André Botha

Population estimates of three vulture species in Kruger National Park, South Africa §

Vultures are globally threatened, yet reliable population data on these birds are few, thus measuring their response to change is difficult. Kruger National Park (KNP) in South Africa is an important stronghold for many avian species, particularly vultures. In this study we generate population estimates for three vulture species in KNP using two plotless density estimators (PDE): a distance estimator based on nearest-neighbour distance and T-square sampling. We flew aerial censuses over large (c. 3 500 km2) sample areas in two ecogeographically separate parts of KNP and counted vulture nests visible within predetermined transects. In total 416 White-backed Vulture Gyps africanus, 22 Lappet-faced Vulture Torgos tracheliotos and 24 White-headed Vulture Trigonoceps occipitalis nests were recorded. The nearest-neighbour distance PDE performed poorly, and we used a T-square PDE calibrated with aerial survey counts to extrapolate across KNP and estimate breeding population sizes. There are an estimated 904 (95% CI±162) pairs of African White-backed Vultures, 78 (95% CI±18) pairs of Lappet-faced Vultures and 60 (95% CI±13) pairs of White-headed Vultures in KNP. These results provide a basis for investigating how large vultures respond to ecosystem change and understanding their resilience within a broader environmental change scenario.

Ivory poachers and poison: drivers of Africa's declining vulture populations

Four species of African vultures have been recategorized as Critically Endangered, and two as Endangered, on the IUCN Red List. Their declining status is attributed partly to the impacts of widespread poisoning. Prior to 2012 poisoning of vultures was mostly associated with illegal predator control by livestock farmers, in which vultures were typically unintended victims. More recently, ivory poachers have been using poisons to kill elephants Loxodonta africana or to contaminate their carcasses specifically to eliminate vultures, whose overhead circling might otherwise reveal the poachers’ presence. Between 2012 and 2014 we recorded 11 poaching-related incidents in seven African countries, in which 155 elephants and 2,044 vultures were killed. In at least two incidents the harvesting of vulture body parts (for fetish) may have provided an additional motive. We show that vulture mortality associated with ivory poaching has increased more rapidly than that associated with other poisoning incidents, and now accounts for one-third of all vulture poisonings recorded since 1970. This recent surge in the illegal use of poisons exposes weaknesses in the regulations, for which we propose measures aimed primarily at retail controls. However, because ivory poachers already operate outside any legal framework, African governments require international support in applying more punitive sentencing against mass wildlife poisoning.

Revisiting the Effect of Capture Heterogeneity on Survival Estimates in Capture-Mark-Recapture Studies: Does It Matter?

Recently developed capture-mark-recapture methods allow us to account for capture heterogeneity among individuals in the form of discrete mixtures and continuous individual random effects. In this article, we used simulations and two case studies to evaluate the effectiveness of continuously distributed individual random effects at removing potential bias due to capture heterogeneity, and to evaluate in what situation the added complexity of these models is justified. Simulations and case studies showed that ignoring individual capture heterogeneity generally led to a small negative bias in survival estimates and that individual random effects effectively removed this bias. As expected, accounting for capture heterogeneity also led to slightly less precise survival estimates. Our case studies also showed that accounting for capture heterogeneity increased in importance towards the end of study. Though ignoring capture heterogeneity led to a small bias in survival estimates, such bias may greatly impact management decisions. We advocate reducing potential heterogeneity at the sampling design stage. Where this is insufficient, we recommend modelling individual capture heterogeneity in situations such as when a large proportion of the individuals has a low detection probability (e.g. in the presence of floaters) and situations where the most recent survival estimates are of great interest (e.g. in applied conservation).

