Gerard Malan

Nesting success of White Terns and White-tailed Tropicbirds on Cousine Island, Seychelles

This study investigates the breeding success of two tropical seabirds that exploit dissimilar nesting habitats on Cousine Island in the Seychelles archipelago, the White Tern Gygis alba and the White-tailed Tropicbird Phaethon lepturus, which nest in trees and in crevices on the ground, respectively. Both species have a clutch of one egg. Over a 23-month study period, the outcomes of 134 nesting attempts by White Terns and 285 by White-tailed Tropicbirds were followed. White Terns produced an average of 0.4 chicks per attempt, significantly more than that of White-tailed Tropicbirds (0.25). Hatching success did not differ between the two species, but fledging success of White Terns (62%) was significantly higher than that of White-tailed Tropicbirds (43%). Nesting success of White-tailed Tropicbirds may be less successful than White Terns because their ground nests are at risk to purely terrestrial predators, in addition to predators that are both terrestrial and arboreal. Many nests of White-tailed Tropicbirds failed during the first two weeks of the incubation and nestling periods, but the reasons for this are unclear. Food availability may influence the reproductive success of both species.

Trends in waterbird diversity at Banzi, Shokwe and Nyamithi pans, Ndumo Game Reserve, South Africa

Our understanding of the timeous changes to pan-associated bird diversity is very important for the conservation of these wetlands. At Ndumo Game Reserve, a Ramsar site located in northern KwaZulu-Natal, seasonal (from March 2005 to January 2006 at Nyamithi Pan) and long-term (1993 to 2008 at Banzi, Shokwe and Nyamithi pans) changes in the composition of waterbird assemblages were investigated. The numbers of waterbirds were determined and their relationship to water level and diet investigated for winter and summer. Banzi Pan was dominated by piscivorous species that used shallow water and the waterbird assemblage of this pan was stable in the long term. At Shokwe Pan, species richness and the overall abundance of waterbirds showed a long-term increase in winter. At this pan, decreasing water levels may have benefited insect-eating, shoreline users, resulting in an increased waterbird population. At Nyamithi Pan, over the short-term, in shallower water the insectivorous shoreline and mudflat users dominated, and in deeper water the larger piscivorous species. Over the long-term, in both summer and winter, variability of bird abundance decreased, although numbers still showed considerable fluctuation. The species composition of waterbirds is different at each of the pans and all are valuable for waterbird conservation.

Alarm calls of Bronze Mannikins communicate predator size to familiar conspecifics

This paper investigates, through experiments using surrogate predators, differences in intraspecific alarm calls between familiar and unfamiliar Bronze Mannikin Spermestes cucculatus groups. Four groups of mannikins were captured with mist nets from four areas in Durban (i.e. original groups) and randomly mixed (i.e. assorted groups). These groups were exposed to latex terrestrial snakes and mounted aerial raptors, and their alarm calls and predator response behaviours recorded. The Bronze Mannikins were able to discriminate between predators of different sizes, and increased their calling rate and decreased the end frequency of the alarm call in response to larger predators. This perhaps signalled increased threat, while simultaneously decreasing the conspicuousness of the flock. When the alarm call structure of the original and assorted groups in response to both raptors and snakes was compared, birds in original groups called more often, but paused longer between calls. Anti-predator behaviour differed in that assorted groups were less vigilant and aggressive toward the predators and panicked more frequently. In these groups, a failure to transfer the predation threat information might have caused the group to stop behaving cohesively and reliably. The manipulated experiments carried out in this study indicated that Bronze Mannikins were able to communicate predator size risk to conspecifics, but not as successfully to unfamiliar group members, showing that the investment, probability through altruistic payback, is greater in stable groups.

Diet of nesting African Crowned Eagles Stephanoaetus coronatus in emerging and forest–savanna habitats in KwaZulu-Natal, South Africa

The aim of this study was to investigate the species composition of prey caught in the forest, savanna and emerging habitats in which African Crowned Eagles Stephanoaetus coronatus breed in KwaZulu-Natal province, South Africa. At the 17 nest sites, the remains of 195 prey individuals were collected. The five dominant prey species caught were Rock Hyrax Procavia capensis, Vervet Monkey Chlorocebus pygerythrus, Blue Duiker Philantomba monticola, Greater Canerat Thryonomys swinderianus and Bushbuck Tragelaphus scriptus. All of these species respond positively to urban expansion. Only eagles that nested inside protected areas were recorded preying on domestic animals. In terms of biomass, Bushbuck was one of the dominant taxa, and the remains of an estimated 28.8 kg Bushbuck ram was found under a nest. The surprisingly high proportion of Rock Hyraxes and low proportion of Vervet Monkeys caught in emerging habitat may indicate that African Crowned Eagles nesting in this habitat are adapting to a more specialised feeding strategy compared with those nesting in habitats that are more natural. Future studies should investigate how and why prey proliferates in emerging habitats and examine the association between land uses and the diet of African Crowned Eagles.

