Insect eating birds tend to go for suet and peanut butter:
chickadees, nuthatches, woodpeckers, jays.  They also go for
sunflower seed.

Seed eaters generally don't go for suet or peanut butter: sparrows,
pigeons, finches etc.

Squirrels go for all of it and make a point of destroying the feeder.

Dick
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http://smith.syr.edu/~ddawson
SU Rifle Club: http://smith.syr.edu/~ddawson/surifleclub.html