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Hot Birds - Climate change and desert birds

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The ‘Hot Birds’ project integrates behavioural and physiological approaches to develop predictions of how climate change is affecting birds that inhabit arid habitats in southern Africa and globally. The main focus of the Hot Birds project is bird communities of the Kalahari Desert, but we also work in a range of other non-desert habitats and arid regions of North America and Australia.

Fitness and the importance of behaviour

The UCT branch of the Hot Birds Team focus on understanding the links between temperature, behaviour and fitness. Since 2010, we have shown that many bird species face temperature thresholds/inflection points around mid-30°C, 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, 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). 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 lost foraging opportunities through reductions in activity and their 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 2017, 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. Susie Cunningham travelled to Australia to forge a collaboration with Dr Janet Gardner at the Australian National University to expand this research into the Australian arid zones. Projects with Janet may include studies of the impacts of temperature on foraging and breeding success in species such as Jacky Winter Microeca fascinans and Chirruping Wedgebill Psophodes cristatus, as well as broader-scale comparative studies with ground foraging birds. Janet was awarded an Australian Research Council grant to fund some of these projects. In December 2017 we engaged Nick Pattinson as a field assistant, 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 will register as a PhD student at UCT in 2018, focussing on the physiological mechanisms underlying the correlations between temperature and breeding outcomes documented by PhD student Tanja van de Ven, including aspects of stress and immune physiology, feather quality and carry-over effects. Nick will also try to disentangle the effects of drought and concomitant low food availability from the effects of high air temperatures using a supplementary feeding experiment. Nick has a long history with the Hot Birds project, having completed his honours with Andrew McKechnie at UP and his MSc with Ben Smit at NMU.

The buffering effects of sociality

PhD student Amanda Bourne completed her third summer of fieldwork 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 a 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. 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 measure-ments 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 will also use the 15 year Pied Babbler Research Project database to investigate the long-term and cumulative consequences of high temperatures on survival and reproduction in Southern Pied Babblers, and the possible influence of group size on these impacts.

Societies and climate change

Postdoctoral fellow Margaux Rat continued 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 combines 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: it becomes less dense and breaks down into more separate components. Hence, changes in social network structure appear to be linked to the severity of heat stress experienced by individuals. Climate change models predict an increase in temperature variation, suggesting that social systems may become increasingly vulnerable.

Hot Birds in the southern scrubland biomes

The Hot Birds team made its first foray into the Fynbos biome in 2013, joining forces with Alan Lee and Phoebe Barnard of the Climate Change and Fynbos Birds team, and Nelson Mandela University (NMU) lecturer Ben Smit (formerly a PhD student of the Hot Birds project). Since then, the project has expanded to study the impacts of climate on birds endemic to the three distinct semi-arid scrubland biomes of South Africa; the Fynbos, Nama Karoo and Succulent Karoo. Ben Smit took up a Senior Lecturer position at Rhodes University during 2017.

Krista Oswald registered for a PhD at Rhodes University during 2017 to continue her work on Cape Rockjumpers Chaetops frenatus under the  supervision of Ben Smit, Susie Cunningham and Alan Lee. Krista undertook trips to various parts of the Cape Rockjumper range to gather blood samples for genetic analysis (over 100 individuals in total), with sampling at Cederberg, Langeberg, Kogelberg, Anysberg, Swartberg, Kammanassie, Kouga, and Groot-Winterhoek, as well as a few Drakensberg Rockjumper C. aurantius samples. Krista also completed data collection for one of her PhD chapters on rockjumper behavioural responses to heat. Krista’s long-term monitoring of tagged rockjumpers came to great use in publishing a short note in Ibis on PIT-tag location and risk assessment in small passerines. This paper showed that while abdominal PIT-tagging was probably low risk to larger passerines, such as rockjumpers (~50 g), smaller passerines (<20 g) may be at risk of injury, and inserting PIT-tags under the skin may be a feasible alternative when obtaining body temperature data. Krista also completed a second year of reproductive data collection from rockjumpers, and it is clear that Boomslang Dispholidus typus are a main predator of rockjumper nestlings with only one of 38 chicks fledging from 19 nests in the 2017 season. These snakes are particularly active on warm days, suggesting an unexpected, indirect link between reduced reproductive success and increasing temperatures.

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.

White-browed Sparrow-weavers

The recent completion of the Small Animal Physiological Research Facility (SAPRF) at U. Pretoria was a significant milestone for the Hot Birds research group. 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. PhD student Matt Noakes has colonies of White-browed Sparrow-weavers at this facility from sites along a temperature and aridity gradient across southern Africa. These birds are housed in three different temperature cycle rooms, with daytime temperatures ranging from 30 to 42°C. This acclimation study investigates the flexibility of heat tolerance in sparrow-weavers, and will specifically determine the source of inter-population differences already documented in this species.

