OpenUCT :: Browsing by Author "Hockey, Phil A R"

Browsing by Author "Hockey, Phil A R"

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Open Access
Aspects of the biology and conservation status of the blue crane Antropoides paradiseus, and the Ludwig's Neotis ludwigii and Stanley's N. Denhami Stanleyi bustards in southern Africa
(1993) Allan, David George; Hockey, Phil A R
The cranes (Gruidae) and bustards (Otididae) are highly threatened taxa. Many species are on the brink of extinction due to anthropogenic factors. On the positive side, several species show a remarkable ability to adapt to man-modified environments. If the cranes and bustards are to survive through the coming century, research on the aspects of their biology directly relevant to understanding their conservation requirements is a high priority. Without a reliable and relevant base of knowledge, no successful conservation management plan can be devised for each threatened species. This thesis presents information on three threatened members of these taxa in southern Africa, the Blue Crane Anthropoides paradiseus, and Ludwig's Neolis ludWigii and Stanley's N. denhami stanleyi Bustards. This information furthers our understanding of their conservation status. The thesis begins with a detailed review of the phylogeny, general biology and conservation status of cranes. This is necessitated by the absence of any thorough and recent review being available. The review provides a point of reference for the research results on the Blue Crane presented in the following seven chapters. Research on the Blue Crane largely focuses on the southwestern Cape and Karoo regions. The past and present distribution of the species in southern Africa is outlined and related to various vegetation types and the effect of various anthropogenic influences. Its colonization of the southwestern Cape is a particularly interesting finding. The abundance of the species in various parts of South Africa is discussed, largely based on road counts and bird atlas data. The total population size in South Africa is estimated and the previously unrecognised importance to the species of the southern Cape coastal plain between Botrivier and Mossel Bay is highlighted. The scarcity of Blue Cranes in the western part of the southwestern Cape, compared with the southern part, is quantified. The reasons for this anomolous dichotomy in abundance betweep these two superficially similar areas are unclear and worthy of further investigation.
Open Access
Aspects of the ecology of migrant shorebirds (Aves: Charadrii) at the Berg River estuary, South Africa
(1992) Kalejta, Bozena; Hockey, Phil A R
The waterbird populations of the Berg River estuary, South Africa, were studied from September 1987 to April 1989. The main objectives of the study were to assess the importance of the estuary for Palearctic-breeding migratory waders and to identify the factors affecting their distribution, abundance and behavioural patterns. The findings were related to the dispersion patterns of waders on the east Atlantic seaboard, and their significance was evaluated in the light of predictions of current models for the migratory behaviour of shorebirds. Controversy over the Winter competition model is discussed. The intertidal mudflats (144 ha) at the Berg River estuary support an exceptionally high density of migratory shorebirds during the austral summer. The high density of birds results in a high predation pressure. Although the rate of prey removal by birds is one of the highest recorded in the east Atlantic, it represents only 17% of the annual production of invertebrates. A bird-exclusion experiment confirmed that birds have little impact on their prey populations. Although the energy balance for the majority of species was apparently negative for much of the austral summer, the energy deficits measured in the field were less than those recorded in north temperate estuaries. The highest predation pressure by birds coincided with the period of highest production of the most important invertebrate prey. Because of low prey diversity in the estuary, there was considerable overlap in the prey species taken by different bird species. The preferred prey of most species were nereid worms. Within this prey class there were clear differences in the size classes of worms eaten by different birds. The distribution of birds on the estuary was related to both biotic and abiotic factors. The observed patterns of partitioning of both food and space resources was attributed to the superabundance of prey and to interspecific differences in foraging techniques unrelated to competition. The spatial redistribution of birds within the estuary during the first four months after their arrival from the breeding grounds was related to changes in feeding conditions on their preferred foraging sites, rather than density-dependent factors mediated by competition. I propose that a combination of high prey abundance and production, coupled with an apparently low level of competition, makes the Berg River an attractive nonbreeding site for migrant waders. Their relatively sound energy budgets and the benign climate may enhance nonbreeding survivorship sufficiently to offset any additional risks incurred in long-distance migration.
