Aquila Verreauxii Research Articles

Differences in the dietary habits of Verreaux’s Eagles Aquila verreauxii between peri-urban and rural populations

SummaryDifferences in the diets of urban and rural avian predators could indicate potential niche vulnerability in a particular habitat. This study compares the core-isotopic niche areas and diet disparity of a declining peri-urban Verreaux’s Eagle Aquila verreauxii population with a stable rural population in South Africa. In addition to stable isotope analyses, the diet of the peri-urban Verreaux’s Eagles was investigated using camera trap footage of prey delivered during the nesting season. Dominant prey consisted of species with a mixed diet of plants with a C3 and/or C4 photosynthetic pathway (browsers and grazers). Rock hyrax Procavia capensis contributed 60% of the total diet composition, scrub hare Lepus saxatilis 26% and Helmeted Guineafowl Numida meleagris 22%. The core-isotopic niche area for each population was calculated using bulk carbon (δ13C) and nitrogen (δ15N) stable isotope values chronological measured along the length of 18 feathers from 21 nests. The isotopic niche of the rural eagle population revealed that they consume prey from multiple trophic levels with a C3-plant-dominated prey base (browsers), likely including small carnivores. In contrast the isotopic niche of the peri-urban Verreaux’s Eagles correlated with the mixed mammalian and avian food-niche determined from camera trapping, confirming that the peri-urban population mainly hunted three abundant species that are all narrowly associated with modified human habitats. The decline in the Magaliesberg Verreaux’s Eagle population is, therefore, unlikely to be due to constraints in their dietary niche, as raptors benefit from the diversity and abundance of human-commensal prey associated with the peri-urban habitats.

Status of the Taita Falcon (Falco fasciinucha) and Other Cliff-Nesting Raptors in Batoka Gorge, Zimbabwe

The Taita Falcon (Falco fasciinucha) is a globally vulnerable cliff-nesting, bird-eating raptor, sparsely distributed down the eastern side of sub-Saharan Africa. It seems to occur in small, isolated pockets of a few breeding pairs, clustered around localized patches of ideal habitat. One such pocket has been the Batoka Gorge system on the Zambezi River, immediately downstream of Victoria Falls on the border of Zimbabwe and Zambia. The species was first recorded here in the late 1950s, and subsequent observations over the next 40–50 yr established Batoka Gorge as an important location for this species worldwide. Regular and intensive surveys in the early to mid-1990s identified at least six breeding territories in the first 40 km of the gorge, and a strong likelihood of more pairs farther downstream. We surveyed this same section of the gorge in July 2013 and November 2014, accumulating >100 hr of observation time at previously occupied Taita Falcon sites. This was the first systematic search of the area for Taita Falcons in nearly two decades. Although we found similar numbers of cliff-nesting Peregrine Falcons (F. peregrinus) and Verreaux's Eagles (Aquila verreauxii) as in the earlier surveys, we did not record any Taita Falcons in the area. The reasons for this decline in numbers and the implications of this finding for the conservation status of this little-known species remain speculative.

Nestling White-backed Vulture (<i>Gyps africanus</i>) eaten by a Verreaux’s Eagle (<i>Aquila verreauxii</i>) at a nest occupied for a record 21 years.

An adult Verreaux’s Eagle ( Aquila verreauxii ) was observed eating a White-backed Vulture ( Gyps africanus ) nestling at a nest at Sango in the Save Valley Conservancy, south-eastern Zimbabwe on 13 October 2017. This nest has been regularly occupied for 21 successive breeding seasons. To our knowledge, this observation represents a previously unrecorded species in the diet of Verreaux’s Eagle, and it is also apparently the longest known continually-occupied White-backed Vulture nest.

Where eagles soar: Fine-resolution tracking reveals the spatiotemporal use of differential soaring modes in a large raptor.