Red Larks:

MSc student Ryno Kemp started his study of the vulnerable Red Lark Calendulauda burra in October 2017. His work focuses on understanding the movements and activity patterns of the lark, but also involves characterising their physiological traits in the context of adaptation to arid environments. He plans to measure the metabolic rates, water fluxes and other physiological variables needed to parametrize a mechanistic model in the NicheMapper framework. This cutting-edge approach links the physiology and behaviour of a species to its physical and biotic environment by means of detailed models of energy and water exchanges. 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 began her MSc examining 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 eight years. She has modelled maximum and average temperatures during summer months in southern Africa for the last millennium (850 – 1850 AD) and modern times (1850 – 2014). Preliminary results indicate that during recent years the occurrence of environmental conditions associated with both acute and chronic heat stress risk have increased in both time and space. Birds occurring in these areas are facing trade-offs between thermoregulation and foraging efficiency, dehydration and/or maintaining body condition more frequently than what the modelled data for the last millennium suggests. These results highlight the importance of mitigation strategies for birds exposed to extreme conditions and the conservation of landscapes with thermally buffered microsites used by birds during extremely hot weather.

Digestive flexibility in sparrow-weavers

Mpho Malematja began her MSc research during 2017 investigating phenotypic flexibility of digestive processes in White-browed Sparrow-weavers in response to diets of varying nutritional content. She will also investigate the physiological mechanisms underlying this digestive flexibility, by quantifying modulation of body mass, gut morphology and dietary enzyme activity. She captured and transported 45 sparrow-weavers from the Kalahari Desert to U. Pretoria SAPRF. During May to September2017, she collected data relating to body mass variation in birds maintained on various diets, as well as data on digestive system morphology following acclimation to various diet regimes. This project is co-supervised by Prof. Bill Karasov of the University of Wisconsin-Madison, who spent part of 2017 at U. Pretoria as a Visiting Professor.

Highlights:

  • PhD student Tanja van de Ven graduated with her research on the link between temperature and reproductive outcomes in Southern Yellow-billed Hornbills.
  • CB MSc student Ryan Olinger graduated with his thesis on the effects of temperature on foraging and parental decision-making in Fork-tailed Drongos.
  • Krista Oswald, Nicholas Pattinson and Jerry Mokgatla Molepo graduated with their MSc degrees during 2017 at NMU.
  • PhD student Ryan O’Connor submitted his PhD thesis in late 2017.
  • New PhD student Nick Pattinson registered at UCT under the supervision of Susie Cunningham and Andrew McKechnie.
  • New PhD student Celiwe Ngcamphalala started her project at U. Pretoria on phylogenetic variation in avian stress responses and the validation of non-invasive techniques for monitoring stress hormones in species that have been the focus of our behavioural studies.
  • Andrew McKechnie was awarded a South African Research Chair in Conservation Physiology which secures funding for Hot Birds work for the next 15 years.
  • Post-doc Margaux Rat was invited as a keynote speaker for the Zoological Foundation Week at the University of Uppsala, Sweden.
  • The team published 18 papers in 15 journals: Proceedings of the National Academy of Science, Austral Ecology, Bird Conservation International, Journal of Experimental Biology, Ostrich, African Journal of Ecology, Journal of Avian Biology, Journal for Ornithology, Journal of Biogeography, Journal of Comparative Physiology B, Ibis, Physiology & Behavior, Trends in Ecology & Evolution, and Proceedings of the Royal Society B.

Key co-sponsors

DST-NRF CoE grant; SARChi Chair in Conservation Physiology, UCT URC, U. Pretoria; NRF Thuthuka Grant; NMMU Research Themes Grant.

Research Team

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 (NMMU)
Dr Blair Wolf (U. New Mexico)

Students:  Amanda Bourne (PhD, UCT); Matthew Noakes (PhD, Pretoria); Celiwe Ngcamphalala (PhD, Pretoria), Ryan O’Connor (PhD, Pretoria), Krista Oswald (PhD, Rhodes), Michelle Thompson (PhD, Pretoria), Tanja van de Ven (PhD UCT), Shannon Conradie (MSc, Pretoria), Jerry Molepo (MSc, NMU), Nick Pattinson (MSc, NMU), Ryno Kemp (MSc, Pretoria), Mpho Malematja (MSc, Pretoria), Ryan Olinger (CB MSc, UCT).

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, Ryno Kemp, Craig Kenny, Noxolo Kinzela, Samantha Kirves, Rita Leal, Sello Matjee, Vuyiseka Mbiko, Sakhile Mkhize, Alia Moller, Sophie Monsarrat, Ana Morales Gonzales, Lisa Nupen, Nick Pattinson, Pearl Rivers, Pauline Ruffenach, Iris Seto, Sofia Scheltinga, Maxine Smit, Lauren Stansfield, Alyssa Stulberg, Jack Thorley, Alex Thouxeau, Mervyn Uys. Tanja van de Ven, Olivia Venter, Tim Vink, Natasha Visser, Laura Wade.