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. Globally, migrant birds are at greater risk of extinction than residents due to the risks they face travelling across an increasingly transformed planet and the need to have secure breeding and nonbreeding 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 moulting process. The costs of moult are significant, so most birds schedule their moult for 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 probably reflect individual health. Unlike breeding, moult is something that all birds must undergo, so monitoring how 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. Given the less marked seasonality in the Southern Hemisphere, more species move in response to rainfall than to 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 and conservation through coastal bird surveys.

Activities in 2025
  • Dr Rachel Dobson was awarded her PhD by Leeds University on nomadic bird movements, which included an analysis of Dr Jessica Shaw’s tracking data for Ludwig’s Bustard Neotis ludwigii. A paper describing individual movements for up to 11 years was published in Ostrich. A second manuscript exploring the environmental triggers for their movements is nearing completion.
  • The shorebird roost site in the southwest of Vilanculos Bay that was discovered in August 2024 was surveyed again in February 2025, together with most major roost sites in the Bazaruto Archipelago National Park and adjacent San Sebastian Peninsula. This survey confirmed that counts made in November 2023 for the Greater Bazaruto IBA/KBA substantially underestimated the importance of this region for shorebirds. The roost is in a fairly remote rural area south of Vilankulo town, but it is not in a protected area. A paper reporting the new roost site will be submitted in 2026.
  • Conservation Biology MSc student Carolina Policarpo is conducting their research project on the distribution of intertidal wetland habitats along the African sector of the East Asian–African flyway. They are using existing global databases estimating the areas of intertidal mudflats, marshes and mangroves to estimate the distribution of shorebird habitat along the east coast of Africa, from the Horn of Africa to Cape Agulhas. Carolina is supervised by Emer. Prof. Peter Ryan and Dr Carlos David Santos (NOVA University Lisbon), who is working on a similar study for the east coast of South America.
Highlights
  • The synoptic survey of coastal birds in the Greater Bazaruto IBA/KBA in November 2023 was published in Ostrich.
  • The newly discovered shorebird roost site in the southwest of Vilanculos Bay was found to support 40 000 waders in February 2025, including 12 000 Bar-tailed Godwits Limosa lapponica, 6 000 Tibetan Sand Plovers Anarhynchus atrifrons, 5 000 Curlew Sandpipers Calidris ferruginea and 4 000 Sanderling Calidris alba. This more than doubles the estimated population of shorebirds in the Greater Bazaruto IBA and makes Vilanculos Bay the most important wetland for shorebirds in southern Africa.
  • Carolina Policarpo’s project highlights the importance of Mozambique for shorebirds along the East African coast. Most areas of suitable habitat in central and northern Mozambique, as well as much of Tanzania, have never been surveyed for migrant shorebirds or other coastal birds.
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
BirdLife International; Mohamed bin Zayed Species Conservation Fund; African Parks.

Research team 2025
Team leaders and collaborators:
Emer. Prof. Peter Ryan (FIAO, UCT)
A/Prof. Robert Thomson (FIAO, UCT)
Dr Gary Allport (BirdLife International)
Dr Alan Lee (BLSA / FIAO, UCT)
Dr Birgit Erni (SEEC, UCT)
Dr Jessica Shaw (NatureScot)
Dr Rachel Dobson (Durham)
Emer. Prof. Les Underhill (BioSci, UCT)
Dr Yann Rime (FIAO, UCT)

Student:
Carolina Policarpo (CB MSc, UCT), Rachel Dobson (PhD, Leeds)