Moult and migration
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. As a result, large birds have to adopt 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 little is known about the migratory routes of intra-continental migrant birds in Africa compared to inter-continental migrants. Phoebe Barnard recruited Post-doc Dayo Osinubi in 2015 to start an intra-African migration project to investigate the migratory patterns of selected intra-African migrant birds. The project attempted to use a broad-scale spatial approach to address questions of phylogeography, movement ecology, phenotypic and genetic variation in intra-African migrant birds. The main focus was on Woodland Kingfishers Halcyon senegalensis, which have resident populations in central Africa and migrant populations at the northern and southern edges of their ranges.
Activities in 2020
- PhD student Emmanuel Adekola completed a paper on tail moult in Amur Falcons Falco amurensis, based on the examination of more than 2000 falcons collected by David Allan from the Durban Natural Science Museum after they were killed by hailstorms in KwaZulu-Natal in March 2019. Emmanuel found considerable individual variation in the extent of tail moult among both adult and juvenile falcons, with moult extent correlated with body condition. A paper describing his findings was recently accepted for publication in the Journal of Ornithology.
- Emmanuel also analysed moult data for adult Cape Gannets Morus capensis, comparing data collected at Malgas Island and Lambert’s Bay in 2002–2004 with data he collected in 2018–2019. His thesis assesses how large, long-winged birds manage to replace their large number of secondaries; unlike primaries, which number 9-11 in all birds, the number of secondaries varies from 8-38 depending on bird size and wing shape.
- Taylyn Risi started an MSc on wing moult in oystercatchers, using existing data from South Africa, Australia and Europe. She also collected several hundred records for African Black Oystercatchers Haematopus moquini from images she and Peter Ryan took after the initial COVID-19 lockdown restrictions eased.
- Alexis Osborne completed his MSc and had a paper accepted in Ostrich on the use of photographs to score moult in breeding seabirds.
- The southern African field site for Woodland Kingfisher tracking work at the Mogalakwena Research Centre was visited at the end of December 2020, recovering a fifth geolocator.
- Abigail Ramudzuli completed work on her MSc project to explore moult patterns of Woodland Kingfishers and the use of stable isotope markers in their flight feathers, with a view to determining whether stable isotopes can indicate where migratory birds spend the non-breeding season. She will submit her thesis in early 2021.
- During summer 2020/21, Peter Ryan conducted repeat surveys of coastal birds in the Western Cape. Previous surveys showed alarming decreases in many migratory shorebird species from 1980/81 to 2010/11.
- Data from the five geolocators retrieved from Woodland Kingfishers are currently being analysed with the support of the Swiss Ornithological Institute to identify the kingfishers’ migration routes, timing and stop-over sites.
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 would provide a useful measure of global change impacts. The intra-African migration project facilitated a research network linking research institutions across Africa. This network serves to support the objectives of the UNEP/CMS African-Eurasian Migratory Land-birds Action Plan recruited Post-doc Dayo Osinubi in 2015 to start an intra-African migration project to investigate the migratory patterns of selected intra-African migrant birds. The project attempted to use a broad-scale spatial approach to address questions of phylogeography, movement ecology, phenotypic and genetic variation in intra-African migrant birds. The main focus was on Woodland Kingfishers Halcyon senegalensis, which have resident populations in central Africa and migrant populations at the northern and southern edges of their range.
DSI-NRF CoE grant; National Zoological Gardens of South Africa (NZG); International Foundation for Science; BirdLife International; A.P. Leventis Ornithological Research Institute; Swiss Ornithological Institute (Vogelwarte); African Bird Club; British Ecological Society; iThemba LABS.
Research team 2020
Dr Samuel Temidayo Osinubi (FIAO, UCT)
Prof. Desire Dalton (NZG)
Prof. Peter Ryan (FIAO, UCT)
Prof. Les Underhill (BioSci, UCT)
Students: Oluwadunsin Emmanuel Adekola (PhD, UCT); Alexis Osborne (MSc, UCT); Abigail Ramudzuli (MSc, UCT); Taylyn Risi (MSc, UCT).