Range expansion of the Hadeda Ibis (Bostrychia hagedash) in Pietermaritzburg, KwaZulu-Natal : an urban environment.

Abstract

Many animal species are typically negatively affected by urbanization; however those species which are not negatively affected are those that can use resources available in urban areas to survive. Hadeda Ibis (Bostrychia hagedash) is an indigenous southern African bird that was previously threatened and associated with wetlands but has become an urban exploiter and increased its population size and expanded its range across South Africa with a pattern following urbanization. The aim of this thesis was to investigate the factors that promoted this range expansion in urban areas particularly in Pietermaritzburg, KwaZulu-Natal. To determine the urban ecology of Hadeda Ibis, flying, foraging, calling and perching activities were compared between summer and winter and between areas differing in proportion of green and grey space. We expected there to be differences between seasons and we predicted that Hadeda Ibis, although an urban exploiter, would show a lower urban tolerance for areas with a larger proportion of grey space. Five suburbs of varying degrees of green to grey space were surveyed in summer and winter for Hadeda Ibis activity. Results indicated that calling behaviours differed between seasons with more calling observed in summer. This may be because of individuals communicating with conspecifics that were more dispersed in summer due to nesting habits while there were more individuals at colonial roosts in winter. There was no significant difference in foraging and flying between seasons or between the different areas. This was probably due to adequate foraging resources being available throughout the year with the maintenance of green spaces in terms of grass lawns kept well watered and short. Hadeda Ibis were observed using urban features to perch but not for nesting or roosting which indicated that although they have a high degree of urban tolerance, they still depend on trees in green spaces for nesting and roosting for their urban persistence and were more common in suburbia than the city centre in Pietermaritzburg. To determine Hadeda Ibis nesting and roosting habits in Pietermaritzburg, we measured roost tree height and analyzed roost and nest location to establish possible roost and nest habitat preference. We expected their roosts and nests to be in close proximity to green spaces, for instance wetlands, and that they would use exotic trees more than indigenous trees. We mapped known nests and roosts onto aerial photographs with a habitat land use layer using ArcGIS and roost tree height was measured. The surrounding habitat types within a radius of 10 km from each roost and nest was analyzed and roost tree height compared. As expected Hadeda Ibis used more exotic trees for roosting and nesting because of availability and there were no differences with roost tree height. The 10 km area around nest and roost locations showed a variety of habitats suggesting that Hadeda Ibis need not nest or roost close to natural habitats like wetlands. This pattern can be explained by the fragmented nature of urban environments where green space is scattered between other urban features thereby providing Hadeda Ibis with nesting, roosting and foraging opportunities throughout the urban area of Pietermaritzburg. To determine the home range and habitat use of urban Hadeda Ibis in Pietermaritzburg, we attached GPS/GSM transmitters to four individuals to track their movements. However all transmitters failed and data were recoverable from only one. Those data combined with general observations of colour ringed individuals, suggested that Hadeda Ibis have a relatively small home range for a bird of its size. We also confirmed that Hadeda Ibis show roost site fidelity. In conclusion, urban areas provide Hadeda Ibis with foraging, nesting and roosting resources required for its urban persistence. Short grass lawns that are well watered are ideal for Hadeda Ibis foraging and exotic trees that are abundant in urban areas provide adequate nesting and roosting sites. The species has also been observed using alternative food sources like garbage and dog food and urban features like swimming pools as a substitute for wetland habitat. The combination of these factors has resulted in Hadeda Ibis having increased its population and expanded its range. Provision of resources factored within urban design and planning may help to conserve species threatened by increased urbanization just as Hadeda Ibis has gone from having low population numbers and being associated with wetlands to urban success.