A clear and present danger: impacts of poisoning on a vulture population and the effect of poison response activities

Vultures in Africa are being poisoned deliberately by poachers to prevent the birds alerting authorities to the poachers’ illegal activities, or for harvesting and sale of body parts for use in witchcraft. Hundreds of vultures can be killed at a single poisoned elephant Loxodonta africana carcass, and although field staff trained in poison response activities can limit the damage, mortalities remain numerous. We used the population viability analysis programme VORTEX to simulate seven 100-year-long scenarios investigating various rates of poisoning mortalities and the remedial effects of poison response activities on a population of Critically Endangered white-backed vultures Gyps africanus breeding in Kruger National Park, South Africa. In six scenarios the population declined (λ

Ranging behaviour and habitat preferences of the Martial Eagle: Implications for the conservation of a declining apex predator

Understanding the ranging behaviours of species can be helpful in effective conservation planning. However, for many species that are rare, occur at low densities, or occupy challenging environments, this information is often lacking. The Martial Eagle (Polemaetus bellicosus) is a low density apex predator declining in both non-protected and protected areas in southern Africa, and little is known about its ranging behaviour. We use GPS tags fitted to Martial Eagles (n = 8) in Kruger National Park (KNP), South Africa to describe their ranging behaviour and habitat preference. This represents the first time that such movements have been quantified in adult Martial Eagles. Territorial eagles (n = 6) held home ranges averaging ca. 108 km2. Home range estimates were similar to expectations based on inter-nest distances, and these large home range sizes could constrain the carrying capacity of even the largest conservation areas. Two tagged individuals classed as adults on plumage apparently did not hold a territory, and accordingly ranged more widely (ca. 44,000 km2), and beyond KNP boundaries as floaters. Another two territorial individuals abandoned their territories and joined the ‘floater’ population, and so ranged widely after leaving their territories. These unexpected movements after territory abandonment could indicate underlying environmental degradation. Relatively high mortality of these wide-ranging ‘floaters’ due to anthropogenic causes (three of four) raises further concerns for the species’ persistence. Habitat preference models suggested Martial Eagles used areas preferentially that were closer to rivers, had higher tree cover, and were classed as dense bush rather than open bush or grassland. These results can be used by conservation managers to help guide actions to preserve breeding Martial Eagles at an appropriate spatial scale.

Survival and Population Dynamics of the Marabou Stork in an Isolated Population, Swaziland

Investigating the ecology of long lived birds is particularly challenging owing to the time scales involved. Here an analysis is presented of a long term study of the survival and population dynamics of the marabou stork (Leptoptilos crumeniferus), a wide ranging scavenging bird from Sub-Saharan Africa. Using resightings data of tagged nestlings and free flying birds we show that the stork population can be divided into three general life stages with unique survival probabilities and fecundities. Fecundity of the storks is inversely related to rainfall during their breeding season. Corroborative evidence for a metapopulation structure is discussed highlighting the impact of the Swaziland birds on the ecology of the species in the broader region. The importance of tag loss or illegibility over time is highlighted. Clearly, any attempt at conserving a species will require a detailed understanding of its population structure, of the sort examined here.

Assessing the accuracy of plotless density estimators using census counts to refine population estimates of the vultures of Kruger National Park

Breeding population estimates for three vulture species in Kruger National Park (KNP), South Africa, were made in 2013 using data from aerial censuses and a plotless density estimator (PDE). PDEs are distance-based methods used to assess sparse populations unsuitable for plot-based methods. A correction factor was applied to the 2013 estimates to reflect the difference between the survey counts and the PDE figures. We flew additional censuses across most of KNP and counted all visible nests to assess the 2013 estimates. Survey counts were within 95% confidence limits of corrected PDE estimates for White-backed Vulture Gyps africanus (count: 892; estimate: 904 [95% CI ±162]), at the limit of confidence for White-headed Vulture Trigonoceps occipitalis (count: 48; estimate: 60 [±13]) and outside confidence limits for Lappet-faced Vulture Torgos tracheliotos (count: 44; estimate: 78 [±18]). Uncorrected PDE estimates accurately reflected White-headed and Lappet-faced Vulture nest counts. The clustered patterns of White-backed Vulture nests and dispersed patterns of White-headed and Lappet-faced Vulture nests offer an explanation for these results and means that corrected PDE densities are inaccurate for estimating dispersed nests but accurate for estimating clustered nests. Using PDE methods, aerial surveys over ∼35% of KNP are probably sufficient to assess changes in these vulture populations over time. Our results highlight these globally important breeding populations.

