Monday, 22 August 2011

How long do Swifts live?

Contributed by Dick

This question is often asked, and one answer is that the oldest known Swift was 21 years old. We know this, because the bird was ringed as a chick in Switzerland and recovered still alive. Just how many Swifts get to 21 years old? For that we need an estimate of survival rate, which Perrins 1971 gives as 83%. In the chart below, you can see what percentage of Swifts there are in the population at each age. For example, ~8% are 5 years old. Swifts that get to 21 and beyond make up 2.4% of the population.
Swift population structure