Hot Birds Research Project

Rising global temperatures resulting from human-caused climate change are likely to have significant impacts on organisms. The extent to which organisms can adjust their behaviour to mitigate fitness costs associated with hot temperatures remains unclear, especially in extreme environments. 

There is growing evidence across a number of taxa in arid zones that increases in temperature under climate change can impose extra thermoregulatory costs that constrain offspring care and result in missed opportunity costs and declining reproductive success. We aim to explore whether organisms adjust their behavior to mitigate thermoregulatory costs in response to changing climatic conditions and how they manage the potential missed-opportunity costs of these behavioural changes, using fork-tailed drongos (Dicurus adsimilis), a southern African bird common in the arid Kalahari desert. 

Preliminary research to date (Olinger 2017; Olinger et al., in prep) has shown that drongos reduce foraging and provisioning when it is hot and increase thermoregulatory behaviour, despite ongoing food availability, implying that they suffer increased provisioning costs at high temperatures. Furthermore, parents consume a higher proportion of foraged prey at hot temperatures. Examination of offspring growth suggests that mass gain is reduced by high temperatures during mid-development, yet mass at fledging is unaffected. 

These findings illustrate a possible thermoregulatory constraint on offspring care at high temperatures and potential for a trade-off between parent and offspring fitness in drongos, yet the maintenance of body mass in fledglings regardless of air temperatures experienced during development is puzzling and suggests that drongos may have a way to compensate for missed opportunity costs of thermoregulation during hot periods and avoid passing costs onto their nestlings. 

With this project, we wish to investigate in further detail foraging, parental care and nest outcomes by drongos in the face of challenging thermal conditions. This will enable us to better understand how drongos, and birds more generally, might maintain constant fledging mass despite high air temperatures, whether there are compensatory behaviours by parents (e.g. changes in shading behaviour at the nest or timing of foraging and provisioning into pre-dawn and post-dusk hours) and if these carry their own costs for parental or offspring fitness, or overall nest success.