The Grinnell Resurvey project being carried out by UC Berkeley Museum of Vertebrate Zoology has been going back over surveys done by Joseph Grinnell in the early 1900s. The surveys are finding a number of small mammals are moving up in elevation. Climate change is the likely reason (http://mvz.berkeley.edu/Grinnell/
The last time I was at McClure in 2007, I was concerned belding's ground squirrels would be gone from Evolution Valley the next year. I'd seen only 6 that year and they'd disappeared from Colby. They have an over-winter mortality of about 20-30%. They'd also disappeared from LeConte Canyon since I'd seen them there in the mid-80s. They have, though, moved up into Dusy Basin and onto the Darwin Bench and Evolution Lake in the last 10 years -- an indicator that climate change is driving their decline at lower elevations. None were seen at McClure in '08, but last year they reappeared in both McClure and Colby. However, their numbers in those meadows are still down significantly from the 80s, when you'd see dozens scampering around.
I've got decades of sightings of pikas from areas I go back to. They seem stable in Sequoia Kings Canyon anyway, though the Grinnell transects have them moving up in elevation as well.
Rodents, though, definitely follow cycles and populations routinely crash. It's very difficult to separate those cycles from the longer fluctuations as a result of climate change.
The mountain yellow-legged frog has extensive research being done on their populations, as well as long threads about them here and elsewhere. They're definitely in trouble in the Sierra and are extinct in about 90% of their former range from only 20 years ago. In Bubbs Creek, I found a new area they'd colonized with dozens of adults and hundreds of tadpoles. Unfortunately, Roland Knapp's recent survey found Chytrid in a nearby population and he fears that it'll spread into the healthy populations. He's got a good post here: http://anuranblog.blogspot.com/2011/10/ ... frogs.html
for more information.
I'll add that it was a great sight seeing them at this new location. Walking along the grassy banks of the ponds, seeing and hearing the frogs leap and plop into the water ahead of me reminded me of what the Sierra was like only 30+ years ago, before their populations started crashing. It's a good reminder that all of these critters (and trees and rocks and streams) are an integral part of what we call the sierra, providing an emotional connection worthy of the effort and expense in preserving them.
A couple of posters have previously brought up questions about porcupines -- that their numbers seem down. I started paying more attention and tend to agree with this. I haven't seen any fresh sign in Bubbs Creek the last few years but this is pretty anecdotal. Like many species, I don't always pay close attention and our ability to track fluctuations is very limited.
In Sequoia Kings the Mustelidae (weasels, marten, wolverine) are slowing increasing from severe trapping in the 30s -- before it was a park. Weasel and pine marten sightings are fairly common, even the fisher is showing up every year or two in some areas. In spite of what some biologists think, the wolverine has had some very reliable sightings over the last 20 years. To me, that shows they're definitely around, though where they come from is unclear.
For both Yosemite and Sequoia Kings, I'd encourage people to send in their sightings. Both parks have extensive wildlife observation records going back to the late 1800s (first sighting recorded for Kings Canyon is by John Muir -- a grizzly in Tehipite Valley).
The web site: http://www.inaturalist.org/
is an excellent community-based place to keep track of your wildlife observations and share them with a wider audience.
Although I work as a seasonal ranger for the NPS, it's important to note that nothing I say here in any way necessarily represents official policy of Sequoia and Kings Canyon National Parks, the National Park Service, His Holiness the Director of NPS or the POTUS.