Carnivalia

May I hijack this post to ask a couple of totally off-topic questions about birds?

I'm located in Washington DC, downtown, and for the last year I've been feeding a group of starlings and sparrows near my office building. Over the year, watching the changes in these birds, watching them raise young, moult (did you know that tail feathers are not required for flight? I sure didn't) has been fascinating.

One of the most interesting changes has been in the starling population. In the fall, there began to be yellow bands at the base of the beaks of some, but not all of these birds. Through the winter these birds have come to have all-yellow or yellow and black banded beaks, but with one exception the overall beak length has not changed (about 1-1.25cm). One bird has about doubled the length of its beak and has a beak that is an easy 2cm long with a black end, a yellow middle section and now, a black base. It does not appear to be interfereing with its eating, yet, and I continue to watch this bird with some fascination.

My questions:

From observation of the color changes, I presume bird beaks grow from the base and wear where they meet, is this correct?

Does the shape of the beak change as it grows or it is a simple conic section?

Do bird's beaks, like rodent teeth, grow contiuously thru the bird's life?

Are they composed of bone-derived material or of dentin-derived material or of a fingernail derived material? (I know that evolutionarily the ancestors of birds were toothed dinosauria but wonder which part of the jaw structure was retained as the beak and what was lost.)

Any idea what is going on with my long-beaked starling? Is that bird in trouble?

And lastly, I know how (more or less) to sex the sparrows, but is there any "tell" on the starlings?