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The ‘Hot Birds Research Project’ (HBRP) is a large international research programme led from the Fitz, which integrates behavioural and ecophysiological approaches to understand the impact of climate change on birds. The HBRP’s research has historically focused on birds in arid habitats in southern Africa, North America and Australia, but increasingly involves birds in mesic and humid environments – and in the subantarctic.

The year began with a stark reminder of our rapidly heating planet when the world was gripped by images of wildfires razing parts of Los Angeles, destroying or damaging more than 18 000 buildings and forcing over 200 000 people to evacuate. Symptomatic of how a hotter, drier background climate is extending fire seasons into periods not historically associated with high fire risk, the Los Angeles fires underscore the urgency of slowing the pace of climate change. As the impacts of a changing climate on humans, birds and other animals become more apparent, the HBRP continues to document, predict and seek ways to mitigate the effects of hotter conditions on avian diversity in southern Africa and globally. 

Temperature effects on behaviour – habitat, hydration and humidity
The HBRP’s research on behavioural responses to hot weather, and on how trade-offs between heat dissipation and foraging affect birds’ body condition and reproductive performance, continued as a major research theme in 2025. A new addition to the team was Dr Elena Mariotti, who joined the University of Pretoria as a postdoctoral fellow in late May. Elena’s research focuses on drinking behaviour in Kalahari birds and seeks to provide a better understanding of how landscapes of heat and landscapes of fear interact to influence drinking behaviour. In late 2025, she began collecting behavioural data at waterholes within the Kgalagadi Transfrontier Park (KTFP), as well as at water points on a farm near Askham, south of the park. The density of predators such as goshawks and falcons is much higher at waterholes in the KTFP than outside it, and this provides an opportunity to evaluate how perceived risk interacts with temperature to affect drinking behaviour patterns in species that use surface water in the Kalahari. Elena is also evaluating how artificial shade provision at waterholes influences drinking behaviour. This work follows on from several previous HBRP projects addressing the same question but involves testing multiple shade designs.

In 2025, CB MSc student Niels Zwartjes (UCT) also joined the team, analysing long-term data on Sociable Weaver Philetairus socius breeding success in collaboration with the Sociable Weaver Team (page 27). Niels’ project aimed to understand whether sociality could buffer the negative effects of high air temperatures on breeding success in this species, continuing a core theme of the behaviour branch of the HBRP. The ‘social buffering hypothesis’ suggests that sharing of workload (e.g. offspring care) between cooperating group members could help social species to cope with environmental harshness and climate change by allowing each individual to allocate more time and energy to self-maintenance behaviours while still providing for adequate care of offspring. The HBRP and our collaborative network have collected data to test this hypothesis since 2016, on Southern Pied Babblers Turdoides bicolor, White-browed Sparrow-Weavers Plocepasser mahali, Southern Ground-Hornbills Bucorvus leadbeateri, and now Sociable Weavers. As was the case in these previous studies, Niels’ analyses suggest that, although larger groups may have higher reproductive output overall, there is no evidence that additional group members can buffer the negative effects of high temperatures.

MSc student Leslie Bayanza is also interested in ecological factors that may buffer climate change impacts. In 2025, she continued her work investigating whether high human presence buffers or exacerbates the impacts of hot weather on the body condition and breeding success of the Upper Campus population of Red-winged Starlings Onychognathus morio at UCT. Further details of Leslie’s work are available in the Global Change and Urban Birds section (page 76). Continuing the urban theme, in 2025 the HBRP collaborated with the urban Crowned Eagle project led by UKZN and the University of Vienna on a pilot study monitoring the behaviour of nestling Crowned Eagles Stephanoaetus coronatus in relation to temperature and humidity conditions at their nest sites in Durban (see page 79).

Carry-over effects and cognition
University of Pretoria MSc student Makgoshi Mogotsi continued her research on cognition in Fork-tailed Drongos Dicrurus adsimilis at the Kuruman River Reserve (KRR) in the southern Kalahari. She assessed cognitive performance in juvenile and adult drongos by testing their ability to solve two behavioural tasks: a problem-solving task requiring object manipulation and an inhibitory control task requiring detouring around transparent barriers. Juveniles, particularly older ones, approached the problem-solving task more quickly and performed it better than adults, achieving a higher proportion of successful trials. In contrast, inhibitory control performance was high across all age groups. These findings provide novel insights into the development of cognition in these unmistakable and charismatic residents of the Kalahari.

