefly considered and the likelihood of the selective advantage in any situation being the result of a balance of factors emphasized. In the apparent absence of regular potential predators the existence of these flocks is interpreted primarily as an adaptation for augmenting available insect food, particularly perhaps at critical times of year, by flushing insects as a result of the foraging activities of flock members. It is suggested that the varied responses of insects on being disturbed coupled with the different and fairly specialized feeding techniques of the birds could ensure benefit for all members of the flock.     

THE FORMATION, STRUCTURE AND FUNCTION OF MIXED-SPECIES INSECTIVOROUS BIRD FLOCKS IN WEST AFRICAN SAVANNA WOODLAND

Mixed-species flocks of birds were observed during the wet season (July to September 1975) in savanna woodland in Ghana. Thirty-four flocks contained birds of 56 species in 20 families, including insectivorous, granivorous, and nectarivorous species, using a wide range of foraging methods. Only two species occurred in more than half the flocks. There was no correlation between the number of flocks joined by a species and its abundance in the community. Among insectivores, but not granivores, the species which joined most flocks were those which habitually occurred in the largest single-species groups. All stages of breeding activity were represented by the various members. Some species joined flocks only while these were passing through their territories. Of the two species which were present most frequently, there were no differences between mixed and single-species flocks for Eremomela pusilla, but Parus leucomelas foraged and called on more occasions in mixed flocks than single-species flocks, though the rates of foraging and calling were related only to the number of P. leucomelas present. Groups of P. leucomelas appeared to initiate some flocks by attraction due to their conspicuous wing-bars, active movement, and loud calls. Black-and-white species joined them first, followed by birds of other plumage patterns. The advantages of mixed flocking are thought to be connected with finding patches of the food of bark- and foliage-searching insectivores, which were the only species regularly seen foraging in the flocks. Because of dry season burning which leaves small unburnt patches of savanna, these insect species may share a common, patchy distribution. Birds may also gain protection from predators, and some species probably gain no advantages. The species composition and behaviour of flocks previously recorded elsewhere in African savannas are similar to the Ghana flocks.     

THE ECOLOGY AND BEHAVIOUR OF THE LONG-TAILED TIT

The behaviour and ecology of a population of Long-tailed Tits in Wytham Great Wood, Oxford, were studied between October 1970 and June 1971. Flocks were found to have a stable composition in autumn, and to occupy fairly discrete territories which they defended against other flocks.
In spring the population was reduced by about 50% and in the pre-nesting period flocks formed only in cold weather or just before going to roost. These flocks occupied the same territories as the autumn flocks and the individuals composing them eventually nested within the flock territory.
Predation of nests was heavy, increasing to a peak in the first half of May. Only nine pairs out of 36 managed to rear young successfully. At six out of these nine nests, supernumerary birds helped to feed the young, but it seems unlikely that this increased their success, since all young hatched fledged successfully. The presence of supernumerary birds at the nest was accompanied by frequent hover-displays by all the adults.
The distribution of nests in relation to habitat shows that there is a preference for scrub rather than mature woodland, although the latter is used extensively for feeding during the winter. There appears to have been a radical change in the height of nest-sites in Wytham Great Wood between 1955–57 and 1971, and this is probably due to predation.     

长白山沼泽山雀的生态习性研究

沼泽山雀(Parus palustris brevirostris Taczanovski)是中山、低山带较常见的典型森林鸟类。关于它的生态习性,La Touche(1925—30),ⅡeMe~TKCB,r.n.等(1954),郑作新等(1958),郑作新等(1963)、范忠民等(1965)及李桂垣等(1982)均有过报道;但鉴于其生态习性的地区差异及某些环节的不足,尤其是对其生长发育的研究欠缺。为此,笔者将1963—1965,1979—1983年,在长白山北坡对该鸟生态习性的研究结果,报道如下。     

ADAPTIVE ADVANTAGES OF MIXED-SPECIES FEEDING FLOCKS AMONG SEED-EATING FINCHES IN COSTA RICA

The feeding ecology of three Costa Rican finches occurring in mixed flocks, Tiaris olivacea, Sporophila aurita corvina and Sporophila torquella , was investigated by measuring both behavioural and ecological variables. Observations on foraging height, rate of hopping and pecking rate, as well as the identity, proximity and number of nearest neighbours were recorded. In addition the duration of all feeding and perching episodes were timed. Comparisons were also made between the abundances of food items (grass seeds) consumed and those potentially available for consumption.
The analysis of variance of the feeding behaviour revealed that the presence or absence of neighbouring birds, whether of the same or different species, influenced the duration of feeding bouts more significantly than did either differences in habitat or species-characteristic behaviour. In addition the dietary comparisons revealed overlap in both species and size of seed consumed. Such similarities suggest that these species are not partitioning fields in the classical sense.
We propose that the increase in the duration of the feeding bout associated with the presence of mixed species aggregations leads to increased feeding efficiency and is the result of intra- and inter-specific social learning. Certainly flocking is often advantageous, since searching in a group facilitates finding clumped resources; mixed species flocking, by increasing exposure to a diversity of foraging places and patterns, can further augment feeding efficiency.     

