I smell a Ryan George video.

See for yourself here! Apparently the call sounds like "go-way", which I can KIND OF get from the audio clip on that page? Not sure I would have naturally made that connection, but sure.

i believe its because of the sound it makes when its startled

That made me look it up, and it turns out goat sucker birds predate the chupacabra by a couple thousand years. There was a myth that these birds drank goat milk (from the goat).

I remember reading the Dragonlance books in the 90s, and one character would talk about a cryptid called the "Goatsucker Bird" that was an amalgamation of those two things, and now I finally get that joke.

That name goes hard!

So what does the Pokémon that runs around screaming “goatsucker” do?

some birds are called after their bird calls. Ie, birds that call their own names like Pokémon.

Kea