The beaver populations are rebounding because of the increase in willow growth along streams. The elk used to hang out in the wet valleys and browse the willows down to nothing. They are easier prey there than on the hillsides, so now they hang out on the hillsides and leave the riparian areas alone.
NJTroutbum:
Actually, wolves are far more likely to take old cows than calves. I briefly dated a girl who was involved with elk mortality studies and both bears (both species) and coyotes were bigger predators of calves.
In regards to the overall numbers of deer and elk, elk numbers have indeed plummeted. One thing that the RMEF never mentions is that the year the wolves were reintroduced was also the all-time high for elk in Yellowstone's Northern Range. With the drop in elk populations, wolf populations even in packs not subject to being hunted (entirely inside the park) have also dropped. The peak year for wolves in YNP was roughly 2004. Deer numbers have little to nothing to do with wolves, because elk are a far more important prey species. Deer populations crashed last year due to hemorrhagic fever, but I still routinely see hundreds or more on a drive from Gardiner to Livingston at dusk. This is not an exaggeration. That's an absolutely terrifying drive at dusk.
