Is there a sin incurred by one who left a bird in an open, unsheltered yard by mistake, and the bird died due to the heat of the sun, and what is the expiation for that?

If you intend to return something to its place but forget, there is no sin upon you, because Allah Almighty says: "Our Lord, do not take us to task if we forget or make a mistake." And in the authentic Hadith, the Prophet, peace and blessings be upon him, said: "Allah Almighty said: 'I have done so,'" and his saying, peace and blessings be upon him: "Indeed, Allah has overlooked for my nation mistakes, forgetfulness, and what they are coerced into."