Browsing by Author "Sherley, Richard"

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    The effects of prey availability on the endangered bank cormorant Phalacroxorax neglectus
    (2014) Botha, Philna; Underhill, Les; Ryan, Peter G; Sherley, Richard; Cook, Timothée
    The bank cormorant Phalacrocorax neglectus is a seabird endemic to the south-western coast of southern Africa and the Benguela Upwelling System and has suffered a decline of more than 50% over three generations. Main threats include displacement by Cape fur seals Arctocephalus pusillus, direct human disturbance, pollution, climate change and food shortage. This thesis focuses on the bank cormorant’s response to food shortage, both directly and indirectly. Four colonies (Jutten Island, Dassen Island, Robben Island and Stony Point) were studied in terms of responses on population level in relation to the spatial distribution of prey surrounding the various colonies, foraging behaviour and breeding success. First, I tested the response of the bank cormorant ’ s population dynamics in relation to the availability of West Coast rock lobster Jasus lalandii in different spatial scales around three colonies (Jutten Island, Dassen Island and Stony Point) over a subset of years. I found that birds at Dassen Island showed the strongest response to the availability of rock lobster. Birds also showed strongest response to the availability of rock lobster in an accumulative distance around colonies, and their largest response was to rock lobster within 30 km distance from the colony. Various aspects including the life - history traits and moulting stages of this particular rock lobster species may be the reason to this response. Second, I present foraging effort data of bank cormorants in localities known to be situated in areas with different prey availability. I found that at Jutten Island, situated in an area where West Coast rock lobster have dramatically decreased, bank cormorants spent significantly longer time at sea than at Robben Island and Stony Point, which were situated in areas where rock lobster were known to be abundant at the time of the study. Third, I tested the effect of food availability on the breeding success of bank cormorants at Jutten Island, Robben Island and Stony Point. There was no significant relationship between food availability and the survival probability of the birds. The number of chicks fledged per successful nest, however was significantly related to the availability of rock lobster during the relevant breeding season, as well as during the relevant month of hatching.
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    Effects of temperature on gular fluttering and evaporative water loss in four sympatric cormorants in southern Africa
    (2014) Campbell, Greg Thomas; Cook, Timothée; Sherley, Richard; Ryan, Peter G
    Climate change continues to cause rising air and sea surface temperatures and changes in precipitation patterns across the globe. Many seabirds will be challenged by increasing temperatures because they must balance conflicting adaptations for dealing with cold environments when foraging and hot environments when nesting. Heat stressed seabirds often gular flutter for thermoregulation, a behaviour that is effective for dissipating heat but expensive in terms of evaporative water loss. This study examined gular fluttering behaviour of four species of southern African cormorants, crowned ( Microcarbo coronatus ), Cape ( Phalacrocorax capensis ), bank ( Phalacrocorax neglectus ), and white-breasted ( Phalacrocorax carbolucidus) cormorants. Results show that gular fluttering is influenced by temperature, body position and body size. Gular fluttering increases with temperature and larger cormorant species spend a greater proportion of time gular fluttering for a given temperature. Threshold temperatures for initiating gular fluttering are lower for large than for small cormorant species. Proportions of time spent gular fluttering are higher when birds are sitting than when crouching over the nest. Water loss shows the same pattern as gular fluttering, with the larger species estimated to lose a higher percentage of their daily water intake. Larger cormorant species can lose as much as 40% of their daily ingested water after eight hours of gular fluttering. These findings indicate that temperature increases from climate change will likely have serious direct impacts on nesting cormorant colonies in southern Africa. Gular fluttering could increase by as much as 25% by 2100 under current projected temperature increases, and increases in water loss could reach nearly 10%. Some species may shift their breeding dates to compensate for increasing temperatures, but if breeding activities are timed to coincide with peaks in their main prey specie s, this may result in poorer diets or increased competition from other species.
