In the videos you’ve seen, only the cowbirds are personified. The warblers are presented in a way that makes you care about them, but they are not described using human motives and emotions. The people who made the video chose to personify the cowbirds for a reason: What could it be?

One reason might be that personification can make the information easier to understand; it's clear that the cowbirds are a problem that needs to be solved. Another reason might be that the story becomes more interesting when the cowbirds are presented as evil—then we may care more about what happens to the songbirds.