Flocks of birds are a familiar sight, from waders on estuaries to city starlings. Mark Carwardine explores the reasons why birds of a feather flock together and discovers the benefits of belonging to a group. See Sue Gaisford's choice on page 118. Producer Brett Westwood. Repeated tomorrow 11am
WEBSITE: www.bbc.co.uk/nature. E-MAIL: nature@bbc.co.uk