Avian Demography Unit
Department of Statistical Sciences
University of Cape Town
|BIRD NUMBERS||Volume 10 Number 1, July 2001|
11. Bird ringing - is it still a useful tool?
H. Dieter Oschadleus
With the Avian Demography Unit celebrating its 10th anniversary, it is appropriate to look at the state of affairs of bird ringing, a project that is now over 50 years old. Bird ringing has been described as the single most useful tool in ornithology over the last 100 years. In recent years, however, new scientific techniques have come into general use, e.g. satellite tracking and DNA analyses, which may challenge the importance of ringing.
Bird ringing, however, still has unique functions to fulfil and will continue be an important tool in ornithology. Firstly, it is not restricted to the professional ornithologist (at least not in southern Africa). Amateur ringers gain a lot of pleasure from ringing as a hobby, plus they are contributing to science and making the general public aware of the beauty and value of birds.
In the last decade or so, satellite transmitters have added greatly to our knowledge of bird movements, showing actual routes taken. Satellite transmitters are very expensive, however. There are also size limitations, although in future, smaller and smaller transmitters will be manufactured for use on small passerines. In the meantime ringing will continue to add to our knowledge of bird movements. Recently a Damara Tern Sterna balaenarum (F44378) gave the first concrete evidence that this species migrates to West Africa (Africa – Birds & Birding 6(3): in press). Similarly, a Whitewinged Tern Chlidonias leucopterus (BC40639) was the first recovery of this species en route on migration (Bird Numbers 9(2): 23). Ringing is of more limited use for other categories of movement, e.g. altitudinal and nomadic, unless a series of ringing sites are set up specifically to study these.
Bird longevity and survival rates
Satellite transmitters do not last long compared to the life-spans of many birds. Ringing will still fill in many gaps on longevity of birds. A recent example is of a Hartlaub’s Gull Larus hartlaubii (561283) retrapped at age 24 years (Africa – Birds & Birding 5(3): 18). While individual longevity records are of more interest to the general public than the ornithologist, all retraps and recoveries add to our database which can be used for scientific survival analysis. Large sample sizes are needed for survival-rate calculations; satellite tracking is so expensive that only small numbers of birds can be tracked.
Causes of mortality
Bird ringing provides data on bird mortality. Even though these data are biased, these data are not generally collected for all species. Some exceptions are surveys of power-line collisions and the drowning of raptors in reservoirs. In fact, this latter (previously unknown) cause of death was discovered because ringed raptors were reported to SAFRING. Recovery data give an indication of bird species taken by owls – the bird skeletons are not always easy to identify while recovered rings give positive identification (Africa – Birds & Birding 5(4): 16). Other common causes of death have been discussed, namely cat kills (Africa – Birds & Birding 5(2): 15) and collisions with windows (Africa – Birds & Birding 4(6): 23).
Using colour rings or engraved rings allows individual birds to be studied in greater detail, e.g. territory size, local movements, and breeding studies. While radio tracking can potentially give more data, it is expensive and short-term, providing information for a few months at most. Colour ringing can be used to involve birders in an exciting way, but it requires some effort. More than 350 Hartlaub’s Gulls Larus hartlaubii have now been ringed in the Cape Peninsula to study their local movements, survival and age of first breeding (Bird Numbers 9(1): 15–16). The number of resightings is now over 30, with three gulls having been resighted more than once.
Moult and morphometrics
Every bird handled by a ringer can give valuable data even if the bird is never caught or recovered again. Moult is an important part of a bird’s annual cycle and is not yet well known in African birds. Morphometrics can be important in ageing and sexing birds, racial variation, identification, etc. While moult and morphometrics can be obtained in other ways (museum specimens, captive birds), ringing is still the primary tool for obtaining such data.
The above categories indicate the areas where general bird ringing will continue to make important contributions to ornithology, though it is advantageous to combine ringing with other tools such as satellite tracking. There are, of course, also many other possibilities for specialized research with birds in the hand, e.g. looking at blood parasites. Bird ringing is definitely here to stay, and its value will be greatly enhanced if used in conjunction with other tools.
Birds found with rings should be reported to SAFRING at safring@gmain-com or telephone (021) 650-2421/2 or fax (021) 650-3434, with details of ring number, date found, exact locality found, cause of death and state of bird, as well as your contact details.
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Document posted: 24-Aug-2001
Office Avian Demography Unit