Unlike smaller raptors, which can readily use flapping flight, large raptors are mainly restricted to soaring flight due to energetic constraints. Soaring comprises of two main strategies: thermal and orographic soaring. These soaring strategies are driven by discrete uplift sources determined by the underlying topography and meteorological conditions in an area. High‐resolution GPS tracking of raptor flight allows the identification of these flight strategies and interpretation of the spatiotemporal occurrence of thermal and orographic soaring. In this study, we develop methods to identify soaring flight behaviors from high‐resolution GPS tracking data of Verreaux’s eagle Aquila verreauxii and analyze these data to understand the conditions that promote the use of thermal and orographic soaring. We use these findings to predict the use of soaring flight both spatially (across the landscape) and temporally (throughout the year) in two topographically contrasting regions in South Africa. We found that topography is important in determining the occurrence of soaring flight and that thermal soaring occurs in relatively flat areas which are likely to have good thermal uplift availability. The predicted use of orographic soaring was predominately determined by terrain slope. Contrary to our expectations, the topography and meteorology of eagle territories in the Sandveld promoted the use of soaring flight to a greater extent than in territories in the more mountainous Cederberg region. Spatiotemporal mapping of predicted flight behaviors can broaden our understanding of how large raptors like the Verreaux’s eagle use their habitat and how that links to energetics (as the preferential use of areas that maximize net energy gain is expected), reproductive success, and ultimately population dynamics. Understanding the fine‐scale landscape use and environmental drivers of raptor flight can also help to predict and mitigate potential detrimental effects of anthropogenic developments, such as mortality via collision with wind turbines.

Ranging Behaviour of Verreaux's Eagles during the Pre-Breeding Period Determined through the Use of High Temporal Resolution Tracking.

Information on movement ecology is key in understanding the drivers and limitations of life history traits and has a potential role in indicating environmental change. Currently we have a limited understanding of the parameters of movement of territory-bound raptors, which are sensitive to environmental change. In this study we used GPS tracking technology to obtain spatially (within 3 m) and temporally (c. 3 mins) high-resolution movement data on a small sample of Verreaux’s eagle Aquila verreauxii during the pre-laying period (n = 4) with one additional example during the chick rearing period. We present GPS-derived home range estimates for this species and we examine temporal (timing, duration, frequency and speed) and spatial (total path length and maximum distance from nest) patterns of trips away from the nest. For eagles tagged in the agriculturally developed Sandveld region (n = 3), which is made up of a mosaic of land use types, we also undertook a habitat selection analysis. Home ranges were small and largely mutually exclusive. Trip activity was centred around midday, which is likely to be related to lift availability. Our habitat selection analysis found that eagles selected for near-natural and degraded habitat over natural or completely modified areas, suggesting that these eagles may have benefitted from some of the agricultural development in this region. Although our sample sizes are small, the resolution of our tracking data was essential in deriving this data over a relatively short time period and paves the way for future research.

Adaptability of a specialist predator: the effects of land use on diet diversification and breeding performance of Verreaux's eagles

Specialist predators are generally negatively impacted by habitat change. Predators that inhabit transformed areas are usually forced to diversify their diet and this departure away from traditional resources can have negative consequences for fitness and demographic parameters. We consider this relationship as it applies to Verreaux's eagles Aquila verreauxii, which is typically considered to be a highly specialised predator of hyraxes (Procavia and Heterohyrax spp.). We investigate diet in relation to land cover in two adjacent areas of South Africa and explore the links between diet diversity, the percentage of hyrax consumed, and the breeding performance of eagles. We also examine these same patterns using data from other studies. We found that diet diversity was greater in the agriculturally developed Sandveld region compared to the natural Cederberg region. Proportions of the three main prey types were correlated with the proportion of agriculturally developed land around the nest site. Breeding performance was correlated with the diet, but not in the manner expected, with breeding productivity being greater in regions with large diet diversity and a small proportion of hyrax in the diet. We found similar patterns when placing our results into a broader geographical context using other dietary studies of Verreaux's eagles, suggesting our results were not unique to our study system. Thus, our results suggest that diet diversification does not necessarily impinge on breeding performance in the presence of adequate alternative prey resources. This research adds to the growing number of studies suggesting that some predators may be adaptable up to a threshold level of habitat transformation. These results have implications for predicting changes on such species by anthropogenic habitat transformation and highlight the potential for agriculturally developed areas to maintain a conservation value when habitat heterogeneity is maintained.

