The ‘Hot Birds Research Project’ (HBRP) is a research programme that integrates behavioural and physiological approaches to predict the impact of climate change on birds in southern Africa and globally. The HBRP’s research has historically focused 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.
September 2022 saw the publication of a critically important analysis of the degree of global warming necessary to trigger dangerous “tipping points”, abrupt and irreversible changes to Earth’s climate that each pose major risks to humanity. These dire scenarios include the collapse of the Greenland Ice Sheet, the dieback of the Amazon rainforest and the abrupt thawing of the boreal permafrost. The message of the paper, authored by researchers from four European countries, was stark: Earth’s climate has now warmed to the extent that several of these tipping points have become possible. The study should have – and under normal conditions would have - made international headlines. Yet it did not, because 30 minutes before the findings were announced to global media, the news broke that Queen Elizabeth II had died.
As we emerged from the COVID-19 pandemic, 2022 proved a successful and productive year for the HBRP. The year saw the completion of several PhD and MSc projects, and the initiation of new projects on species ranging from Karoo Chats Cercomela schlegelii in the arid Tankwa basin to Trumpeter Hornbills Bycanistes bucinator in the humid coastal forests of KwaZulu-Natal.
Climate change impacts on behaviour and breeding success
Nicholas Pattinson submitted his PhD on the impacts of temperature and resource availability on physiology and breeding success in Southern Yellow-billed Hornbills Tockus leucomelas in the Kalahari. Conditions at Nick’s study site varied enormously during his PhD, from drought to extreme rainfall. These large differences in background conditions, together with a supplementary feeding experiment, affected physiological patterns of thermoregulation. Birds with access to more food resources thermo-regulated more precisely. Previous work on Nick’s study population by Dr Tanja van de Ven between2012 and 2015 showed very strong negative effects of high air temperatures on breeding output and female and nestling body condition. Nick trialled a thermally- buffered nestbox design which largely mitigated the impacts of high temperatures on breeding female body condition but did not fully remove impacts on nestlings. For example, nestlings, but not females, deposited higher levels of corticosterone metabolites in growing tail feathers when conditions were hot, suggesting they were under physiological stress. Nestlings also grew more slowly under hot conditions. High temperatures and drought have had large negative impacts on the breeding output of this study population. In 2022 Nick published a paper in Frontiers in Ecology and Evolution in which he analysed breeding effort and success of the hornbills at his study site between 2008 and 2018, documenting a dramatic collapse in breeding success associated with the rapid climate warming in the region. Monitoring work in the 2022/3 breeding season focused on the impacts of nest microclimate on nestling growth and breeding success, with a view to developing applied conservation solutions for this and other cavity-nesting species in the region.
Ben Murphy continued work on his PhD write- up in 2022. Preliminary results suggest Fork- tailed Drongo Dicrurus adsimilis parents mitigate impacts of high temperatures on nestling growth through multiple behaviour adjustments. For example, on hotter days drongos increase foraging and provisioning behaviour during the morning, compensating for declines in these behaviours associated with high temperatures at midday. Reduced foraging effort at midday during hot weather might allow drongos to instead shade nests, buffering nestlings from high solar radiation loads. Unlike other species we have studied, drongos also seem able to avoid foraging opportunity costs associated with shade seeking, with prey capture rates from shaded perches equivalent to those in the sun. Drongos are also able to switch from a rate-maximising to an efficiency-maximising provisioning strategy: bringing fewer but larger loads of prey to the nest at high air temperatures. Behavioural flexibility has been touted as a mechanism underlying the success of many species which cope well with dramatic anthropogenic modification of habitats, e.g. urbanisation. Drongos’ considerable behavioural flexibility associated with thermoregulation and parental care behaviours may similarly be successful in mitigating impacts of hot weather on nestling growth. This provides a novel example of how behavioural flexibility might help some species to cope with changing climates as well as changing habitats.
However, despite their success in mitigating impacts of high air temperature on nestling growth, drongos still face costs associated with climate change in the Kalahari. CB MSc student Bruce Chrispo investigated the impacts of air temperature and rainfall on nest predation rates of Fork-tailed Drongos using a multi-year dataset of drongo nest outcomes at the Kuruman River Reserve. Bruce analysed data from 2016 – 2021 and found a quadratic relationship between air temperature and nest success, with fledging probability increasing up to 35°C mean air temperature during the nestling period and declining thereafter. Cox survival analysis models showed that high air temperatures (> 35°C) were associated with very low survival rates of nests in the early stages of the nesting period. Of all nest failures, 90% were due to predation. This suggests these patterns are largely driven by temperature-related changes in predator behaviour and highlights the importance of considering species interactions when assessing vulnerability of species to climate change.
