I'm curious if there is any good reference for animal calls (wolf's howl, horse's whinney, etc.), specifically North American animals, and how far their calls can be heard. Thanks!

I can give you a few sites:
http://members.tripod.com/Thryomanes/AnimalSounds.html
Animal Calls
ANIMAL INFO - Animal Sounds Library
Macaulay Library - Animal Sound & Video Catalog
Elephants Call Long-Distance After-Hours