Mike,
As far as his appearing to sleep while being held is concerned, it is probably either that he is tired from trying to resist your grip, or that he is 'hiding' from you. Alligators, even very large ones, close their eyes in an effort to relieve the stress they feel from external visual sources.
As for the yulping, let me expound on my previous post by pointing out that the yulp is a more than just a crying out in a dangerous situation. It is, generally speaking, a sign of excitement. In the case of yulping at feeding time, they are excited -- 'happy,' if you will -- that you are feeding or are about to feed them.
I've had crocodilians that I've trained to yulp for their food, or to yulp when I approached a certain area of the enclosure, or to yulp when I vocalize first.
It is interesting that the yulp is the alligator's first means of communication, as it is hatching, and the mother is involved in taking them from the nest to the water. It is a testament to how the strong maternal-related influence is on alligator behavior. When an adult is dying in the throes of a violent fight, it yulps as if it's a baby (it's quite striking to me to see the big animal suddenly crying like a hatchling, but with deeper tone and lower pitch)...reminds me of grown men in battle, dying in the field, calling out for their mothers...
I hope that answers your questions.
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Israel Dupont
Winter Haven, FL