Physiology

Identifying physiological stress and plasticity

Desert birds routinely experience air temperatures that exceed their normal body temperatures, and under conditions of intense solar radiation may need to defend body temperatures 15-20 °C below operative temperature. Relatively little is known about the upper limits to avian heat tolerance and evaporative cooling capacity. As part of a collaborative project with Blair Wolf (University of New Mexico), we have recently examined the interactions between body temperature, evaporative water loss and metabolic rate at high air temperatures in arid-zone bird communities in the Kalahari Desert. This study is providing novel insights into how evaporative cooling capacity and heat tolerance vary with body mass, and factors such as the importance of respiratory versus cutaneous evaporative heat loss.

We have also investigated intraspecific variation in heat tolerance among populations of White-browed Sparrow-weavers across a 10 °C gradient in maximum summer air temperatures. Sparrow-weavers at a hot desert site showed significantly greater heat tolerance in summer compared to populations at cooler sites, but this difference was not evident in winter. These data provide the first evidence for seasonal acclimatization in avian heat tolerance and evaporative cooling capacity, and raise a number of questions regarding the roles of phenotypic plasticity versus local adaptation as determinants of physiological variation.  A better understanding of the processes affecting birds’ physiological capacities to cope with extreme heat is critical for predicting their responses to higher maximum temperatures and more frequent heat waves, and testing the assumption implicit in climate-envelope models that birds will not be able to persist in future climates hotter than those they presently occupy.

Prof. Andrew McKechnie, Principal Investigator

Respirometry, fieldwork, Andrew McKechnie lab, metabolic, hot birds

Current Projects

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A trait-based approach to assessing the sensitivity and exposure of arid-zone birds to climate change

Dr Stephanie Payne (Post-Doc)

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Completed Projects

2014

2020

Matthew Noakes (Ph.D.)

Thesis: Phenotypic and genotypic sources of variation in the thermal physiology of a passerine bird

Supervisors: Prof. Andrew McKechnie

Barry van Jaarsveld (M.Sc.)

Thesis: Thermoregulatory adaptation to tree cavity microclimates in endotherms living in a hot desert: intra- and interspecific variation

Supervisors: Prof. Andrew McKechnie, Prof. Nigel Bennett 

2019

Andries Janse van Vuuren (B.Sc. Hons)

Thesis: The beak and facial skin as heat radiators in the Southern Ground-Hornbills (Bucorvus leadbeateri)

 

Supervisor: Prof. Andrew McKechnie, Dr. Lucy Kemp

Michelle Bouwer (B.Sc. Hons)

 

Thesis: Non-invasive quantification of physiological stress in southern yellow-billed hornbills (Tockus
leucomelas
): a validation of faecal glucocorticoid metabolite assays

 

Supervisors: Prof. Andrew McKechnie, Prof. André Ganswindt, Celiwe Ngcamphalala

Sekgwari Mpho Malematja (M.Sc.)

Thesis: Phenotypic flexibility of digestion in White-browed Sparrow-Weavers (Plocepasser mahali): limits to digestive flexibility and dietary enzyme modulation

Supervisors: Prof. Andrew McKechnie, Prof. William Karasov

2018

Ryan O'Connor (Ph.D.)

 

Thesis: Chilled birds in hot places: thermal physiology of arid-zone caprimulgids

Supervisors: Prof. Andrew McKechnie, Prof Mark Brigham

Shannon Conradie (M.Sc.)

 

Thesis: Acute and chronic heat stress risk in desert birds under past, present and future climates​

 

Supervisor: Prof. Stephan Woodborne, Prof. Andrew McKechnie

Anne Ankermann (B.Sc. Hons)

Thesis: Global variation of avian metabolic rates and body temperature

 

Supervisor: Prof. Andrew McKechnie

Emma Jepsen (B.Sc. Hons)

 

Thesis: Validation of a non-invasive assay for circulating stress hormones in an Afrotropical arid-zone passerine
bird, the southern pied babbler

 

Supervisors: Prof. Andrew McKechnie, Prof André Ganswindt, Celiwe Ngcamphalala

Monique van Dyk (B.Sc. Hons)

 

Thesis: The effect of humidity on evaporative cooling efficiency in a passerine bird

 

Supervisors: Prof. Andrew McKechnie, Matthew Noakes

2017

Krista Oswald (M.Sc.)

 

Thesis: Seasonal physiological responses in the Cape Rockjumper (Chaetops frenatus): a Fynbos endemic shows limited capacity to cope with temperature extremes

 

Supervisors: Dr Ben SmitDr Alan Lee

Nevanya Lubbe (B.Sc. Hons)

 

Thesis: The energetic significance of communal roosting and insulated roost nests in a small arid-zone bird

 

Supervisors: Prof. Andrew McKechnie, Matthew Noakes

2016

Sekgwari Mpho Malematja (B.Sc. Hons)

 

Thesis: Heat tolerance and evaporative cooling capacity in speckled mousebirds (Colius striatus)

 

Supervisors: Prof. Andrew McKechnie, Matthew Noakes

2015

Matthew Noakes (M.Sc.)


Thesis: Spatial and seasonal variation in thermoregulatory limits in a widespread southern African passerine

 

Supervisors: Prof. Andrew McKechnie, Prof. Blair Wolf

Ben Smit (Ph.D.)

 

Thesis: Taking the heat: integrating behavioural and physiological variables to predict avian responses to climate change in the Kalahari Desert

 

Supervisors: Prof. Andrew McKechnie, Prof. Phil Hockey

 

 

Maxine Whitfield (M.Sc.)

 

Thesis: Evaporative cooling capacity and heat tolerance in Kalahari Desert birds: effects of body mass and phylogeny

 

Supervisors: Prof. Andrew McKechnie, Prof. Blair Wolf

2008

Ben Smit (M.Sc.)

 

Thesis: Patterns of thermoregulation and seasonal metabolic adjustments in small owls in an arid environment

 

Supervisors: Prof. Andrew McKechnie, Prof. Graham Alexander