Well, at least, the only thing THESE birds have to fear is fear itself.
This is one of those studies that, when you lay it out, seems really...simple. Clear layout. Clear results. But it challenges a lot of the things that we once assumed about predator:prey relationships. Most particularly, it overturns the idea that the only thing making prey die from predation is the predators themselves.
This seems really simple, right? Fox eats bunny, lots of foxes mean the bunny population declines. Just foxes being AROUND bunnies (but eating, say, SmartOnes meals or something), well the bunnies wouldn't get eaten and the prey population would stay the same or even increase. Right?
Well...wrong. It turns out that sometimes what the prey population has to fear, is FEAR of predation itself.
Zanette et al. "Perceived Predation Risk Reduces the Number of Offspring Songbirds Produce per Year" Science, 2011.
(this is a full video by the authors, showing the results of their finding! Wish more people could do this!)