Open Access
Assessing conservation of a tropical African estuary : waterbird disturbance, livelihoods, and ecotourism
(2011) England, Kate; Hockey, Phil A R
The aim of this study was to evaluate the potential costs and benefits of increasing conservation in the Sabaki River Mouth Important Bird Area. This was achieved by assessing the vulnerability of waterbirds to disturbance from human activity in the estuary, the current use and importance of the area to local livelihoods, and the value (current and potential) of tourism. Waterbird densities and levels of human activity were quantified from 20 September to 25 November 2010 in the intertidal area of the Sabaki River Mouth Important Bird Area on the central Kenyan coast. Household surveys were conducted in the adjacent Sabaki Village from 15 October to 24 November 2010 (N = 190). The current and potential value of ecotourism was investigated by recording visitation rates and interviewing visitors to ascertain their preferences and willingness to pay an entry fee from 5 October to 4 November 2010. Three types of response variables were collected at six sites to characterize relative responses of waterbirds to simulated human disturbances. These were 1) changes in bird density within a 40 m radius of a stationary disturbance (D40); 2) minimum distance of birds from the source of a stationary disturbance (¡Ü 40 m); and 3) the time for 90% of original bird abundance to recover following a mobile human disturbance which caused all birds to flee the immediate vicinity. Disturbance response metrics were estimated from these variables by calculating normalized mean residuals from regressions of density (D40) and minimum approach distance against expected densities measured in the absence of disturbance, for 14 waterbird species.
Open Access
Behavioural ecology of Peregrine and Lanner falcons in South Africa
(1998) Jenkins, Andrew Robert; Hockey, Phil A R
The Peregrine Falcon Falco peregrinus is a specialized predator of birds. It occurs almost worldwide but is generally uncommon. In many areas, it is sympatric with one of a complex of similar, less specialized, congeneric species (subgenus Hierofalco, the desert falcons). Peregrine density and productivity tend to decrease with latitude, while desert falcons may be most successful in the tropics. This study compares the biology of Peregrines and sympatric Lanner Falcons F. biarmicus in South Africa, and examines the relative influence of resource limitation and interspecific competition with congeners on the natural regulation of Peregrine populations in tropical environments.
Open Access
Behavioural ecology of the Redbilled Woodhoopoe Phoeniculus purpureus in South Africa
(1989) Du Plessis, Morne Andre; Hockey, Phil A R
A study was made of two Redbilled (Green) Woodhoopoe Phoeniculus purpureus populations spanning an eight year period (1981-1988) and 258 'flock-years', in the eastern Cape Province of South Mrica. The main objectives of the study were to investigate (1) why woodhoopoes live in groups; (2) why nonbreeders do not breed; and, (3) why nonbreeders provision young that are not their own? Ecological and demographic data were gathered in addition to detailed behavioural observations of 54 woodhoopoe flocks. The following experimental manipulations were performed: (1) breeders were removed from flocks to (a) monitor dispersal patterns and restructuring of flocks; and, (b) observe behavioural reactions by remaining birds; (2) cavity availability was (a) decreased, to enable quantification of availability; and, (b) increased, by addition of nest/roost boxes to an area which supported no permanent woodhoopoe territories; and, (3) stimuli, associated with the food provisioning response of adult birds, were manipulated to investigate the evolutionary basis of allofeeding behaviour Variability in social and reproductive behaviour reflects environmental selection pressures, in the form of roost-cavity availability, with a reduction in cavity availability leading to increased group size. The group-territorial social system and high level of inbreeding of Redbilled Woodhoopoes have evolved primarily in response to environmental constraints on dispersal, rather than by particular benefits that arise from group living. Therefore, the habitat-saturation hypothesis best explains group living of woodhoopoes. Behavioural dominance hierarchies ensure that dominance relationships are well-defined among potential competitors (for breeding status), and thereby minimize disruption to flock cohesion upon the death (or removal) of a breeder. If competition for a breeding vacancy arose at the time of the breeder's death, the resultant delay in occupancy of the breeding vacancy would increase the likelihood of competition from unrelated birds. The establishment of such hierarchies is therefore adaptive in the context of the direct component of kin selection. The presence of nonbreeding helpers do not increase fledgling success, breeding frequency, survivorship (of any age, sex or social class), or number of breeder-offspring produced. Because no unambiguous indirect fitness benefits could be shown to result from helping behaviour (specifically allofeeding), I propose that the unselected (misdirected parental care) hypothesis is a viable alternative to the 'functional hypotheses.' This hypothesis is supported by observations/manipulations of misdirected food provisioning by both breeders and helpers.
Open Access
Bird reproductive success and faunal habitat selection as tools for understanding the impacts of land-use management on moist highland grassland biodiversity in South Africa
(2011) Little, Ian Tchagra; Hockey, Phil A R
It has been suggested that natural fires in these grasslands would have occurred as infrequently as every four or more years. Currently, the majority of the system is managed by livestock farmers who burn their land annually at the onset of the rainy season (early in the austral summer).
