[CT Birds] Migration dates

David F Provencher david.f.provencher at dom.com
Tue Feb 8 09:37:15 EST 2011


Good point Paul. There are a number of reasons this happens. Immature birds sometimes do not complete the full migration that adult birds undertake, particularly if the species is a long distance migrant and particularly on the northbound migration (in the northern hemisphere). This can also happen as a result of injury, illness, or poor feeding that results in a failure to build the necessary fat reserves to continue. There are also distinct advantages to shortening up the migratory distance. Staying closer to the breeding grounds means returning earlier than most individuals and therefore having the pick of territories. Additionally, a shortened migration route means less mortality through misadventure, so the behavior is genetically selected as successful by the species through a higher breeding success rate. With winter becoming milder (despite what this one has seemed so far) staying further north during the non-breeding season is becoming more and more viable.

Dave 

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