Olive Sided Flycatcher, Tilden RP
Well, that's what I'm assuming it was.
I actually camped last night in what of the group camps near The Little Farm in Tilden. Regrettably, I forgot my binoculars, but I nonetheless took a lovely early morning stroll down to Jewel Lake and back. I had been walking about 5 minutes when I heard the unmistakable "Quick Three Beers" call, repeated maybe every 20-30 seconds. Wandering around, I was able to trace it to very high in the pines behind the Visitors' Center, but I saw no bird. I very much doubt binoculars would have helped. Nonetheless a very enjoyable sound, and since I haven't seen these guys reported yet by anybody else, I'm curious as to whether this would be a typical date for them to appear in the area.
Further on down the pain path to Jewel Lake, I had the odd site of a pair of Mallards walking side by side down the trail. I got quite close to them before they took any notice: they were looking from side to side and the male was squawking in a low tone of voice. I imagined him saying: "I thought it was your job to pack the binoculars." The lake itself was notable for a single remaining female Bufflehead among the Mallards and turtles. It appears the Mergansers, Common and Hooded, have moved on since last weekend. Black-headed Grosbeaks, OC and Wilson's Warblers dominated the soundscape in addition to Stellars' Jays and Bewick's Wrens. Anyway an absolute gorgeous morning and day, and quite a contrast to when I took the walk about 4 hours later and there were hordes of people about.