Abstract
BackgroundThis 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.ResultsWe 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.ConclusionsA 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.
Highlights
This study investigates the ranging behavior of elephants in relation to precipitation-driven dynamics of vegetation
We investigate how well models driven solely by normalized difference vegetation index time series (NDVI) can predict the movement of the elephants, their seasonal home ranges, and the sharing of home ranges in the landscape at biweekly timescales
To estimate how much of their home range animals shared with other elephants, we relied on the Rainfall-vegetation dynamics inferred from NDVI At 32 day intervals, NDVI increases with rainfall accumulated in the previous month (r = 0.53, p < 0.01, n = 43), but the NDVI reflects the ability of plants and soils to store water and responds to short as well longer term rainfall patterns: a Random Forest model accurately predicted NDVI values at 16 day intervals (n = 86), based on the NDVI value 16 days earlier and the rainfall accumulated in the past week and month
Summary
This study investigates the ranging behavior of elephants in relation to precipitation-driven dynamics of vegetation. Elephants play an important role in East-African ecosystems, both ecologically and as a source of revenue via tourism [6]. Their activity can dramatically affect vegetation composition and structure, in particular of woody species [7,8,9,10]. The study of elephants’ migration has considered home range size [17,18,19,20,21], elephants’ travelling speed [22,23] and has described differences and movement between elephants’ seasonal habitats [24,25]. Murwira and Skidmore [26] showed that vegetation heterogeneity and patch size, estimated using remote sensing, are good predictors of elephant presence in savannah landscapes
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