I think there is also a logical fallacy in that, when people donate they are not really focused on how their donation "would" affect the final outcome. Instead, people are thinking about how much they "could" donate. Personally speaking, when I donate, I'm confident that my donation couldn't save the whole pack, I'm just content with just helping out one of them, if possible.

I think it's not that the scale of the flock didn't matter to me, but if you spell it out how much it would take to rescue "one of" the people or animal in need, people would definitely donate differently.