Also working on species interactions in 2022 was CB MSc student Kim Daniels. Kim studied the potential for mistletoes Plicosepalus kalachariensis to provide thermal refuges for small birds in the southern Kalahari. She discovered that mistletoe clumps were cooler during the heat of the day and had a different humidity profile from their blackthorn Senegalia melifera host shrubs and from non-host blackthorns. Despite this, patterns of use of mistletoes and blackthorn by small birds (including Black-chested Prinias Prinia flavicans and Kalahari Scrub-robins Cercotricha paena) suggested that mistletoes were mostly targeted by birds as a foraging resource rather than a thermal refuge, at least under the conditions Kim encountered during her study period. At the same time, Kim’s co-supervisor Dr Mia Momberg was collecting similar data on interactions between mistletoes and birds at the other side of the country at a site near Hoedspruit. The combined data set, from both the Lowveld and the Kalahari, will provide important new insights into the role of mistletoes as thermal refugia on very hot days.
MSc student Jaimie Whyte completed fieldwork on the impacts of temperature on behavioural thermoregulation, microsite use, and breeding behaviour in White-browed Sparrow-Weavers Plocepasser mahali at Murray Guest Farm. Jaimie’s work follows a long tradition of HBRP physiology research on this species and was designed to add pieces of the puzzle associated with behavioural changes and sub-lethal fitness impacts linked to high temperatures. Despite good rain in the Kalahari during Jaimie’s field season, sparrow-weaver breeding success was poor. This might have been linked to the fact that the early, dry part of the summer season was extremely hot and the birds did not attempt to breed then, followed by difficulties they faced foraging in very thick and high sour grass that appeared after the rain. These interactions between temperature, rainfall and plant responses can affect species’ ecology in complex ways and highlight that in rain-driven systems like the Kalahari, the timing of rainfall is important, as well as the amount. In response to the poor breeding of the birds, Jaimie pivoted her focus to impacts of the interaction between habitat characteristics, social group size and temperature on the birds’ behaviour; and measured thermal landscapes in detail. Jaimie collected a large and detailed behavioural dataset. She discovered that shade availability in sparrow- weaver home ranges at midday can buffer foraging-thermoregulatory trade-offs by reducing the panting rates of birds at high air temperatures. She also showed that the shadiest home ranges significantly buffered evaporative water loss rates calculated for the birds, and that habitat structure may therefore be extremely important for persistence of this and other species under ongoing climate warming. At the time of writing, Jaimie is in the final stages of her thesis write-up.
Moving away from the Kalahari, Nazley Liddle began a MSc in 2022 to examine interactions between temperature and humidity on thermoregulation and behaviour in Blue Waxbills Uraeginthus angolensis in northern Kwa-Zulu Natal. Nazley’s thesis targets Blue Waxbills due to their significant representation in a mass mortality event of birds and bats during a heatwave in the Pongola region in late 2020. Nazley completed physiology data collection on waxbills under dry and humid conditions in the respirometry chamber, showing that waxbill thermal tolerance limits under humid conditions could explain their losses in the 2020 mortality event. Although Blue Waxbill breeding was also poor in 2022, she was able to collect a considerable behaviour dataset on this and sympatric species at her study site in Ukuwela Reserve, KZN. These data will allow her to assess the behavioural vulnerability of waxbills to high temperatures and humidity compared to other species in the region. Preliminary analyses suggest that panting behaviour is less frequent in birds in this humid environment than in the Kalahari, but shade-seeking may be more prevalent; and that significant interactions between temperature and humidity affect thermoregulatory and foraging behaviour in several species.
In 2022, a new MSc student, James Short, began work on the behaviour and physiology of larks and chats in the Tankwa Karoo desert. James is working on comparing physiological heat tolerances of Large-billed Larks Galerida magnirostris between summer and winter in this extreme arid environment; and comparing behavioural changes for thermoregulation between summer and winter in Karoo Chats Emarginata schlegelii. James intends to assess the likely impacts of relaxed cold stress in winter versus exacerbated heat stress in summer under climate warming for these birds of South Africa’s most extreme desert.
Red-list species and practical conservation interventions
The impacts of climate change are becoming ever clearer with extreme events including heatwaves, fire and flooding now a regular occurrence. There is no time left for a ‘wait and see’ approach to conservation in the face of climate change for already-threatened species or those living in already-extreme environments. In 2022, the HBRP continued efforts to engage in research on red-listed species and testing of applied conservation mitigation measures.
