Just had my 3rd manticore egg drop from the nest on one of my games, but have only had 1 egg from my other game and that was ages ago. Ironically, it was the game with only 1 manticore that I've had the goal that required lots of their whiskers (and it was painfully slow progress). I haven't had that goal yet on my game that now has 3 manticores, but at least when I do, it shouldn't take very long!