麻雀 has two distinct meanings: a small common bird (sparrow) and a popular four-player tile game (mahjong, also written 麻将). The game sense is especially common in southern dialects and in Japanese, while in standard Mandarin the bird meaning is primary. Context usually makes the sense clear — if someone is playing 麻雀, they mean the game. If you see 麻雀 in a tree, it's the bird.