鸟类 (niǎolèi) means 'birds' as a category or class of animals. The suffix 类 indicates a classification, so 鸟类 refers to birds collectively as a biological group rather than a single bird.
这个地区的鸟类种类非常丰富。
zhège dìqū de niǎolèi zhǒnglèi fēicháng fēngfù.
The bird species in this region are very diverse.
科学家发现了一种新的鸟类。
kēxuéjiā fāxiàn le yì zhǒng xīn de niǎolèi.
Scientists discovered a new species of bird.
保护鸟类就是保护我们的生态环境。
bǎohù niǎolèi jiùshì bǎohù wǒmen de shēngtài huánjìng.
Protecting birds means protecting our ecological environment.