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Hot Birds - Climate change and desert birds

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The ‘Hot Birds Research Project’ (HBRP) is a research programme that integrates behavioural and physiological approaches to predict the impact of climate change on arid-zone birds in southern Africa and globally. The HBRP’s research focuses mainly on birds in arid habitats in southern Africa, but also involves work in North America and Australia, and increasingly extends to habitats other than deserts.

In 2020, South Africa passed a grim milestone in terms of the impacts of global heating on birds. For the first time, on 8 November 2020, the country recorded a mass mortality event of birds and bats linked to an extreme heatwave in northern KwaZulu-Natal. Air temperatures on this day exceeded 40°C by mid-morning and rose to between 43 and 45°C by mid-afternoon. Staff at the Phongolo Nature Reserve reported large numbers of dead and dying birds, mostly passerines, around the reserve headquarters. Wahlberg’s fruit bats Epomophorus wahlbergi were found dead in Pongola and Hluhluwe.

While devastating events like this are likely to become more common as climate warming progresses, HBRP work over the last 11 years has highlighted the importance of impacts that occur at cooler temperatures. In 2019, Shannon Conradie published a paper showing that the sublethal, chronic costs of behavioural changes for thermoregulation are likely to cause greater impacts on birds across southern Africa than acute mortality events. The responses of birds to hot temperatures below lethal limits, such as shade-seeking and reduced activity, limit the opportunity to forage, with important impacts on body mass and breeding success. In 2020, the HBRP expanded into Nambia, with MSc student Jess Roberts investigating thermal landscape use, opportunity costs and consequences in Dune Larks Calendulauda erythroclamys. In addition, Susie Cunningham, Rowan Martin and Janet Gardner published a review paper in the prestigious journal Frontiers in Ecology and the Environment on the likely impacts of behavioural thermoregulation on fitness and population demographics in birds and mammals, and the potential of behavioural changes under high temperatures to have knock-on effects for ecosystem functioning.

Climate change impacts on breeding success

Krista Oswald was awarded her PhD at Rhodes University on Cape Rockjumpers Chaetops frenatus in the Fynbos mountains. She concluded that Rockjumper populations are likely to see strong negative impacts from climate change, predominantly through reduced breeding success. Warm temperatures increase nest predation by snakes, although nests in recently burned habitat have higher success. Krista also found Rockjumpers have little genetic diversity, and so may show limited adaptive capacity to rapid environmental changes. Krista published one paper in Ibis in 2020, and is preparing other manuscripts for publication.

Carrie Hickman began her MSc on the impacts of temperature on parental provisioning, nestling growth and telomere dynamics in Southern Ground-Hornbills, co-supervised by Susie Cunningham and Rita Covas.

Sociality and climate change

PhD student Amanda Bourne graduated in December 2020 with a thesis on the potential for helpers to buffer the fitness costs and consequences of exposure to high temperatures and drought in Southern Pied Babblers Turdoides bicolor. She assessed the factors that drive the evolution and maintenance of cooperation in harsh environments, while also providing insight into the ability of group living species to cope with climate change. Amanda found that both reproduction and survival are compromised during hot, dry weather, suggesting that Pied Babblers may struggle to persist as climate change advances. Although babbler groups with more helpers often produce more surviving young, larger group sizes do not appear to moderate the effects of high temperatures and drought, suggesting that these conditions act on individuals via physiological tolerance limits and resource constraints. Amanda’s examiners were highly impressed with her work. She published three papers from her thesis in 2020, in Ecology Letters, Proceedings of the Royal Society B, and Frontiers in Ecology and Evolution, and currently has two further papers under review.

Former HBRP post-doc Margaux Rat published her data on the impacts of high and variable environmental temperatures on Sociable Weaver Philetairus socius social networks in Oikos, showing that increases in extreme temperatures and temperature variability under climate change may affect the social cohesion of colonies of this iconic Kalahari bird, with implications for individual fitness and colony function.

Non-invasive techniques

Handling stress may obscure the very signatures of environmental stress that the HBRP team is interested in, so finding less invasive ways to measure physiology in wild birds is an important research priority. The HBRP team have developed and tested non-invasive methods for measuring metabolic rates and water turnover using oral dosing with doubly-labelled water followed by faecal sampling instead of the more traditional injecting and blood sampling. Proof of this concept was published in 2019 by Amanda Bourne in Functional Ecology. In 2020, Amanda submitted a second study using this method to show that Pied Babbler nest failure during hot weather was linked to dehydration in incubating birds. In early 2020 Amanda went to Australia to use this methodology on Jacky Winters Microeca fascinans with HBRP collaborator Janet Gardner at the Australian National University (ANU). She was caught there by the pandemic and has now settled permanently in Australia. Sadly, Janet’s funding was cut by COVID-induced austerity measures, so this study will not be completed as planned.

Another part of this research, led by PhD student Celiwe Ngcamphalala, focuses on quantifying glucocorticoid (“stress hormone”) concentrations. This involves validating appropriate enzyme immunoassays to quantify faecal glucocorticoid metabolites in four bird species. This analysis allows for non-invasive sampling by removing the need to catch and bleed birds to quantify stress responses. Using the assays validated by former HBRP Honours student Emma Jepsen, Celiwe and BTech student Lesedi Moagi have shown that stress responses to maximum daily temperatures differ between captive and free-ranging Pied Babblers, which reinforces the importance of these non-invasive sampling techniques. Lesedi Moagi completed this work in 2020 and is preparing a paper for publication. Honours student Michelle Bouwer validated this technique for Southern Yellow-Billed Hornbills Tockus leucomelas in 2020, and submitted her findings for publication, paving the way for Nick Pattinson to use faecal samples to examine stress glucocorticoid responses in breeding hornbills as part of his PhD.

