Collins C.T.,California State University, Long Beach |
Anderson M.D.,BirdLife South Africa |
Johnson D.N.,156 Golf Road
Ostrich | Year: 2010
The food habits of the Little Swift Apus affinis and African Black Swift Apus barbatus were quantified at Kimberley, Northern Cape province and Makapansgat, Limpopo province, South Africa. As previously documented for other species, both of these swifts took a wide variety of aerial arthropods including spiders as well as 10 orders and 64 families of insects in the combined samples. Little Swift prey items at Kimberley averaged 3.2 mm in body length (SD = 1.6, n = 2 178) and ranged from 1.2 to 16.0 mm. Prey items of African Black Swifts at Kimberley averaged 4.4 mm (SD = 4.1, n = 185) with a range of 0.9 to 15.9 mm, and 2.8 mm (SD = 0.8, n = 2 099) at Makapansgat with a range of 1.2 to 10.8 mm. At Kimberley, African Black Swifts took more (8.3%) larger prey items (>8 mm), such as termites, than Little Swifts (2.3%). As also true of other swifts, both African Black Swifts and Little Swifts took a majority (>90%) of smaller prey items that are abundant in the air column. Mean prey size is significantly correlated with predator body size in Apus and Tachymarptis swifts. © NISC (Pty) Ltd.
Altwegg R.,South African National Biodiversity Institute |
Altwegg R.,University of Cape Town |
Doutrelant C.,French National Center for Scientific Research |
Anderson M.D.,BirdLife South Africa |
And 5 more authors.
Oecologia | Year: 2014
Population trends are determined by gains through reproduction and immigration, and losses through mortality and emigration. These demographic quantities and resulting population dynamics are affected by different external and internal drivers. We examined how these demographic quantities were affected by weather, research-induced disturbance, local density, colony site and year in a metapopulation of 17 sociable weaver (Philetairus socius) colonies over 17 years of study (4 years for reproduction). Most colonies declined, but at different rates. The four demographic quantities were related to different drivers. Survival strongly varied among years and colonies and was positively related to rainfall and negatively related to extreme temperature (together explaining 30 % of variation) and disturbance (measured as number of captures conducted at a colony; 7 %). There was a trend for a positive relationship between reproduction and rainfall (50 %). Movement was mainly related to local density: individuals were more likely to emigrate from small to large colonies and from colonies that were either well below or above their long-term mean. They were more likely to immigrate into colonies that were nearby, and below their mean size. We then quantified the effects of these relationships on metapopulation dynamics using a multi-site matrix projection model. Rainfall was potentially a strong driver of metapopulation dynamics. In addition, field-work disturbance might have contributed to the decline of this metapopulation but could not explain its full magnitude. Hence, through a combination of analytical methods we were able to obtain information on the main drivers affecting dynamics in a declining metapopulation. © 2013 Springer-Verlag Berlin Heidelberg.
Croxall J.,Global Seabird Programme |
Small C.,Royal Society for the Protection of Birds |
Sullivan B.,Royal Society for the Protection of Birds |
Wanless R.,BirdLife South Africa |
And 6 more authors.
Marine Ecology Progress Series | Year: 2013
Torres et al. (2013; Mar Ecol Prog Ser 473:275-289) use fine-scale data on tracked locations of one species of albatross and fishing vessels to make a variety of assertions on interactions between them, especially in relation to risk of bycatch. Some of these assertions are incorrect, and we seek to clarify the issues and perspectives involved. We argue that while a fine-scale approach can provide interesting insights into foraging behaviour, large-scale risk analysis is needed because management measures (e.g. for bycatch mitigation) need to operate across all vessels in a fishery and across all seabird species at risk from the fishing operation. In addition, an estimate of 10% time spent in close proximity to vessels cannot be used to infer low bycatch risk alone: such an inference would need comparison to bycatch rate data. The analysis also does not take into account a number of factors known to affect the nature and duration of the association of albatrosses with fishing vessels, which limits the conclusions that can be drawn. However, finescale studies can provide important insight into factors affecting individual bycatch events, and studies at fine and broad scales will be complementary. © Inter-Research 2013.
Groom G.,University of Aarhus |
Petersen I.K.,University of Aarhus |
Anderson M.D.,BirdLife South Africa |
Fox A.D.,University of Aarhus
International Journal of Remote Sensing | Year: 2011
Knowing instantaneous locations and numbers of individuals in animal populations is a major requirement for wildlife and conservation ecology. Recent advances in very high spatial resolution digital-imaging systems and in objectbased image-analysis methods offer great potential for developing remote sensing in new application arenas, including direct mapping and counting of birds, mammals and other larger organisms. We present the successful application of an automated object-based image-mapping strategy that has been applied to total mapping, using aerial image data, of Phoeniconaias minor (Lesser Flamingo) individuals at Kamfers Dam, a large perennial lake in central South Africa. The object-based method used quadtree image segmentation and sequential objectbrightness thresholding to identify individual birds with high accuracy (.99% compared to human visual interpretation). Accuracy-assessment results are presented, with discussion of the error factors related to the object-based method and the reference data. An under-estimation by the object-based method of less than 0.5% is indicated. The automated procedure mapped 81 664 Lesser Flamingos at this one site, which is 30% above the most recent estimated size of the entire southern Africa Lesser Flamingo population, indicating a need for further work to reassess this population's size. © 2011 Taylor & Francis.
An African White Backed Vulture sits on a tree in the Serengeti National Park plains August 18, 2012. REUTERS/Noor Khamis More CAPE TOWN (Reuters) - Africa's vultures are vanishing, according to a report released on Thursday, a situation that could affect human health and livestock since populations of other scavengers such as rats and jackals could rise as a result. The assessment, carried out by conservation group BirdLife International, found that six of Africa's 11 vulture species were at risk of extinction. Deliberate targeting by poachers is one of the reasons as the birds, which circle the sights where they feed, can alert authorities to the carcasses of illegally slain animals. Africa's elephant and rhino populations are being relentlessly poached for their ivory and horns to meet red-hot demand in newly-affluent Asian economies. "Vultures are important. They come in, they clean up and they leave," said Ross Wanless of BirdLife South Africa. "Other scavengers like rats and jackals will eat a carcass and then will go after livestock or become a pest to humans. And if vultures are removed their numbers can increase." Vultures also help to stem the spread of disease on the world's poorest continent by eating carcasses that would otherwise rot. Other reasons behind the decline of the big birds include indiscriminate poisonings and the popularity of vulture parts for traditional medicine. Since the late 1980s, 98 percent of West Africa’s vultures outside protected nature areas have disappeared, while half the population of the Gyps vulture species in Kenya’s Masai Mara park have gone, the report said. In South Africa, cape vultures have declined by 60-70 percent over the past 20-30 years. The assessment was conducted for the International Union for Conservation of Nature's (IUCN) "Red List of Threatened Species", which is considered to be the most authoritative estimate of wild bird and animal populations.