Kanto Route 1

Ash persists in his attempt to capture a Pidgey, but instead, he and Pikachu end up inadvertently agitating a Spearow. A very territorial and aggressive flying Pokémon, the bird calls a flock of other Spearow that suddenly take off the lush tree on this hill, and head toward Ash and Pikachu.

The tree hiding a host of angry Spearow.

Season 1 - Episode 1

"I Choose You!"

Ash and Pikachu are attacked by a flock of Spearow.