Breeding seasons are considered the most important period of the annual cycle of birds, but we still lack a full understanding of why birds breed when they do. Answering this long-standing question in life history research is crucial to understanding how climate change will impact bird populations, and how those effects can be mitigated.

Our current understanding of life-history evolution and phenology is heavily biased towards the north-temperate zone, where breeding seasonality is tightly correlated with temperature and photoperiod. This has led to the notion that breeding is prioritized over other annual cycle events and that food availability for nestlings is the main determinant of breeding seasonality in birds. However, in the tropical and south-temperate zones, the link between breeding phenology and food abundance is less clear-cut. Moreover, the determinants of environmental productivity cycles may differ among tropical environments. Here, we might expect other patterns of environmental variability to be more important for the timing of birds’ annual cycles. This is because where annual reproductive output is low or unpredictable, birds should prioritise investing in processes promoting self-maintenance and survival (such as moult and immunity) rather than necessarily timing breeding to coincide with periods of peak food abundance for nestlings and juveniles. This alternative hypothesis remains untested to explain both the adaptive fine-tuning of timing of breeding according to environmental conditions within species, and the striking and unexplained differences among species. Furthermore, rainfall is considered the key determinant of food availability in seasonally arid tropical environments, but it remains unclear how a single wet season influences food availability across the year for different breeding communities.

In 2021 we started a research project to address these knowledge gaps in Choma, Zambia. Choma is a seasonally arid environment with distinct wet and dry seasons and a species-rich bird community including species breeding within and across seasons. By combining year-round field sampling of invertebrates and grass seeds with analyses of long-term avian breeding data from the work of Major John Colebrook-Robjent from 1970–2008, we have identified peak periods of specific food availability and peak breeding periods of different species. Three clear breeding peaks occur in Choma – shortly before, just after, and three months after the onset of the rains, creating three clear seasonal breeding clusters and one weakly seasonal cluster within the bird community assemblage. We are conducting trait-based analyses to identify the specific traits that link each species to a cluster and determine whether this pattern is generalisable across bird communities. Early indications suggest that foraging substrate is an important determinant of breeding seasonality. Thanks to our resident colleagues in Choma who helped to maintain our year-round invertebrate sampling, and MSc students Matthew Lobenhofer (Conservation Biology 2022/3) and Yinka Abayomi (MSc student by dissertation) who helped identify invertebrate samples, we now know that invertebrate abundance peaks before the onset of the rains rather than after, although multiple smaller peaks occur during the rains.

In 2024, we conducted additional fieldwork in Choma to understand the determinants of pre-rain leaf flush, which coincides with large bird breeding and invertebrate abundance peaks. Through Yinka Abayomi’s work, we now know that vegetation green-up before the rain is associated with a fourfold increase in invertebrate abundance compared to vegetation green-up after the rains. We will combine long-term bird breeding datasets with more recent data collected by colleagues in the Fitz (see AfricanHoneyguides.com) for a selection of species identified from our previous multispecies analyses to test how aspects of environmental productivity before the rains, such as leaf flush, and after the rains, such as increased grass seed availability, influence the timing of breeding in different breeding communities across the Choma bird assemblage.

We continued fieldwork during the dry season of 2025, monitoring nest survival and sampling blood from breeding adults and nestling birds of selected species. We plan to conduct immune assays to test how the immune function of birds varies across transitions between dry and wet seasons. This will allow us to unravel the environmental components of rain-driven seasonal transitions that influence immune function and how factors other than the onset of the wet season or food availability can influence breeding decisions.

These projects provide an exciting opportunity to disentangle components of seasonal environmental conditions that drive timing of bird breeding in Afrotropical ecosystems. Achieving this fundamental objective will help us detect and predict impacts of rapidly changing environmental conditions in Africa and other understudied biodiverse environments.

