Abstract:

Dry season rainfall and food determine white rhino calf survival in the Ithala Game Reserve, South Africa

Olivier Bonnet, Adrian M Shrader
University of KwaZulu-Natal, Pietermaritzburg, Scottsville, 3209

Since 1999, 51 white rhino calves have been born in the Ithala Game Reserve, South Africa. Of these, 15 have died resulting in a calf mortality of approximately 30%. To explore whether these deaths were the result of density dependence, we used the long-term white rhino database of the reserve. This provided us with the unique opportunity to explore how environmental factors such as climate and home range quality influenced calf survival over the the past 13 years. Each calf died of starvation during the dry season. These individuals were mostly between five and eight months of age. Surprisingly, all individuals less than four months old survived this critical period. This was likely because these individuals obtained their nourishment purely via suckling. In our analysis, we tested calf survival against the variables: calf sex, age of mother, and local white rhino density. In addition, we included the environmental variables: wet and dry season rainfall (as indicators of food availability), and the proportion of woodlands (dry season food) and grazing lawns (wet season food) found within the mothers’ home ranges. Our results indicate that dry season rainfall during the first year of life was the most important factor influencing calf survival. Interestingly, in years where the accumulative dry season rainfall (i.e. May-September) was below 70 mm, calves only had a 40% chance of survival. In contrast, when this rainfall was above 70 mm, calf survival jumped to 96%. The only other variable to affect calf survival was the proportion of woodlands found within a mother’s home range. As the proportion of this key resource increased from 0.20 to >0.50, calf survival jumped from 14% to 75%. Ultimately, our results indicate that density dependence does not influence calf survival, but rather a combination of dry season rainfall and dry season food availability.

Presentation Topic

Dry season rainfall and food determine white rhino calf survival in the Ithala Game Reserve, South Africa

 

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University of KwaZulu-Natal, Pietermaritzburg, Scottsville, 3209

 

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