Browsing by Author "Sherley, Richard B"

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    Factors influencing the foraging behaviour of African Penguins (Spheniscus demersus) provisioning chicks at Robben Island, South Africa
    (2016) Campbell, Katrina; Underhill, Leslie G; Sherley, Richard B; Steinfurth, Antje; Crawford, Robert J M
    Urgent and effective conservation is needed to halt the declines of endangered African Penguins. A purse-seine fisheries closure zone was in place out to 20 km around Robben Island for three years. It provided an opportunity to investigate penguin foraging behaviour in relation to estimated local prey abundance and other factors without the confounding variable of local fishing. Penguins provisioning chicks were equipped with GPS temperature depth devices for a foraging trip. Dive data (N = 75) and GPS tracks (N = 78) were collected from 78 penguins. Of those, 14 penguins were at-sea within two days of a fine-scale hydro-acoustic pelagic fish survey. Diet sampling, breeding success and chick body condition monitoring took place in the colony. Nests were followed to outcome. Morphological indicators were developed for sex determination and body condition. Intrinsic factors, brood mass, prey abundance, wave height and direction were explored in respect to foraging behaviour. Kernel density analysis identified foraging areas, confirming consistent use of the closure area. Annual differences in foraging effort were explained by variation in local prey abundance. The time the penguins spent diving and the distance travelled from the colony were negatively related to local prey abundance. There was greater variation in foraging distance when prey abundance was lower. Foraging areas and dive behaviour were similar for the sexes. The survival of chicks in the foraging study did not differ from chicks monitored in the colony for breeding success (control chicks). The trips of penguins with nesting success (N = 44) were on average 4.5 km closer to the colony than the penguins that had nesting failure (N = 21). Chick body condition in the colony was positively related to the Anchovy (Engraulis encrasicolus) mass percentage in the diet and the local pelagic fish abundance; condition was predicted to vary by 245% over the range of local fish abundance observed during the study period (0.5 to 187 thousand tonnes). Identifying ways to avoid depletion of prey resources around penguin colonies is important for conservation of the species.
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    Hand-rearing, release and survival of african penguin chicks abandoned before independence by moulting parents
    (Public Library of Science, 2014) Sherley, Richard B; Waller, Lauren J; Strauss, Venessa; Geldenhuys, Deon; Underhill, Les G; Parsons, Nola J
    The African penguin Spheniscus demersus has an ‘Endangered’ conservation status and a decreasing population. Following abandonment, 841 African penguin chicks in 2006 and 481 in 2007 were admitted to SANCCOB (Southern African Foundation for the Conservation of Coastal Birds) for hand-rearing from colonies in the Western Cape, South Africa, after large numbers of breeding adults commenced moult with chicks still in the nest. Of those admitted, 91% and 73% respectively were released into the wild. There were veterinary concerns about avian malaria, airsacculitis and pneumonia, feather-loss and pododermatitis (bumblefoot). Post-release juvenile (0.32, s.e. = 0.08) and adult (0.76, s.e. = 0.10) survival rates were similar to African penguin chicks reared after oil spills and to recent survival rates recorded for naturally-reared birds. By December 2012, 12 birds had bred, six at their colony of origin, and the apparent recruitment rate was 0.11 (s.e. = 0.03). Hand-rearing of abandoned penguin chicks is recommended as a conservation tool to limit mortality and to bolster the population at specific colonies. The feasibility of conservation translocations for the creation of new colonies for this species using hand-reared chicks warrants investigation. Any such programme would be predicated on adequate disease surveillance programmes established to minimise the risk of disease introduction to wild birds.
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    Investigating the foraging ecology and energy requirements of a seabird population increasing in an intensely exploited marine environment
    (2017) Gaglio, Davide; Ryan, Peter G; Cook, Timothée R; Sherley, Richard B
    Their high energetic demands make seabirds sensitive to changes in prey availability, which is often reflected in their diet and energetic expenditure during breeding. Populations of the three seabirds endemic to southern Africa's Benguela upwelling ecosystem that rely on small pelagic fish have decreased dramatically over the last decade. In contrast, the population of the greater crested tern Thalasseus bergii has increased. To understand these conflicting trends, I investigated the foraging ecology and energy requirements of greater crested tern breeding in the Western Cape, South Africa. Diet was assessed by a novel non-invasive methodology developed in this study, using digital photography. More than 24,000 prey items from at least 51 different prey taxa were identified, with 34 new prey species recorded, revealing a high degree of foraging plasticity for this seabird. Greater crested terns rely mainly on anchovy Engraulis encrasicolus (65%), which averaged 84 mm long. Prey composition differed significantly between breeding stages, with anchovy especially dominant at the onset of the breeding period and the diet becoming more variable as the season progressed. Time-energy models for breeding terns were built based on activity budgets collected from non-invasive video-recordings and focal observations. Foraging trips were significantly longer during incubation than the chick provisioning stages, and feeding rates doubled from early to late chick provisioning. This study illustrated a steady increase in energy needs of adults throughout the breeding season, due to their increased foraging effort to meet chick energy needs. In comparison to other Benguela endemic seabirds that also rely on small pelagic fish, terns displayed substantially lower energy requirements at both individual and population levels. I also explored the benefits underlying interactions within mixed-species aggregations by investigating the costs induced by kleptoparasitism between mixed colonies of greater crested terns and Hartlaub's gulls Chroicocephalus hartlaubii and colonies with greater crested terns alone. Video-recordings coupled with focal observations showed that terns suffer direct costs to chick provisioning rates and indirect costs through energy expenditure in a mixed-species colony, suggesting that these breeding assemblages may be a form of parasitism rather than a mutualistic association. Despite the detrimental effects of interspecific kleptoparasitism, the marked foraging plasticity and low energetic requirements of greater crested terns, described in this study, coupled with specific life history traits such as low fidelity to breeding sites and extended post-fledging care, are key factors that allow this species to cope with changes in the availability and abundance of their main prey. Understanding species-specific behavioural responses to ecosystem variations in the Benguela upwelling system is vital for assessing the impact of commercial fisheries on seabird populations and fish stocks. Finally, the implementation of the method developed in this study, in long-term monitoring programmes, may provide crucial knowledge for conservation plans and key input to realising an ecosystem approach to fisheries management.