Generally, life expectancy in birds is greatest in the larger birds but this is by no means exact owing to the difficulty in obtaining accurate information. A common method of aging birds is through ringing schemes:
Nestlings taken briefly from their nests and birds captured in mist nets have their vital statistics recorded and then a small metal or plastic ring that carries a unique identity is fixed to their leg. If the bird is subsequently recaptured or found dead, the details on the ring can be used to determine the age of the bird.
The table below shows the average and reported longest life spans for some of our common wild garden birds (not captive birds, which can live much longer):
So, the stark reality is that it is unlikely to be the same Robin that visits your garden year after year. This is because mortality (or death rate) in their first year is incredibly high and in fact only about one in four Robins reach their first birthday.
Up-to-date longevity records are published by EURING, The European Union for Bird Ringing.