statistics on endangered animals

[Heidimuss@AOL.COM]

Hi folks!  One of my fifth grade classes is searching for statistics on
endangered animals to produce graphs.  Specifically, they need to know how
many of certain animals were on this earth at one time, and how many are
left.  We have checked books, encyclopedias, almanacs, magazines and have not
been able to find a single source with this information.  Can anyone help.
 Thanks.  Heidi