Arrrooooooo!

Nick is probably about to repeat his line.

We might get it but I don't Nick ever will.

This proves that animals haven't gotten rid of their biological instincts.

As Mr Big said... My child, we may have evolved but deep down we're still animals.

Exactly.

The movie only spells out the bare basics of the nature of prejudice, but it highlights all the complexities of it too. This is probably one of the ones they were least eager to highlight, as what's to be taken away from it is that prejudices don't just come from nothing. Sometimes, in fact, they are completely legitimate conclusions.

Which is no doubt what Nick finds so detestable about the howling: That, despite everyone knowing that howling is a part of the wolf stereotype, the wolves keep doing it. Not only sufficing to further validate the stereotypes of wolves, but possibly also reinforcing all the other existing stereotypes against other predators.

Though I would hope he at least has a little bit more empathy for them, now that he knows they can't always stop themselves from howling even when they know damn well they shouldn't.

You wrote - " . . . they can't always stop themselves from howling even when they know damn well they shouldn't. "

My turn - This was shown during the break into the asylum scenes when it was Judy who initiated the howl that allowed her and Nick to get past the Timber wolf guards. If they could help themselves then one might speculate that they're doing it to bug someone they know is irritated by their stereotypical behavior.

*nods* Which is what Nick might have thought at first.

And indeed, some wolves were observed howling without provocation. The two of them on the clip (most likely done to signal the successful capture of Mr. Manchas), and twice in the bullpen, first at Bogo's entrance, second when Francine gets wished a happy birthday (both visible here).

So it is, to some extent, a part of the wolves' culture. Only thing is that it's a part of their culture with its origins in their biology. It's not something they just decided to claim as some canine alternative to an elephant trumpeting -- it's something they've had since long before they were even walking upright.

If the line had come after the break-in, it wouldn't have worked. Which is half of what makes it so brilliant, actually.