The speaker doesn't explicitly state why she offered food to the bird. Perhaps she took pity on him because all he'd had to eat up until then was a raw angleworm.

Whatever her motives, in offering a morsel of bread to the little bird, the speaker is unwittingly intruding upon nature. She can't quite free herself from the notion that the bird would be better off eating some good old-fashioned human food. It's as if she's infantilizing the bird, turning him into a human child in need of constant care. Though perfectly admirable in some ways, such an attitude doesn't show much in the way of respect toward nature. And the speaker is intruding upon nature, even though she undoubtedly means well.

The bird's dismissive response to the offer of the bread is almost an expression of contempt at the speaker's presumption. Instead of gratefully accepting the little morsel, he immediately takes wing and flies off into the sky. It turns out that the little fellow was doing just fine with raw angleworms after all.