G. L. Maclean

Bio: G. L. Maclean is an academic researcher from University of Natal. The author has contributed to research in topics: Nest & Vanellus coronatus. The author has an hindex of 6, co-authored 12 publications receiving 174 citations.

The sociable weaver, part 1: description, distribution, dispersion and populations

Abstract: Summary Maclean, G. L. 1973. The Sociable Weaver, Part 1: Description, distribution, dispersion and populations. Ostrich 44: 176–190. The Sociable Weaver Philetairus socius is a cryptically coloured passerine about 14 cm in length, weighing about 27 g and living in a semi-arid to arid region of southwestern Africa. Its range coincides with that of stout trees like Acacia giraffae, and of stiff dry grasses like Aristida ciliata; these plants provide nest sites and building material respectively. A colony of Sociable Weavers may number from two birds to over 500 birds and may occupy a single large nest mass, several nest masses in one tree, or several nest masses in two or more adjacent trees. In the study area in the Kalahari Gemsbok National Park, the density of Sociable Weavers was about 80 birds/km during the 19-month study period. Neighbouring colonies may be as little as 0,8 km apart, but are usually further apart than this, so that the density of colonies is not directly proportional to the density o...

Altitudinal migration in natal

Abstract: Summary Johnson, D.N. & Maclean, G.L. 1994. Altitudinal migration in Natal. Ostrich 65: 86–94. The province of Natal, South Africa, ranges from sea level to an elevation of 3000 m over a distance of only 160 km. Evidence from the literature and from ringing shows that at least 76 species of birds are altitudinal migrants in Natal, moving to lower elevations in winter (from about March to September). Most can be grouped roughly into four categories, depending on their breeding areas (montane, high- or mid-altitude) and the distances over which they migrate (short-distance or long-distance (A) montane to high-altitude, (B) high-altitude to mid-altitude. (C) high-altitude to low-altitude and (D) mid-altitude to low-altitude; there is some overlap between the categories, some species falling into two or even three altitudinal migration patterns. Birds in category (A) move to lower altitudes from the Afromontane region of the Drakensberg regularly or only when winter weather conditions are very severe, but som...

Egg-covering in the charadrii

Abstract: Summary Maclean, G. L. 1974. Egg-covering in the Charadrii. Ostrich 45: 167–174. Deliberate egg-covering in the Charadrii (waders) occurs in at least 13 species in four families (Jacanidae, Glareolidae, Charadriidae and Thinocoridae). The habit is most widely developed in the genus Gharadrius, of which at least four species cover their eggs. Egg-covering is done by kicking material over the eggs with the feet in most species, but in the Glareolidae and probably some other groups, only the bill is used. The primary function of egg-covering appears to be concealment, but the secondary function of thermoregulation appears to have become almost as important in a few species, especially as a device to insulate the eggs against exposure to the sun. It is not surprising that egg-covering is most highly evolved in tropical and subtropical regions where predator-pressureMaybe higher, and the danger of overheating by direct sun is greater, than elsewhere.

Breeding behaviour of larks in the Kalahari Sandveld

Abstract: There are eight species of larks (Alaudidae) breeding in the southern part of the Kalahari Gemsbok National Park; they belong to the genera Mirafra (three spp.), Chersomanes(one sp.), Eremopterix (two spp.), Spizocorys (one sp.) and Alauda (one sp.). Each species has its own characteristic song, usually associated with a song-flight over the territory. The nest in most, if not all, species is built by the female alone, usually within four to seven days. Eggs are laid at 24-hour intervals. To judge from the difference between mean egg measurements in summer and in winter, it is possible that two different subspecies of Eremopterix verticalis breed at different times in the Gemsbok Park. Incubation takes 12 days in all species and the chicks leave the nest at about 10 days, well before they can fly. Chicks are led away from the nest by the female parent, although both parents feed the chicks. In the genus Eremopterix both parents incubate the eggs. All species of sandveld larks have characteristic alarm- and intruder-reactions at the nest; some of them have distraction displays of the injury-feigning type, others apparently do not.