Open Access
Birds at risk in warming southern African deserts: inferences from behavioural and physiological thermoregulation
(2011) Louw, Gina; Hockey, Phil A R
The study focused on avian species' responses to high ambient temperature. Ambient temperature is a variable to which birds are particularly sensitive and which climate-change models predict will increase disproportionately rapidly in southern Africa's hot deserts, especially the Kalahari.
Open Access
The causes of avian extinction and rarity
(1997) Lennard, Christopher James; Hockey, Phil A R
Biological extinction rates have escalated by as much as 1000 times the background extinction rate over the last 1500 years, causing concern over the long-term survival of many species. Avian extinctions since 1600 have been well documented relative to other taxa, as have current levels of avian threat. This study analyses avian extinctions post-1600 and current threats in an attempt to develop some predictive capacity about which avian taxa should be awarded the highest conservation priority. Analyses performed include examinations of the causes of avian extinction and threat, geographical location of extinct and threatened species, prehistoric and historical extinction rates, endemicity, migration, bird body size and phylogenetic diversity. An analysis dealing with historical and phylogenetic aspects of endangered and critically threatened species was performed, from which the world's most threatened species were identified. Factors which were the primary cause of historical extinctions are generally not the primary factors threatening today's extant avifauna. Whilst introduced predators and exploitation were primary causes of historical extinctions, habitat destruction poses the greatest threat to extant birds. Species predisposed to extinction typically have restricted ranges, and, compounded by habitat loss, these ranges are becoming more restricted. This has resulted in mainland-dwelling species becoming as prone to extinction as island-dwelling species have been historically. Introduced predators, however, do still threaten many of the world's most threatened species and their potential effects are highlighted in the phylogenetic analysis. Already, many extinctions may be inevitable over the next 25 years as a result of habitat loss. The magnitude of extinctions across all animal and plant species in the next few decades could be comparable with that of previous mass extinctions unless immediate conservation action is taken. However, future conservation efforts will have to be prioritized, and this study is intended as a contribution towards such a prioritization exercise.
Open Access
Comparative foraging ecology of two broad-ranging migrants, grey plover Pluvialis Squatarola and whimbrel Numenius Phaeopus (Aves: Charadrii), in tropical and temperate latitudes of the Western Indian Ocean
(1994) Turpie, Jane; Hockey, Phil A R
A seasonal study of the nonbreeding foraging ecology of Grey Plovers and Whimbrels was undertaken at the Zwartkops estuary, South Africa, and additional data were collected from a variety of sites in tropical and south temperate latitudes during the premigratory period. The main objective of the study was to provide comparative data on shorebird foraging ecology in the southern hemisphere, in order to contribute to the general understanding of shorebird foraging behaviour and migration patterns.
Open Access
A comparitive analysis of patterns of recent extinction in birds and mammals
(2010) Githiora, Yvonne; Hockey, Phil A R
Exploring past extinction patterns among taxa can inform us about risks facing currently threatened taxa if such extinctions have been non-random with respect to phylogeny and/or geographical patterns. This study analyses patterns of recent extinctions among birds and mammals in order to determine factors influencing these patterns and whether these factors differed between the two groups. Data on bird and mammal species that have become extinct since 1500, including their distributions and body-masses, were collected from diverse sources. GIS mapping was used to determine spatial patterns of species extinctions. The body-mass distributions of extinct species were also compared with body-mass distributions of samples of extant species. Patterns of extinction were found to differ geographically among birds and mammals. However, underlying factors influencing these patterns were found to be similar, with species endemism being an important predictor of recent extinctions. Recently extinct species were larger, on average, than extant species in both birds and mammals pointing to the influence of human over-exploitation in the extinctions. Invasive species, particularly mammals such as rats, were also an important driver, influencing species extinctions by preying on native birds and competing with native mammals of similar biology. These findings can most likely be extrapolated to reptiles, whose extinctions have been similarly influenced by invasive mammals but not necessarily to amphibians whose recent extinctions and declines are being driven primarily by a complex interaction of factors including emerging infectious diseases.
Open Access
Determinants and consequences of territory quality in the Bar-throated Apalis Apalis thoracica
(2011) Chaskda, Adams Adamanyiwa; Hockey, Phil A R; Lloyd, Penn
The underlying principles of territoriality propose that competition for resources compels individuals to defend areas (territories) that give them exclusive access to critical resources. The theory suggests that only high-quality individuals succeed in occupying areas rich in these resources with consequent benefits in terms of higher reproductive success and/or chances of survival. The main aims of this study were: i) to determine the ecological factors influencing variation in territory size and quality among Bar-throated Apalises Apalis thoracica; ii) to investigate the consequences of these factors for reproductive effort and reward, pair stability and survival; and iii) to investigate the signalling properties of the species' black breast band (a prominent 'badge' emblazoned across the white underparts) in relation to both male and territory quality.