Red List species and mitigation interventions
As climate change impacts mount, the HBRP increasingly focuses on the potential to use knowledge of species’ physiology and behaviour to develop conservation tools that buffer birds from increasingly extreme air temperatures. The start of the year saw honours student Anton Schultz based in Aggeneys in the Northern Cape, working on Red Larks Calendulauda burra. Anton’s project involved evaluating whether Red Larks and other species inhabiting sparsely vegetated sand dunes would use artificial shade if it were provided within their territories. He placed a single shade structure, a 750 mm piece of 400 mm diameter irrigation tubing, in each of several territories and observed the birds’ responses. Whereas the Red Larks were initially hesitant to enter the shade structures, Fawn-coloured Larks Calendulauda africanoides quickly took advantage of the shade. By the end of January, Red Larks had begun entering the structures, and a follow-up study will be conducted in early 2026 to determine whether they are making greater use of them now that they have in place for over a year. If successful, this approach may offer a way to reduce the impact of rising temperatures on this threatened desert denizen.

In 2025, we also completed data collection on a long-running (2022–2025) experiment with Southern Yellow-billed Hornbills Tockus leucomelas at KRR. We experimentally assessed whether impacts of hot weather on nestling growth and nest success documented by former HBRP PhD student Dr Tanja van de Ven in 2020 could be mitigated by providing thermally buffered nest boxes. Final results suggest that nests in insulated boxes are more likely to succeed than those in uninsulated boxes, and nestlings in insulated boxes weigh more than those in uninsulated boxes throughout the nestling period. The negative effects of high temperatures are not completely removed by box insulation, however: nestlings in insulated boxes lose ~4 g per 1 °C increase in temperature, while those in uninsulated boxes lose three times as much: ~12 g per 1 °C. This probably reflects reduced provisioning rates by their parents during hot weather. We have now rolled out insulation to all nest boxes in this study population, and new nest boxes designed by the Southern Ground-Hornbill Project (page 59) also now have double-walled insulation. 

Wesley Gush’s PhD research on Secretarybirds Sagittarius serpentarius progressed well during 2025. A highlight of the year was when Wesley, assisted by Bianca Coulson, Dr Marc Freeman and Prof. Andrew McKechnie, worked with three captive Secretarybirds at the Dullstroom Bird of Prey Centre in Mpumalanga to obtain the first data on the species’ thermal physiology. This work revealed that the reasons Secretarybirds can inhabit even the hottest regions include a low rate of metabolic heat production for their size, their capacity to efficiently dissipate heat through evaporation, and an unexpectedly flexible body temperature. The data collected will facilitate more accurate modelling of how rising temperatures are likely to affect the species across its range, as well as provide new insights into body temperature regulation in large raptors generally.

Finally, 2024/25 research assistant Vanessa Stephen on subantarctic Marion Island was relieved by new assistant Avumile Bawuli in April 2025. Avumile spent the remainder of 2025 on Marion Island, collecting data on thermoregulatory behaviours, ecophysiology, and landscape and microsite temperatures for surface-nesting seabirds (see page 63).

Thermal physiology 
Thermal physiology continued to be a core focus area for HBRP research in 2025. PhD student Bianca Coulson and postdoctoral fellow Marc Freeman continued their research on birds in the Afromontane forests of the Magoebaskloof region in Limpopo. Bianca’s PhD focuses on how birds’ thermal physiology and ability to tolerate hot weather vary between species occupying different parts of thermal landscapes, for instance the sun-exposed forest canopy compared to the cooler, more shaded conditions on the forest floor. She is comparing such species’ physiological responses to temperatures to test the hypothesis that vertical temperature gradients within forests have driven the evolution of adaptive variation in avian thermal physiology. Data collection for this aspect of her PhD was completed in October 2025, and Bianca will be presenting her results at several conferences in 2026.

After wrapping up data collection in the cool, misty Magoebaskloof forests, Bianca and Marc moved their research to the blazingly hot Limpopo Valley. The last two months of 2025 saw them based near Tshipise, with a shift in their focus to species in mopane woodland and other habitats in one of the hottest parts of South Africa. Mopane woodland, which is widespread in northeastern SA, is of particular interest to members of the HBRP because the leaves of mopane trees Colophospermum mopane are oriented vertically and provide very little shade. Birds in this habitat therefore probably contend with higher solar heat loads than species in other woodland types, and one of Bianca’s PhD chapters evaluates how birds in mopane cope with this thermoregulatory challenge. By the end of the year, Bianca and Marc had collected data from approximately 25 species in the area. In December 2025, they were joined by three new members of the HBRP team – Grace Ross, Liam du Toit and Paul Erasmus – who collected data for honours projects they will be completing in 2026.

