Collective nouns for animals are interesting. For example, tigers ambush and rhinos bust things up, therefore, we have an ambush of tigers or a crash of rhinos. We have lots of bird feeders, thus we have drays of squirrels in the yard, dray referring the nests they build, although I’m not quite sure of the etymology in the sense of dray and nest.
There’s a deductive poetics to the practice. I always felt that all you needed was a decent eye.
We have a shadow (not a murder) of crows. The grackles have visited the feeders. And they certainly arrived and left like a storm, hence storm of grackles.
There is practicality to this.
“So, what did you see?”
“Lots of grackles.”
“A storm then.”
“No, not a cloud in the sky.”