[Tweeters] Why don't we see birds on blackberries?

[Stan Bezimienny via Tweeters]

Jim, 

I am rather positive birds feed on blackberries - and contribute to their spread, I see colonies of seedlings of trinity of invasives: Himalayan blackberry, English ivy, English holly in my garden in the areas where birds (I suspect robins) frequent. Our light color deck is often splattered with purple from bird poop, of course to prove my point I would have to run a formal experiment and germinate the seeds from it, but it coincides with blackberry fruiting. 

As I photograph in local parks, I notice blackberry thickets with lots if birds, eg in Magnuson there are always house finches in abundance, also golden-crown and fox sparrows, towhees etc. in blackberry thickets. In fact it is often difficult to find birds perching on anything else (within camera  reach) than a blackberry stem, so they must accept life with the thorns. I have lots of pictures of this sort, too many for my taste. I think the thorny thickets offer birds protection, rather than deterring them. 

Best,

Stan