A new era of bird migration research has been launched with the use of miniaturized geolocators. The newest geolocators are small enough (0.5 g), in theory, to be deployed safely on large warblers, so the taxonomic scope of migration data is broadening each year. Despite small sample sizes, geolocators have already changed major assumptions about migratory connectivity, migration routes, non-breeding sites, and migration timing.
New Discoveries in Landbird Migration using Geolocators, and a Flight Plan for the Future
McKinnon, E.; Fraser, K.; Stutchbury, B. (2013). New Discoveries in Landbird Migration using Geolocators, and a Flight Plan for the Future. The Auk, 130(2), 211-222.