Activities in 2025
  • Chima Nwaogu had a successful field season in Choma, Zambia from October to December 2025. We continued field experiments for our research addressing the question of why Afrotropical birds breed when they do. We monitored breeding events in Black-crowned Tchagra Tchagra senegalus, Brown-crowned Tchagra T. australis and Dark-capped Bulbul Pycnonotus tricolor (called Common Bulbul in the region) across the transition from dry to wet season. We collected blood samples for immune function assays and cloacal swabs for gut microbiome analyses.
  • Chima collaborated with Prof. Barbara Helm and Dr Crinan Jarrett at the Swiss Ornithological Institute, Switzerland and other colleagues at the A. P. Leventis Ornithological Research Institute, Nigeria, on a project studying aspects of the wintering ecology of palearctic migrants in Nigeria. They investigated body reserve accumulation patterns and the timing of passage of Palearctic migrants through Nigeria.
  • MSc student Yinka Abayomi completed the final year of his project on the determinants of pre-rain green-up and its association with insect abundance and bird breeding seasonality in the Afrotropics.
  • Matthew Lobenhofer is writing up findings from his MSc CB thesis, assessing the association between invertebrate abundance, environmental seasonality and habitat modification.
  • Chima is collaborating with Dr Yann Rime, a new Swiss National Science Foundation Postdoctoral Research Fellow at the Fitz, investigating intra-African migration. Chima conducted fieldwork with Yann in November 2025 at our field site in Choma, Zambia. They caught Pennant-winged Nightjars Caprimulgus vexillarius and fitted pressure loggers on them to monitor their movement.
  • Chima is leading a new project investigating the links between diet shifts, immune function and the gut microbiome in birds, in the form of a PhD study being undertaken by Ojodomo Godday Simon. The project is jointly supervised with Claire Spottiswoode, Prof. Irene Tieleman at the University of Groningen, the Netherlands, and Dr Mark Gillingham and Prof. Bart Kempenaers at the Max Planck Institute for Biological Intelligence, Germany.
Highlights
  • In 2025, Chima returned to working in Cape Town in person after four years of being away due to visa challenges.
  • Chima’s Carnegie-funded Developing Emerging Academic Leaders Junior Research Fellowship ended in 2025. We are grateful to the Carnegie Developing Emerging Academic Leaders (DEAL) Programme for their support. The Max Planck–UCT Centre for Behaviour and Coevolution will now support his research going forward.
  • UCT and Groningen Nuffic–NRF joint PhD student, Rebecca Muller, co-supervised with Arjun Amar, Irene Tieleman (U. Groningen), and Prof. Barbara Helm (Swiss Ornithological Institute), submitted and received approval for her PhD thesis. Rebecca explored how the South African Nest Record Scheme can be used to detect changes in phenology in southern African birds. She will defend her thesis in a public ceremony at the University of Groningen in June 2026.
  • Ojodomo Godday Simon joined the FitzPatrick in September 2025 to start a PhD project investigating how the gut microbiome links diet and immune function over the annual cycle of birds.
  • Rebecca Muller published the first paper from her PhD entitled ‘Exploring the use of the South African Nest Record Scheme to detect changes in phenology: a case study using four well-represented species’.
  • Rebecca will join Chima’s team as a postdoctoral fellow in 2026, supported by the Carnegie Developing Emerging Academic Leaders (DEAL) Programme and the Max Planck–UCT Centre for Behaviour and Coevolution. She will help with setting up the Avian Phenology Africa Database (APAD). The project aims to collate and analyse bird phenology data across different regions in Africa.
  • We published a paper entitled ‘Temporal and environmental drivers of pre-migratory fuel loads in songbirds in West Africa’ in Proceedings of the Royal Society B from our collaborative work on the wintering ecology of palearctic migrants in Nigeria.
  • In collaboration with colleagues at the University of Groningen, the Swiss Ornithological Research Institute, and the A. P. Leventis Ornithological Research Institute, we contributed two papers entitled ‘Diet-manipulated body condition affects onset and speed of moult in common bulbuls in a tropical environment‘ and ‘Species-specific trends in migratory passage time through Nigeria based on long-term ringing data’ to the Journal of Avian Biology special issue in honour of their retiring Editor-in-Chief, Prof. Jan-Åke Nilsson, a renowned ecological and evolutionary physiologist at Lund University, Sweden.

Key co-supporters
Carnegie Developing Emerging Academic Leaders Programme; Max Planck – UCT Centre for Behaviour and Coevolution; British Ecological Society; British Ornithologists’ Union.

Research team 2025
Team leaders and collaborators:
Dr Chima Nwaogu (FIAO, UCT)
Prof. Claire Spottiswoode (FIAO UCT / U. Cambridge)
Dr Gabriel Jamie (FIAO, UCT)
A/Prof. Susan Cunningham (FIAO, UCT)
A/Prof. Arjun Amar (FIAO, UCT)
Dr Charlene Janion-Scheepers (Biological Sciences, UCT)
Prof. Irene Tieleman (U. Groningen)
A/Prof. Martijn van de Pol (James Cook U., Townsville, Australia)
Dr Crinan Jarrett (Swiss Ornithological Institute)
Prof. Barbara Helm (Swiss Ornithological Institute)
Dr Mark Gillingham (Max Planck Institute for Biological Intelligence, Germany)
Prof. Bart Kempenaers (Max Planck Institute for Biological Intelligence, Germany)

Students:
Yinka Abayomi (MSc, UCT), Ojodomo Godday Simon (PhD, UCT), Rebecca Muller (PhD, UCT)