The way that I saw this one (after the fact) which I do not think anyone has stated so far is that we cannot assume that the birds know that they would be safe from the predators if they did not bark. The stimulus states that the barking is the only way that the predators know they are there, but what if the birds do not know that? If they don't (which we have to assume they don't) then they bark in order to scare away the predators- the only thing they think works.
This was my thought process (hope it is correct) but it justifies answer B
#16 - Babblers, a bird species, live in large cooperative
I don't think we have to assume anything about the babblers' knowledge either way, JiminyC. Maybe they do know that they are giving away their position, but they figure it is better to scare the predators off than to hide and hope that this time they will get away with it. After all, it's not that they ALWAYS feed safely and the predators NEVER become aware of them until they bark. It's that they USUALLY feed safely and GENERALLY aren't noticed until they bark. Maybe they figure it's better to be proactive and try to create the best result (scare the predators away) than it is to remain passive and hope for the best? Then again, maybe they really don't know that they are creating a risk for themselves, and they are just lucky that it works most of the time. Their knowledge really isn't important to this question - it's the actual results that matter.
Adam M. Tyson
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