Monitoring breeding success of known groups of Southern Ground Hornbills Bucorvus leadbeateri in Botswana
The Southern Ground Hornbill is a Red Data species in Southern Africa, mainly due to its decline in South Africa where it is now virtually restricted to protected areas. It also has a very low breeding success, with only one juvenile surviving to maturity on average every nine years. Its status and breeding success in Botswana are not well documented; consequently it is regarded by BirdLife Botswana as a species for which further information is urgently required.
A project initiated by BirdLife Botswana members in Maun aims to gather data on breeding success in known groups that are regularly seen along the Thamalakane River in and around Maun, and along the Khwai River in Moremi Game Reserve. The reason for choosing these two specific populations is to compare breeding success under 'natural' conditions (Khwai) with that in semi-urban areas. In the first area, Ground Hornbills are living in a man-modified environment where land use is residential, and agricultural.The second area however, is entirely 'natural', and the only humans encountered by Ground Hornbills are those on safari in the area.
Other incidental information that will be collected includes density (number of groups/individuals in a defined area), mean group size, and territory and home range size. Information on distribution and movements is being stored in a Geographical Information System, set up with the assistance of the Harry Oppenheimer Okavango Research Centre. Three GPSs were kindly donated to the project by the Royal Society for the Protection of Birds.
The Maun component of the study is being undertaken by BirdLife Botswana members resident in Maun, while the Ground Hornbills at Khwai are being monitored by professional guides working for Gametrackers Botswana. This is a long-term project due for completion in 2005.
Progress report - Ground Hornbill study (August 2003)
The Southern Ground Hornbill is a Red data species in South Africa where it is virtually restricted to protected areas. By contrast, Botswana apparently has a large and healthy population. Is there really cause for concern?
The truth is, there is no information on the status of this bird in Botswana. Ideally a census of the population should be done to measure its size, and this should be repeated regularly to determine the trend in numbers. Currently this is not possible with the human resources and funding available. As an alternative, a measure of the breeding success of a sample of hornbill groups will give an indication of how the Botswana population is faring. This is the aim of the project being conducted by members of the Maun Branch.
Information is being collected on Ground Hornbills in Maun and at Khwai to provide a comparison between groups in a semi-urban area with those living in natural conditions. By recording regularly all birds seen, specific groups have become relatively well known, and their numbers and composition can be monitored.
The study is in the early stages, but it is interesting to compare some of the findings with those of Alan Kemp's 20 year study in the Kruger National Park in South Africa.
- Individual groups varied in their breeding success, and fledging rates ranged from one chick once every two or three years to none at all in 20 years.
- Ground Hornbills were found to rear, on average, only a single chick per breeding group, every nine to ten years.
- During the first breeding season, no nests were located. However subsequently new juveniles were seen in some groups. The survival of these immatures is being monitored.
- Almost every group for which an age classification was made had at least one immature (identified by its yellow throat-pouch). Some had three - probably this year's chick, last year's chick and the one from the year before. This indicates that the recruitment to the populations in both Maun and Khwai is relatively high.
Home ranges in South Africa are approximately 100 km2 according to Kemp. Preliminary data from groups in Maun and Khwai indicate that their home ranges are less than 10 km2. This shows that all the birds' habitat requirements are being met within a relatively small area i.e. the habitat in both study areas is good for Ground Hornbills.
The project has generated interest among other birders around the Okavango, and other groups outside the study area are being monitored, mainly by guides. A relatively large number of groups have been reported from throughout the Delta - if sufficient coverage is obtained, it may be possible to obtain a minimum estimate for the Delta.
Without the input of Onx Manga and Joe Bayei - professional guides at Khwai - this study would not have been possible. Thanks also to Kevin Torrens, and numerous other observers, for reporting sightings regularly.