Do migrants know when the've gone far enough?

[Goldfynche]

A thought has just occurred to me, whilst watching 'Coast' on TV. They are on the island of St. Kilda. Way out, in the Atlantic, beyond the outer Hebrides. Yet, there is a Chiffchaff singing in the background. Will that Chiffchaff now decide "Yes, this is the ideal place?" Or will it strive to go even further, and certain doom? How powerful is that urge to fly north?

[Picidae]

If it was a Chiffchaff you heard (and the programme was live!?) then it was very likely one from the Scandinavian population (ssp abietinus) that move down through the Shetlands in the Autumn. It will continue to move Southwards I suspect during the next few weeks.

As for your question, no, migrants do not always know they've gone far enough - they sometimes overshoot, reverse migrate, or simply get lost, that's why we get rarities in the UK!!

[Goldfynche]

Definitely not a live show. SKY TV repeats programmes 'ad nausium'.