Browsing by Author "Mullers, Ralf"

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    Bird-borne video-cameras show that seabird movement patterns relate to previously unrevealed proximate environment, not prey
    (Public Library of Science, 2014) Tremblay, Yann; Thiebault, Andréa; Mullers, Ralf; Pistorius, Pierre
    The study of ecological and behavioral processes has been revolutionized in the last two decades with the rapid development of biologging-science. Recently, using image-capturing devices, some pilot studies demonstrated the potential of understanding marine vertebrate movement patterns in relation to their proximate, as opposed to remote sensed environmental contexts. Here, using miniaturized video cameras and GPS tracking recorders simultaneously, we show for the first time that information on the immediate visual surroundings of a foraging seabird, the Cape gannet, is fundamental in understanding the origins of its movement patterns. We found that movement patterns were related to specific stimuli which were mostly other predators such as gannets, dolphins or fishing boats. Contrary to a widely accepted idea, our data suggest that foraging seabirds are not directly looking for prey. Instead, they search for indicators of the presence of prey, the latter being targeted at the very last moment and at a very small scale. We demonstrate that movement patterns of foraging seabirds can be heavily driven by processes unobservable with conventional methodology. Except perhaps for large scale processes, local-enhancement seems to be the only ruling mechanism; this has profounds implications for ecosystem-based management of marine areas.
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    Quantifying Shoebill (Balaeniceps rex) habitat suitability in the Bangweulu Wetlands, Zambia
    (2013) Musker, Seth; Mullers, Ralf; Amar, Arjun
    A quantitative analysis of suitable habitat for the Shoebill (Balaeniceps rex), a large waterbird confined to African swamps, was conducted by using a combination of aerial photographs and a previously determined habitat suitability model from the Bangweulu Wetlands, Zambia. The Shoebill is considered Vulnerable on the IUCN red list, but there are no pre-existing quantitative data on the composition of suitable habitat for this species. Both univariate and multivariate analyses revealed that non-wetland habitats as well as non-vegetated wetland habitats have low suitability compared to vegetated wetland habitats. Notably, reeds correlated significantly and positively with suitability (rs = 0.338, p < 0.001). We found little support for the hypothesis that floating vegetation is highly suitable for Shoebills, but the analysis for this habitat may have suffered as a result of confounding factors. The relationship between flooded grassland and suitability was highly variable and was not significant (rs = 0.009, p = 0.807). In contrast, dry grassland correlated positively with suitability (rs =0.289, p < 0.001), but its suitability scores were generally much lower than for flooded grassland. Quantitative data on Shoebill habitat suitability will be useful for future Shoebill population surveys, and will improve our ability to make informed decisions regarding its conservation.