OpenUCT :: Browsing by Author "Simmons, Robert E"

Browsing by Author "Simmons, Robert E"

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Open Access
Are foraging patterns of aerial predators influencing diurnal activity of their prey?
(2011) Retief, Kirsten; Simmons, Robert E
There is often a reciprocal relationship between predators and their dominant prey. This results in continuous co-evolution, where the prey selects more efficient ways to avoid predation and the predator selects more efficient ways of catching prey. The aim of this study was to determine if aerial predators (raptors) influence diurnal activity patterns of their prey (mice). Sampling of both raptors and mice was done simultaneously during autumn, winter and spring at two different study sites in three different habitats on South Africa's arid west coast. Sixty PVC mouse traps were checked every half hour throughout all daylight hours and raptors were observed using scan sampling every two minutes. A total of 1228 rodents were trapped consisting mainly of the diurnal mouse, Rhabodmys pumilio and a total of 197 hours was spent observing hunting behaviour of four raptor species: Black and African Marsh Harriers (Circus maurus and C. ranivorus), Black-shouldered Kite (Elanus caeruleus) and Rock Kestrel (Falco rupicolus). All birds hunt rodents on a regular basis and all were beginning to breed towards the end of my study. Results showed significantly higher small mammal activity during winter and in habitats with dense vegetation. Diurnal small mammal activity peaks appeared to shift randomly between sites, habitats and seasons, thereby avoiding predation through unpredictability of activity. Small mammal activity patterns deliberately avoided peak foraging times of raptors during winter at the Pelican site; however this relationship was not linked to any climatic variables to explain how mice avoid high predation periods. Raptors selected peak foraging times dming periods of high small mammal activity at the Dune site during winter; however wind speed and cloud cover were correlated with both raptor foraging and small mammal activity, thereby influencing the relationship between the predator and the prey. In conclusion, no reoccurring diurnal peaks in small mammal activity were seen across the three seasons and this may have been an anti-predation strategy, because predators would find it more difficult to predict high prey activity. However the raptors it seemed were selecting periods of high mice activity at one site when weather conditions allowed.
Open Access
Assessment of pesticide concentrations in environmental and biological parameters from two Kenyan Rift Valley Lakes
(2012) Gudka, Masumi; Simmons, Robert E; Virani, Munir
In the last two decades Kenyan agriculture has developed rapidly. In particular, horticultural and floricultural activities have intensified on the riparian fringe of Lake Naivasha, a RAMSAR site. The lake supports a large variety of wildlife and avifauna in particular. In the 1980s, the African Fish-Eagle (Haliaeetus vocifer) population on the lake was the densest in Africa. As a top predator resident in the Kenyan Rift Valley Lakes the African Fish-Eagle is a good indicator of general ecosystem health but is also highly susceptible to toxic effects of pesticide contamination...Globally, most organochlorine pesticides have been banned, but endosulfan, HCH and methoxychlor are widely used in Kenya, while aldrin, dieldrin and lindane are restricted and DDT, endrin, and heptachlor banned. Studies examining residue levels of these harmful chemicals in African Fish-Eagles are limited to small sample sizes examined in the 1970s and 1980s. This study is the first comprehensive investigation of organochlorine residue contamination in biological and environmental parameters from Lake Naivasha and the control water body at Lake Baringo.
Open Access
The biology and conservation of the Damara Tern in Namibia
(2011) Braby, Justine; Underhill, Les; Simmons, Robert E; Roux, Jean-Paul
The globally Near-threatened Damara Tern Sterna balaenarum is little known and faces several conservation issues. The aim of this study was to provide a description of the ecology and numbers of the species and discuss conservation management plans that will effectively ensure its survival.