Three papers exploring how high humidity affects thermoregulation in the heat were published in 2025. Former MSc student Nazley Liddle led a paper in Biology Letters in which we examined how high humidity affects the ability of Blue Waxbills Uraeginthus angolensis to maintain body temperatures within safe limits during extremely hot conditions. These waxbills have been a priority species for the HBRP ever since South Africa’s first documented heat-related mass mortality event involving wild birds in late 2020, when this species represented approximately 50% of the victims. Another humidity-focused paper emanated from Bianca Coulson’s MSc research on Trumpeter Hornbills Bycanistes bucinator. Published in Conservation Physiology, this study modelled the hornbills’ current and future exposure to combinations of temperature and humidity exceeding the maximum wet-bulb temperature the species can tolerate. The third humidity paper reported Marc Freeman’s research on Red-billed Queleas Quelea quelea, a species that shows the most extreme capacity to increase body temperature above resting levels reported in any bird to date. The second half of the year also saw Marc and Andrew McKechnie collaborating with Dr Andreas Nord of Lund University in Sweden on a paper synthesising current knowledge on physiological constraints on climate change adaptation in birds.

Modelling climate change impacts
The biophysical modelling expertise Dr Shannon Conradie (Senior Lecturer, Wits University) has brought to the HBRP over the last decade continued to provide novel methods for understanding how birds operate in thermal environments and how rising temperatures will affect their water and energy balance. The year saw the publication of two papers based on biophysical modelling approaches. The first, emanating from the MSc project of former HBRP student Lara Strydom, involved mapping thermal landscapes in southern Kruger National Park. By linking biophysical models of thermal conditions within tree canopies to high-resolution maps of tree structure, Lara, Shannon and their co-authors generated highly detailed models of the cool, shaded refugia provided by trees in a study plot between Skukuza and Lower Sabie. The model predicted that, at present, > 95% of trees taller than 2 m provide conditions cool enough for songbirds such as Dark-capped Bulbuls Pycnonotus tricolor to survive extremely hot days. Under conditions predicted for the end of century, however, this falls to < 5%. The sobering results of this study underscore the need for vegetation management in protected areas with the aim of maximizing cool refugia for birds and other animals in coming decades.

Shannon and her co-authors also published a paper in Ecography on how best to combine biophysical models with behavioural data to generate accurate, species-specific predictions of responses to climate change. By integrating species-specific physiology, microsite use, and continuous behavioural observations, the study revealed that three Kalahari bird species are more vulnerable to lethal hyperthermia than dehydration under climate change, contrary to previous assessments. Southern Yellow-billed Hornbills, Southern Pied Babblers and Southern Fiscals Lanius collaris are predicted to experience substantial increases in the number of days with hyperthermia risk by 2100, highlighting the critical importance of incorporating behaviour and microsite selection when predicting climate-driven thermal vulnerability.

Finally, MSc student Martiné van den Berg completed her work on a project validating biophysical models for thermal physiology and microclimates of Fynbos birds, with a view to predicting future physiological costs under changing temperatures and fire regimes in the Cape Floristic Region. Martiné will submit her thesis for examination in early 2026.

Climate change vulnerability: assessing the assessments
High-level conservation decision-making under climate change requires an understanding of which species and ecosystems are most vulnerable. Several methods exist for predicting this, but one of the most popular for assessing relative vulnerability of suites of species at once is the ‘trait-based climate change vulnerability assessment’ (tb-CCVA), which assesses known traits of species (usually derived from the literature or expert opinion) to score likely climate sensitivity, then estimates predicted exposure from climate change projection models. Together, high sensitivity and high exposure equal high vulnerability. Trait-based CCVAs are rapid and cost effective but fraught with subjectivity due to the need for decisions to be made about which traits to include, how to score and weight them, and what to do when trait data are missing. In 2023, HBRP postdoc Dr Stephanie Payne completed and published a tb-CCVA for > 200 species of Southern African arid-zone birds. She included behavioural and physiological traits that are normally left out and tried 16 different combinations of methods of weighting traits and dealing with missing data, producing 16 different possible climate change vulnerability rankings for these species. In 2025, Dr Bukola Azaki joined the HBRP as a postdoc on a project aiming to validate Stephanie’s tb-CCVA and assess which of the 16 different rankings best reflected true vulnerability. 