The influence of agricultural transformation on the breeding performance of a top predator: Verreaux's Eagles in contrasting land use areas

ABSTRACT Breeding productivity frequently shows variation across a species' range or locally between different habitat types. Agricultural transformation generally has negative effects on biodiversity and often results in reduced prey abundance or increased foraging effort in top predators and, consequently, often reduces breeding productivity. Major factors that affect reproductive success also include climatic variables, breeding density, and timing of breeding. We explored the influence of agricultural transformation on a specialist raptor, Verreaux's Eagle (Aquila verreauxii). From 2011 to 2014, we examined productivity in 2 adjacent populations in the Western Cape Province, South Africa: an unspoiled area of Fynbos vegetation with little human development (the Cederberg Mountains) and an agriculturally transformed area (the Sandveld region). Counterintuitively, breeding productivity was higher in the agricultural than in the natural site. In particular, the proportion of pairs that attempted to breed...

Taphonomy of Verreaux's Eagle (Aquila verreauxii) prey accumulations from the Cape Floral Region, South Africa: implications for archaeological interpretations

We conducted a taphonomic analysis of modern prey accumulations of Verreaux's Eagle (VE; Aquila verreauxii) from the Cape Floral Region of South Africa. VE nest in or around cliffs and rocky outcrops, places that also attract other bone accumulators, including humans. Therefore, it is necessary to characterize the signatures of VE bone accumulation with as much precision as possible in order to differentiate between the prey remains of other bone accumulators, especially in relation to fossil assemblages that originate in and around cliffs, rock shelters, and caves. Towards this end, we describe the taxonomic composition, skeletal-part representation, bone breakage patterns, and bone surface modifications of mammal bones as well as the range of variability within those signatures. Based on the frequency of bone modifications we determine that VE modify the bones of their prey more often than do other eagle species. We suggest that taphonomic patterns derived from predation by other eagle taxa are not the most appropriate means to identify VE predation in faunal assemblages. In addition, we conclude that there is patterned variability in the ways that VE accumulate and modify the bones of their prey. There are two distinct skeletal-parts preservation, bone breakage, and bone surface modification patterns among the prey in our sample: one that characterizes hyraxes, mole-rats, and carnivores, and another that characterizes hares and bovids. Faunal analysts investigating the potential role of VE at fossil sites should be aware of 1) these taphonomic patterns and differences and 2) that there is no singular pattern of accumulation. We define patterns of preservation, breakage, and bone modification that can be employed on a taxon-specific basis to distinguish VE prey remains from other bone accumulators.

The Persistence of an Apex Avian Predator, Verreauxs' Eagle,Aquila verreauxii, in a Rapidly Urbanizing Environment

Anthropogenic land transformation processes in the vicinity of the Walter Sisulu National Botanical Garden, Johannesburg, South Africa, are a significant threat to natural vegetation and biodiversity. Breeding and feeding records of a Verreauxs' eagle (Aquila verreauxii),pair in the garden were analysed in relation to changes in the local environment due to urbanization. Natural prey-suitable habitat within a 10 km radius of the nest diminished by approximately 29.7 km2 (9.5%) during 1984–2007. In 2007 approximately 116.7 km2 (37.2%) of suitable prey habitat remained within this radius. Feeding data within a more recent period (1996–2008) suggest that there has been a switch from an optimal diet of rock hyrax (Procavia capensis)to less characteristic avian prey species such as helmeted guineafowl (Numida meleagris),francolins (Francolinus spp.) and supplemented food. Annual breeding success indicated few inconsistencies in incubation period, nestling period and postfledging dispersal period relative to br...