Open Access
Cape Town's cats: reassessing predation through kitty-cams
(2014) Morling, Frances; Simmons, Robert E; O'Riain, Justin
Domestic cats (Felis catus) are abundant generalist predators that exploit a wide range of prey within and adjacent to the urban matrix. Cats are known to have contributed to the extinction and endangerment (mostly on islands) of a number of indigenous species, including birds, small mammals, reptiles and amphibians. Most research on this important topic has been carried out in the developed world, predominantly in Australia, New Zealand, the U.K., the U.S. and Canada with only four studies carried out in Africa. Of these, two studies in Cape Town suggest that domestic cats have a big impact on wildlife but these studies may have underestimated predation because they failed to account for the proportion of prey not returned to participants’ homes. In this study I used kitty-cams in an attempt to provide a prey correction factor for urban cats in Cape Town, South Africa. I investigated hunting of wildlife by free-ranging domestic cats in Newlands, a suburb of Cape Town, South Africa over 5 weeks in 2013. I monitored 13 cats (6 deep-urban and 7 urban-edge) by questionnaire survey, asking cat owners to record all prey items returned by their cats. A total of 43 prey items were returned, 42% of which were small mammals, 30% invertebrates, 12% reptiles, 9% amphibians and 7% birds. Combining these data with two similar survey studies carried out in Cape Town I estimated that a total of 118 cats caught an average of 0.04 prey items per cat per day. Ten of the 13 cats were also monitored for 3 weeks using kitty-cam video cameras. Participating cats wore a video camera and all activity was analysed for prey captures and behavioural activity patterns.
Open Access
Cape Town's domestic cats : prey and movement patterns in deep-urban and urban-edge areas
(2010) George, Sharon; Simmons, Robert E; O'Riain, Justin
Domestic and feral cats (Felis catus) have impacted negatively on native wildlife on both islands and on the mainland. Impacts range from a reduction in numbers of prey species to local extinctions, especially of birds on islands. This study provides the first data on the impacts of domestic cats on wildlife on the African mainland continent by comparing the diet and movement patterns of cats that live within urban areas with those of cats that live on the urban?edge adjacent to natural areas of Cape Town, South Africa. The findings suggest that domestic cats in urban areas of Cape Town pose a significant threat to wildlife, with indigenous small mammals most at risk. This agrees with many other studies carried out in New Zealand, Australia and the United Kingdom.
Open Access
Environmental factors influencing the breeding and health of a predator endemic to southern Africa: the endangered Black Harrier Circus Maurus
(2017) García-Heras, Marie-Sophie; Simmons, Robert E; Arroyo, Beatriz; Mougeot, François; Amar, Arjun
A general and increasing biodiversity loss has been observed since the 20th century. Faced with the extreme rapidity of population declines, conservation biologists seek to understand the limiting and regulating factors driving changes in animal populations. This is particularly important for rare species as small population size increases extinction risk. Birds are amongst the most studied animals in this context. As a group that occupies a high trophic level, raptors are particularly vulnerable to external changes and are generally regarded as useful indicators of ecological change. The Black Harrier Circus maurus is an avian predator endemic to southern Africa, which breeds essentially along the South African coast within the Fynbos biome, and inland within the Karoo biome. Its population size has been estimated at less than 1,000 breeding birds, and the species is currently considered as Endangered in South Africa, Namibia and Lesotho. Although some studies have been conducted on Black Harriers in the last four decades, the reasons for its scarcity currently remain little known and insufficiently explored. Filling this knowledge gap is therefore essential for its conservation. In this context, the main goal of this thesis is to develop an overall comprehension of how various environmental factors may affect the breeding and health of this Endangered species, at both population and individual levels. I conducted my fieldwork during the 2012-2015 breeding seasons in two contrasting geographical regions: one along the west coast in the Western Cape Province, and the second one inland in the surroundings of Nieuwoudtville in the Northern Cape Province. For some chapters (Chapters 1-3), I analysed historical data collected by Dr. R. E. Simmons during 2000-2011 breeding seasons.
