Global change and urban birds

Urban environments create novel challenges and opportunities for birds. Understanding why and how some birds are able to adapt to urban landscapes, and others are not, is important to predict how ongoing urbanisation is likely to impact birds. This project aims to understand how birds in human-altered landscapes cope with the opportunities and pressures of human life.

The Red-winged Starling project
Since 2017 we have studied how Red-winged Starlings Onychognathus morio on UCT’s highly urbanised Upper Campus cope with highly variable food quality and quantity in urban environments, the stresses of sharing their space with large numbers of people, and of high summer temperatures as Cape Town’s climate warms. Early correlative work showed that adult starlings benefit from high availability of anthropogenic food, gaining more weight on weekdays than on weekends, but that chicks seem to suffer, with those experiencing many high-human-presence days while in the nest showing reduced growth compared to those raised during lower-human-presence days (i.e. those whose nestling period overlaps with public holidays and vacations). We also found that more built-up areas on campus were occupied by larger birds, suggesting that starlings perceive these areas to be higher quality. Indeed, faecal glucocorticoid metabolite concentrations in starling droppings are negatively correlated with human foot traffic levels outside of the breeding season, suggesting that starlings experience less stress in the presence of high human numbers, perhaps because of the ready availability of anthropogenic food or because humans deter natural starling predators.

However, even though adults benefit from high human presence on campus, nestlings appear to be negatively affected, and experimental work (e.g. by Miqkayla Stofberg over the last several years) has not clarified whether food quality or other correlated urban stressors are to blame. In 2024, MSc student Abiodun Ademola finalised her data collection; she is investigating whether the negative impacts of high human presence on nestling growth may be related to stress effects associated with adult nest defence behaviours (breeding adults frequently divebomb passersby) and how adult starlings respond to human presence in terms of stress hormone expression while breeding versus not.

The starlings again played an important role in undergraduate and post-graduate teaching in 2024. Susie Cunningham led a 3rd-year project on the BIO3013F Global Change Ecology course looking at starling responses to hot weather on campus. This project teaches 3rd-year students how to collect and analyse behaviour data from free-living animals. This was the 9th year this project has run (2015–24, with a 1-year COVID-19-related hiatus) and it is becoming apparent that starlings adjust the onset of heat-dissipation behaviours annually in relation to the prevailing weather conditions that year, suggesting a great deal of behavioural plasticity in heat-load management. Dr Celiwe Ngcamphalala again used our annual starling ‘catch week’ in mid-winter to expose Biological Sciences Honours students to methods used to study avian stress physiology, inviting the students to take part in catching efforts and observe and record data on blood-sampling, measurement and ringing, to aid their understanding of invasive versus non-invasive methods of studying wild animals.

Interactions between urbanisation and climate change
Climate change and urbanisation are two of the most pervasive current drivers of global change. Impacts of climate change on wildlife could be exacerbated or buffered in urban areas. This is because major changes in habitat structure, food and water availability, disease exposure, species interactions, and pollution (light, sound and chemical) may all affect how wildlife can respond to rising temperatures and changing weather patterns. Additionally, urban environments tend to be hotter than surrounding natural landscapes (the ‘urban heat island’ effect), except in arid areas where they may be cooler. In 2023, we published a major perspectives paper in the journal Global Change Biology highlighting how we might expect the forces of urbanisation and climate change to interact in their effects on wildlife. In 2024, we began research to investigate interactions between weather conditions and a correlate of urbanisation: human presence. For this we are using the long-term database on the behaviour, body mass and breeding success of Red-winged Starlings on Upper Campus. This study is led by new MSc student Leslie Bayanza, who builds on Miqkayla Stofberg’s preliminary pre-pandemic work on this topic. Leslie’s preliminary analyses suggest an interaction between heat and human presence on the body mass of starlings recorded between 2017 and the present, such that starlings lose mass on hot low-human-presence days but are able to maintain body mass regardless of temperature on high-human presence days.

