There are hundreds of reasons, but some very common ones are, food shortage, global warming, habitat loss, and poaching. Is this what you were looking for?
they become endangered in 2099.
they started to become endangered when global warming had started to increase
they become endangered when the food they eat is scarce.
They are listed as vulnurable or threatened, not endangered.
Peacocks and peahens are not endangered.
Yes. There are five endangered species now. Twelve are not endangered.
cougars are not endangered,save for the Florida race.
Not entirely. But they might become endangered soon.
It was endangered in 1997.
The Nile crocodile is not endangered.
it has just become endangered http://www.environment.nsw.gov.au/determinations/BlueWhaleEndSpListing.htm
It become endangered when people started hunting and killing the animal too much.