Open Access
An investigation into the decline of the bearded vulture : Gypaetus barbatus in southern Africa
(2014) Kruger, Sonja C; Amar, Arjun; Simmons, Robert E
The Bearded Vulture Gypaetus barbatus is a Critically Endangered species in southern Africa whose entire range in the Southern Hemisphere falls within the Maloti-Drakensberg mountains of South Africa and Lesotho, which forms the area of focus for this research. In this thesis I have attempted to synthesize 15 years of research on the Bearded Vulture population of southern Africa using various approaches to quantify the decline in the species, investigate the mechanisms of this decline and determine the most appropriate management actions necessary to attain the short-term species’ conservation target of a positive population growth rate. Firstly I assessed the territory occupancy, distribution and density of the population over two time periods to identify population trends. The number of occupied territories decreased by between 32%-51%, the breeding range decreased by 27% and breeding densities decreased by 20% over the past five decades. The birds occupy a breeding range of 28,125 km2 with higher densities recorded in the core of the range than in the peripheral areas. The population is estimated at between 368-408 individuals (109-221 breeding pairs). Three hypotheses were then examined in an attempt to explain which factors were associated with territories recorded as abandoned; those related to human impact, food availability and climate change. Of the seven covariates examined within the home range of an adult pair using a model selection process using Akaike’s Information Criterion, the strongest support was for the human impact hypothesis, with abandonment more likely in territories with higher densities of power lines and human settlements. These findings were in accordance with the main causes of mortality. The movements of all age classes were investigated using data from satellite transmitters affixed to 18 birds to determine exposure to perceived benefits or anthropogenic risks. The overall foraging range of the population was estimated to be 51,767 km2 and non-adults were found to use 65% of this area whereas adults focussed their activities in an area of about 286 km2 around their nests. Non-adults increased the size of their range as they aged, with birds aged between 4-6 years facing the greatest exposure to risk factors. The genetic risk was examined by sampling two populations in sub-Saharan Africa to ascertain genetic variation, evolutionary placement and connectivity using Mitochondrial DNA fragment analyses. My results showed little to no differentiation between populations in southern Africa and Ethiopia suggesting that translocations of individuals from Ethiopia could be considered for introduction into the local population. The reduced haplotype diversity found in southern Africa suggests that translocations may be necessary to improve genetic diversity. Lastly I used population viability analysis models to determine the future population trend and identify the primary demographic and environmental constraints on the population. The models predicted a negative growth rate for the population over the next 50 years (ë=0.99) with a high probability (0.89) of extinction as a result of low survival estimates (particularly for adults; 86%) and reduced productivity (55%). Human activities (69%) and power line collisions (21%) were the primary reasons for the low survival rates with poisoning alone accounting for 90% of the deaths. To achieve a positive growth rate, mortality rates should be reduced by >50%, productivity increased by >25% and the population should be supplemented by at least six individuals annually for the next 20 years. Several recommendations are listed to address the primary threat of poisoning and continued monitoring of the population is essential to evaluate the success of the implementation of these recommendations. My research demonstrates the importance of focussing on small populations, declining populations and populations at the periphery of the species’ range and my results confirm that urgent intervention is required to improve the status of the population. My findings also contribute to achieving vulture conservation objectives regionally, continentally and internationally.
Open Access
Siblicide provides food benefits for raptor chicks: Re-evaluating brood manipulation studies
(2002) Simmons, Robert E
Implicit in most ideas explaining the siblicidal behaviour of nestlings that kill related siblings is that, by eliminating a competitor, surviving nestlings increase their share of food resources from the parents (e.g. O’Connor 1978; Stinson 1979; Simmons 1988; Mock et al. 1990; Mock & Parker 1997). However, in a detailed paper assessing the food benefits to pelicans (Pelicanusspp.), Ploger (1997) found that senior (surviving) nestlings did not receive more food once their nest mate had been eliminated.

Browsing by Author "Simmons, Robert E"

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