Editor's note: the following is quoted from save-wildlife.org/counters.php, altered only slightly to reflect this website.
What are those counters at the bottom of the previous page?
The human population counter has been created using the statistic of the US Census Bureau. The counter of the reducing number of natural habitats uses the data / information from the following publications: - " A reconnaissance-level inventory of the amount of wilderness remaining in the world" by J. M. McCloskey and H. Spalding - "Review state of the world's forest 1999", FAO 4/3/99.
It should be noted that the evident reduction on the counter is only related to tropical forests (the habitat most threatened and of which there is consistent data). It doesn't include the reduction of other types of habitat. Therefore the real level of shrinking territories is definitely higher.
The Counters are courtesy of Fondo per la Terra (Earth Fund).