Greg;
Fun question

When you speak of "
Hazelnuts" I assume you're talking about our native "Wild Hazelnuts." The local "
Filbert" industry has adopted the name
Hazelnut due to the fact it's the preferred name in Europe for this European-highbred. I still call the tree-crops
Filberts; but then I've spent
too many hours kneeling in muddy Filbert orchards picking these little things off the ground while attempting to fill a gunny-sack! They don't do it that way any more...
Assuming you are referring to the "
wild nuts" - and not their domesticated pals (which aren't ripe until early to mid September), here's what I've noticed around the woods of home: I've just begun to find cracked "Hazelnut" shells on my trails. The
Stellar Jay's (J-birds) are the major culprit; you can hear them pounding them open to eat the soft kernel inside. And yes, the kernel is still soft - and it may even be bitter. I'd also bet our native Douglas Squirrel's do a job on them too?
The last time I feasted on wild hazelnuts was while waiting for a school buss - that time of year - not yet. The nuts had firmed up, no longer soft & "milky," and the wild husks left tiny needle-like stickers in our finger tips. I'd simply cracked them open with rocks, and all-in-all the effort seemed worthwhile. But that was about 5 years ago and the wildlife have beaten me to them ever since...
I think it's too early to harvest the nuts "right now." But - as with most fruit - birds will take it long before we do... You may need "netting?" Our Hazelnuts grow wild in large scattered clumps and would be extremely difficult to net. The best I can do is watch for what they've missed, while giving the "Hazel Brush" a couple more weeks before I'd even mess with those prickly little husks that do turn light brown.
If you like their "pre-dried" flavor, I know a couple local orchards where me and the kids - sneak - a few fresh nuts for instant cracking and consumption. And they're much better than the dry, hard nuts you eventually get after the commercial processing... But you should ask a frindly "Filbert" Grower first

- - - I hope there's an answer in here somewhere.