Carrie Hickman successfully upgraded her MSc on Southern Ground Hornbills Bucorvus leadbeateri to a PhD in 2022. She continued data collection on the impacts of temperature on behaviour and breeding outcomes in Southern Ground Hornbills. Carrie’s continued data collection confirmed that high temperatures cause birds to display heat dissipation behaviour year-round (even in winter), and that their thermal thresholds for engagement in heat dissipation behaviour in winter are lower than in summer, but shade seeking and foraging thresholds are higher. These changes potentially impact their ability to gain breeding condition following hot winters and may be related to scarcity of shade and food resources in winter. She also showed that winters are warming faster than summers in the lowveld, highlighting an unexpected avenue of vulnerability for birds in this region. Preliminary analyses of data Carrie collected using nest cameras highlights a thermoregulatory cost of provisioning, with panting thresholds lower at the nest than in the field, likely due to metabolic heat load incurred during the provisioning flight. Provisioning may also result in elevated body temperatures because panting is inhibited while birds are carrying food packages. This they do for an extended period of time prior to provisioning, a strange behaviour that may be associated with social signalling in this group living bird. Carrie’s early data suggest temperature effects in some aspects of the growth curves of nestlings, and she is collecting blood samples early and late in the nestling period to assess telomere attrition in relation to environmental conditions.
CB MSc student Michelle Bouwer completed data collection for her project assessing whether climate or land use change is driving changes in the breeding productivity of Blue Cranes Anthropoides paradiseus in the Overberg. Michelle found a near significant negative effect of air temperature on hatching success in this species, but no relationship between hatching success and land-use type, and no difference in hatching success now versus 20 years ago, when this was last assessed in the Overberg Blue Crane population. The most important predictor of hatching success in Blue Cranes was nest attendance behaviour, in turn affected by disturbance – providing important information for farmers wishing to protect Blue Crane nests on their properties. Analyses of citizen science CAR data suggests that Blue Crane population densities in the Overberg are falling. Investigation of threats at different stages of the life cycle (e.g. juvenile and adult survival) are therefore imperative if we are to conserve the cranes in this population stronghold.
CB MSc student Sean Morar completed his study assessing whether providing artificial shade at water points can keep water accessible to the small birds of the Tankwa Karoo on days when ground temperatures can exceed 60℃. Sean showed that adding shade at water points significantly reduces operative temperature at the waters’ edge and increases overall visitation rates by small birds to the water on hot afternoons. However, impacts are species-specific with some birds avoiding shaded waterholes and others selecting them. Therefore roll-out of this climate change mitigation measure needs to be done sensitively to benefit all birds in the landscape. Sean was funded by WWF USA’s Wildlife Adaptation Innovation Fund and was visited in the field by the manager of the programme, Nikhil Advani, and film crew. The video they created about his project can be viewed here.
The HBRP thermal physiology programme remained in top gear during 2022, with work taking place at study sites spanning the driest to the wettest parts of South Africa. A highlight of the year was the publication of a paper emanating from Marc Freeman’s PhD in the high-impact Proceedings of the National Academy of Sciences. The paper reported novel and unexpected variation in the maximum body temperatures of southern African birds, with birds inhabiting humid lowland forest in KwaZulu-Natal having significantly greater hyperthermia tolerance compared to birds from arid regions and cool, montane habitats. Marc also completed data collection for a study testing the hypothesis that humidity has driven the evolution of adaptation in thermal physiology, with his findings confirming that birds from humid habitats tolerate hot, humid conditions much better than birds from dryer habitats. Body temperature has long been considered a nonadaptive constant in birds, with most tests of hypotheses of climate adaptation in thermal physiology focussing on metabolic or evaporative water loss rates. Marc’s work has challenged this paradigm, by providing strong evidence that body temperature has evolved in response to selection arising from thermal environments.
The year also saw physiological data collection at James Short’s study site in the arid Tankwa Karoo and at Nazley Liddle’s site in northern KZN. In addition, Bianca Coulson collected data on relationships between body temperature, evaporative heat loss and metabolic heat production in Trumpeter Hornbills at St Lucia as part of her MSc project, which seeks to understand how air temperature and humidity interact to constrain physiological performance in these large forest frugivores. Bianca’s data reveal that, at humidity levels slightly higher than the hornbills currently experience under natural conditions, their thermoregulatory performance on very hot days declines precipitously, findings that underscore the importance of considering both temperature and humidity when predicting the effects of anticipated future climates. The second part of Bianca’s MSc uses thermal imaging to understand the importance of heat loss across hornbills’ large beaks for thermoregulation. In addition to Trumpeter and Crowned Hornbills in St. Lucia, Bianca was also able to collect data for captive Silvery-cheeked Hornbills Bycanistes brevis and Black-casqued Wattled Hornbills Ceratogymna atrata. These data will provide the basis for an analysis of the role of the beak as a heat radiator among some of Africa’s forest hornbills.
