Our research focuses on the Southern Ground-Hornbill’s social system, and the dynamics and benefits of group living. We aim to understand the mechanisms underlying the stability of cooperation in this species and the consequences of social behaviour for individual fitness and population dynamics. We are particularly interested in understanding whether cooperation helps Ground-Hornbills to cope with the weather extremes that they experience (and which are increasing under the climate emergency that our planet is facing). Our research uses a combination of long-term data, field observations and experiments and data ranges from behaviour to physiology. Given these birds endangered status in South Africa, our research is also used to inform conservation efforts, such as the re-introduction program ran by the Mabula Ground-Hornbill Project.
Sociality and cooperation within species are intriguing because although cooperation provides important benefits to group members, these benefits are associated with a cost to individuals. Therefore, understanding the individual contributions to vital behaviours that benefit the group and how these benefit the individuals that cooperate is crucial to provide an understanding of how social behaviour is maintained.
The aim of my study is to investigate the social structure of Southern Ground-Hornbills, and to understand how individual group members contribute to two vital group functions: territory defence and reproduction, two poorly understood topics
In order to study territory defence, one of my main focuses has been on vocal communication. Southern Ground-Hornbills are known for their iconic territorial vocalisations produced at dawn and occasionally dusk. However, little is known about them and even less is known about the other types of vocalisations produced in other various contexts. I have been focusing on describing their vocal repertoire and investigating how these vocalisations are used to advertise and defend their territories. By experimentally simulating intrusions of neighbour and stranger groups, we hope to understand what information is being transferred between groups and how the different members of the group invest in the response.
The other main aspect of my PhD project is investigating how the individual group members contribute to provisioning the incubating female and the single nestling, and whether cooperative breeding in this species contributes to decrease the effects of adverse environmental conditions. We use camera traps installed at the nesting sites to record provisioning behaviour and determine whether it changes with varying temperatures. High temperatures have been shown to have a number of implications for foraging activity, thermoregulation and body condition. I am currently analysing the long-term data from the APNR Ground Hornbill Project to assess whether increasing occurrence of above-average warm weather events is likely to have an impact on the reproductive output in species.
Effects of high temperatures on nestling growth and physiology in the Southern Ground-Hornbill Bucorvis leadbeateri (Carrie Hickman, M.Sc. student; Supervisors: Rita Covas, Susan Cunningham)
Daily maximum temperatures have increased in southern Africa over the last three decades, and the increase in temperature and frequency of extreme wheather events is predicted to continue over the coming decades. Recent work in birds has shown that during hot weather, individuals decrease their foraging activity and efficiency, which can lead to lower provisioning rates of dependent young, resulting in reduced growth. In addition, developing young may be directly affected by hot temperatures, as their need for evaporative water loss increases, and some physiological functions may become compromised. Under these extreme conditions, the location and characteristics of nests may have a strong influence on the environment experienced by the developing young and parents are expected to select cooler sites. This, however, may not be possible for cavity nesting species, which are limited by the natural cavities available or, in some cases, by artificial nests structures provided.
The Southern Ground-Hornbills are large, terrestrial cavity-nestersthat readily occupy artificial nest boxes. Here, our specific objectives will be: 1) to investigate whether high ambient and nest temperatures lead to detrimental sub-lethal effect in developing Southern Ground-Hornbill nestlings – measured as nestling growth, fledging size and condition, and telomere length (telomere length has been shown to be directly influenced by physiological stress and to correlate strongly with survival probability); 2) to use piecewise modelling (a type of path analyses) in order to investigate whether these negative effects arise from a decrease in the frequency or quality of nest provisioning by adults or from direct effects of temperature on the developing nestling.
It is expected that a better understanding of whether Southern Ground-Hornbills nestlings are suffering from high temperatures and how these effects arise, will allow us to propose measures to decrease possible detrimental effects of temperature in this species.
Nest boxes as a conservation tool for the Southern Ground-Hornbill Bucovus leadbeateri (Kate Carstens, PhD student – 2017)
Populations of secondary tree-cavity nesting bird species are often limited by a shortage of natural nesting sites. For the endangered Southern Ground-Hornbill Bucorvus leadbeateri that nests typically in natural tree cavities, the shortage of nesting sites is one factor limiting population growth in South Africa. Artificial nests can improve the conservation status of threatened birds that are limited by nest-site availability. However, nest boxes or other types of artificial nests are not always beneficial to the target species, and their value as a conservation tool needs to be tested in each case. Wooden nest boxes were installed for Ground-Hornbills in a study area with a paucity of natural nesting sites. This study tested the role of nest boxes as a conservation tool for Ground-Hornbills using multiple approaches that included an assessment of productivity and changes in the number of breeding groups, as well as describing novel insights into dispersal in a study area supplemented with nest boxes.
Breeding success averaged 14 % higher in nest boxes than in natural cavities. Predation levels were not significantly different between nest boxes (10 %) and natural nests (12 %). Thus, although predation was an important cause of nest failures (42 % of nests), nest boxes were not more susceptible to predation than natural nests. Nests with thicker nest walls and those positioned with higher entrances above the ground improved breeding success. Breeding attempts that were initiated early in the season were more likely to fledge a chick than those initiated later in the season. Breeding success in the study area increased following the installation of nest boxes from 2002. However, productivity decreased after 2007, when the number of breeding groups rose above 20. The availability of nest boxes apparently increased breeding density to the extent that was evidence of a density dependent decrease in breeding success.
