The barn swallows siblings compete for food and parental attention is an interesting process and the feeding can be observed in plain sight. The youngster contend for better position, consistently push the next guy down anyway they can and elevate to reach their parent when food arrive.
In number of occasions, i’ve seen they flew off, made a quick turn back to the perch then push the top guy off position. Too bad i didn’t get any keepers when the perch was filled. There were as many as 8 young barn swallows at one point.