title: African vultures don't follow migratory herds: scavenger habitat use is not mediated by prey abundance.
abstract: The ongoing global decline in vulture populations raises major conservation concerns, but little is known about the factors that mediate scavenger habitat use, in particular the importance of abundance of live prey versus prey mortality. We test this using data from the Serengeti-Mara ecosystem in East Africa. The two hypotheses that prey abundance or prey mortality are the main drivers of vulture habitat use provide alternative predictions. If vultures select areas based only on prey abundance, we expect tracked vultures to remain close to herds of migratory wildebeest regardless of season. However, if vultures select areas where mortality rates are greatest then we expect vultures to select the driest regions, where animals are more likely to die of starvation, and to be attracted to migratory wildebeest only during the dry season when wildebeest mortality is greatest. We used data from GSM-GPS transmitters to assess the relationship between three vulture species and migratory wildebeest in the Mara-Serengeti ecosystem. Results indicate that vultures preferentially cluster around migratory herds only during the dry season, when herds experience their highest mortality. Additionally during the wet season, Ruppell's and Lappet-faced vultures select relatively dry areas, based on Normalized Difference Vegetation Index, whereas White-backed vultures preferred wetter areas during the wet season. Differences in habitat use among species may mediate coexistence in this scavenger guild. In general, our results suggest that prey abundance is not the primary driver of avian scavenger habitat use. The apparent reliance of vultures on non-migratory ungulates during the wet season has important conservation implications for vultures in light of on-going declines in non-migratory ungulate species and use of poisons in unprotected areas.
authors.affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America ; Ornithology Section, Department of Zoology, National Museums of Kenya, Nairobi, Kenya.
authors.forename: Corinne J
authors.initials: CJ
authors.lastname: Kendall
authors.affiliation: Ornithology Section, Department of Zoology, National Museums of Kenya, Nairobi, Kenya ; The Peregrine Fund, Boise, Idaho, United States of America.
authors.forename: Munir Z
authors.initials: MZ
authors.lastname: Virani
authors.affiliation: Frankfurt Zoological Society, Arusha, Tanzania.
authors.forename: J Grant C
authors.initials: JG
authors.lastname: Hopcraft
authors.affiliation: Acopian Center for Conservation Learning, Hawk Mountain Sanctuary, Orwigsburg, Pennsylvania, United States of America.
authors.forename: Keith L
authors.initials: KL
authors.lastname: Bildstein
authors.affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America.
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Rubenstein
mesh_terms: D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D001188:Artiodactyla / Q000502:physiology*; D017753:Ecosystem; D046093:Falconiformes / Q000502:physiology*; D007630:Kenya; D016014:Linear Models; D011235:Predatory Behavior / Q000502:physiology*; D018401:Sample Size; D012621:Seasons; D013045:Species Specificity; D014197:Trees