These Yellow Warblers are busy feeding their young chicks which is extra work with a cowbird chick in the nest too who is so much bigger than the little warblers. So a majority of the insects the parents bring to the nest are given to the bigger mouth of the freeloader.
Brown-headed Cowbird females skips building nests and instead put all their energy into producing eggs, sometimes more than three dozen a summer. They deposit their eggs in other birds nest to raise their young, often though at the expense of the unwilling foster bird’s own chicks. But the cowbirds don’t just dump and run but keep an eye on their eggs and young and if their egg are removed, they retaliate by destroying the host chicks eggs in a term called “mafia behavior”.
The nests of the Yellow Warbler are frequently parasitized by the Brown-headed Cowbird so the warbler often builds a new nest directly on top of one containing the cowbird egg along with their own eggs. Sometimes there may be up to six layers if the cowbird keeps redepositing eggs but it appears this nest is only one layer.
Yellow Warblers Feeding Their Young
The video has some clips of the Yellow Warblers feeding their four chicks and the extra cowbird (but I was mad at the freeloader so I cut out most of the clips where the big mouth was getting all the food).