The impact of weather variation on the body condition of cape cobras (Naja nivea) in the Kalahari — implications for climate change

Abstract

Hot and dry weather conditions are known to impact the body condition and the fitness of many organisms. However, this relationship has not been extensively studied in snakes. We examined the impact of variation in rainfall and temperature on body condition for a population of cape cobras (Naja nivea) at Tswalu Kalahari Reserve (Northern Cape Province, South Africa) over a period of five years during which time environmental conditions fluctuated substantially. We measured the mass and body length of 105 cobras, 58 from which we collected repeat measures, and calculated a body condition index (BCI) for each observation. We tested whether BCI was impacted by season, sex, and/or differences from expected mean monthly rainfall (during the preceding four-, 12-, and 24-week periods) and mean daily maximum temperature (during the preceding four-, 12-, and 24-week periods). Secondly, we tested whether BCI measures of cobras during the mating-season (September–November) were different between sexes and impacted by an index of environmental conditions (PC1 of rainfall and temperature) in the preceding summer. For our initial analysis, we found that the best-fitting model included season, sex, the relative amount of rain in the preceding twelve weeks (positive relationship), and the temperature in the preceding twelve weeks (negative relationship). Moreover, the BCI of cobras during the mating season was correlated with environmental conditions during the previous summer, with mating cobras exhibiting lower BCI measures following hot and dry summers. Our study reveals detrimental impacts of hot and dry conditions on cape cobra body condition, including measurable effects on body condition of mate-searching animals, following hot and dry summers. Taken together, we predict that prolonged hot dry periods, or increased frequency of hot dry periods in the future, might have detrimental effects on cape cobra populations in the Kalahari.