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Response to habitat modification by foraging Dark-chanting Goshawks Melierax metabates in a West African savanna
- RALPH BUIJ, NIKIE VAN DORST, HENRIËTTE F. SALOMONS, BARBARA M. CROES, MAURINE W. DIETZ, JAN KOMDEUR
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- Journal:
- Bird Conservation International / Volume 25 / Issue 3 / September 2015
- Published online by Cambridge University Press:
- 11 December 2014, pp. 335-352
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- Article
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Anthropogenic habitat alteration has probably contributed significantly to the decrease of raptor populations in West African savannas. To evaluate the impact of habitat degradation on foraging by sedentary Afrotropical raptors, we investigated the differences in microhabitat selection, foraging effort and energy returns between Dark-chanting Goshawks Melierax metabates inhabiting natural and transformed savannas in Cameroon. We expected that the agro-ecosystems in the transformed savannas have become unprofitable for Dark-chanting Goshawks due to scarcity of food resources. In both savanna types we radio-tracked six mated, adult males during the non-breeding season and determined foraging effort, by time spent at each perch and distance covered between perches, and energy intake through estimation of the energy value of prey items. Goshawks in natural habitats had smaller home-ranges and exploited their range more intensively than Goshawks in transformed habitats. In both natural and transformed habitats, Goshawks selected foraging patches with comparatively tall trees, underlining their importance to foraging Goshawks. The extent of shrub and herbaceous layer cover, agriculture cover, and tree density were other important predictors of foraging patch use, but their importance differed between habitats. The extent of shrub, herbaceous layer and agriculture cover were positively associated with foraging patch use in transformed habitats, suggesting that cultivated fields and ground vegetation support important prey resources for Goshawks in agro-ecosystems. The composition of broad prey categories to the diet, foraging effort and returns were comparable between habitats. However, we found indications that the proportion of heavy-bodied lizard species among reptile prey items was higher in natural than transformed habitats, whereas on average smaller lizards were more commonly caught in the latter. Mean herbaceous layer height and tree density within home ranges, both higher in natural habitat, were negatively related to prey capture rates. Tree clearance and livestock grazing thus favored greater prey capture rates in transformed habitat, offsetting a lower meal energy value compared to natural habitat. We conclude that foraging Dark-chanting Goshawks may cope with moderate land transformation, but practices focused on conservation of tall trees and ground vegetation cover would be beneficial by maintaining important prey resources and their exploitability under growing land pressure.
7 - The assessment of body composition and other parameters by ultrasound scanning
- Edited by John R. Speakman, University of Aberdeen
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- Book:
- Body Composition Analysis of Animals
- Published online:
- 19 January 2010
- Print publication:
- 02 August 2001, pp 188-210
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Summary
Introduction
Ultrasound has been employed in various technologies. It is a tool for civil and military marine location and navigation (SONAR, Sound Navigation and Ranging), and is also used for quality control in material sciences, and as a non-invasive tool for diagnostic imaging in human and veterinary medicine. Evolution has made use of ultrasonic physical phenomena, and many animals use ultrasound for orientation and communication, e.g. bats, whales, small mammals, some birds.
The physical principle underlying all ultrasound applications, technical and biological, is basically the same: a very high frequency sound is emitted from a source and travels some distance through a medium until it hits a reflector that returns it as an echo to its source. Time differences between sound emission and the returning echo, and the intensity of the echo may be used to obtain information about distance and about the properties of the reflector. It depends on the computational procedure whether the echo information is employed to give local information, navigational cues, or to produce images.
This chapter is about imaging, and we leave ranging and navigation for other discussions. Ultrasound imaging was developed in the 1950s to provide a diagnostic tool in human medicine (Morneburg, 1995). Much progress has been made since the late 1960s, when advanced algorithms and computer technologies allowed for faster data processing and real time imaging. Today, ultrasound imaging is a pivotal diagnostic tool in almost all fields of human medicine, and has gained increasing importance in veterinary medicine and reproductive management (Göritz, 1993; Hildebrandt et al., 1998). However, it is still a rather rare tool in zoological and ecological research.