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Hot Birds - Climate change and desert birds

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 southern Kalahari Desert, but we also work in the arid regions of North America and Australia.

Fitness and the importance of behaviour

Ongoing research by Susie Cunningham and PhD student Tanja van de Ven has shown that many bird species face temperature thresholds, inflection points above which they experience sublethal fitness costs. These temperatures normally fall around mid-30°C, with associated costs including reduced foraging success (recorded in Southern Fiscals Lanius collaris, Southern Yellow-billed Hornbills Tockus leucomelas, Southern Pied Babblers Turdoides bicolor), accompanied by inability of adults to maintain body mass (hornbills and babblers); declines in nestling provisioning rates, 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 in order to minimise exposure to the physiological costs of high temperatures. These trade-offs result in lost foraging opportunities through reductions in activity and birds’ use of shaded locations suboptimal for foraging (fiscals, hornbills); and/or handicaps on foraging efficiency imposed by the use of respiratory evaporative cooling (panting & gular flutter; babblers and hornbills).

CB MSc student Ryan Olinger carried out experiments with Fork-tailed Drongos Dicrurus adsimilis in November and December 2016, to assess whether (a) changes in prey availability or increasing costs of foraging drive reduced foraging effort under high temperatures; (b) reduction in provisioning rates to nests at high temperatures is due to changes in prey capture rates or changes in parental decision-making, and (c) high temperatures negatively affect growth rates of drongo chicks. Ryan found that thermo-regulatory costs caused declines in foraging and provisioning at high temperatures, even when prey availability was held constant. However, these costs did not seem to be passed on to chicks; as temperature did not affect nestling growth. The Hot Birds team will engage a new MSc student in 2017 to examine these questions further. In addition, Susie Cunningham will travel to Australia in March 2017 to expand research into the costs of thermoregulatory trade-offs for desert birds in the Outback, in collaboration with Dr Janet Gardner from the Australian National University.

The buffering effects of sociality

In July 2016, PhD student, Amanda Bourne registered to assess whether social behaviour can buffer the fitness costs of high temperatures. Amanda’s work is part of a collaboration between the local Hot Birds team and the Pied Babbler Research Project lead by Fitz Honorary Research Associate, Assoc. Prof. Mandy Ridley (UWA). The study uses cooperatively breeding Southern Pied Babblers as the model species to investigate the hypothesis that cooperation, and particularly cooperation in larger groups, should reduce the physiological costs of heat stress and the fitness costs of time spent on thermoregulation. Behavioural data collected through the summer over three field seasons will be used to assess the impacts of heat stress and behavioural thermoregulation on individual survival, body mass, and reproductive success in birds belonging to smaller and larger social groups. Fifteen years of life history data collected as part of the Pied Babbler Research Project will be applied to identify long term patterns related to critical temperature thresholds. Amanda is working on the Kuruman River Reserve in the Northern Cape with 17 groups of free-living, habituated babblers.

Societies and climate change

Post-doc 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 Philetarius socius. Margaux has combined a correlative field study (Feb-Mar 2016) and an experimental, laboratory-controlled approach (Dec 2016-Feb 2017) to examine the impacts of variation in temperature on the nature and frequency of social interactions exhibited by Sociable Weavers and ultimately the impact on their social network. Results to date from the field component of the project suggest that when individuals experience high air temperatures, their social network becomes less dense and breaks down into smaller components. This suggests that individuals interact less with their conspecifics during periods of hot weather. Hence, changes in social network structure appear to be linked to the severity of heat stress experienced by individuals. Margaux presented these preliminary results at the North America Ornithological Congress 2016 in Washington DC.

Hot Birds in the southern scrubland biomes

The Hot Birds team ventured into the Fynbos biome in 2013, joining forces with Alan Lee, Phoebe Barnard and Ben Smit. Since then, the project has expanded to study the impacts of climate on the large array of small birds endemic to the three distinct semi-arid scrubland biomes of South Africa; the Fynbos, Nama Karoo and Succulent Karoo. Since 2015 three projects have been concluded under this topic, involving NMMU MSc students Krista Oswald (supervised by Ben Smit and Alan Lee) and Jerry Molepo (supervised by Ben Smit, Alan Lee and Susie Cunningham) working on two Fynbos species, and Nick Pattinson (supervised by Ben Smit) working on a Succulent Karoo species. Jerry is in the final stages of writing up his MSc dissertation, and Krista and Nick will graduate with their MSc degrees in April 2017.

