Regular censuses conducted over a long time allow the calculation of b
oth extinction and immigration rates. We present formulae for estimati
on of those rates. We use them on bird censuses of three British islan
ds. These formulae mulae improve on previous estimators of extinction
but reaffirm that smaller populations have a higher probability of bec
oming extinct. On the other hand, they suggest no correlation between
extinction rate and either body size or migratory status among birds.