this is not uncommon. first the bees will fly and live to tell about it any day its 50F or warmer. what draws them to the birdfeeder, as far as i can tell, is pollen! some small amount of pollen is probably carried along with the seed in processing (plausible?). they will ignore the seeds in your feeder as soon as the 'natural' stuff makes its appearance. and at this time of year they have started brooding their spring/summer family and need the protein available in pollen. Rick Haver