Warbler Guy, how do I know if my California bird sightings are rare ones? Are species of special concern in California present in a book?

Sherry, feel free to see:

http://www.dfg.ca.gov/wildlife/nongame/ssc/birds.html

Here, you'll see the publication whose cover is shown below. 

It's an excellent resource to read analysis of the status of California's at-risk birds using the latest data to describe current populations, ranges, and threats. 

Species highlighted in this 450-page book include seabirds, raptors, shorebirds, waterfowl, and perching birds, all of which are represented on a Bird Species of Special Concern list.

This list also notes California habitats with high numbers of special concern bird species, including wetlands, scrublands, grasslands, and riparian forests.

Traveling soon to Wisconsin, Warbler Guy....so where do I look up recent warbler sightings? Warbler sightings in Wisconsin are posted on ebird?

"Yes" to your question, Theo (in Chicago).

You would do well to see:

http://ebird.org/ebird/atlaswi/map?zh=true

Then type in the warbler species you'd like to pursue in Wisconsin.

This link shows the latest survey results from WI Breeding Bird Atlas volunteers documenting
nesting bird species throughout the state.

For example, I recently visited WI to pursue Connecticut Warbler.

The ONLY documented sighting I noticed in n. WI is linked from a 5/24/15 observation at:

http://ebird.org/ebird/atlaswi/map/conwar?neg=true&env.minX=-96.46825195312499&env.minY=41.84614104137589&env.maxX=-80.80174804687499&env.maxY=46.80861629908459&zh=true&gp=false&ev=Z&mr=1-12&bmo=1&emo=12&yr=EBIRD_ATL_WI_2015

Let me know if I can further help.

Regards, Daniel

(My "Bird Tours" information is at my web site via the "Bird Tours" tab:
warblerwatch.com)