Open Access
Dispersion patterns of Holarctic-breeding, migrant landbirds : global paradigms or regional patterns?
(2003) Hamblin, Jane V; Hockey, Phil A R
This study quantifies the breeding and wintering ranges, habitat occupancy, diet and foraging mode of each migrant taxon on each of the three flyways. It aims to compare how patterns of migration between the temperate and tropical latitudes vary spatially in response to a) the geography of the land masses, b) relative availability of different habitat types, c) dietary preferences and d) foraging mode.
Open Access
Distribution, diet and kleptoparasitic behaviour of gulls (Aves: Laridae) in the southwestern Cape Province, South Africa
(1991) Steele, William K; Hockey, Phil A R
The southwestern Cape coastline supports only two common, resident gull species, Hartlaub's Gull Larus hartlaubii and the larger Kelp Gull L. dominicanus. Hartlaub's Gull is endemic to southern Africa and the Kelp Gull that occurs in this region is sub-specifically distinct, L. d. vetula. Although locally abundant, both the Kelp and particularly Hartlaub's Gull have been relatively little studied. This study addressed three aspects of the two gull species' ecology related to foraging. The diet of both species was studied through direct observation and analysis of pellets, scats and stomach samples. Diet was quantified at a range of foraging habitats; (i) a sandy beach; (ii). a rocky shore; (iii) a fishing harbour; and, (iv) a refuse dump. In addition, the proportion of marine prey in the diet of Kelp Gulls at a refuse dump, a sandy beach and at archaeological sites was estimated using stable carbon isotope analysis of bone collagen. Both gulls are generalist foragers feeding on a wide and diverse range of prey species. The Kelp Gull is able to feed on a wider range of prey species than is Hartlaub's Gull due to its larger size. The preferred natural foraging habitat of the Kelp Gull is sandy beaches, where the sand mussel Donax serra is the most important prey. Present day Kelp Gull diet at an undisturbed• sandy beach includes a similar proportion of marine protein to prehistoric gull diet in the same area. Hartlaub's Gull most commonly forages on swarms of invertebrates associated with accumulations of stranded kelp e.g. Ecklonia maxima.
Open Access
The eco-ethology of the Karoo Korhaan Eupodotis Vigorsii
(1989) Boobyer, M G; Hockey, Phil A R
The following study was undertaken as part of the Karoo Biome Project (KBP) and sets out to investigate an aspect of karoo ecology that will contribute to a predictive understanding of both biotic and abiotic processes in the region for the development of meaningful management guidelines (Cowling, 1986).
Open Access
Ecological and evolutionary processes in two southern African endemic birds
(2011) Ribeiro, Angela M; Hockey, Phil A R; Lloyd, Penn
In this dissertation, I propose a population-level framework that integrates ecology and population genetics to rethink the mechanisms that promote divergence. To accomplish that I studied two southern African endemic Cercotrichas scrub-robins: C. coryphaeus and C. signata. Despite its phylogenetic proximity the two study species occupy the two ends of the habitat spectrum available in southern Africa: semi-arid Karoo vs. Forest.
Open Access
Ecological impacts of biological invasions on native birds in Africa
(2010) Gichohi, Nathan W; Hockey, Phil A R
The impacts of biological invasions on native avian diversity have been the subject of many studies in Africa. However, a holistic synthesis of available information from different taxa and their impacts on native birds is lacking. From published information, I analysed the negative and positive effects of biological invaders on native African birds from five taxa: plants, invertebrates, fish, mammals and birds. In order to assess functional gains and losses, native birds were categorized into their functional guilds defined by their primary diet. I limited my scope to mainland Africa at the biome level. ArcView GIS 3.3 software was used to map locational data of impacts within the major biomes. The results indicate that a minimum of 572 native birds are negatively impacted by invasive species from the five taxa. This represents ca 29% of all the bird species in Africa. In contrast, only 191 species of native birds benefited from such invasions. Birds whose diet was primarily insects were disproportionally impacted. The majority of the impacts were caused by invasive plants. At the biome level, the greatest numbers of native birds impacted were in the Montane grassland and shrubland biome. It is predicted that native birds will continue to lose more than they gain from biological invasions in the continent.
