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 behaviour of intra-continental migrant birds in Africa compared to inter-continental migrants, which tend to move in relation to seasonal signals driven primarily by the strongly continental climate in the Northern Hemisphere. Like the triggers affecting breeding in Afrotropical birds, movement within the Afrotropics likely is more related to rainfall than temperature. Dayo Osinubi is studying the movements of Woodland Kingfishers Halcyon senegalensis, which have resident populations in central Africa and migrant populations at the northern and southern edges of their range, with individuals breeding in the south migrating to spend their non-breeding period in the north. At a smaller scale, many Ludwig’s Bustards Neotis ludwigii undertake more or less regular migrations between the Nama and Succulent Karoo each year, following seasonal rains. Finally, another migration study led by Gary Allport to find the breeding grounds of the critically endangered Steppe Whimbrel Numenius [phaeopus] alboaxillaris by fitting satellite tags onto birds on the non-breeding grounds in Mozambique remains on hold pending the location of catchable birds. 

Activities in 2021

  • Oluwadunsin Adekola completed his PhD on the challenges of wing moult in large birds, graduating in December 2022. His thesis comprised five data chapters on moult in three seabirds and one migratory raptor, the Amur Falcon Falco amurensis. He is currently a post-doctoral fellow at Coventry University.
  • Ben Heather-Clark (BSc Hons) used a mix of photographic and traditional moult data to explore patterns of incomplete wing moult among petrels. He obtained moult data for 15 of the 16 genera of petrels. Of these, eight had incomplete moult of the secondaries and upperwing coverts, but only two (Pterodroma and Ardenna) had species that exhibited both incomplete and complete wing moults. Pterodroma offers an interesting opportunity to explore the factors determining moult extent, with considerable variation both among and within species.
  • Taylyn Risi (MSc) made good progress with her study of wing moult in oystercatchers, and will submit her dissertation in February 2023. Abigail Ramudzuli completed the requirements for her MSc on the moult and migration of Woodland Kingfishers and will graduate in 2023.
  • Rebecca Irons (BSc Hons) worked on moult data of 9 sunbird and sugarbird species in South Africa collected mainly through citizen science projects. She explored the use of General Additive Models (GAMs) to visualise and interpret these moult data and found that GAMs hold potential to be used as a supplementary tool to enhance primary moult studies. These models seem especially useful when noisy, error prone citizen science data are used, but which are an invaluable resource for the scant information available for many of Africa’s birds.
  • Dayo Osinubi helped organise a symposium on integrating science, policy and sustainable development to address African-Eurasian migrant landbird declines at the 15th Pan-African Ornithological Congress (PAOC). The symposium was attended by individuals and agencies working across a wide range of disciplines, and provided cross-sectoral feedback on achievements, challenges and opportunities. 
  • Dayo also wrote an editorial in Ostrich on the ‘ownership’ of Palearctic-breeding birds that winter in Africa.
  • PhD student Rachel Dobson (Leeds) is trying to identify the environmental triggers for Ludwig’s Bustard movements based on Jessica Shaw’s tracking data, which has up to 11 years of data for some individuals.
  • Christine Read arranged a survey of coastal birds in southern end of Vilanculos Bay in November 2022, which included the use of a helicopter to reach inaccessible wetlands. Unfortunately, a comprehensive survey of coastal birds in Bazaruto/Save region planned for the end of January 2023 had to be postponed due to Tropical Storm Cheneso.

Highlights

  • Two papers arising from Dayo Osinubi’s work on intra-African migrant kingfishers were published reporting the phylogeography of Woodland and African Pygmy Kingfishers Ispidina picta.
  • Dayo served as the Vice-Chair of the Scientific Committee for the 15th PAOC, which took place in Victoria Falls, Zimbabwe in November 2022. At the meeting, he was appointed as Chair of the Scientific Committee for the 16th PAOC. 
  • Three papers were submitted to 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
DSI-NRF CoE grant; BirdLife International; Mohamed bin Zayed Species Conservation Fund, African Parks.

Research team 2022
Prof. Peter Ryan (FIAO, UCT)
Dr Gary Allport (BirdLife International) 
Prof. Desire Dalton (NZG)
Dr Alan Lee (BirdLife SA)
Dr Birgit Erni (Stats - SEEC, UCT) 
Dr Samuel Temidayo Osinubi (FIAO, UCT)
Dr Jessica Shaw (NatureScot)
Prof. Les Underhill (BioSci, UCT)

Students: Oluwadunsin Adekola (PhD, UCT); Rachel Dobson (visiting PhD student, Leeds); Taylyn Risi (MSc, UCT); Ben Heather-Clark (BSc Hons, UCT); Rebecca Irons (BSc Hons, UCT).