It is often said that birds of a feather flock together.
In fact, birds who flock together become firm friends and even set up home near each other.
A study of great tits found that when the birds settle down to breed in the spring, they chose sites near the flockmates they spent the most time with over the winter.
Researcher Josh Firth said studied great tits that live in woods.
The birds wore ankle tags that provide information on which feeding boxes they visit.