Environmental Drivers of an Urban Hadeda Ibis Population
2014
Duckworth, Gregory Duncan | Altwegg, Res
Weather and habitat-use are key factors that influence the survival of a species. A central goal in conservation biology is to gain a mechanistic understanding of how these quantities limit a species' range. We examined how weather, season and geographic location influenced the demographic rates of an urban population of Hadeda Ibises Bostrychia hagedash on the leading edge of its expanding range in the Western Cape of South Africa. The Hadeda Ibis has increased its South African range 2.5 times within the last 50 years and is now a common urban resident throughout most of the country. Using capture—mark—recapture and generalized linear models, we build upon previous demographic analyses of this species. Our results show no significant influence of weather on demographic rates. Rainfall triggered the onset of the main breeding season (although breeding pairs were found at any time throughout the year), and Hadeda Ibises adjusted their breeding phenology according to the rainfall season of the areas into which they expanded. There was no evidence of spatial correlation within the study area. Hadedas have quickly adapted well to urban areas outside of their original range. Because weather had little effect on Hadeda demographics we suggest that urban areas may potentially buffer unfavourable effects of weather on Hadeda survival and are an important factor in the successful range expansion. This finding is consistent with the explanations of range expansions of other ibis species throughout the world.
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