Threats to waterfall population data was not tracked until the 20th century, though experts believe waterfowl populations were up to __________ times larger than current populations Populations of waterfowl began to shrink until conservationists like Theodore Roosevelt and Gerogle Bird Grinnell began to notice and advocate for hunting regulations though establishing ___________, setting limits on harvest numbers and banning commercial hunting. Conservation ___________ populations are limited by their habitats. There are four primary factors which must be available for each bird to thrive--_________, _________, ________, and __________. The population will grow until one of these factors runs of for an individual. In many __________ habitats, all factors may be _________, but there will still be one limiting factor influencing the population size mroe than the remaining factors.