A question I am often asked by visitors to the Wildlife Centre is "How long do birds live?" Like many simple questions this is hard to answer. While we know a lot about the longevity of humans, birds’ statistics are more difficult to capture.
The main method of discovering facts about birds is by ringing them. This involves catching the bird and placing a small metal ring on its leg which has a unique number and the address of where to send the ring if it is found. About three-quarters of a million birds are ringed in Britain each year and from the rings read from recaptured birds or found on dead birds data is collected about the birds’ lives. Unfortunately, only a very small number of rings are returned so it takes many years to build up a picture of where particular species go and how long they live.
In Angus, the Mute swan is the focus of a long term ringing programme which enables data to be collected about the local birds. In the case of swans, a large coloured plastic ring is fitted as well as the metal BTO ring. This ring is inscribed with three letters which, together with the colour of the ring, uniquely identify the bird and can be read using binoculars. This means their identity can be noted without having to re-capture the bird. This enables data to be collected about individual birds when they are seen throughout their life. This might include whether they are breeding and the number of cygnets.
Usually, swans are relatively easy to find (alive or dead) and therefore the data about individuals is more complete. However, other species, despite their sometimes gaudy colours and tuneful song are usually well camouflaged in their normal environment even when alive, so finding dead ones is quite hard. Researchers wanting to find a dead specimen must do so before it is recycled as a sparrowhawk, cat or fox!
So anyway, how long do they live? The data on Angus swan ringing and sighting is held on computer at the Wildlife Centre and we can bring up a lot of information about individual birds. Of the 1760 birds ringed, we know of 190 that have died. The average age of these birds is 3.5 years while the oldest bird was 15 when it died. The British record for the oldest mute swan is 21. This large range of ages for the mute swan shows why it is hard answer the question of longevity with any certainty. Other birds show a similar pattern. For instance, the robin has an average life span of 18 months yet the oldest recorded was nearly 13 years old when it died.
You can help to improve this database by recording the ring details of any swan you see, where and when it was seen and send the details to the Montrose Basin Wildlife Centre. Do not approach a swan too closely, especially if they are on a nest or have cygnets close by - their reputation for "vigorous" defence is well founded. Use binoculars or telescope to read the plastic ring, which are white for Angus birds. Any other colour will be an "in-comer" and of particular interest. Even if you can’t read the letters of these "foreigners" please let the Centre know the details and we can investigate more fully.
Of the commonly seen species on the Basin, the Arctic tern has the age record at 34 years. The Black-headed gull at 32, and the Mallard at 29 are close behind. The actual birds you can see at the moment are probably much younger.
"How long do birds live?" - it’s just a hard question to answer!