Conspecific Nest Parasitism
This is the first time I’ve heard of this happening. A flighted juvenile VGSW from some other nest (not one of the nest boxes that were being monitored, none of them had fledged at this time) decided to take up residence inside this nest box which already housed 4 other VGSW chicks. The small chicks were about 14 days old at this point. He would beg from these parents (not his own) on the wing as they foraged and then race them back to the nest box and get inside just in time to turn around and stick his head out of the entrance hole and open his mouth for the bugs. I admit that I chased him off whenever I noticed him hanging out in the nest box. I was concerned he would stop the flow of food to the smaller chicks in the nest box. While I was impressed with his cunning, his deviousness was hurting the offspring of these hard-working parents, so he had to go! He hung around for about 2 days then he must have decided to put forth some effort and feed himself.