Bukola used historical weather datasets to assess the actual exposure of each species to climate change over the last 20 years. She combined this exposure with Stephanie’s sensitivity scores to assess which species should have been most vulnerable to climate-change-related decline during the SABAP2 period. Bukola then compared these predicted vulnerability rankings with population trends estimated from the SABAP2 data (using the method developed by Fitz RA Dr Alan Lee at BirdLife South Africa for the Red Data Book of Birds of South Africa, Lesotho and Eswatini 2025). She found that Stephanie’s tb-CCVA successfully predicted species’ relative vulnerabilities to climate change in 12 of the 16 different rankings. Surprisingly, the four that performed least well were those which assumed a ‘high sensitivity’ score for traits for which data were missing for any given species (i.e. that applied the ‘precautionary principle’). This suggests tb-CCVAs can be successful, so long as we are not pessimistic about missing data. Bukola is now preparing her findings for submission to Biological Conservation.
 

Highlights

  • The HBRP published eight papers in international peer-reviewed journals in 2025, with one more in press at year-end.
  • Andrew McKechnie received an A-rating from the National Research Foundation.
  • The HBRP held a highly successful biennial research workshop at Thornybush Game Reserve in Mpumalanga.
  • Marc Freeman and Andrew McKechnie both spent several weeks at the University of New England in Armidale, Australia, working with former HBRP postdoc Dr Zenon Czenze and his students.
  • CB MSc student Obakeng Pule graduated from the University of Cape Town with distinction for his dissertation on the Southern Yellow-billed Hornbill nestbox project.
  • PhD student Ben Murphy’s thesis on Fork-tailed Drongos Dicrurus adsimilis ‘Taking the heat: how do parent birds mitigate costs of breeding at high temperatures?’ was accepted with only minor revisions, and he will graduate in early 2026.
     

Key co-supporters
NRF SARChi Chair in Conservation Physiology; UCT URC; U. Pretoria; NRF Thuthuka Grant; Francois van der Merwe; John Solomon; WWF USA; Rufford Foundation; VC Future Leaders Programme, UCT; Associated Private Nature Reserves.

Research team 2025
Team leaders and collaborators:
Prof. Andrew McKechnie (U. Pretoria / SANBI)
A/Prof. Susie Cunningham (FIAO, UCT)
Dr Alan Lee (BLSA / FIAO, UCT)
Prof. Ben Smit (Rhodes U.)
Dr Melissa Whitecross (Conservation Alpha, Wits)
Dr Christiaan Brink (FIAO, UCT)
Dr Blair Wolf (U. New Mexico)
A/Prof. Amanda Ridley (U. Western Australia)
Dr Tom Flower (FIAO, UCT / Capilano U.)
Dr Izak Smit (SANParks)
Dr Rita Covas (U. Porto / FIAO, UCT)
Dr Shannon Conradie (Wits)
Dr Celiwe Ngcamphalala (UCT)
Dr Chima Nwaogu (FIAO, UCT)
Dr Bukola Azaki (FIAO, UCT)
Dr Kyle-Mark Middleton (FIAO, UCT),
Dr Marc Freeman (U. Pretoria)
Dr Lisa Nupen (U. Pretoria / SANCCOB)
Dr Elena Mariotti (U. Pretoria)
Dr Amanda Bourne (Australian Wildlife Conservancy)

Students:
Carrie Hickman (PhD, UCT); Benjamin Murphy (PhD, UCT); Bianca Coulson (PhD, Pretoria); Wesley Gush (PhD, Pretoria); Leslie Bayanza (MSc, UCT); Martiné van den Berg (MSc, UCT); Makgoshi Mogotsi (MSc, Pretoria); Jochen Voges (MSc, Pretoria); Obakeng Pule (CB MSc, UCT); Niels Zwartjes (CB MSc, UCT); Caitlin Read (MSc, Pretoria), Anton Schultz (BSc Hons, Pretoria).

Research Assistants:
Bianca Koste, Alex Gumede, Samantha Murphy, Vanessa Stephen, Whitney Fourie, Avumile Bawuli.