My sister got excited when she saw the waterfowl.

Literal

Younger-sister [topic-は] waterfowl [object-を] see-[sequential-て] got-excited.

水鳥 (みずとり, 'waterfowl') is 水 ('water') + 鳥 ('bird'). 興奮する ('to get excited') is a Sino-Japanese compound. The て-form connects seeing to the resulting emotional response.