Fynbos projects

Krista Oswald’s MSc showed that Cape Rockjumpers Chaetopos frenatus, endemic to the mountain peaks of the Fynbos, have comparatively limited capacity to seasonally adjust their thermoregulatory responses to hot temperatures. The most important finding was that Cape Rockjumpers have higher evaporative water rates during summer (i.e. the driest and hottest part of the year) with no change in metabolic heat load or body temperature regulation patterns. These patterns are opposite to those observed in desert species where adjustments are centered on reducing the costs of thermoregulation under hot conditions. These results help to explain why Cape Rockjumpers appear limited to the coolest regions of the Fynbos biome, and specifically why their reporting rates have declined most in regions showing significant climate warming over the past two decades.

Jerry Molepo started behavioural and physiological work on Cape Sugarbirds Promerops cafer in 2015. His aim was to determine if there are differences between male and female Cape Sugarbirds in 1) daily feeding patterns at different air temperatures (wild birds), and 2) thermoregulatory responses at hot temperatures (under laboratory conditions). Jerry spent several months in the Van Stadens Wild Flower Reserve (near Port Elizabeth) where he conducted behavioural observations on Cape Sugarbirds feeding on Protea flowers. He also obtained physiological measurements, using a field laboratory setup, in wild birds of both sexes (20 males and 20 females). Jerry’s findings suggest that female Cape Sugarbirds are more prone to energy-, water- and thermal stress during hot and dry summers in the Fynbos region. This has implications for understanding Cape Sugarbird population responses to climate change in the Fynbos region, and could explain why female sugarbirds (but not males) show reduced body mass during unusually warm and dry periods over the last 30 years (SAFRING database).

Succulent- and Nama Karoo projects

Nick Pattinson started his MSc at the beginning of 2015, studying the physiological and behavioural seasonal responses of a small passerine, the Rufous-eared Warbler Malcorus pectoralis, which is resident in the Nama and Succulent Karoo regions of South Africa. Nick demonstrated that Rufous-eared Warblers show seasonal flexibility in both their physiological and behavioural responses to high temperatures, which illustrates the links between physiological and behavioural adjustments of a small bird and the environmental extremes they face when foraging.

Thermoregulation in the heat

Another major research theme of Hot Birds focuses on the physiological mechanisms that allow birds in hot environments to maintain body temperatures below environmental temperatures. Work in this area during 2016 focused on validating a behavioural index of heat stress, and testing predictions about how birds respond to temperatures higher than they currently experience. In an attempt to assess the usefulness of a behavioural heat dissipation variable as a proxy for assessing species’ vulnerability to rising temperatures, PhD student Michelle Thompson has observed nine Kalahari bird species in large outdoor aviaries to examine the functional links between heat dissipation, shade seeking and activity patterns, hydration status and body temperature on days differing in air temperature maxima. These species all differ in their relationship between the onset of heat dissipation behaviour and air temperature, and in six out of nine species wild populations behave similarly to captive populations when it comes to dissipating heat. However, White-browed Sparrow-Weavers Plocepasser mahali, Cape Glossy Starlings Lamprotornis nitens and Cape Turtle-Doves Streptopelia capicola all began dissipating heat at higher air temperatures in captivity.

During the 2015/16 summer, PhD student Ryan O’Connor investigated the thermal environments of six Rufous-cheeked Nightjar Caprimulgis rufigena roost sites. Roost site thermal conditions were quantified by measuring operative temperature using 3-D printed biophysical models designed to match the morphological dimensions and thermal properties of the nightjars. Ryan found that Rufous-cheeked Nightjars regularly chose partially shaded roost sites where individuals were frequently subjected to periods of intense solar radiation. Roosting nightjars can experience periods of operative temperatures well above body temperature, a circumstance undoubtedly exposing individuals to prolonged periods of evaporative water loss. Furthermore, given that Rufous-cheeked Nightjars are nocturnal birds, Ryan’s data raises questions as to how individuals can maintain water balance throughout the day without taking in water.

White-browed Sparrow-weaver translocation project

During most of 2016 the Pretoria-based members of the Hot Birds team constructed an ambitious aviary translocation experiment that is part of Matt Noakes’ PhD. This project, dedicated to and based on an idea by the late Phil Hockey, investigates the flexibility of physiological and behavioural heat-coping mechanisms in White-browed Sparrow-weavers by translocation experiments where birds from cooler sites are housed in aviaries at a hotter site.