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    The endangered bank cormorant Phalacrocorax neglectus: the heat is on : understanding the effect of climate change and associated environmental variable changes on the breeding biology and population dynamics of the bank cormorant in the W. C., S. A
    (2014) Meyer,Corlia; Underhill, Les; Ryan, Peter G; Sherley, Richard; Cook, T
    The bank cormorant Phalacrocorax neglectus was listed as ‘Endangered’ in 2004, following a decrease of more than 60% in the total population from 1975-2011. It ranges from central Namibia to the Western Cape, South Africa, with most of the population occurring on offshore islands in Namibia. The main reason for this study was to determine if climate change could be identified as a factor which has influenced the decreasing numbers of bank cormorants. This involved research on the heat stress behaviour, breeding success and population trends of the bank cormorant in the Western Cape, South Africa. High environmental temperatures resulting in heat stress and storms with associated extreme environmental variables was predicted to cause breeding failures, decreasing breeding success. As a result, climate change can also affect long-term trends in the adult population of the bank cormorant, and this was examined using the population data of nine bank cormorant colonies in the Western Cape, South Africa. A link existed between ambient and operative temperature, and the latter was used for statistical analysis. Mean operative temperatures of over 30°C were experienced. Temperatures were highest at the bank cormorant colony at Robben Island when three colonies were compared (Robben Island, Jutten Island and Stony Point). Increased environmental temperatures resulted in the average bank cormorant increasing its time spent employing thermoregulatory behaviour. Bank cormorants were shown to start gular fluttering at 21°C on average and spend all their time gular fluttering when they experienced an operative temperature of 34.2°C or higher. The birds also started employing this thermoregulatory behaviour at a lower temperature when on eggs or small chicks. During the study period, the breeding success of the bank cormorant was not impacted by high temperatures at the three bank cormorant colonies studied. Wave and wind action, associated with storms, resulted in a lowered reproductive output during the breeding seasons of 2012 and 2013. Both incubation success and chick rearing success did not differ significantly between 2012 and 2013 for the three bank cormorant colonies at Robben Island, Jutten Island and Stony Point. The study of long-term trends in colony sizes of nine bank cormorant colonies in the Western Cape, South Africa revealed a decrease in the bank cormorants breeding population. The decrease could not be directly associated with climate change in the region. An increase in the mean maximum temperatures and a decrease in the annual rainfall did not affect the bank cormorant numbers, but rather the fecundity. This resulted in a lagged effect of climate change on the bank cormorant population. Climate change and extreme weather events can cause massive breeding failures.
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    Factors impacting the breeding success of African penguins Spheniscus demersus on Robben Island
    (2016) Tol, Leanne; Underhill, Leslie G; Barham, Peter; Sherley, Richard
    The African penguin Spheniscus demersus is a seabird endemic to the south-western coast of Africa and can be found in three main breeding localities; southern Namibia, the Western Cape and Algoa Bay, Eastern Cape, South Africa. The African penguin has been listed as Endangered since 2010, having experienced a decline in population of more than 50% over the past three generations. This study was conducted at the breeding colony on Robben Island, South Africa, and examined two factors that have the potential to affect breeding success of African penguins; body mass at the onset of breeding and the suitability of various nest types to mitigate changing climatic conditions. Body mass was measured by recording weights using an automated weighing scale set up in front of a nest. Weights were taken at the start of breeding of each penguin in a breeding pair and these weights were compared to the number of chicks fledged, fledging period, hatching success, clutch size, and chick fledging weight. Hatching success, clutch size, and fledging weight were not influenced by the mass of either parent. There was a trend of shorter fledging periods as the mass of the heavier parent increased. The greatest effect was from the body mass of the lighter parent on the number of chicks that fledged from the nest; as the mass of the lightest adult increased, more chicks were fledged. If the lighter adult weighed below 2 kg there were always no chicks at the nest that fledged. This suggests evidence for a carry-over effect of body mass from the time before breeding starts into the breeding season, and highlights the importance of food availability for African penguins on a global scale, and not just a local one. The proportion of nest failures of six nest types (vegetation, open, natural burrow, building, wooden nest box, and artificial fibreglass burrow) at the incubation and chick-rearing stage were compared to rainfall and maximum temperature.
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    Penguins
    (2014-09-12) Sherley, Richard; Neary, Tim
    In this radio broadcast, Richard Sherley discusses penguin tracking in South Africa, and how tracking mechanisms support research on feeding, breeding and migration patterns. Also discussed are how the miniturisation of tracking devices has dramatically improved information gathering, especially for tracking young birds and breeding populations. This information feeds into the Departmental of Environmental Affairs and the Department of Agriculture, Forestry and Fisheries for national planning purposes. Image provided courtesy of Namastesa under a Creative Commons Attribution 1.0 Generic license.