Hi Jenny --

The yellow variant in House Finches is not uncommon at least in my 
experience in banding many hundreds. It is possible it is related to the 
food source. During the late 1980s and early 1990s when I was actively 
banding we had many variations of the yellow and yellow and red in the 
plumage. The ones with the yellow rump may be older females as older 
female Purple Finches can have a blush of red on the rump. Sorry I don't 
know more about this variation in the eastern birds but remember that they 
were western birds that were released and started the eastern population. 
The biggest difference is that the western population is sedentary and the 
eastern population is migratory. Probably more than you wanted to know but 
here it is!

Cheers,
Kathy

Kathy Klimkiewicz, Biologist
USGS Patuxent WRC BBL
12100 Beech Forest RD STE 4037
Laurel MD 20708-4037
301-497-5795 work
Fax 301-497-5717

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