British scientists investigating a decline in the number of migrating cuckoos say five birds fitted with tiny satellite tracking devices have reached Africa on their journey south.

The five cuckoos were fitted with the tags — which look like miniature backpacks — before they began their migration in July, bound from eastern England to southern Africa. Four of them have already crossed the Sahara, while the fifth has stopped off in Morocco.

Scientists said on Friday information about the routes the cuckoos are taking will help them study the impact of population growth and climate change on the birds’ habitats.

The British Trust for Ornithology is examining where and when the migrating cuckoos stop off on their journey to Africa, hoping to understand more about why fewer and fewer birds return.