Southern Fiscals & the sublethal fitness costs of hot weather
Dr. Susie Cunningham (PI)
Collaborators: Dr. Rowan Martin, Prof. Phil Hockey, Phenias Sadondo
We used Southern Fiscals Lanius collaris as a model species to understand the effects of thermoregulatory trade-offs on foraging behaviour and parental care and the knock-on effects on breeding success: that is, to examine the sub-lethal fitness costs of high air temperatures.
Fiscals lent themselves to this study because they are socially monogamous and territorial, and hunt from conspicuous perches making them easy to find and observe. They also have easy to find and access nests and birds in our study population were very tolerant of human disturbance at the nest.
We colour banded a study population of approximately 30 pairs in the dunefields of Tswalu Kalahari Reserve in South Africa. We followed these birds for two years and recorded the behaviour of breeding males, incubation and brooding patterns, provisioning rates, growth rates of chicks, fledging dates, etc. We also measured environmental temperatures using arrays of black bulbs and weather conditions with an onsite weather station.
We discovered that breeding male fiscals make a trade-off between foraging and thermoregulation in the heat, moving to shaded perches and reducing their foraging success, with knock-on effects for provisioning rates.
Hot weather caused both reduced provisioning rates and direct effects of heat on nestlings, resulting in slower-growing chicks that fledged smaller and later. This has potential consequences for the lifetime fitness of fiscals that experience heat waves while in the nest.
We are still writing up the results of this study and have published three papers to date:
Cunningham, S.J., Kruger, A.C., Nxumalo, M.P. & Hockey, P.A.R. 2013. Identifying biologically meaningful hot-weather events using threshold temperatures that affect life-history. PLoS ONE 8(12): e82492.
Cunningham, S.J., Martin, R.O., Hojem, C.L. & Hockey, P.A.R. 2013. Temperatures in excess of critical thresholds threaten nestling growth and survival in a rapidly-warming arid savanna: a study of common fiscals. PLoS ONE 8 (9): e74613