With many ringed nestlings fledging from the study area after the installation of nest boxes, it was possible to observe their dispersal within the study area and farther away into the adjacent Kruger National Park. There was no evidence that males were more philopatry than females. Males and females dispersed at similar ages, and over similar distances, raising interesting questions about inbreeding avoidance mechanisms in this species.
This thesis provides several management implications to install nest boxes that increases the reproductive rate and success of breeding Ground-Hornbill groups. Given that Southern Ground-Hornbills appear to exhibit density dependent breeding success, spacing nest boxes to promote suitable densities of breeding groups could maximise reproductive output. The height of the nest entrance above the ground improved breeding success, and nests placed so that the entrances are situated > 6 m above the ground will provide attractive nesting sites. Future nest boxes should be made with thick cavity walls (≥ 6 cm) that can not only improve breeding success but can also assist in buffering against high ambient temperatures experienced during the breeding season. Given that the threats to Ground-Hornbills also include persecution and poisoning, increasing the reproductive rate by installing nest boxes would balance the loss of individuals, at least in some way, by the increased recruitment of offspring into the population.
Fine-scale movements and habitat use of the Southern Ground-Hornbill Bucorvus leadbeateri (Blair Zoghby, M.Sc. student – 2015)
Understanding the factors affecting their movement patterns and how they interact with their habitat is useful to inform conservation and habitat management options for the species, to select sites for artificial nests and to identify suitable areas for reintroduction initiatives. In this study, daily and seasonal patterns of habitat use as well as patterns of roost site use of four Southern Ground-Hornbills’ groups, based on the GPS-satellite tags collected over one year from 2010 to 2011.
Daily travel distances averaged 7.4 km per day and were greater during the breeding season, when birds were constrained to forage close to their nest, and were lower in winter, when birds ranged more widely. Hourly travel distances were affected by time of day, season, and temperature. Birds travelled farthest per hour in the morning, decreasing in the afternoon in winter. However, in summer hourly travel distances were greatest in the morning and afternoon, with a minimum during the middle of the day when ambient temperatures exceed 25˚C. Acacia-dominated vegetation and riparian habitats were favoured during the heat of the day, probably because they offer more shade than other habitats. Optimal habitat configurations for Ground-Hornbills include a mosaic of habitat types, with open areas for foraging and dense trees for shade.
An average of 15 roost sites was used per month across all groups, with little evidence of strong preferences for specific sites. This number was least during summer when actively breeding groups frequently roosted close to the nest. As might be expected, the mean monthly number of nights per roost peaked during the breeding season, when riparian habitats were preferred for roosting. Adequate large trees for nesting and roosting, particularly in riparian habitats, may therefore be an important and potentially limiting factor for the successful reproduction of Southern Ground-Hornbills.
Home range use by Southern Ground-Hornbills (Bucorvus leadbeateri) – quantifying seasonal habitat selection and vegetation characteristics (William Wyness, BSc. Honours student – 2011)
The habitat of an animal is extremely important as it provides that animal with the necessary resources for fulfilling its life-history requirements. A habitat is defined as a region in environmental space which comprises of multiple abiotic and biotic variables influencing an animal’s location. Animals tend to utilise discrete areas within a habitat, constituting part of their home range. Home range analysis helps to delineate the area used by an animal habitually and areas of concentrated use. Patterns of differential use of space within an animal’s home range are the result of competing demands and trade-offs.
In this study, a kernel technique was used to determine the home range of four satellite-tracked groups of Southern Ground-Hornbills Bucorvus leadbeateri in the Associated Private Nature Reserves (APNR). Satellite data were analysed to quantify habitat selectivity by groups of Ground-hornbills at different times of the year to determine a) favoured habitat types, and b) the resolution with which they perceive their environment.
Each of the groups showed variation in the utilisation and extent of their home ranges on a seasonal basis. Home range sizes ranged from 55 km2 to 103 km2, contracting towards the nest during the summer breeding season (December to March) and expanding during the dry season (April to September). Three of the four groups bred successfully and, during the breeding season they used only 24 – 36% of the areas they used in winter. The fourth group attempted to breed, but failed at the chick stage, and ended up using 70% of their winter range during the summer. In summer, there was no overlap between home ranges. In fact, groups never even got close to one another. In winter, however, when groups ranged over much larger areas, there was a small amount of home-range overlap.
A detailed geo-referenced vegetation map also allowed for the analysis of seasonal patterns of habitat preference in more detail. Despite the large home ranges, the proportions of these that were favoured at any time of year were relatively small (0.5 – 22% across four groups and four seasons). On average, more habitat types were avoided than preferred (2 – 55%), but most habitats were used in proportion to their availability (23 – 98%). The birds were more constricted in their movement during the breeding season, mainly because group members regularly visit the nest to feed the incubating female or the chick. One habitat type that was consistently favoured was open ground and since open habitats are fairly rare, this may explain why groups with relatively large amounts of open ground close to their nest are the most successful. It also suggests that bush clearance should be used as a management tool to provide optimal sites elsewhere for the placement of artificial nests or for the reintroduction of Southern Ground-Hornbills.