Predicting the Impacts of Climate Change on Desert Birds: the 'Hot Birds Programme
Core research team
Dr Rowan Martin
Dr Ben Smit (NMMU)
Margaux Rat (Joint PostDoctoral Fellow, PFIAO/Pretoria)
Ryan O’Connor (PhD student, University of Pretoria)
Michelle Thompson (PhD student, University of Pretoria)
Tanja van de Ven (PhD student, PFIAO)
Matt Noakes (MSc student, University of Pretoria)
Penny Pistorius (CB MSc student, PFIAO)
Salamatu Abdu (CB MSc student)
Justine Cordingley (CB MSc)
Kate du Plessis (CB MSc)
Gina Louw (CB MSc)
Robyn Milne (CB MSc)
Phenias Sadondo (CB MSc)
Ben Smit (PhD, Pretoria)
Maxine Whitfield (MSc, Pretoria)
Climate change is having profound impacts on biological systems. Desert birds are particularly vulnerable to rising temperatures, since many species inhabit areas characterized by extremely hot weather in summer and water resources that are scarce and highly unpredictable. Catastrophic mortality events among desert bird communities during extreme heat waves have been recorded in the past, particularly in the Australian deserts. Our research into the impacts of climate change on desert birds uses several complementary approaches to model the impacts of increased temperatures on avian behaviour and physiology.
Heat stress in free-ranging birds: integrating physiology and behaviour
A bird's thermoregulatory demands are tightly linked to its energy and water balance and behavioural responses. It is critical to understand the temperature-dependency of physiological and behavioural responses in free-ranging birds to better predict how and when birds might experience dehydration or heat stress during extremely hot events. Most of our research in this area has used free-ranging White-browed Sparrow-Weavers Plocepasser mahali as a model species to answer some of these questions. We are also undertaking a large scale project investigating sensitivity to heat stress in a diverse range of Kalahari species by monitoring heat dissipation patterns in the field under different weather conditions. Our future projects aim to investigate if water and food supplementation can equip free-ranging birds to handle heat waves better when their body condition is increased and the need to forage under hot conditions is reduced.
Evaporative cooling and heat tolerance
During an extreme heat event, birds must avoid lethal body temperatures by offloading heat to the environment - a process which is facilitated by high rates of evaporative water loss (EWL). The efficiency of EWL is affected by the mechanisms utilized by the bird, which in turn are largely determined by evolutionary history. Species that are able to pump out water at high rates, but with a relatively low metabolic cost, are theoretically better equipped to survive heat waves – assuming water is freely available. We aim to explore, under laboratory conditions, the effects of evolutionary history and body mass on maximum EWL rates as well as energetic efficiency of EWL at a range of air temperatures above body temperature, in a diverse suite of bird species. By understanding the physiological capabilities of birds under heat stress, we will be better able to predict the effects of anthropogenic climate change on future avian community structure.
High temperatures and fitness
In order to understand how temperature-related changes in behaviour and physiology of birds are likely to affect population processes, we need to understand the implications of these changes for fitness. ‘Fitness’ contains components of both survival and breeding success and is defined in terms of lifetime reproductive output: the total contribution of an individual’s genes to the next generation. Because of the difficulties of measuring fitness directly, we use various proxies, including body mass changes and aspects of breeding success, to investigate the links between temperature, behavioural changes and fitness. Our aim is to elucidate the effects of high temperature on survival and reproduction, and how these effects are mediated by behavioural changes. For example, we have investigated the effect of high maximum daily temperatures on the foraging behaviour of Southern Pied Babblers Turdoides bicolor, and the implications of this for their ability to maintain body mass: a measure related to both survival and breeding success. We are also looking at how high temperatures affect the growth rates, fledging size and length of the nestling period in Common Fiscals Lanius collaris, both directly and via behavioural changes affecting parental investment in the breeding attempt. These measures relate directly to the breeding success of adults and the survival of offspring. We currently have a PhD project underway looking at how temperature affects decision-making by breeding male Southern Yellow-Billed Hornbills Tockus leucomelas, with implications for parental investment, offspring growth, and nesting success.
The thermal environment animals experience varies dramatically within landscapes in both time and space. Using a combination of behavioural observations and direct measurements of microclimatic conditions we are investigating the consequences of patterns of behaviour in order to understand how thermal landscapes can buffer the effects of climate change. We focus in particular on how different-sized bird species experience the thermal landscape and use a comparative approach to explore the relationship between temperature and behaviour.
For more informatin, visit the Hot Birds website www.hotbirdsproject.com
Cunningham, S.J., Martin, R.O. & Hockey, P.A.R. 2015. Can behaviour buffer the impacts of climate change on an arid-zone bird? Ostrich: Journal of African Ornithology 86(1&2): 119-126.
Martin, R.O., Cunningham, S.J. & Hockey, P.A.R. 2015.Elevated temperatures drive fine-scale patterns of habitat use in a savannah bird community. Ostrich: Journal of African Ornithology 86(1&2): 127-135.
McKechnie, A.E., Noakes, M.J. and Smit, B. (in press) Global patterns of seasonal acclimatization in avian resting metabolic rates. Journal of Ornithology
McKechnie, A.E. 2015. FE Spotlight: Global variation in avian metabolic rates and the slow pace of life of tropical birds [Invited Commentary]. Functional Ecology 29: 297-298.
Milne, R., Cunningham, S.J., Lee, A. & Smit, B. (2015). The role of thermal physiology in recent declines of birds in a biodiversity hotspot. Conservation Physiology doi:10.1093/conphys/cov048.
Whitfield, M.C., Smit, B., McKechnie, A.E. & Wolf, B.O. 2015. Avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern African arid-zone passerines. Journal of Experimental Biology 218: 1705-1714.
Gerson, A.R., Smith, E.K., Smit, B. McKechnie, A.E. and Wolf, B.O. 2014. The impact of humidity on evaporative cooling in small desert birds exposed to high air temperatures. Physiological and Biochemical Zoology 87(6): 782-795.
Jacobs, P.J. and McKechnie, A.E. 2014. Experimental sources of variation in avian energetics: estimated basal metabolic rate decreases with successive measurements. Physiological and Biochemical Zoology 87(5): 762-769.
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: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:e74613.
Smit, B., Harding, C.T., Hockey, P.A.R. & McKechnie A.E. 2013. Adaptive thermoregulation during summer in two populations of an arid-zone passerine. Ecology 94:1142-1154.
Du Plessis, K.L., Martin, R.O., Hockey, P.A.R., Cunningham, S.J. & Ridley, A.R. 2012. The costs of keeping cool in a warming world: implications of high temperatures for foraging, thermoregulation and body condition of an arid-zone bird. Global Change Biology 18:3063-3070.
McKechnie, A.E., Hockey, P.A.R. & Wolf, B.O. 2012. Feeling the heat: Australian landbirds and climate change. Emu 112, i-vii.
McKechnie, A.E. & Wolf, B.O. 2010. Climate change increases the likelihood of catastrophic avian mortality events during extreme heat waves. Biology Letters 6:253-256
E. Oppenheimer & Son allowed this work to take place at Tswalu Kalahari Private Game Reserve, and provided generous logistical support.