Together with breeding, moult and migration are the greatest challenges in a bird’s annual cycle. Moulting birds suffer increased metabolic costs as well as impaired flight ability, insulation and camouflage/signalling. Birds vary greatly in how they manage these costs through changing the timing and intensity of moult, both within and between species. Migrant birds are at greater risk of extinction globally than are resident species due to the risks they face travelling across an increasingly transformed planet, and the need to have secure breeding and non-breeding areas. Understanding the strategies birds use to moult and migrate is crucial for their conservation.

Once formed, feathers are dead structures that start to degrade through mechanical abrasion, damage by UV light, and attack by ectoparasites, fungi and bacteria. Most feathers need to be replaced every year or so through a regular process of moult. The costs of moult are significant, so most birds schedule their moult to periods when they are not breeding or migrating (although there are numerous exceptions). New feathers grow from a ring of cells in the feather follicle, which limits their rate of growth to around 4-6 mm per day. Feathers that grow faster tend to be of poorer quality, providing less insulation and wearing faster than feathers grown more slowly. This largely invariant growth rate means that large birds take longer to replace a given feather than small birds, and so typically have more complex moult strategies than small birds, either greatly increasing the intensity of moult (e.g replacing all flight feathers at once and becoming flightless for a few weeks while they grow new feathers) or staggering their moult over several years. The timing, intensity and symmetry of moult likely reflect individual health. And unlike breeding, moult is something that all birds must undergo. Thus monitoring how different birds moult, and how this changes over time, might be a way to track population health. Migration is better studied than moult, but there is still much to learn regarding movement patterns among African birds. And given the less marked seasonality in the Southern Hemisphere, more species move in response to rainfall rather than temperature, especially in more arid areas. Our understanding of these nomadic movements is still in its infancy. Finally, we also contribute to an understanding of global shorebird movements through coastal bird surveys.

Activities in 2023

  • MSc student Taylyn Risi completed her dissertation on wing moult in oystercatchers, based on data from both traditional studies of birds in the hand and photographs of birds in flight.
  • PhD student Rachel Dobson (Leeds) made good progress on a manuscript exploring the environmental triggers for Ludwig’s Bustard Neotis ludwigii movements based on Jessica Shaw’s tracking data, which has up to 11 years of data for some individuals. Some bustards undertake more or less regular migrations between the Nama and Succulent Karoo each year, following seasonal rains, whereas others are more sedentary.
  • BSc Hons student Rebecca Irons completed her mini-thesis by exploring the primary feather moult of sunbirds and sugarbirds in South Africa using generalised additive models (GAMs) to visualise patterns.
  • Peter Ryan led a synoptic survey of coastal birds in the Greater Bazaruto IBA/KBA in November 2023, in collaboration with African Parks (Evan Trotzuk) and the Vilanculos Coastal Wildlife Sanctuary (Christine Read and Dave Gilroy). The survey covered all five islands in the Bazaruto Archipelago National Park, the San Sebastian Peninsula, and the mangrove embayments north of the Save River Delta. More than 55 000 coastal birds were counted, of which 60% were shorebirds (mainly Charadriidae and Scolopacidae), 25% terns and gulls (Laridae), and 10% flamingos (Phoenicopteridae). Non-breeding migrants dominated among both shorebirds (95%) and terns (94%).


  • Taylyn Risi was awarded her MSc with distinction for her dissertation on the moult of oystercatchers.
  • Three papers were published in a special issue of Ostrich on moult edited by Adrian Craig and Birgit Erni: on moult in the African Oystercatcher Haematopus moquini by Les Underhill and Taylyn Risi, on moult in the White-capped Albatross Thalassarche [cauta] steadi by Peter Ryan and Oluwadunsin Adekola, and on visualising moult data using GAMs by Rebecca Irons, Alan Lee, Robert Thomson and Birgit Erni.

Impact of the project
The timing and intensity of moult is thought to be related to stress in bird populations, and monitoring changes in these parameters might provide a useful measure of global change impacts. The intra-African migration project facilitated networking among research institutions across Africa. This programme helps to support the objectives of the UNEP/CMS African-Eurasian Migratory Land-birds Action Plan (AEMLAP) and the Migrant Landbird Study Group (MLSG), and meets the growing need for better understanding of the drivers of avian migratory patterns on the continent.

Key co-supporters
SI-NRF CoE grant; BirdLife International; Mohamed bin Zayed Species Conservation Fund; African Parks.

Research team 2023
Emer. Prof. Peter Ryan (FIAO, UCT)
A/Prof. Robert Thomson (FIAO, UCT)
Dr Gary Allport (BirdLife International)
Dr Alan Lee (BirdLife SA)
Dr Birgit Erni (SEEC, UCT)
Dr Samuel Temidayo Osinubi (FIAO, UCT)
Dr Jessica Shaw (NatureScot)
Prof. Les Underhill (BioSci, UCT)

Students: Rachel Dobson (visiting PhD student, Leeds); Taylyn Risi (MSc, UCT); Rebecca Irons (BSc Hons, UCT).