Mitigating the current biodiversity crisis requires a better understanding of how species will respond to future climate change and human impacts on habitat. Decreased reproductive capability, due to changes in phenology, output, and success, is one of the main indicators of species’ vulnerability. For terrestrial ground-nesting birds, overall reproductive success is often related to nest-site selection (e.g. increased nest concealment), and weather changes (e.g. higher air temperatures alter nest success).
We investigated the reproductive success of Cape Rockjumpers (Chaetops frenatus; “Rockjumpers”), a ground-nesting alpine bird, endemic to the Fynbos biome of South Africa, whose population decline correlates to warmer temperatures. We predicted that breeding success would be positively correlated with increased nest concealment, and negatively correlated with increasing temperature. We collected data over three years, including two full breeding seasons, from 2016 to 2018 (n=5, n=20 and n=43 respectively), which included nest-site selection variables (i.e. vegetative cover, rock cover, time since fire in years), success or failure (whether nest resulted in ≥ fledgling), and cause if nest failed (i.e. predation events, weather). We tested the overall success in relation to nest-site selection variables, and then examined how nest failure (specifically snake predation) was correlated with air temperature.
Results/Conclusions
Nineteen out of 65 nests were successful (2016 n = 3, 2017 n = 4, 2018 n = 12). For nest-site selection, recent fire was the only significant predictor of success (Z1,65 = -2.457, p < 0.05), with probability of success negatively correlated with time since fire. Snake predation, primarily boomslang (Dispholydus typus), was the most common cause of failure (n=17 of 29), increasingly significantly with increasing temperature (Z1, 2027 = 2.010, p < 0.05). Our results suggest: (1) immediate after-effects of fire benefit Rockjumpers, with strong implications for conservation management as many privately-owned areas with large tracts of Fynbos practice active fire suppression; and (2) increasing temperatures increase the risk of snake predation, which may contribute to the observed population decline of Rockjumpers associated with warmer temperatures.
Climate change in South Africa is predicted to cause overall warmer temperatures, and also increases in fire frequency. This may lead to contradictory outcomes for Rockjumper reproductive success, with unknown consequences for the ability of Rockjumpers to maintain recruitment levels under predicted conditions. Our findings illustrate the complexity of species’ response to changing environmental conditions and call for a better consideration of multi-dimensional effect of threats to understand species vulnerability to climate change.