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 are listed as vulnurable or threatened, not endangered.
Peacocks and peahens are not endangered.
they become endangered when the food they eat is scarce.
Yes. There are five endangered species now. Twelve are 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.
cougars are not endangered,save for the Florida race.
Not entirely. But they might become endangered soon.
The Nile crocodile is not endangered.
It was endangered in 1997.