Is the Redness of the Mouth a Signal of Need?

The project looked at whether parents or their offspring were in control of food allocation. If the brood is uniformly super hungry, the offspring have control and they compete to be closest. But if there's variation within the brood and who's hungry, then the parents reach over and feed the hungry chick as identified by the signals. The second part of the project was to identify what those signals might be. One day when I was hand feeding some chicks, I noticed that as the chick opened its mouth to beg, there was a sudden rapid flush of presumably blood into its mouth so that its previously pink gape suddenly became intensely red. And so I thought, well, maybe this is a signal of need