Replacing Grasslands with Pine Plantations on the Karkloof Plateau: The Edge Effects on Downslope Forest Understorey Birds

The aim of this study was to examine if and how the exposure of indigenous forest edges to flanking exotic pine plantations transform the avian community and forest ecosystem found in the forest periphery. I compared bird diversity indices between forest bordering grassland and forest bordering pine plantation at 10 study locations. At each location, understorey birds were sampled with mist nets at the edge (0 m) and progressively deeper into each forest interior in spring and autumn. Crown cover was measured at these sites in autumn. Crown cover decreased from the edge into the forest, more so in forest bordering plantation, and at 60 m was, on average, 18% lower than forest bordering grassland. Furthermore, in forest bordering grassland, bird species richness and total abundance (of individuals) increased with edge distance in both seasons, but in forest bordering plantation, these trends were absent. In addition, in forest bordering plantation, different dominant species were recorded in spring and species only found in this habitat only fed in the forest mid-stratum. I therefore recommend that plantations be planted 15 m from forest edges to prevent perforation and edge-effect loss that will allow the edge and understorey avifauna to function as a natural part of the indigenous Afrotemperate forest patch in South Africa.

Nest site selection of the Southern Pale Chanting Goshawk in the Little Karoo, South Africa

This study investigated whether Southern Pale Chanting Goshawks Melierax canorus that nest in the low woody vegetation of the arid Little Karoo reduce nest predation by selecting nest trees and sites that are less accessible to and conspicuous for terrestrial predators. The 114 nest trees and shrubs sampled were taller (0 = 4.4m) than surrounding random trees (0 = 3.0m). The birds selected bush clumps for nesting that contained, on average, two plants, including creepers, compared to the 1.4 plants in random clumps. The birds also nested mainly in irregular and dome-shaped trees, a selection that differed from the dominant shapes of random trees. Most nests were placed in the centre of the trees and thorns and shoots covered the main stem of 68% of nest trees. In spite of these preferences, only nest height and — to a lesser extent — nest placement and tree shape, prevented predation by visually hiding the nest. The other features had no impact on predation, indicating that once a nest was discovered, the predators were able to climb through the foliage to the nest. Pale Chanting Goshawks therefore had some success in hiding their large nests in the low and sparsely-growing arid trees and shrubs. Although 19% of nests studied were depredated, the seasonal, irregular and low-density breeding pattern of the birds probably resulted in their offspring being an unpredictable food source for opportunistic predators.

The relative influence of prey abundance and co-breeders on the reproductive performance of polyandrous Pale Chanting-goshawks

This study investigates if the reproductive performance of polyandrous Pale Chanting-goshawks, Melierax canorus, is governed by the abundance of dominant rodent-prey species or a co-breeding male participating fully in prey being delivered to the female and young. Polyandrous trios in prey-rich habitat, the only habitat where these trios occurred, failed to produce more offspring than monogamous pairs, but attempted more second broods in years of high prey abundance. The higher the prey-delivering rates at the nesting sites by either one monogamous male or two polyandrous males (combined effort), the higher the proportion of time their females spent in close proximity to the nest. Since there were no significant differences between the body masses of nestlings fledged by polyandrous and monogamous groups, higher delivery rates relieved females from away-from-the-nest hunting duties and permitted them to feed on prey not fed to offspring. Although breeding in polyandrous trios held fitness benefits for females, e.g. to accumulate the necessary body reserves for laying a second clutch in years of high prey abundance, it is still not clear how males benefited. The reproductive performance of each group was strongly linked to the abundance of the dominant, otomyine rodent prey (Otomys unisulcatus and Parotomys brantsii) and it was therefore prey abundance, and not the number of males delivering prey to the female and nestlings at each nesting site, that controlled the reproductive performance of cooperative-breeding Pale Chanting-goshawks.

Association between avian assemblages and mountain bushveld communities along a single mountain slope in the Usuthu Gorge, South Africa

The study investigated the bird species diversity associated with vegetation communities found on a single mountain slope in the Usuthu Gorge Community Conservation Area, northern KwaZulu-Natal. Thirteen sample sites were surveyed on a monthly basis for 12 months. Over this period, 279 birds and 55 species were recorded, of which the Dark-capped Bulbul Pycnonotus tricolor was the most abundant. The Rattling Cisticola Cisticola chiniana was the indicator species in the highest community, Open Bushveld, which is characterised by grassland and bush patches. The White-bellied Sunbird Cinnyris talatala was an indicator in the second-lowest community, Dense Bushveld–Woodland, which is characterised by steep slopes and thickets. In Wooded Grassland, located between the above two communities, the highest beta diversity (species turnover) was recorded and this outcome was probably caused by large areas covered by rocks that compelled woodland birds to move through this community. Contrary to expectation, the gamma diversity per vegetation community increased with elevation from 18 to 33 species in Dense Bushveld–Woodland, Wooded Grassland and Open Bushveld. A future study should measure bird species diversity on larger elevational gradients, i.e. slopes from 500 to 3 000 m above sea level, which also include more distinct vegetation communities.