The paper looks impressive; I'm going to read it further. But in the abstract they cautiously say "Our results suggest the functional extinction of vultures ... increased human mortality" (emphasis mine).
Usage of “hedging” terms like this is normal practice in academic writing. For a variety of reasons, some social and political, some practical. The short explanation is that the current scientific process values humility.
It's a scary realization that a lot of climate scientist, including the IPCC, give us the lower number that they can be more confident with, because the higher number will get people yelling "Crackpot!" at them. (the number being temperature rise, CO2 concentration rise, and all the bad things).