adUlt migrations | 79today’s global population numbers around 1,500 birds. One of those
birds, tracked during its moulting period, spent no fewer than 39 days
drifting on the water among the islands of the Aleutian Arc. Daily it
drifted to north and to south as the tide ebbed and flowed in these pro-
ductive waters. Presumably enough food came within reach of the bird’s
mighty bill to sustain life until flight could be resumed.
So much of the information in this chapter has come from geoloca-
tors, miraculous packets of electronics now smaller than a broad bean.
Attached to seabirds weighing 100 g and upwards, they have trans-
formed our knowledge of the truly astronomical distances covered by
seabirds, plus the routes and the rests taken. When combined with su-
perficially simple information on whether the bird is flying or swim-
ming, it is possible for an extraordinarily detailed picture of a seabird’s
non- breeding adventures to emerge. Doubtless, in the next few years,
the devices will be further miniaturized so that they can be attached to
the very smallest species, such as storm petrels. However the relative
coarseness of the positional information, often no better than 200 km,
means that geolocators fail to provide truly detailed information on
a bird’s comings and goings during the breeding season. The necessary
precision is available from GPS trackers which are key aids in under-
standing activities of breeding birds.