In the morning garden, a few titmice were hopping cheerfully among the branches.

titmice 是 titmouse 的复数形式。titmouse 由 tit（小型鸟类）和 mouse（老鼠）组成，字面意思是"像老鼠的小鸟"，指一种体型小巧、活泼好动的山雀类鸣禽。