Black Eagles and hyraxes — the two flagship species in the conservation of wildlife in the Matobo Hills, Zimbabwe

The Black Eagle (Aquila verreauxii) in the Matobo National Park is heavily dependent on two hyrax species, which form 98% of the diet. This raptor has been the subject of study in the Matobo Hills for the past 45 years. Its two main prey species, the Yellow-spotted Hyrax (Heterohyrax brucei) and the Rock Hyrax (Procavia capensis), have been under study for the past 13 years. There are three categories of land use in the Matobo Hills — national park, commercial farmland and communal land — and therefore varying levels of protection for the raptor and its prey. Local communities within the Matobo Hills depend on the hyrax as their main source of protein. This heavy utilisation has lead to population declines in both the prey (hyrax) and the raptor in some areas. In an effort to reverse or reduce this imbalance, since 1995 wildlife conservation education programmes have been introduced, focusing on 21 schools immediately surrounding the Matobo National Park. This educational programme is aimed at conserving not only the Black Eagle and hyraxes but the whole biodiversity of the hills.

Conservation status and community structure of cliff-nesting raptors and ravens on the Cape Peninsula, South Africa

We detail the sizes, spatial distributions and trends in nest site selection of cliff-nesting raptor and raven populations resident in the mountains of the Cape Peninsula, South Africa. We also assess the conservation value of these populations to inform the future management of the newly-established Table Mountain National Park (TMNP), and examine the structure and interrelations within the raptor community. The combined number, dispersion and density of nests (n = 96 nests, mean inter-nest distance = 0.59km, density = 30.0 pairs/100km2) are comparable with those of high-density raptor populations studied elsewhere in Africa and the world. Densities of Verreauxs' Eagle Aquila verreauxii (n = 2, 12.01km, 0.6 pairs/100km2, respectively) and Jackal Buzzard Buteo rufofuscus (n = 9, 4.63, 2.8 pairs/100km2), are low, Rock Kestrel Falco rupicolus (n = 44, 1.75km, 13.8 pairs/100km2) high and Peregrine Falcon Falco peregrinus (n = 19, 3.13km, 5.9 pairs/100km2) exceptional, relative to populations of the same or similar species in other areas. There are no comparable data for White-necked Raven Corvus albicollis (n = 22, 3.22km, 6.9 pairs/100km2). All species combined, and Peregrines in particular, significantly prefer high cliffs from the available habitat. Peregrines generally dominate the other species, may affect cliff site selection and dispersion in the rest of the community, and tend to locate their nests close to those of White-necked Ravens. Numbers of Verreauxs' Eagle are lower than recent historical levels, perhaps because key prey populations are depleted. Any future recovery of this large predator could subtly affect the entire assemblage. This cliff-nesting raptor community is a significant asset of the TMNP, and should be considered in management decisions taken in the Park, particularly those concerning the regulation of leisure activities in the vicinity of nesting areas.

A multi-gene phylogeny of aquiline eagles (Aves: Accipitriformes) reveals extensive paraphyly at the genus level

The phylogeny of the tribe Aquilini (eagles with fully feathered tarsi) was investigated using 4.2 kb of DNA sequence of one mitochondrial (cyt b) and three nuclear loci (RAG-1 coding region, LDH intron 3, and adenylate-kinase intron 5). Phylogenetic signal was highly congruent and complementary between mtDNA and nuclear genes. In addition to single-nucleotide variation, shared deletions in nuclear introns supported one basal and two peripheral clades within the Aquilini. Monophyly of the Aquilini relative to other birds of prey was confirmed. However, all polytypic genera within the tribe, Spizaetus, Aquila, Hieraaetus, turned out to be non-monophyletic. Old World Spizaetus and Stephanoaetus together appear to be the sister group of the rest of the Aquilini. Spizastur melanoleucus and Oroaetus isidori are nested among the New World Spizaetus species and should be merged with that genus. The Old World ‘Spizaetus’ species should be assigned to the genus Nisaetus (Hodgson, 1836). The sister species of the two spotted eagles ( Aquila clanga and Aquila pomarina) is the African Long-crested Eagle ( Lophaetus occipitalis). Hieraaetus fasciatus/spilogaster are closest to Aquila verreauxii and should be merged with that genus. Wahlberg’s Eagle H. wahlbergi, formerly placed in Aquila, is part of a clade including three small Hieraaetus species ( pennatus, ayresii, and morphnoides). The Martial Eagle ( Polemaetus bellicosus) is the sister species of the Aquila/Hieraaetus/Lophaetus clade. Basal relationships within this clade remained unresolved. Parsimony reconstruction of the evolution of plumage pattern within Aquilini suggests that: (1) transverse barring of parts of the body plumage was lost in the Palearctic Aquila–Hieraaetus clade, (2) pale underparts in adult plumage evolved three times independently, and (3) dimorphic adult plumage is a derived character of the small-bodied Hieraaetus clade.

