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Global change and urban birds

Anyone who has spent time at the University of Cape Town will know about the Red-winged Starlings Onychognathus morio on Upper Campus. These birds have developed a reputation amongst the UCT community for being sly, lunch-thieving pests and many students can recount a story of having a starling swoop past their heads on Jammie Plaza in pursuit of a sandwich or some other treat. Since 2017 we have been conducting research on our favourite campus mascots, looking at how city-slicking birds cope with highly variable food quality and quantity in urban environments, the stresses of sharing their space with high numbers of people, and of high summer temperatures as Cape Town’s climate warms.

Red-winged Starlings are an excellent example of a species that has taken advantage of the opportunities offered by urban environments. While many birds avoid urban areas due to disturbance, pollution, habitat transformation and other threats that they pose, some actively exploit cities. In their natural environment, Red-winged Starlings nest on cliffs in rocky and mountainous areas, but in cities they nest on buildings. Similarly, while they would normally feed primarily on fruit and insects, they have learned that cities offer rich opportunities for scavenging on anthropogenic food.

We aim to understand how Red-winged Starlings on campus cope with the opportunities and pressures of city life under climate change. One of the major themes of the project is to unpick the costs and benefits of a diet high in “junk food”. In 2017 and 2018, MSc students Miqkalya Stofberg and Sarah Catto showed that adult starlings seem to benefit from easily available anthropogenic food, gaining more body mass on weekdays than on weekend and vacation days when campus is quiet and food stalls are shut. Parent starlings feed both junk food and natural food to their nestlings, but provision a higher proportion of junk food on high human presence days. This junk food diet appears to be bad for the young birds: chicks that experienced more high human presence days during the nestling period were smaller and lighter at ringing age than those whose early development overlapped with public holidays and vacations. In 2019, Miqkayla Stofberg completed a supplementary feeding experiment designed to untangle whether these impacts on nestling growth were indeed due to the poor quality of a diet high in anthropogenic food. At the time of writing, Miqkayla is analysing the results of this work.

In a linked study, University of Lund MSc student Johan Jensen examined blood samples from the same population to quantify fatty acid profiles of adult birds. He found large variation in fatty acid profiles among birds, but no evidence that these were linked to temporal fluctuations in anthropogenic food availability over weekend – weekday  timescales.

Also during 2019, BSc Hons student Taylyn Risi mapped home ranges of colour-ringed starlings across campus, and using GIS technology calculated the proportion of these ranges that were covered by built-up, impervious surfaces. She showed that starlings with more built-up home ranges enjoyed higher foraging efficiency and were both heavier and larger than birds with more “natural” home ranges. These data suggest that higher quality birds are attracted to settle in more urbanised areas of campus.

Finally, a team of undergraduate students led by Mila Truter and supervised by Prof. Res Altwegg carried out a 2nd year statistics project to understand whether starlings are able to recognise humans as individuals and provided evidence that they do. This result has enormous implications for how we conduct our fieldwork, highlighting the need to keep carefully separate the team members engaged in “threatening” activities such as capture of adults and nest access work, and those engaged in “friendly activities” such as behavioural observations and weighing of adults on top pan balances in return for a small food reward. Mila and Taylyn are now writing up their results for publication in 2020.

Activities in 2019

  • The colour-ringed population now consists of 204 adults and 77 juveniles and subadults that were ringed between 2017 and 2019.
  • The first generation of nestlings ringed in 2017 began to join the breeding population in 2019, with two females and one male attempting to breed for the first time.
  • Taylyn Risi continued data collection on the birds outside the breeding season.
  • Miqkayla Stofberg continued supplementary-feeding experiments looking at the impacts of anthropogenic food on parental behaviour and chick growth.

Highlights

  • Miqkayla Stofberg published the first paper from the project in Urban Ecosystems.
  • MSc student Johan Jensen and Honours student Taylyn Risi graduated with their degrees.

Impact of the project

Studying a resident and high-profile population of starlings that are well-known 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. Through the help of such volunteers, the project has managed to collect a large volume of data in its first two years.

Key co-supporters
DST-NRF CoE grant; NRF-STINT South Africa-Sweden Research Collaboration.

Research team 2019
A/Prof. Arjun Amar (FIAO, UCT)
Dr Martin Andersson (MEEL, Lund University)
Dr Susan Cunningham (FIAO, UCT)
Dr Arne Hegemann (MEEL, Lund University)
A/Prof. Caroline Isaksson (MEEL, Lund University)
Dr Johan Nilsson (OIKOS office, Lund University)
Dr Petra Sumasgutner (FIAO, UCT)
Dr Hannah Watson (MEEL, Lund University)

Students: Miqkayla Stofberg (MSc, UCT); Johan Jensen (MSc, Lund); Taylyn Risi (BSc Hons, UCT).

Volunteers: Adam Begg, Laura Figenschou, Tsilavo Razafimanantsoa, UCT Mountain and Ski Club, Olivia Venter, Vince Ward, and many others.