Blue tits and great tits are struggling to breed in city parks planted with exotic trees and shrubs, research reveals.The birds are less able to rear chicks in 'man-made' areas filled with non-native trees and shrubs than in natural landscapes like woodlands and hedgerows, the research shows.The study by Anglia Ruskin University and the Centre for Ecology and Hydrology monitored breeding success of blue and great tits in nest boxes in the Botanic Gardens in Cambridge, and compared it with those in nest boxes in more traditional woodland and hedgerow habitats.Struggling to survive: The left image shows an 11-day old great tit chick from a nest