Beaks are too simple, in that they only posesses two digits and aren't articulated. And the current function - eating - isn't likely to be sacrificed for tool manipulation. [Simplisticly]When our ancestors stood up, that freed the front paws to develop into hands - birds don't have those 'free appendages' apart from wings, but those are so specialized that it would take a lot to bring them back to 'arms & hands'.
Indeed, bird's wings are so extremely adapted for flight (and ONLY for flight) that it is very hard to adapt these wings for something else than flying and showing off feathers.
Another thing is that bird's wings have only three digits whose sole function is supporting feathers and optimising flight.
It will be very hard to adapt such specialized limbs to fulfill some purpose other than flying and showing off feathers.
The only real possebility of a bird species evolving fairly complex manipulators would be to let an atavism that makes primitive fingers and claws develop instead of real wings become very common in a species of bird that is (nearly) flightless.
This was, by the way, the premise of the Carakilla's in the
The Future is Wild-series, allthough I have to add to that that such atavisms are pretty rare, and IMHO, the Carakilla's seemed to be more of an attempt to recreate a dinosaur from a bird rather than an attempt to create a very plausible flightless bird of prey...
setreoscopic/colour vision is very important to birds for flying and hunting, but that doesn't alone provide the mental tool set for complex thought. In fact, you could say that the specialization they require precludes the development of different mental structures.
That's quite true - both birds and primates began developing complex brains because they lived in a threedimensional world (in trees and, in the case of the birds, in the sky).
Though living in a complex environment and eating easily digestable, high-energy food like meat certainly helps species to develop their brain, allthough like MarkA already pointed out; exactly
what made our ancestors develop sentience and human-level intelligence is still a bit of a mystery
Brains are already incredibly efficient - we don't carry around a lot of excess brain mass just for the heck of it, becuase the energy requirements are just too great. Evolution weeds out inefficiencies (at least, until very recently when we started producing reliable food surpluses), so I don't know there's that much scope there.
For flight-balance purposes, you could have a larger avian brain that's decentralized throughout the nervous system rather than clumped in the head, but you still have a problem of energy consumption that pushes out other vital functions.
Hmmm.....you could be right about the weight of brains not really being a problem...
However, there's still another important issue concerning brains that IIRC hasn't been adressed yet;
exactly
how big does a brain need to be in order to be capable of true sentience?
I'm talking about both brainsize in relation to bodymass and absolute brainsize here;
exactly
what would be the minimal size of a sentient brain?
Is the human brain pretty much the smallest possible brain that's capable of sentience, or could we theoretically have
sentient creatures that are, say, the size of a large dog, or a cat, or perhaps even something smaller than that?
As for the huge energy consumption of brains - that's very true. For example: the human brain makes up only 2%
of the average human's bodymass, yet it consumes about 25% percent of the energy that the human body produces.
Evolving a brain that is as big and advanced as the human brain automatically means sacrificing
a lot of energy
that would otherwise be used or even neccesary to run other organs, especially the digestive track.
