[CT Birds] Thoughts on Varied Thursh

David F Provencher david.f.provencher at dom.com
Wed Jan 6 07:29:13 EST 2010


Dennis,

Population size is only one parameter that affects vagrancy. It is true that a population decline will affect vagrancy on a purely empirical basis but using a small geopolitical area such as CT may not be the best way to quantify that affect. Simply stated, not all vagrants end up in CT, so if a particular year sees no Varied Thrushes in CT there may still be more in New England overall than usual. Other factors that affect vagrancy include weather patterns, breeding success (different migratory behavior in immature birds versus adults), migratory behavior of the species in question (long distance migrant vs short distance, etc), food source availability where the vagrant ends up, and of course the randomness of discovery (many vagrants are never detected and this percentage varies from year to year.) I know we have beaten this horse before but extracting accurate information from vagrants about a particular species population is difficult. If you were to factor in the other variables with the vagrant discovery patterns you might be able to learn more about what are the most influential factors at play in vagrancy to CT. Oh and aren't we lucky that there is such a thing as vagrancy in bird migration. It makes things so much more interesting, regardless of why and how it happens.

Dave

Dave Provencher
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