Merlins are highly aggressive towards other raptors and crows during the nesting period. This is beneficial to the song and ground birds of nearby woodlands, since their territory is kept fairly free of predators during the entire mating season. The survival rate amongst young merlins is exceptionally high, with three birds per nest often reaching breeding age. Found throughout the northern hemisphere, they favour areas of open country such as grassland, dunes and coastal areas. The merlin is the smallest falcon in the UK.