First record of Verreaux's Eagle Aquila verreauxii nesting on the ground

First record of Verreaux's Eagle Aquila verreauxii nesting on the ground

The diurnal Afro-alpine raptor community of the Ethiopian Bale Highlands

Clouet, M, Barrau, C & Gar, J-L. 2000. The diurnal Afro-alpine raptor community of the Ethiopian Bale Highlands. Ostrich 71(3&4): 380-384.The diurnal raptor community of the Afro-alpine level of the Bale Highlands (i.e. 3500-4000 m a.s.l.) Ethiopia was observed during eight expeditions spread over five consecutive years. Among the 25 species recorded, nine are residents, including three which nest at lower altitudes. Small mammal hunters are the most numeraus species, including a unique assemblage of various Aquila species, among which the Golden Eogle Aquila chrysaetos is the outstanding feature. Population densities are high for Golden Eagle and Verreaux's Eagle, Aquila verreauxii, Tawny and Steppe Eagles, Aquila rapox and A. niplensis, Augur Buzzard, Buteo augur and Lanner Falcon, Falco biarmicus. This is related to the abundance of prey, mainly hyraxes, hares and rodents. For the largest species, the start of breeding coincides with the onset of the dry season (Navember). The period with the largest number of young raptors on the nest (February-March) corresponds to the peak in the prey papulation. Migrants and Palaearctic winter visitors are present at the same time and use the same faad resources as the breeders. The main factors isolating closely related species are diet for the Golden and Verreaux's Eagles and the period of habitat use for the Tawny and Steppe Eagles.

Raptors drowning in farm reservoirs in South Africa

Anderson, M.D., Maritz, A.W.A. & Oosthuysen, E. 1999. Raptors drowning in farm reserviors in South Africa. Ostrich 70 (2): 139–144 In the arid areas of southern Africa, the drowning of raptors in small reservoirs on farms is a significant cause of mortality. Records of 322 raptors of 29 species which drowned during 163 separate incidents have been collated. Whitebacked Gyps africanus and Cape Vultures Gyps coprotheres, and Martial Polemaetus bellicosus and Black Eagles Aquila verreauxii, were the species most frequently recovered from reservoirs. There are few records of small raptors (<300 g) succumbing in this manner. There are several possible explanations as to why raptors drown. The simplest is that these birds enter the reservoir to drink or bathe and if it is not full are then unable to climb up the structure's steep sides. There have been 12 recorded vulture mass drowning events, involving as many as 38 buds at one time. The reason for these mass drownings is probably different to the individual drowning of other raptors, with the “intimate lifestyle” hypothesis being the most plausible. There are simple, cheap and effective solutions to prevent the drowning of raptors and these are being advocated with success in the Northern Cape Province, South Africa.

