@Lady I can see why they did. Without the citation, someone is going to complain that bowerbirds and pufferfish have complex mating habits, octopi can use tools, etc. With the citation, if someone complains, the author can at least say "well, that doesn't agree with the source I used".
@Lady I definitely agree! The author should not have to make such a citation. But reviewers and readers are persnickety pedants sometimes.