Distribution and breeding biology of the african skimmer on the upper and middle zambezi river

Abstract: Summary Coppinger, M. P., Williams, G. D. & Maclean, G. L. 1988. Distribution and breeding biology of the African Skimmer on the Upper and Middle Zambezi River. Ostrich 59: 85–96. Observations were made on the distribution and breeding biology of the African Skimmer Rynchops flavirostris from May to November 1986 and April to December 1987, along 1550 km of the Zambezi River from its source to the Luangwa-Zambezi confluence at the Mozambique border. The 280-km Angolan section was omitted. Bird habitats along the river were mapped and the distribution of the African Skimmer was compared with the availability of its breeding habitat. 35 breeding colonies were found of which 33 were on the Barotse floodplain. Eggs were noted during August, September and October; they were laid in scrapes on bare sand in clutches of mostly 2–3. 260 eggs were measured from 101 clutches (a 39,6 x 28,4 mm). Both parents incubated and cared for the young. In hot weather, adults drank often and belly-wetted at nest relief. Chicks ...

Risks and rewards of nest defence by parent birds

Abstract: Nest and offspring defence by birds can be treated as an optimization problem wherein fitness benefits are determined by the survival of the current brood and fitness costs depend upon the probability that the parent will survive to breed again. At the optimal intensity of defence, net fitness benefits are maximized. Unlike many other aspects of animal behavior, the reproductive consequences of nest defence can often be measured directly. Within this optimality framework, we review the current adaptive hypotheses to explain both interspecific and intraspecific variation in nest defence behavior, and we present some new ideas of our own. Most research to date has focused on seasonal patterns of nest defence to test the prediction that the intensity of nest defence should increase through the nesting cycle either because renesting potential declines or because the probability of offspring survival increases rapidly relative to that of the parents. Studies testing the renesting potential hypothesis have both...

Avian Communal Breeding Systems

Abstract: Communal breeding in birds may be the most critical test case for the application of Hamilton's (54, 55) ideas about inclusive fitness, altruism, and kin selection (73a) among vertebrates. Avian communal breeding systems (A CBS) feature precisely that phenomenon that seems most likely to require kin selection as a part of its evolutionary explanation, namely, the presence of a form of operational altruism [in which gains and losses are empirically determined ( 1 6)] known as helping behavior. A helper was defined by Skutch (99) as "a bird which assists in the nesting of an individual other than its mate, or feeds or otherwise attends a bird of whatever age which is neither its mate nor its dependent offspring." The obvious questions are then: (a) What selection pressures shape the kind and degree of helping behavior? (b) Is kin selection implicated in an evolutionary explanation of helping behavior, and, if so, to what extent? (c) Does helping behav­ ior qualify as altruism in the sense of Hamilton? As subjects for the study of such questions among vertebrates, communal birds have numerous practical advantages. The number of avian species having helpers runs in the hundreds. The giving of food and other kinds of aid by helpers to recipients is easily observable and quantifiable. The genetic relatedness of the partici­ pants can be determined by following successive generations of individually marked animals. Most species are diurnal, relatively conspicuous, and easily watched. Their small home ranges enable numerous social units to be monitored.

The atlas of southern African birds

Abstract: This is a major work covering the breeding and non-breeding birds of the Southern African sub-region. Published in two volumes, Volume One includes introductory chapters describing methodology and the 'avi'-geography of the region, with habitat photos, and coverage of the non-passerines, whilst Volume Two covers the passerines. Some 900 species are covered in total, including 200 vagrants, with detailed species accounts, maps and statistics for at least 500 species. Conservation issues are discussed for most species. '...sets new standards in its scope and in its methods...it will come to be valued ever more as years go by, for setting a measured baseline against which to judge environmental trends across the great range of southern Africa.' - Colin Bibby, "BirdLife International".