Ikul specified that the players had "gone through most of their rations," so I presume the answer to 'why?' would be 'because I'm hungry.' If the players are running low on food, it makes sense to turn to what is provided to them for sustennance. Eating insects is nasty by Western tastes, but in other parts of the world, not so much. Furthermore, if you're facing starvation, it's perfectly reasonable to allow one's standards to slip a bit.
As for the ostrich things (I still have no idea what we're actually talking about here, but the details aren't important) make perfect sense to eat if one disregards the whole sentience thing--which the players don't know about. I mean, really, we eat fowl of all sorts. Chicken, turkey, duck, quail, so on--I have no idea what ostrich tastes like, but if I were really hungry and there was nothing else available, I'd endeavor to find out.
In the end, given what we know of the situation, I think the players are behaving well within reason here. Perhaps even smartly, depending on how dire their food situation may be. Now, if they start eating things that are inherently and obviously magical in nature? I retract that assessment.