watcher
watch‧er /ˈwɒtʃə $ ˈwɑːtʃər, ˈwɒː-/
noun [countable]someone who watches someone or something for pleasure or as part of their job
bird/whale/royal etc watcher
Fifteen thousand bird watchers visit annually.
Industry-watchers hailed the takeover as a triumph.
watch‧er /ˈwɒtʃə $ ˈwɑːtʃər, ˈwɒː-/
noun [countable]someone who watches someone or something for pleasure or as part of their jobbird/whale/royal etc watcher