a giant field rat  

In summary, have patience, stay south of blackburrow, and hunt bats, rats and snakes. Most of this is common sense. I would also like to thank all the helpful people that posted their findings on this subject as well.

To do the surefall glade ranger newbie quests you need drops from a large king snake, large and giant whiskered bats, and large and giant field rats.

I found that the southern part of the zone is a good place to hunt, no farther north than blackburrow.

The king snakes lead to large king snakes

The whiskered bats lead to large whiskered bats and large myotis bats, which lead to giant bats of both species (that's what it looks like on radar anyway).

The large field rats lead to giant rats and giant field rats. Scruffy pops up from time to time too.

Of course I’m hunting the bats, rats and snakes at the same time so things may be interrelated, and the guards are killing things too, so who knows.

By the time I had my large king snake drop, and my large and gaint whiskered bat drops, I had 2/3 of the giant field rat pelts and 2/6 of the giant field rat whiskers.

I went up north, near the undead ruins in the northeast corner, and had some success forcing the giant field rat spawn, but something strange is going on up there. As many as 6 or 7 large field rats and mangy rats have spawned and then go to the ruins to despawn. It’s not clear to me how the despawns factor into the process so I decided to leave it alone.

So, have patience, stay south of blackburrow, and hunt bats, rats and snakes.

These also drop "giant" field rat pelt, which are not stackable. And I assume not common, as I've killed a few of these and the pelt didn't always drop. These rats themselfs aren't a common spawn either. No known ph for them yet.