Hot Birds - Climate change and desert birds
The ‘Hot Birds Research Project’ (HBRP) integrates behavioural and physiological approaches to understand and predict the impacts of climate change on arid-zone birds in southern Africa and globally. The main focus of the HBRP is bird communities of the Kalahari Desert, but we also work in other habitats and in arid regions of North America and Australia.
Fitness and the importance of behaviour
The UCT branch of the HBRP Team focuses on understanding the links between temperature, behaviour and fitness. Since 2010, we have shown that many bird species face temperature thresholds/inflection points in the mid-30°C range, above which they experience sublethal fitness costs. These costs include reduced foraging success in Southern Fiscals Lanius collaris, Southern Yellow-billed Hornbills Tockus leucomelas, Southern Pied Babblers Turdoides bicolor, and Fork-tailed Drongos Dicrurus adsimilis, accompanied by inability of adults to maintain body mass (hornbills and pied babblers); declines in nestling provisioning rates (hornbills, fiscals and drongos), growth rates of nestlings, size and quality of fledglings, and fledging success (hornbills and fiscals). New data collected in 2018 by MSc student Ryno Kemp suggests loss of mass at temperatures > 35°C also applies to extreme arid-zone specialists such as Red Larks Calendulauda burra. The underlying mechanism driving these sublethal fitness costs appears to be behavioural trade-offs made by adults to minimise exposure to the physiological costs of high temperatures. These trade-offs result in missed foraging opportunities through reductions in activity and use of shaded locations suboptimal for foraging (fiscals, hornbills, drongos); and/or handicaps on foraging efficiency imposed by the use of respiratory evaporative cooling (babblers and hornbills).
In 2018, the team continued research into the mechanisms underlying these patterns to improve our ability to predict the vulnerability of a wide range of arid-zone species to ongoing climate change. We engaged two new PhD students: Nicholas Pattinson and Benjamin Murphy. Nick worked as a field assistant in the summer of 2017/18 to continue the long-term monitoring of changes in breeding success and ultimately population dynamics of Southern Yellow-billed Hornbills at Kuruman River Reserve. Nick registered in early 2018 andbegan his fieldwork in October focussing on the physiological mechanisms underlying the correlations between temperature and breeding outcomes in hornbills, including aspects of stress and immune physiology, feather quality and carry-over effects. He is also trying to disentangle the effects of drought and concomitant low food availability from the effects of high air temperatures using a supplementary feeding experiment. Nick is supervised by Susie Cunningham and Andrew McKechnie.
Ben Murphy joined the team in mid-2018 and is working with the HBRP in collaboration with the Fork-tailed Drongo Project to investigate how Fork-tailed Drongo parents mitigate the impacts of high temperatures on their own foraging behaviour in order to maintain nestling growth rates (more information on pages 15-16). Ben is supervised by Susie Cunningham and Tom Flower. Andrew McKechnie and Susie Cunningham also recruited a new MSc student, Jessica Roberts, who will investigate trade-offs between foraging and thermoregulation in Dune Larks Calendulauda erythrochlamys in the Namib sand landscapes, starting in 2019.
The buffering effects of sociality
In late 2018, PhD student Amanda Bourne began her final fieldwork season studying the ways in which cooperative social behaviour could buffer the fitness costs of high temperatures. Amanda works with 20 groups of habituated Southern Pied Babblers on the Kuruman River Reserve. The babblers are cooperative breeders with natural variation in group size that makes them an ideal model species to study the effect of cooperation on physiological costs of heat stress and fitness costs of behavioural thermo-regulation. Amanda has validated a non-invasive technique for measuring field metabolic rate using doubly-labelled water with oral dosing and faecal sampling, removing the need to capture and handle study animals. This study was accepted for publication in Functional Ecology at the end of 2018. Data collection in the field using this technique will allow the team to correlate daily energy expenditure with individual time budgets and foraging success in addition to environmental conditions. Preliminary data from measurements of nestling daily growth rates suggest profoundly negative consequences of heat stress on nestling development and survival, regardless of group size. In addition, monitoring of breeding attempts has revealed that ‘hot nests’ are half as likely to hatch as those incubated during cooler periods. Amanda is examining long term data from the Pied Babbler Project in addition to her own data to investigate effects of group size on the recovery of individuals and groups after hot dry periods.
