title: Response of African elephants (Loxodonta africana) to seasonal changes in rainfall.
abstract: The factors that trigger sudden, seasonal movements of elephants are uncertain. We hypothesized that savannah elephant movements at the end of the dry season may be a response to their detection of distant thunderstorms. Nine elephants carrying Global Positioning System (GPS) receivers were tracked over seven years in the extremely dry and rugged region of northwestern Namibia. The transition date from dry to wet season conditions was determined annually from surface- and satellite-derived rainfall. The distance, location, and timing of rain events relative to the elephants were determined using the Tropical Rainfall Measurement Mission (TRMM) satellite precipitation observations. Behavioral Change Point Analysis (BCPA) was applied to four of these seven years demonstrating a response in movement of these elephants to intra- and inter-seasonal occurrences of rainfall. Statistically significant changes in movement were found prior to or near the time of onset of the wet season and before the occurrence of wet episodes within the dry season, although the characteristics of the movement changes are not consistent between elephants and years. Elephants in overlapping ranges, but following separate tracks, exhibited statistically valid non-random near-simultaneous changes in movements when rainfall was occurring more than 100 km from their location. While the environmental trigger that causes these excursions remains uncertain, rain-system generated infrasound, which can travel such distances and be detected by elephants, is a possible trigger for such changes in movement.
authors.affiliation: University of Virginia, Department of Environmental Sciences, Charlottesville, Virginia, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: Garstang
authors.affiliation: University of Virginia, Department of Environmental Sciences, Charlottesville, Virginia, United States of America.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Davis
authors.affiliation: Fowlers Gap Arid Zone Research Station, School of Biological, Earth and Environmental Sciences, University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: Keith
authors.initials: K
authors.lastname: Leggett
authors.affiliation: Texas A&M University, Department of Geography, College Station, Texas, United States of America.
authors.forename: Oliver W
authors.initials: OW
authors.lastname: Frauenfeld
authors.affiliation: Simpson Weather Associates, Inc., Charlottesville, Virginia, United States of America.
authors.forename: Steven
authors.initials: S
authors.lastname: Greco
authors.affiliation: University of Utah, Atmospheric Sciences Department, Salt Lake City, Utah, United States of America.
authors.forename: Edward
authors.initials: E
authors.lastname: Zipser
authors.affiliation: University of Utah, Atmospheric Sciences Department, Salt Lake City, Utah, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: Peterson
mesh_terms: D000818:Animals; D017753:Ecosystem; D004606:Elephants / Q000502:physiology*; D004777:Environment; D040362:Geographic Information Systems; D009276:Namibia; D011891:Rain; D012621:Seasons