precursors to migration in birds.-------A 2006 related paper:Phylogenetic tests of hypotheses for the evolution of avian migration: a case study using the MotacillidaeDiana C Outlaw and Gary VoelkerThe Auk April 2006 123:455-466The evolution of avian migration continues to be an intriguing research subject, even though relationships between migration and factors such as seasonality clearly exist.