Modelling climate change impacts
Predicting the impacts of rising temperatures and more frequent extreme weather events on birds and other animals requires a detailed under- standing of how birds operate in the thermal landscapes they occupy, and how heat transfer between those landscapes and birds constrains their ability to survive and reproduce. In 2022 Shannon Conradie graduated with her PhD thesis which focused on developing and validating biophysical models of birds’ responses to the heat both in laboratory settings and in the field. Shannon has since taken up a post-doc in Susie Cunningham’s lab where she is developing methods to assess the amount of empirical behaviour data required to ensure model predictions of thermoregulatory costs are accurate under complex field conditions. She is also working on assessing the capacity of biophysical modelling to predict breeding outcomes of bird populations based on remote sensing data of conditions in the field.
The HBRP’s collaboration with SANParks continued in 2022, with University of Pretoria Masters in Environmental Management student Lara Strydom completing her data collection in southern Kruger Park. Although some data collection opportunities were lost on account of an obstreperous buffalo bull that managed to sneak into the exclosure plot that was the study site, Lara was nonetheless able to collect the data she needed to link drone-collected LiDAR data on vegetation structure with biophysical modelling in order to assess the availability of shaded refugia across landscapes in KNP. The project, which was nearing completion at the end of the year, provides a novel approach to understanding the consequences of vegetation management for thermal landscapes experienced by birds, and particularly the cool, shady microsites they rely to escape the heat during extremely hot weather.
- The HBRP published 21 papers in international peer-reviewed journals in 2022.
- The SARChI Chair in Conservation Physiology, held by HBRP co-PI Andrew McKechnie, was renewed for a second 5-year cycle.
- Shannon Conradie graduated with her PhD from the University of Pretoria and accepted a post-doc in Susie Cunningham’s lab at the University of Cape Town. Her PhD research focused developing and validating biophysical models to predict endotherm thermoregulatory responses to the heat.
- Carrie Hickman successfully upgraded her MSc on Southern Ground-hornbills to a PhD.
- Marc Freeman submitted his PhD thesis for examination.
- A paper emanating from Marc Freeman’s PhD was published in Proceedings of the National Academy of Sciences.
- Postdoctoral Fellow Dr Mia Momberg joined the U. Pretoria branch of the HBRP.
DSI-NRF CoE grant; SARChi Chair in Conservation Physiology; UCT URC; U. Pretoria; NRF Thuthuka Grant; Tygerberg Bird Club; WWF USA; Rufford Foundation; VC Future Leaders Programme UCT.
Research team 2022
Prof. Andrew McKechnie (U. Pretoria / SANBI)
A/Prof. 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 Ben Smit (Rhodes)
Dr Zenon Czenze (U. New England)
Dr Blair Wolf (U. New Mexico)
A/Prof. Amanda Ridley (U. Western Australia)
Dr Tom Flower (FIAO, UCT / Capilano University)
Dr Izak Smit (SANParks)
Dr Stephanie Payne (U. Pretoria)
Dr Rita Covas (U. Porto, UCT)
Dr Shannon Conradie (UCT)
Dr Celiwe Ngcamphalala (UCT)
Dr Chima Nwaogu (UCT)
Dr Mia Momberg (U. Pretoria)
Students: Marc Freeman (PhD, Pretoria); Carrie Hickman (PhD, UCT); Ryno Kemp (PhD, Pretoria); Benjamin Murphy (PhD, UCT); Nicholas Pattinson (PhD, UCT); Miqkayla Stofberg (PhD, UCT); Nazley Liddle (MSc, Pretoria); Otto Makola (MSc, Pretoria); James Short (MSc, Pretoria); Jaimie Whyte (MSc, Pretoria); Michelle Bouwer (CB MSc, UCT); Bruce Chrispo (CB MSc; UCT); Kim Daniels (CB MSc, UCT); Sean Morar (CB MSc, UCT); Lara Strydom (M.Environ. Mgmt., Pretoria), Olivia Chalwin-Milton (BSc Hons, Pretoria).
Research Assistants: James Crossley, Samantha Fourie, Stephan Horn, Amy Hunter, Justin Jacobs, Lesedi Moagi, Mbali Mohlala, Samantha Murphy, Lisa Nupen, Miqkayla Stofberg, Ansunel van Rooyen, Jochen Voges.