Southbound
03 Jul 2014
One of many valuable outputs from projects that use satellite tags to follow migratory species' journeys is the opportunity to compare actual departure dates with the patterns apparent in the BirdTrack data.
Take Cuckoo, for example. In mid May, about 20% of complete lists feature Cuckoo. The reporting rate then plummets to less than 3% by late June. One explanation for this pattern could be that Cuckoos are harder to detect later in the season as males stop calling, rather than because birds are actually leaving the country. However, the BTO's fascinating tracking work on Cuckoos shows that by late June, male Cuckoos are indeed heading south. The autumn migrations of 35 Cuckoos were followed in 2011–13, revealing that the average first date for a bird's tag to transmit from the Continent is 28 June. In the first year of the project, one bird had even left Britain by 3 June! These figures tie in closely with the timing of the disappearance of Cuckoos from BirdTrack complete lists.
Share this page