Influence of Ranging Behavior and Vegetation Quality on Stress Hormone Levels of African Elephants at Mpala Ranch, Laikipia County, Ke
Heterogeneous landscapes like those characteristic of Laikipia County, Kenya, consist of a mosaic of land-use types, which exert differential physiological stress on elephants that occupy and traverse them. Previous studies have showed elephants to be more stressed outside protected areas, however, little is known of whether ranging behavior and their persistence in private ranchlands offers a better alternative to communal ranchlands where lethal methods are used to control human-elephant conflicts. This study was therefore designed to determine: i) how stress hormone concentrations between resident and migrant elephant families that are found within Mpala Ranch vary; ii) the relationship between stress hormone concentrations and the sampling location within Mpala Ranch; and iii) determine whether a change in Normalized Difference Vegetation Index influences stress hormone concentrations in elephants at Mpala Ranch. Existing catalog recognition files for monitoring elephant families prepared during the period 2009 to 2014 was used to identify the resident and migrant families using their ears and tusks idiosyncrasies while a cross-sectional survey method was used to obtain data from the study area. Whenever a family herd or individual bull(s) of known elephant was encountered, their behavioral response to the observer was recorded and the vehicle’s engine was turned off. The individuals were then monitored until defecation occurred. Dung samples were collected from successfully identified individuals within thirty minutes after elephants had dispersed from the area and immediately placed in a cooler box with ice packs until freezing at the laboratory. Their behavioral response to vehicle presence as a proxy for past negative human elephant interaction also was recorded. Sentinel 2 satellite images for the period April 2019 to August 2019 were processed using Google Earth Engine and exported to R programming for analysis of vegetation greenness. Stress hormones were analyzed using enzyme immunoassay validated for African elephants. The concentrations of fecal glucocorticoid metabolite was calculated from optical densities from Multiskan plate reader at 450 nm using sigmoidal dose response. Contrary to what was hypothesized, resident elephants had a higher stress response compared to the migrant elephants. Resident elephants had higher physiological stress response compared to the migrant elephants overall but further differences were found to be related to region. Migrant elephants had lower physiological stress response than resident elephants in the northern part of Mpala but no differences were found in the southern part of Mpala. Additionally, individuals that were terrified and running away had a higher physiological stress response compared to other behavioral reactions. Similarly, a higher stress response was observed during the dry season compared to the wet season. Findings from this study therefore reveal differing physiological and behavioral response to environmental and anthropogenic factors between resident and migrant elephants at Mpala ranch. Result of this study will benefit Laikipia Ranch Owners Association and communal ranches in identifying land use types that are compatible with conservation which will be critical in establishing wildlife corridors and connectivity for wildlife to minimize human-wildlife conflict and reduce overall physiological stress response in elephants that are traversing the area.