Sex differences in giraffe foraging behavior at two spatial scales |
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Authors: | T F Ginnett Montague W Demment |
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Institution: | (1) Department of Agronomy and Range Science, University of California-Davis, Davis, CA 95616, USA, US |
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Abstract: | We test predictions about differences in the foraging behaviors of male and female giraffes (Giraffa camelopardalis tippelskirchi Matchie) that derive from a hypothesis linking sexual size dimorphism to foraging behavior. This body-size hypothesis predicts
that males will exhibit specific behaviors that increase their dry-matter intake rate relative to females. Foraging behavior
was examined at two hierarchical levels corresponding to two spatial and temporal scales, within patches and within habitats.
Patches are defined as individual trees or shrubs and habitats are defined as collections of patches within plant communities.
Males were predicted to increase dry-matter intake rate within patches by taking larger bites, cropping bites more quickly,
chewing less, and chewing faster. Within habitats, males were expected to increase intake rate by increasing the proportion
of foraging time devoted to food ingestion as opposed to inter-patch travel time and vigilance. The predictions were tested
in a free-ranging population of giraffes in Mikumi National Park, Tanzania. Males spent less total time foraging than females
but allocated a greater proportion of their foraging time to forage ingestion as opposed to travel between patches. There
was no sex difference in rumination time but males spent more time in activities other than foraging and rumination, such
as walking. Within patches, males took larger bites than females, but females cropped bites more quickly and chewed faster.
Males had longer per-bite handling times than females but had shorter handling times per gram of intake. Within habitats,
males had longer average patch residence times but there was no significant sex difference in inter-patch travel times. There
was no overall difference between sexes in vigilance while foraging, although there were significant sex by habitat and sex
by season interactions. Although not all the predictions were confirmed, overall the results agree qualitatively with the
body-size hypothesis. Sex-related differences in foraging behavior led to greater estimated intake rates for males at the
within-patch and within-habitat scales.
Received: 20 November 1995 / Accepted: 5 November 1996 |
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Keywords: | Giraffe Herbivore Foraging behavior Ruminant Sexual dimorphism |
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