Does an expiatory offering (kaffarah) become obligatory and a sin befall one who causes harm to a pigeon while attempting to treat it with good intentions?

What happened from you to the bird unintentionally, there is no sin in it, nor expiation, and we hope that you will be rewarded for your attempt to treat it; for the saying of the Messenger of Allah, peace and blessings be upon him: "In every moist liver, there is a reward."