Treetop Dining?

A short walk at Lyons Woods FP today produced no new birds for the year, but you could tell someone had been busy:

These are the cones from Norway Spruce trees, planted there while the property was still a tree farm. Here's what one looks like close up:

Norway Spruce cone (Picea abies), Lyons Woods FP, Lake Co, IL 3/10/2014

Quite a few of them, though, looked like this:

What's going on here?

These are the leftovers from this guy's breakfast:

Gray Squirrel (Sciurus carolinensis), Lyons Woods FP, Lake Co, IL 11/7/2012

Here's one he just got started on:

But why are they on the ground? Squirrels can climb -- surely it makes sense to eat in the trees where it's safer?

I can't say for sure with Gray Squirrels, but with Red Squirrels like this one, someone found very interesting behaviors in this regard.

Red Squirrel (Tamiasciurus hudsonicus),
Alaska Zoo, Anchorage, AK 8/12/2012

Red Squirrels spend the morning and evening hours up in the treetops, cutting cones off and simply dropping most of them to the ground. In the middle of the day, they come down to the ground and collect them, actually eating them on particular posts. When you see a well-used post, it's quite noticeable -- there's cone scales piled up around for several feet.

So again, what's the point? In the morning, it's nice and cool up in the treetops, and the sun is falling on them and warming things up. As the sun gets higher and things start to really heat up, the squirrels move down to the well-shaded ground to avoid the heat. By dropping the cones, they provide themselves with a meal that they can take all day to eat.

The demands on a wild animal's life are often obvious -- a Cooper's Hawk in hot pursuit of  a squirrel isn't something you're likely to miss. Many selective pressures, though, are much more subtle, and we shouldn't be surprised when the adaptations to them are similarly hard to spot.