Several weeks pass before the young birds lose their 

 awkwardness on the wing. 



until the following year. Manitoba Crow families likewise leave the nesting 

 places soon after the young are on the wing, young and old joining bands 

 which eventually make up the large migrant flocks. 



By and large, however, the evidence suggests a random scattering of the 

 young of many species away from the natal range. The true nature of the 

 scattering is sometimes confused — by ecological barriers, which inhibit 

 movement in certain directions (e.g., the failure of sea birds to wander over 

 forested country) ; by human bias in band recoveries (e.g., as between settled 

 and unsettled districts); or by elements in the weather (e.g., the dominance 

 of certain air masses, spoken of on p. 208) that may give random travel a 

 geographic bias in the direction of the dominant flow of air. 



Winter vagrancy 



However direct the autumn migration, however ancient the wintering 

 locality, there is strong evidence of vagrant travels by both young and old 

 birds about the wintering grounds or from stopping places along the fly- 

 ways of migration. These may be "explosive" movements in any direction, 

 like those of the Louisiana Ring-necked Ducks or the McGinnis Slough teal 

 described elsewhere (p. 112) . They may be "weather movements" - south in 



147 



