Hi Ann, I cannot tell you why they're not using it, but I can tell you that I have seen the same thing in my garden. The Sparrows sometimes ignore the seed feeder for days on end and then all of a sudden they're swarming all over it. It could be a seasonal thing. Cold weather certainly affects their dietary requirements. I'm sure others will offer a more scientific answer.
Unicum arbustum haud alit duos erithacos
(One bush does not shelter two Robins)
Zenodotus (3rd Century B.C.)
Hi Ann, try putting sunflower hearts in that feeder and see if they still don't go to it.
Jim
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Hi Ann, I feed a number of feeders too and also mixed seed, in fact sunflower hearts mixed with poultry corn, which the sparrows and starlings consume pretty rapidly, as MC has said it could be just the temperature and the birds wanting the fat and oil from the sunflowers at the moment.
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I think they are picking at the best ones first like the sunflower hearts and fatty stuff as it's easier to eat and they get more energy from these I guess and what sort of mixed seeds are you feeding ? If it's large seeds they may be leaving them because they can't get threw them and are more preferred by pigeons.