Tern bathing. What's interesting is that there is actually some sibling rivalry in some clutches that I have observed. This involves bullying the smaller chick, younger one I suppose by pecking at the feathers to make it move from a prime spot or also calling out frantically when food is served to deny the smaller chick of a meal. The necitating membrane has been fully developed by the time of fledging, we see the membrane in early form during the first day of hatching.