I once watched several seagulls peck at a closed clamshell container containing pizza crusts for over half an hour. Clearly there is an upper bound to their intelligence.
I watched a crack head at the park look for something on the ground for an hour once. Clearly there is an upper bound for human intelligence as well /s
It's been reported that younger gulls initially try to open clams (the animal clams, not plastic containers) by pecking. I believe they learn the dropping-from-a-height tactic from observation, and suspect that the pecking at a plastic container is merely due to them not having seen it being open by a gull before. Also, worth considering that in their natural habitat, the only transparent things around (jellyfish) are squishy and stingy.
I once spent ten minutes frantically looking for my wristwatch. It was very stressful, because I had to go to school, and I did not have much time left to catch the bus. So after a while (like I said, about ten minutes), I looked at my wristwatch to see how much time I had left. It took another 30 seconds for me to realize that I had been wearing my wristwatch the whole time.
Being smart does not save you (and not me, either!) from being dumb. And there have been times in my life when I was able to substitute inventiveness with stubbornness.
So there are upper bounds to everyone's intelligence, human or animal[0], genius or idiot. Given the variety we can observe in our fellow humans, I think it's fair to assume birds have their "village idiots", too.
[0] Except for barnacles, of course, but they are very discreet about it.