Ageing Afrotropical birds in the hand: a revised new system

Red-capped Robin-chat, Cossypha natalensis, undergoing moult check

Many bird studies rely on knowing the age of birds in order to calculate breeding success and survival rates. The age and sex of birds may determine their migration, moult strategies, survival rates and their foraging and roosting behaviour.

Ringing studies in Europe make use of the EURING numbered code system to age birds in the hand, and ageing often also helps to determine the sex of individual birds. The well-tried European system is based on the calendar year, since the annual breeding cycle occurs at a regular, fixed time of year. The system can be used in Africa for those birds that migrate between Europe and Africa but it cannot be used for species that are resident in tropical Africa where the breeding season is highly variable between species, location and year.

Ageing systems for ringers in Africa already exist in southern Africa, east Africa and elsewhere but are not widely understood or closely followed. The numbering system in use in the south may be easier to use than the others since the climate is more temperate and the breeding cycle is more regular, but none of the systems are well defined and there are many ambiguities. There is much variation in the interpretation by individual ringers, even within the same ringing groups.

Training to age and sex an African Paradise Flycatcher, Terpsiphone viridis

To assist and improve the ageing techniques of bird ringers working in the Afrotropical region a new ageing system was submitted to AFRING news by Colin Jackson, Director of A Rocha Kenya (Jackson, 2007). The proposed new system sets out clear definitions for each age class (pullus, juvenile, immature, sub-adult, full adult, unknown adult, fully grown) and backs up each definition with explanatory and cautionary advice in a succinct and helpful way. It is based on ringing experience in Kenya with the Nairobi Ringing Group as well as studies carried out at, and in the vicinity of, the A Rocha field study centre at Watamu, and elsewhere, including South Africa and Uganda. The system has been refined through contact and discussion with other ringers in Africa who are seeking a better ageing system (and from a personal need for clarity and simplicity of explanation while leading training courses for new ringers). No doubt further discussion and modifications will be required as ringers apply the ideas in parts of Africa where conditions will differ from those in Kenya. Indeed the system is already a refinement of an earlier paper published in Ostrich: Journal of African Ornithology (Jackson, 2001).

If this new ageing system is widely adopted in the Afrotropical region it will have important biological and conservation importance by making data gathering more efficient, more reliable and more comparable.

Project leader: Colin Jackson

Partners: Ornithology Department of National Museums of Kenya, Nairobi Ringing Group