Monogamous animals include wolves, jackals, foxes, beavers, marmosets, most bird species, and humans (some humans, anyway). However, if one of a pair dies, the other will generally find a new mate. It's very rare for an animal to never mate again if its mate dies, though this does sometimes happen with wolves (and humans).
One example of a positive feedback loop in childbirth is contractions. When the contractions start, they produce oxytocin, which stimulates stronger contractions, which produce more oxytocin.