Population dynamics of two species of hyraxes in the Matobo National Park, Zimbabwe

Populations of the syntopic rock hyrax, Procavia capensis (Pallas), and yellow‐spotted rock hyrax, Heterohyrax brucei (Gray), in the 42,400‐ha Matobo National Park (MNP), Zimbabwe, were characterized from 1992 to 1996. The Procavia:Heterohyrax species ratio varied significantly (P&lt; 0.01) across years from 1.43:1.00 to 0.74:1.00. Estimates of abundance (31,114–39,869 Procavia and 21,833–46,619 Heterohyrax) and densities (0.73–0.94 Procavia ha−1 and 0.51–1.10 Heterohyrax ha−1) indicated that populations had experienced a considerable decline since 1978, with drought suspected as the principal cause. The Heterohyrax population fluctuated more than the Procavia population. Although sex ratios of individuals trapped and collected in 1991–92 did not differ from 1:1 for either species, female Procavia nearly outnumbered males (P&lt; 0.10) among the prey of black eagles (Aquila verreauxii Lesson), suggesting the possibility of divergence in the social organization and vigilance of the two species. In each year of the study, pups comprised &lt; 30% of individuals in the two populations after the interspecifically synchronous annual birth event in March–April, and evidence exists for an effect by drought on fecundity. Females appear to breed, on average, no more than every other year. We estimated juvenile (0–1 year of age) mortality at 52.4–61.3% for Heterohyrax and 59.6–75.6% for Procavia. Mean mass (±1 SE) of Procavia adults was 3.4±0.2 kg and of Heterohyrax adults, 2.4±0.1 kg. Procavia had a significantly (P&lt; 0.01) greater condition index (body mass/total length) than Heterohyrax. Adults are especially important reservoirs of biomass for the diverse and numerous predators of the MNP, accounting for &gt; 84% of hyrax biomass intraspecifically.

Species Composition and Age Structure of Remains of Hyraxes (Hyracoidea: Procaviidae) at Nests of Black Eagles

Hyraxes ( Procavia capensis and Heterohyrax brucei ) constitute the nearly exclusive prey of the black eagle ( Aquila verreauxii ) in the Matobo National Park, Zimbabwe. Skulls and mandibles of hyraxes were collected from within and beneath nests of 40 black eagles from October 1991 to May 1992. Skulls and mandibles of Heterohyrax were represented significantly more often ( P < 0.01) at eagle nests than those of the equally abundant but larger Procavia . About 68% of Procavia and 86% of Heterohyrax fragments of skulls and mandibles collected were those of adults. Differential susceptibility of hyraxes to predation can be explained in part by their comparative accessibilities and sizes as prey for optimally foraging black eagles.

THE INFLUENCE OF RAINFALL ON BLACK EAGLE BREEDING OVER 31 YEARS IN THE MATOBO HILLS, ZIMBABWE

Summary Gargett, V., Gargett, E. & Damania, D. 1995. The influence of rainfall on Black Eagle breeding over 31 years in the Matobo Hills, Zimbabwe. Ostrich 66: 114–121. The effect of rainfall from 1964 to 1994 on the annual reproductive rate and number of resident pairs of Black Eagles Aquila verreauxii in the Matobo Hills, Zimbabwe, and on the abundance of their staple prey, hyrax, Procavia capensis and Heterohyrax brucei is reviewed. The number of resident pairs of Black Eagles increased with increased rainfall, when hyrax numbers were estimated to be at a very high level. Subsequent poor rainfall years coincided with a decrease in the number of resident pairs, a smaller proportion of pairs breeding, a lower reproductive rate and a dramatic decline in prey numbers.

THE FOOD REQUIREMENT OF A BLACK EAGLE CHICK

Summary Gargett, V. 1982. The food requirement of a Black Eagle chick. Ostrich 53:178-181. A hand-reared Black Eagle Aquila verreauxii chick that was fed on hyraxes, Heterohyrax brucei and Procavia capensis, ate 29 626 g from hatching to flying at 93 days. For 18 days after its first flight it ate 5 910 g, (mean 328 g per day). The eaglet's food intake increased in cold weather and decreased during a hot spell.

SIBLING AGGRESSION IN THE BLACK EAGLE IN THE MATOPOS, RHODESIA

Gargett, V. 1978. Sibling aggression in the Black Eagle in the Matopos, Rhodesia. Ostrich 49:57-63. A two-egg clutch of the Black Eagle Aquila verreauxii was observed from the hatching of the first...