Hot Birds in the southern scrubland biomes
PhD student Krista Oswald, registered at Rhodes University, continued her work on Cape Rockjumpers Chaetops frenatus under the supervision of Ben Smit, Susie Cunningham, Shelley Edwards and Alan Lee. Krista is currently polishing up her chapter on temperature-related changes in rockjumper behaviour and finishing her gene-sequencing to examine meta-population structure. In 2018, Krista also completed her final year of reproductive data collection. Her reproductive data are showing some interesting results, the main being that Boomslang Dispholidus typus are a key predator of rockjumper nestlings, responsible for the majority of 49 nest failures recorded during 2016-2018. These snakes are particularly active on warm days, suggesting an unexpected, indirect link between reduced reproductive success andincreasing temperatures. Krista is also writing up the results of her PhD research for publication.
Thermoregulation in the heat
The Hot Birds team is developing a behavioural index of heat stress in birds. Establishing whether functional links exist between inter- and intraspecific variation in heat dissipation and body temperature regulation was the focus of PhD student Michelle Thompson during 2017. Michelle maintained populations of nine bird species in large outdoor aviaries during the Kalahari summer to examine the interactions between behavioural and physiological thermoregulation. On hot days, most species reduced activity and increased shade-seeking sufficiently to manage heat load without resorting to hyperthermia. Michelle also examined the effect of water availability on thermoregulation in these nine species, with a short-term lack of water causing two passerines (White-browed Sparrow-weavers Plocepasser mahali and Cape Glossy Starlings Lamprotornis nitens) to maintain lower body temperatures on afternoons when water availability was restricted. In contrast, two columbids (Namaqua Oena capensis and Laughing Doves Streptopelia senegalensis) increased body temperature when water was not available. Michelle’s data reveal that Kalahari species vary substantially in the suite of behavioural and physiological strategies they use to thermoregulate.
Societies and climate change
Post-doc Margaux Rat completed her work investigating the impact of climate change on the social structure of group-living Kalahari birds, with a focus on Sociable Weavers Philetairus socius. Margaux’s work combined correlative field observations with experimental laboratory-controlled approaches to examine the impact of variation in temperature on the nature and frequency of social interactions and ultimately the impact on social networks of Sociable Weavers. Results from the field component of the project suggest that when individuals experience extreme and unstable environmental temperatures they interact less with their conspecifics. This is reflected in the cohesiveness of their social network as it becomes less dense and breaks down into more separate components. Margaux is now finalising her manuscripts for publication.
Matt Noakes completed data collection for his PhD on the thermal physiology of sparrow-weavers during 2018, taking advantage of the University of Pretoria’s recently-completed Small Animal Physiological Research Facility (SAPRF) This state-of-the-art climate-controlled facility allows us to explore the plasticity of avian thermoregulatory responses with insights into the capacity of birds for adaptive physiological responses to changing climates at a level previously not possible. Matt is due to submit his PhD in mid-2019. Also during 2018, BSc Hons student Monique van Dyk completed her research into the effects of humidity on evaporative cooling in the sparrow-weavers. After solving the technical issues related to experimentally manipulating humidity in respirometry chambers, Monique was able to demonstrate that increasing humidity made thermoregulation a far more costly exercise, as the birds had to work harder to dissipate heat via panting. A manuscript based on Monique’s data was submitted to Journal of Comparative Physiology B in late 2018.
Another sparrow-weaver project that continued during 2018 was Mpho Malematja’s MSc on their digestive flexibility. In April, Prof. Enrique Caviedes-Vidal travelled from Argentina to Pretoria to help Mpho complete the digestive enzyme assays she needed to test predictions about how the sparrow-weavers adjust their gut physiology in response to changes in diet. Mpho spent most of the year writing up her MSc, which will be submitted in the first few months of 2019.
