Isn't it always the case - the animals come take all your fruit just when it's perfectly ripe! I have cherry trees and it seems like they all wait for the exact second it's perfect then it's a feeding frenzy and it's stripped in a matter of hours...
Anyway, is the tree under other trees that they can jump from? If not, squirrels can do about a 4' vertical leap and if there's no branches lower than 4', you can put a metal shield around the tree and they won't be able to climb up the trunk.