When we first set out to pilot GPS tags on headstarted Curlew back in 2021, little did we realise the level of insight we would gain into a previously poorly understood period of most birds’ lives. Wild juveniles and immature Curlew are hard to track with biologging technology, simply because at point of fledge (when field researchers can most easily run and catch by hand a young bird that is still a poor flyer), most birds are still not sufficiently fully-grown to safely carry a tag from a welfare perspective. Headstarting provides the advantage of keeping birds in captivity until they are strong flyers and near full-adult body size, plus the added benefit of being able to attach a tag pre-release and observe the bird’s behaviour while still in captivity. Should anything seem amiss, the tag can be safely removed before the bird is released into the wild.
Most of our GPS tags tend to either stop transmitting or the backpack harness falls off after about two years. Occasionally they continue to transmit data into their third year. Tracking data from previous years’ cohorts of released Curlew have led us to breeding attempts we would never have detected, and have given us insight into how immature birds ‘discover’ breeding sites where other Curlew are nesting. It is as close as we can get to understanding what is going on in the minds of these young birds as they figure out how to be a Curlew, and has led to a host of new questions and ideas. GPS tracking has shown that immature birds in their first, second and sometimes third year ‘prospect’ at potential breeding sites during spring. How do they discover these sites? Do they cue into large expanses of seemingly suitable habitat (i.e. large expanses of natural grassland), and then drop in to see if there are any other Curlew there? Future years may hopefully see improvements in the duration of tag deployments as we switch to a potentially longer-lasting harness material, meaning even greater potential to capture the movements and behaviour of immature birds as they return to breeding sites.
