After retirement, he took up birding and often visits parks with binoculars to document new bird species.

birding 是动词 bird（观察鸟类）加上后缀 -ing 构成的动名词形式，指"观察和识别野生鸟类"的活动，即"观鸟"。 binoculars 是名词，由前缀 bi-（表示"双"）和词根 ocular（与"眼睛"相关）组成，指"双筒望远镜"，是观鸟时常用的工具。