Can you hear the birds sing in the morning?

Can the birds be heard to sing in the morning
hear只有两种用法为：hear sb do sth,这是一种不带to的不定式,当为被动时to需要补回来,另外一种则是hear sb doing sth表示正在进行的事,由于这里sing是原形,故只有填上be heard to 了