鸟 means 'bird' — a common noun that typically uses the measure word 只 (for small animals) or 群 (for flocks). In HSK 2, only the 'bird' sense is needed. Note that 鸟 is also a Kangxi radical and appears in some dialects as a verb ('to pay attention to') or as a vulgar intensifier (damned/goddamn), but those uses are not part of standard Mandarin and should be avoided at this level.