Open Access
The effect of grassland shifts on the avifauna of a South African savanna
(2005) Krook, Kristine; Bond, William J; Hockey, Phil A R
Two distinct grassland types occur within Hluhluwe-iMfolozi Park (HiP); short stoloniferous grazing lawns and tall, tussock-like 'bunch' grasslands. Grazing lawns are maintained by grazing mammals, among which White Rhinoceros Ceratotherium simum is of major importance. By contrast, tall bunch grasslands are promoted by frequent burning. The extent of each grassland type within the park is highly dynamic and can be altered by changes in mammal numbers and/or fire regimes. Such changes may have cascading consequences on other components of the ecosystem if they show specialisation towards one or other grassland state. This study compared avifaunal assemblages of grazing lawns and bunch grasslands to assess how bird species of the park might change with shifts in the grassland mosaic. Distinct bird communities were associated with each grassland type, including several specialists, and bird distribution as linked to vegetation structure, rather than floristics.
Open Access
Environmental influences on moult and movement strategies in southern African waterfowl
(2012) Ndlovu, Mduduzi; Cumming, Graeme S; Hockey, Phil A R
Waterfowl annual life history events in north-temperate regions are driven primarily by predictable seasonal variations in temperature. In contrast, the spatio-temporal availability of adequate resources to waterfowl in the semi-arid regions of southern Africa is determined by rainfall which is extremely variable in timing and intensity. I studied the environmental influences on flight-feather moult and movement strategies of southern African waterfowl. Six duck species that are fairly common in most parts of South Africa were selected for the study, namely; Egyptian Geese, Alopochen aegyptiaca, Spur-winged Geese, Plectropterus gambensis, South African Shelducks, Tadorna cana, Yellow-billed Ducks, Anas undulata, Red-billed Teals, A. erythrorhyncha and Southern Pochards, Netta erythrophthalma. I chose two study sites to represent the extremes of environmental conditions in southern African, namely Barberspan (summer-rainfall region) and Strandfontein (temperate winter-rainfall region). I investigated the underlying responses of Afrotropical waterfowl to stochastic varying environmental conditions in southern Africa and the life-history strategies they have evolved to cope with this variability. The study also compares and contrasts the life-history strategies of southern hemisphere waterfowl with those of the northern hemisphere.
Open Access
Fine-scale movements and habitat use of the Southern Ground Hornbill Bucorvus Leadbeateri
(2015) Zoghby, Blair Anthony; Ryan, Peter G; Little, Rob M; Hockey, Phil A R
Southern Ground-Hornbills Bucorvus leadbeateri are listed as Endangered in South Africa and there is a concerted effort to reverse their population decline. Understanding the factors affecting their movement patterns and how they interact with their habitat is useful to inform conservation and habitat management options for the species, to select sites for artificial nests and to identify suitable areas for reintroduction initiatives. In this study, I report daily and seasonal patterns of habitat use as well as patterns of roost site use of four Southern Ground-Hornbill groups in the Associated Private Nature Reserves, northeast South Africa, based on data from GPS-satellite tags collected over one year from October 2010 to September 2011. Home ranges varied from 5.9-10.3 km² and were larger in winter than during the summer breeding season. Daily travel distances were greater during the breeding season, when birds were constrained to forage close to their nest, and were lower in winter, when birds ranged more widely. Hourly travel distances were affected by time of day, season, air temperature and group. Birds travelled farthest per hour in the morning, decreasing in the afternoon in winter. However, in summer hourly travel distances were bimodally distributed, with a minimum during the middle of the day when ambient temperatures exceed 25⁰C. Acacia-dominated vegetation and riparian habitats were favoured disproportionately during the heat of the day in summer, presumably because they offer more shade than other habitats. The number of roost sites used per month decreased progressively throughout the Early Wet season (October-December) and was lowest during the Late Wet season (January-March) for three groups that bred successfully. Mean monthly nights per roost were highest for these groups in the Early Wet and Late Wet seasons, specifically over December and January, coinciding with the peak breeding period. Throughout the Early Wet season, all four groups frequently roosted in close proximity to the nest, with 54-83% of roosts being within 1 000 m of the nest. During the Wet season, riparian habitats were favoured for roosting by the three groups that bred successfully, while during the dry season, disturbed areas, combretum-dominated habitats and mopane-dominated habitats were used. I conclude that the optimal habitat configurations for ground-hornbills include a mosaic of habitat types, including open areas for foraging and dense trees for shade as well as adequate large trees for nesting and roosting, particularly in riparian habitats.
Open Access
The foraging ecology, demographics and conservation of African black oystercatchers Haematopus moquini in Namibia nursery areas
(2001) Leseberg, Antje; Hockey, Phil A R
Research was carried out at the Walvis Bay/Swakopmund nursery during four visits between Aug/Sep and May/Jun 2000. The study aimed to quantify seasonal and tidal patterns of habitat use and responses to changes in prey abundance, and to investigate whether nurseries provide favourable foraging conditions and high energetic returns for juvenile oystercatchers.