Energy expenditure in urban landscapes
Although urban areas pose novel challenges for wildlife, they also provide opportunities. Some species, such as the Red-winged Starlings, manage to take advantage of these opportunities and become very abundant in urban centres. Another such African urban ‘success story’ is that of the Crowned Eagle Stephanoaetus coronatus, which has reached higher densities in the Durban metropolitan area than anywhere else documented within its range. In 2024, we collaborated with researchers from the University of Vienna and University of KwaZulu-Natal (UKZN) on a project looking at how urban Crowned Eagles use the different habitat types available within the Durban Metropolitan Open Space System (DMOSS) and assessing the energetic costs associated with use of these habitat types. This project was taken up by CB MSc student Lara Howard, who is working with a dataset comprising movement data from five Durban Crowned Eagles wearing GPS tags fitted with accelerometers. Using location data, Lara was able to show that the forested areas of the DMOSS are instrumental in anchoring the eagles in this environment, although the birds do make hunting forays into suburban areas. In general, they avoid the highly built-up areas of the city, and this may be associated with a higher energy expenditure in these areas (as suggested by the accelerometer data), perhaps due to human disturbance.

Activities in 2024

• Abiodun Ademola finished data collection and lab work for her MSc project, which focuses on understanding the effect of fluctuations in human foot traffic on stress levels in adult and nestling Red-winged Starlings, using faecal glucocorticoid metabolites as a proxy for stress. She is now working on her write-up, for submission in 2025. Abiodun is supervised by Susie Cunningham and Celiwe Ngcamphalala.
• Leslie Bayanza began data collection for her project on the interaction between weather and human presence on starling body mass maintenance and breeding success. Leslie is using the long-term datasets amassed by the project since 2017 and collecting novel data of her own. Leslie is supervised by Susie Cunningham and Celiwe Ngcamphalala.
• Muano Ramavhoya studied relationships between built-up surfaces around nest sites and chick growth in the Red-winged Starlings for her BSc Hons, discovering no clear correlation between the two. Next steps will include assessing interactions between nest location and day status.
• Lara Howard joined Crowned Eagle researchers from UKZN and the University of Vienna in Durban to learn about the birds first-hand and witness transmitter fittings.
• A highly successful trapping effort in mid-2024 saw 39 new colour-ringed starlings added to the study population, bringing the total number of adult starlings ringed during the course of the project to 351. An additional 43 nestlings were ringed in 2024.
• Body mass maintenance and breeding monitoring of the starlings continued throughout 2024: these data will be used to investigate the effects of societal recovery from the COVID-19 pandemic on the productivity of urban wildlife, and, in the long term, to assess how climate change and urbanisation together impact the fitness of urban wildlife.

HIghlights

• MSc student Leslie Bayanza joined the team from the DRC on a Mandela Rhodes scholarship.
• CB MSc student Lara Howard joined the team, facilitating collaboration with the Durban Crowned Eagle Project.
• The team had an exceptional catch week in June, capturing 47 starlings, illustrating the success of Celiwe’s trap training methods. Of these, 39 were new captures and 8 were re-traps (mostly of birds ringed as nestlings in previous years).

Impact of the project
Studying the starlings on campus has allowed us to involve the wider university community in a citizen science project, making our research more visible and relevant. The accessibility of the project and its fieldwork has also resulted in an ideal training opportunity for younger students wanting to gain experience in behavioural research and bird observation/handling under careful supervision. In addition, the starling project supports teaching at undergraduate (third year) and post-graduate (honours) levels, exposing students to the skills needed for field ornithology.

Key co-supporters
Vice-Chancellors’ Future Leaders programme, Mandela Rhodes Scholarship programme, Mastercard scholarship programme, Ralph Buij, Jesus Bautista.

Research team 2024
Team leaders and collaborators:
A/Prof. Arjun Amar (FIAO, UCT)
A/Prof. Res Altwegg (SEEC, UCT)
A/Prof Susan Cunningham (FIAO, UCT)
Dr Celiwe Ngamphalala (BioSci, UCT)
Dr Sally Hofmeyr (FIAO, UCT)
Dr Petra Sumasgutner (KLF, University of Vienna)
Dr Shane Sumasgutner (KLF, University of Vienna UKZN)
A/Prof. Caroline Isaksson (MEEL, Lund University)
A/Prof. Robert Thomson (FIAO, UCT)
Varalika Jain (KLF, University of Vienna)

Students:
Jessleena Suri (PhD, UCT Stats); Abiodun Ademola (MSc, UCT), Leslie Bayanza (MSc, UCT), Lara Howard (CB MSc, UCT), Muano Ramavhoya (BSc Hons, UCT)

Volunteers:
Mila Truter, Joel Radue, Daniella Mhangwana, Josua Wenzel, Suzanne Hofmeyr, Ilana Engelbrecht, Ben Wittenberg, Anthony Boetcher, Edith Binnema and many others.