Body temperature, heat tolerance, and variation in evaporative cooling capacity

PhD student Marc Freeman, together with post-doc Zenon Czenze, continued to investigate evaporative cooling capacity in multiple bird species across a gradient of maximum air temperatures within three climatically-contrasting biomes: desert, montane grassland, and subtropical thicket/forests. A key variable in Marc’s research is humidity: even though maximum air temperatures in coastal forests are lower than those in deserts, high humidity is likely to limit the capacity of birds to use evaporative cooling. Marc and Zenon worked in the Richards Bay area throughout the beginning of 2020. As part of this work, they tested the temperature and heat tolerances of Red-billed Queleas Quelea quelea. Remarkably, they discovered that queleas could tolerate body temperatures up to 49°C, far in excess of those generally considered lethal for birds, and setting a new record for hyperthermia tolerance. These data were published in Scientific Reports. In addition, Zenon and his co-authors published a paper on the co-evolution of thermal physiology and movement ecology among arid-zone passerines in Functional Ecology.

Climate change past, present and future

Shannon Conradie continued work towards her PhD on developing novel modelling approaches integrating the thermal landscape, heat and water fluxes and behavioural decisions and trade-offs for desert birds. Ultimately, her study will enable us to construct detailed models of survival and reproduction in birds, reducing the need for detailed species-specific empirical datasets to predict avian responses to climate change. In 2020, Shannon worked on her biophysical modelling approaches and dynamic state variable models, refining these modelling techniques and validating model outputs with empirical data for Southern Yellow-billed Hornbills and Pied Babblers collected in the Kalahari.

Highlights:

  • The HBRP published 21 papers in international peer-reviewed journals in 2020.
  • Members of the Pretoria branch of the HBRP were involved in papers reporting new upper and lower records to avian body temperature: 49.1°C from a Red-billed Quelea and 3.3°C in a hummingbird from the Peruvian Andes.
  • Amanda Bourne, Matt Noakes and Krista Oswald all graduated with PhDs. Matt and Amanda each had four papers published from their PhDs prior to graduation, and Krista had three.
  • Amanda Bourne was awarded the Purcell Prize for the best UCT PhD thesis on a topic in Zoology.
  • Barry van Jaarsveld received his MSc cum laude in September and Matthew Orolowitz graduated with his CB MSc in December.
  • Matt Noakes left to take up a post-doctoral fellowship at Nicolaus Copernicus University in Poland, and Zenon Czenze was appointed as a lecturer at the University of New England, Australia, providing an important new Australian node for future HBRP research.
  • The HBRP mobile physiology lab – a converted trailer with state-of-the-art thermal physiology equipment – was completed and will be deployed in Namaqualand in early 2021.
  • Susie Cunningham was awarded a UCT College of Fellows Young Researcher Award, and Andrew McKechnie was elected an Honorary Fellow of the American Ornithological Society. 
  • HBRP team members presented at online conferences included the BOUSci 2020 Climate change and birds: solutions to the crisis conference, the United Nations Deserts and Desertification conference and the North American Ornithological Conference.
  • The HBRP became officially affiliated to the IUCN Species Survival Commission, with PIs Andrew McKechnie and Susie Cunningham now serving as members of the IUCN Climate Change Specialist Group.

Key co-supporters

DSI-NRF CoE grant; SARChi Chair in Conservation Physiology, UCT URC, U. Pretoria; NRF Thuthuka Grant; Tygerberg Bird Club.

Research team 2020

Prof. Andrew McKechnie (U. Pretoria / SANBI)
Dr Susie Cunningham (FIAO, UCT)
Dr Janet Gardner (Australian National University)
Dr Alex Gerson (U. Massachusetts)
Dr Alan Lee (FIAO, UCT / SANBI)
Dr Rowan Martin (FIAO, UCT)
Dr Todd McWhorter (U. Adelaide)
Dr Ben Smit (Rhodes)
Dr Zenon Czenze (U. Pretoria)
Dr Blair Wolf (U. New Mexico)
A/Prof. Amanda Ridley (U. Western Australia)
Dr Tom Flower (FIAO, UCT / Capilano University)

Students: Amanda Bourne (PhD, UCT); Shannon Conradie (PhD, Pretoria); Marc Freeman (PhD, Pretoria); Ryno Kemp (PhD, Pretoria); Benjamin Murphy (PhD, UCT); Celiwe Ngcamphalala (PhD, Pretoria); Matthew Noakes (PhD, Pretoria); Krista Oswald (PhD, Rhodes); Nicholas Pattinson (PhD, UCT); Michelle Thompson (PhD, Pretoria); Miqkayla Stofberg (MSc, UCT); Jessica Roberts (MSc, Pretoria); Barry van Jaarsveld (MSc, Pretoria); Otto Makola (MSc, Pretoria); Matthew Orolowitz (CB MSc, UCT); Lesedi Moagi (BTech, TUT); Liamé Marais (Hons, Pretoria); Andries Janse van Vuuren (Hons, Pretoria); Michelle Bouwer (Hons, Pretoria).

Research Assistants:  Lauren Bailey, Jo Balmer, Shelby Bohn, Cameron Brock, Rachel Bucksey, Josephine Bruning, John Diener, Lizzie Diener, Carla Dodd, Gabe Foley, Samantha Fourie, Amy Hunter, Justin Jacobs, Rowan Jordaan, Craig Kenny, Danielle Keys, Noxolo Kinzela, Vuyiseka Mbiko, Sakhile Mkhize, Sophie Monsarrat, Angela Moreras, Ceili Peng, Anna Probert, Keegan Schoeman, Alyssa Stulberg, Jack Thorley, Alex Thouxeau, Amy Tipton, Samantha Wagstaff.