Visitors to nests of Hooded Vultures Necrosyrtes monachus in northeastern South Africa

Hooded Vultures Necrosyrtes monachus are critically endangered but little is known of their year-round use of nests or whether other species usurp Hooded Vulture nest sites. We investigated visitation rates by Hooded Vultures and other species (including potential nest predators and usurpers) to examine their effect on Hooded Vulture breeding success. We present observations of 33 species recorded by camera traps at 12 Hooded Vulture nests over a total of 93 nest-months (2 095 nest-days). Several pairs of Hooded Vultures visited their nests regularly during the non-breeding season, some adding nesting material, highlighting that pairs visited their nest(s) year round. Egyptian Geese Alopochen aegyptiaca, potential usurpers of raptor nests, were present at occupied and unoccupied Hooded Vulture nests, but we recorded no usurpation of nests by Egyptian Geese and they had no impact on vulture breeding success. Hooded Vulture breeding failure was linked to two species only: camera-trap imagery recorded one case of predation of a vulture egg by a Chacma Baboon Papio ursinus, and one case of a Martial Eagle Polemaetus bellicosus predating a vulture nestling. We recommend expanding the Hooded Vulture nest monitoring programme to include more pairs.

Birds in a Changing Environment: Report on the 13th Pan-African Ornithological Congress in Arusha, Tanzania

The 13th Pan-African Ornithological Congress (PAOC) was held in Arusha, Tanzania, on 14–21 October 2012. The PAOC is held every four years and is one of the only Pan African conferences dedicated to a taxon. The conference gives opportunity for those working on birds in Africa to meet and get an overview of current research and discuss possible important future areas of research. With the human population now over seven billion there is continued and increased pressure on the environment. Land transformation for urban sprawl, agriculture and biofuels continues at high rates. The effects of accelerated climate change further exacerbate the situation. Despite all this there is a need to understand and conserve biodiversity and sustain ecosystem function. Africa is possibly the continent that is undergoing the greatest change and that has the most to lose. The theme of the thirteenth PAOC was ‘Birds in a Changing Environment’, and thus many of the 160 presentations dealt with the effects of changing ecosystems (including savanna, forests and wetlands), and the effects of accelerated climate change on bird diversity and persistence in Africa. In particular, the effects on migration of avian species and on raptors were highlighted. Also, the effects of changing land use and urban environments on bird diversity and survival were shown. In comparison, little on the general biology and taxonomy of African birds was presented. With technological advances, particularly in global positioning system telemetry, knowledge of movements, spatial use and presence of birds in Africa is advancing and some of this was presented. The involvement of the general public in monitoring birds in Africa was highlighted, especially as people gain greater access to the internet. The negative effects of disease and invasive species were shown by a few but may be important for future research. The outstanding plenary speakers (Anthony Sinclair, Kathy Martin, John Wingfi eld, Wolfgang Goymann, Irene Tieleman, Julius Arnatiwe, Rob Davies, Will Cresswell and Les Underhill) kindly gave of their time and monies to attend and present at the congress. Monies raised from sponsors were used to allow deserving postgraduate students and members of local communities and NGOs to attend the PAOC. A format of one main session with an occasional parallel session was followed. One benefi t of this was that most delegates got an overview of current avian research in Africa. It is hoped that from the presentations and discussion future directions for research and management that further our ability to conserve and understand African birds were highlighted as well as the need for interand intra-continental collaborations.

Spatially explicit poisoning risk affects survival rates of an obligate scavenger

Obligate scavengers such as vultures provide critical ecosystem services and their populations have undergone severe declines in Asia and Africa. Intentional poisoning is a major threat to vultures in Africa, yet the impact on vulture populations of where poisoned carcasses are positioned is not known. We used re-sightings of 183 African white-backed vultures captured and tagged in two regions of South Africa, some 200 km apart, to estimate spatial differences in relative survival rates across life stages. Juvenile survival rates were similar in the two regions, whilst subadult and adult survival rates differed significantly. Using agent-based modelling, we show that this pattern of relative survival rates is consistent between regions that differ in intensity of poisoning, despite the proximity of the two regions. This may have important consequences for vulture conservation and the targeting of conservation efforts, particularly with regard to the efficacy of “vulture safe zones” around vulture breeding populations.