MSc student Ryno Kemp continued his study of the vulnerable Red Lark Calendulauda burra in 2018. His work mainly focused on the larks’ thermal physiology, and a paper on these findings has been accepted in Journal of Comparative Physiology B. Also during 2018, he habituated larks to the point where he was able to train them to weigh themselves, and collected a large data set on the larks’ behaviour and the thermal landscapes in which they operate. The study will put us in a position to better understand the Red Lark’s habitat requirements and how the species will respond to climate change, thereby providing the basis for developing and implementing more effective conservation management plans.
Climate change past, present and future
Shannon Conradie completed her MSc (which was awarded cum laude) in which she examined heat stress risk in desert birds under past, present and future climates. Shannon’s work uses existing physiological and behavioural data on acute (12 species) and chronic (3 species) heat stress thresholds in southern African desert birds collected by the Hot Birds team over the last nine years. The major finding to emanate from this study is that, for birds in southern African deserts, sub-lethal fitness costs associated with exposure to sustained hot weather pose a far greater threat than mass mortality events during extreme heat waves. This situation contrasts with that in the American southwest, where birds will face a risk of lethal dehydration on upwards of 50 days per year by the end of the century, and the similar scenario for Australia. A manuscript based on Shannon’s MSc has been submitted to Proceedings of the National Academy of Sciences USA. In 2019, Shannon will be registering for a PhD that will expand on the findings of her MSc.
- New PhD students Nick Pattinson and Ben Murphy registered at UCT.
- The HBRP organized and ran a symposium on mechanistic responses of birds to climate change at the International Ornithological Congress in Vancouver in August 2018. The symposium was co-chaired by Susie Cunningham and Janet Gardner.
- Post-doc Dr Zenon Czenze joined the team at the University of Pretoria, and will be pursuing a number of projects related to the thermal physiology of birds and bats in the next few years.
- Andrew McKechnie presented a seminar at the Australian National University in Canberra.
- The team published 14 papers in 8 journals: the Journal of Experimental Biology, Scientific Reports, Physiology and Behaviour, Ostrich, Emu, Journal of Ornithology, Canadian Journal of Zoology, and the Journal of Arid Environments.
DST-NRF CoE grant, SARChi Chair in Conservation Physiology, UCT URC, U. Pretoria, NRF Thuthuka Grant.
Prof. Andrew McKechnie (U. Pretoria)
Dr Susie Cunningham (FIAO, UCT)
Dr Janet Gardner (Australian National University)
Dr Alex Gerson (U. Massachusetts)
Dr Alan Lee (FIAO, UCT and SANBI)
Dr Rowan Martin (FIAO, UCT)
Dr Todd McWhorter (U. Adelaide)
Dr Margaux Rat (FIAO, UCT and U. Pretoria)
Dr Ben Smit (Rhodes)
Dr Blair Wolf (U. New Mexico)
Students: Amanda Bourne (PhD, UCT); Ben Murphy (PhD, UCT); Nick Pattinson (PhD, UCT); Celiwe Ngcamphalala (PhD, Pretoria); Matthew Noakes (PhD, Pretoria); Ryan O’Connor (PhD, Pretoria); Michelle Thompson (PhD, Pretoria); Krista Oswald (PhD, Rhodes); Shannon Conradie (MSc, Pretoria); Ryno Kemp (MSc, Pretoria); Mpho Malematja (MSc, Pretoria); Barry van Jaarsveld (MSc, Pretoria); Emma Jepsen (BSc Hons, Pretoria); Monique van Dyk (BSc Hons, Pretoria).
Research Assistants: Lauren Bailey, Cathy Bester, Shelby Bohn, Cameron Brock, Rachel Bucksey, Josephine Bruning, John Diener, Lizzie Diener, Carla Dodd, Pieter Erasmus, Paige Ezzey, Samantha Fourie, Marc Freeman, Aurora Garcia-Berro Nava, Clerize Kemp, Craig Kenny, Noxolo Kinzela, , Vuyiseka Mbiko, Sakhile Mkhize, Lesedi Moagi, Alia Moller, Sophie Monsarrat, Ana Morales Gonzales, Angela Moreras, Iris Seto, Maxine Smit, Lauren Stansfield, Alyssa Stulberg, Jack Thorley, Alex Thouxeau, Mervyn Uys, Natasha Visser, Laura Wade.