In December 2016, three eager teams of researchers travelled to sites about 700 km apart along a climatic gradient across South Africa. Each team set up an outdoor aviary, caught 15 sparrow-weavers, and collected pre-translocation baseline data for two weeks at their respective sites. It was then time for the much-anticipated “assisted migration” of sparrow-weavers to the Kalahari Desert, and thus began a two-day, 1400 km, cross-country trip with birds and aviaries in tow. By mid-December we were at our study site near Askham in the Kalahari Desert with three aviaries and 45 sparrow-weavers: 15 birds native to this hot arid environment, 15 from a warm semi-arid site and 15 from a cool, more mesic location. We monitored post-translocation responses of the birds to assess the manner and extent that birds from the cooler sites could adjust their physiology and behaviour in response to hotter conditions. The results are currently being analysed, and we anticipate submitting the manuscripts emanating from this project during 2017.

Highlights:

  • The Hot Birds team was well-represented at the North American Ornithological Congress where we organised a symposium in which team members from UCT, U. Pretoria, Nelson Mandela Metropolitan University, and the University of New Mexico presented talks. This symposium received coverage in Science News. 
  • PhD student Amanda Bourne joined the team, funded by an NRF grant to Susie Cunningham.
  • CB MSc student Penny Pistorius graduated with distinction in June 2016 with her thesis on the effects of temperature on flight initiation distances in Kalahari birds.
  • Susie Cunningham was awarded a URC travel grant to visit Dr Janet Gardner at the Australian National University and set up a collaborative project investigating whether variation in physiological traits underpins differences in susceptibility to sublethal fitness costs at high temperatures.
  • The team had an excellent year in terms of publication output, collectively publishing 10 papers in Diversity Distributions, Journal of Experimental Biology, PLoS ONE; Climate Change Responses; Journal of Comparative Physiology, Physiological Biochemical Zoology. and Proceedings of the National Academy of Sciences. USA during 2016.
  • Krista Oswald graduated with her MSc on the seasonal thermal physiological responses of  Cape Rock Jumpers, and registered for a PhD to continue work on this species
  • Nick Pattinson graduated with his MSc cum laude for his dissertation on seasonal physiological and behavioural responses of Rufous-eared Warblers.
  • Andrew McKechnie presented a paper at the 15th International Hibernation Symposium in Las Vegas, USA.

Key co-sponsors

DST-NRF CoE grant; NRF Thuthuka Grant; NMMU Research Themes Grant; University of Cape Town URC; University of Pretoria.

Research Team

Prof. Andrew McKechnie (U. Pretoria)
Dr Susie Cunningham (FIAO, UCT)
Assoc. Prof. Mandy Ridley (FIAO, UCT and UWA)
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 amd U. Pretoria)
Dr Ben Smit (NMMU)
Dr Blair Wolf (U. New Mexico)

Students: Amanda Bourne (PhD, UCT), Matthew Noakes (PhD, Pretoria), Ryan O’Connor (PhD, Pretoria), Krista Oswald (PhD, NMMU), Michelle Thompson (PhD, Pretoria), Tanja van de Ven (PhD, UCT), Mokgatla Jerry Molepo (MSc, NMMU), Ryan Olinger (CB MSc, UCT), Nick Pattinson MSc, NMMU), Penny Pistorius (CB MSc, UCT), Ryno Kemp (BSc Hons, Pretoria), Mpho Malematja (BSc Hons, Pretoria)

Research Assistants: Alex Atkins, Cathy Bester, Rachel Bucksey, Josephine Bruning, Carla Dodd, Ashleigh Donaldson, Pieter Erasmus, Samantha Fourie, Aurora Garcia-Berro Nava, Alexandra Howard, Craig Kenny, Noxolo Kinzela, Samantha Kirves, Rita Leal, Sello Matjee, Vuyiseka Mbiko, Dean Portelli, Alia Moller, Ana Morales Gonzales, Lisa Nupen, Aurélie Quinard, Pearl Rivers, Pauline Ruffenach, Sofia Scheltinga, Iris Seto, Sue-Joy Schultz, Lauren Stansfield, Jack Thorley, Mervyn Uys, Tim Vink, Natasha Visser, Laura Wade.