ECOLOGY AND BEHAVIOUR OF THE LITTLE AUK ALLE ALLE IN WEST GREENLAND

A study of the breeding biology, feeding ecology, and behaviour of the Little Auk was carried out on Horse Head Island (73° 38′ N, 57° 08′ W) in west Greenland between July and August 1974. Distinct subcolony groups were recognized within the colony. During incubation, attendance at the colony increased to a peak between 2100 and 2400 h, with large rafts building up on the sea before engaging in aerial flights and then settling on land. During the nestling period, this pattern changed with further peaks at 0600 and 1800 h, and a decline during the afternoon, particularly during the late nestling period. Little Auks fed exclusively on copepods and amphipods (94%Calanus finmarchicus) usually captured within 2.5 km of the colony. Feeding rhythms fitted closely the known diurnal vertical migrations of Calanus with peaks between 2200 and 0800 h. Some individuals within subcolony groups showed synchrony of feeds, mainly between 1800 and 2400 h. The mean number of feeds to a chick in 24 h was 5.25. Growth rates of young were comparable between all four experimental groups and controls, although the latter attained higher weights. Mean daily weight increases were constant until 18 days of age when they declined sharply. This was not reflected in a change in mean daily weight increases with date and so suggests that food availability had not declined. Instead there was a reduced feeding rate to chicks from age 21 days to fledging. Breeding success was 50 %, mainly the result of egg desertion and predation by Arctic Foxes, and this may have been reduced by our own activities. Behaviour postures and the responses they elicited are described together with the diurnal patterns of different activities. Aerial flights are also described and their possible function discussed. It is concluded that the shortness of the time when abundant food is available has encouraged close breeding synchrony and this is achieved by mass flights and rafting on the sea beside the colony, and subdivision of the colony into groups with communal behaviour close to the nests.     

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.     

OBSERVATIONS ON THE BEHAVIOUR AND ECOLOGY OF THE FLIGHTLESS CORMORANT NANNOPTERUM HARRISI

From 25 September to 8 October 1963 daily observations were made on a group of Flightless Cormorants Nannopterum harrisi nesting on the west side of Albemarle Island in the Galápagos. Flightless Cormorants are apparently bottom-feeders, and confined to shallow coasts at the western end of the Galapagos Archipelago where there is an upwelling of cold nutrient-rich water. There is no reason to suppose that they are declining in numbers. Males are very much larger than females, the size difference between the sexes being greater than in other species of cormorants. Courtship behaviour, nest-building and mating are described. The earliest phases of courtship take place on the water, later phases at the nest-site. Homologies are traced with other cormorant species. In contrast to other members of the family, allopreening apparently does not occur. Both sexes incubate and care for the young. Observations on families of different ages over the 12-day period allowed the development of the young to be traced up to the age of about 40 days. Egg-laying takes place in most months of the year, with a peak in April-June and perhaps a second peak about October. Observations on birds colour-ringed on an earlier visit suggested that individuals do not breed more than once in the year. Nesting success appeared to be very low in 1963.     

ASPECTS OF THE BREEDING STATUS AND ECOLOGY OF THE BATELEUR AND TAWNY EAGLE IN THE KALAHARI GEMSBOK NATIONAL PARK,SOUTH AFRICA

Herholdt, J.J., Kemp, A.C. & Du Plessis, D. 1996. Aspects of the breeding status and ecology of the Bateleur and Tawny Eagle in the Kalahari Gemsbok National Park. Ostrich 67:126-137.

The nesting success at 13 nesting territories of Bateleur Terathopius ecaudatus and 19 nesting territorites of Tawny Eagle Aquila rapax was monitored for seven successive years (1988–1994) in a protected area in the Kalahari desert of South Africa. On average Bateleurs laid one year in two (51/95 pair-years) and fledged 0.33 young/pair/year (31/95). Tawny Eagles laid, on average, in two out of three years (66/105), and fledged 0.4 young/pair/year (42/105). Most Bateleurs laid eggs in January and February, while Tawny Eagles mostly laid from May to June. Almost all Bateleur and Tawny Eagle nesting territories located were in the Acacia erioloba savanna in the dry Auob and Nossob riverbeds. Bateleur nesting territories were spaced at intervals of 7.2 km (2.5–14.6 km; n = 9) along the Nossob River. Tawny Eagle nesting territories were spaced at intervals of 17.6 km (6.1–32.7 km) in the Nossob River and 11.3 km (8–14 km) in the Auob River respectively. A total of 13 Bateleur and 30–40 Tawny Eagle nesting territories (27 known active nesting territories) respectively occurred in the Kalahari Gemsbok National Park during the study period. There was evidence of a 13% decline in active nesting territories of Bateleur during the seven year study, and at least a 40% decline over the previous 10 years. Vacated nesting territories were not reoccupied. There was no safe buffer zone around the Kalahari Gemsbok National Park and persecution in the adjacent farmlands, when foraging Bateleur from the protected Park enter these areas, as well as nesting site disturbance, could have been part of the reason for this decline. Poisoned and suspected poisoned Bateleurs have been found in the Park during the study period. There was no obvious decline in active Tawny Eagle nesting territories.     

