Abstract:
Conservation biologists can use hormone measurements to assess animals’welfare, reproductive state, susceptibility to stressors, as well as energy expenditure. Quantifying hormone concentrations from faecal samples is particularly advantageous
as samples can be collected without disturbing animals’ behaviour. In order for an endocrine marker to be useful for wildlife
managers, we need to understand how extrinsic and intrinsic factors affect hormone concentrations in free-ranging animal
populations. Thyroid hormones are linked to basal metabolic rate and energy expenditure. Previous research demonstrated
that triiodothyronine (T3) can be measured successfully in faecal matter of African elephants, Loxodonta africana. However, to
our knowledge, research into factors affecting changes in elephant T3 levels has only been carried out in captive elephants so
far. Thus, we present the first study of faecal T3 metabolite (mT3) concentrations of a large population of free-ranging African
elephants. Over 15 months, we collected faecal samples from identified (n = 43 samples) and unidentified (n = 145 samples)
individuals in Madikwe Game Reserve, South Africa. We investigated whether vegetative productivity [normalized difference
vegetation index (NDVI)] in interaction with mean monthly temperature, age and sex affected mT3 concentrations. We found
a significant negative interaction effect of NDVI and temperature. Increasing NDVI was related to higher concentrations of
mT3, but increasing temperature was related to a decrease in mT3 concentrations in individually identified and unidentified
elephants. In unidentified individuals, juvenile elephants had significantly higher mT3 concentrations compared to adult
elephants. Faecal T3 can successfully be quantified in samples from free-ranging elephant populations and thus provides
insight into energy expenditure in large herbivores.
