title: Elephant movement closely tracks precipitation-driven vegetation dynamics in a Kenyan forest-savanna landscape.
abstract: BACKGROUND
  This study investigates the ranging behavior of elephants in relation to precipitation-driven dynamics of vegetation. Movement data were acquired for five bachelors and five female family herds during three years in the Marsabit protected area in Kenya and changes in vegetation were mapped using MODIS normalized difference vegetation index time series (NDVI). In the study area, elevations of 650 to 1100 m.a.s.l experience two growth periods per year, while above 1100 m.a.s.l. growth periods last a year or longer.
  
  
  RESULTS
  We find that elephants respond quickly to changes in forage and water availability, making migrations in response to both large and small rainfall events. The elevational migration of individual elephants closely matched the patterns of greening and senescing of vegetation in their home range. Elephants occupied lower elevations when vegetation activity was high, whereas they retreated to the evergreen forest at higher elevations while vegetation senesced. Elephant home ranges decreased in size, and overlapped less with increasing elevation.
  
  
  CONCLUSIONS
  A recent hypothesis that ungulate migrations in savannas result from countervailing seasonally driven rainfall and fertility gradients is demonstrated, and extended to shorter-distance migrations. In other words, the trade-off between the poor forage quality and accessibility in the forest with its year-round water sources on the one hand and the higher quality forage in the low-elevation scrubland with its seasonal availability of water on the other hand, drives the relatively short migrations (the two main corridors are 20 and 90 km) of the elephants. In addition, increased intra-specific competition appears to influence the animals' habitat use during the dry season indicating that the human encroachment on the forest is affecting the elephant population.
authors.affiliation: The Ohio State University, Department of Civil, Environmental and Geodetic Engineering, 2070 Neil Ave., Columbus, OH 43210 USA.
authors.forename: Gil
authors.initials: G
authors.lastname: Bohrer
authors.affiliation: Woods Hole Research Center, 149 Woods Hole Road, Falmouth, MA 02540-1644 USA.
authors.forename: Pieter Sa
authors.initials: PS
authors.lastname: Beck
authors.affiliation: Kenya Wildlife Service, Meru National Park, P.O. Box 11, Maua, Kenya.
authors.forename: Shadrack M
authors.initials: SM
authors.lastname: Ngene
authors.affiliation: International Institute of Geo-information Science and Earth Observation, Hengelosestraat 99, P.O. Box 6, 7500 AA Enschede, The Netherlands.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Skidmore
authors.affiliation: Save the Elephant Trust, P.O. Box 54667, Nairobi, 00200 Kenya.
authors.forename: Ian
authors.initials: I
authors.lastname: Douglas-Hamilton
keywords: Human-elephant conflict; NDVI; Rainfall; Remote sensing; Seasonality