ASPECTS OF THE BEHAVIOUR OF THE MAGPIE GOOSE ANSERANAS SEMIPALMATA

Part 1.
Some action patterns of the Magpie Goose are clearly ritualized as signal actions, whilst others, although not so ritualized, are none the less characteristic of particular moods of the bird. It is considered that the action patterns form a simple language such that individual geese are aware and can often anticipate the actions of other geese.
Particular attention is given to fighting actions, which appear on the second day of a goose's life, and to "concerting", at first a threat display but later also used in pair maintenance, where it appears very similar in function to the triumph display of true geese.
Part 2.
The family, comprising the reproductive group and its offspring, is the fundamental entity in Magpie Goose flocks. Males may be paired to one or two females, but they dominate their mates and offspring and defend a "territory" around them from other geese.
Magpie Goose flocks are built up of families, each of which acts independently except in an alarm situation, when the flock acts as an entity. Flocks build up at feeding, roosting and watering sites, and although constant in location are probably composed of a different combination of families each day. The flock behaviour of Magpie Geese closely parallels that of the true geese.
No alarm stimuli have been found which are innately recognized by Magpie Geese. The fact that alarm stimuli are learnt, taken with the unstable nature of the flocks, suggests that it may be very difficult to produce a "magic wand" which effectively scares the birds from rice crops.     

ECOLOGY AND BEHAVIOUR OF THE SOUTH GEORGIA PINTAIL ANAS G. GEORGICA

A study of the feeding ecology and breeding biology of the South Georgia Pintail was conducted in East Cumberland Bay during November and December 1971. Of a variety of water areas available, pintails fed and reared their broods in tussock-trimmed ponds. The second most important feeding areas were sheltered fjords and seashores. Food included freshwater invertebrates such as fairy shrimp, marine amphipods and snails, and small amounts of marine algae. Considering the climatic conditions, the breeding season spans a long season from late October to early March. Courtship and social behaviour are very similar to that of the pintail, and displays and calls could not be differentiated from those of A. g. spinicauda. There is now one other species of duck on South Georgia, the Speckled Teal, but, because it occurs sympatrically with A. g. spinicauda throughout temperate South America and tends to use different food resources, no serious competition is expected. It is concluded that these species have successfully adapted to South Georgia because of the availability of protected, food-rich ponds for rearing young and because of the semimarine adaptations that have developed in Tierra del Fuego and the Falkland Islands.     

EXPERIMENTS ON THE LIMITATION OF BIRD NUMBERS BY TERRITORIAL BEHAVIOUR

(1) This paper examines removal and other experimental studies on the role of territorial behaviour in the limitation of bird densities. Experimental design is discussed, as are the types of conclusions that can be drawn. (2) Experiments have been conducted on more than 40 species from a wide range of taxonomic groups. Most provided evidence for density limitation, probably mediated by territorial behaviour, and for the existence of a non-territorial sector able to take territories when territory owners were removed or when additional habitat was made available. Experiments in the breeding season indicated that some surplus birds, although younger on average then territorial birds, were sexually mature and able to breed when given the chance. In some species, replacement birds bred less well than other territorial birds, but in other species no difference was apparent between the two groups. (3) Other experiments indicated that, while density was limited by territorial behaviour in good habitats, this was not the case in poor habitats, and that some individuals would move from poor to good habitat when territory owners were removed from good habitat. (4) In some species, non-territorial birds of breeding age were present in the population despite the existence of vacant territorial sites, while in others replacements were observed on good territories but not on poor ones. The implications were that site quality influenced whether settlement, defence and breeding occurred, and that some individuals had more stringent site requirements than others. In some seabirds' sites in the centre of a colony were more attractive than sites on the edges. (5) Many land-bird species that have been studied show two peaks of territorial activity each year, in autumn and in spring, and a limitation on breeding density can occur at either or both seasons, depending on conditions. (6) The fact that densities of many bird species fluctuate greatly from year to year is not inconsistent with the limitation of density by territorial behaviour. Several mechanisms are apparent through which density might be limited by territorialism at different levels in different years, so that surplus non-territorial birds are present in years of low territorial density, as well as in years of high territorial density. (7) Experiments have shown that density is limited by the presence of territorial birds, in some species at different levels in different areas or years. The next step is to find whether density is regulated by the presence of territorial birds over a period of years in a density-dependent manner. For this, observational data are required to find whether the proportion of birds that is excluded by territorial behaviour each year varies with the total number available for settlement. Such studies can be made only on species in which non-territorial birds can be counted accurately, as well as territorial ones.