Geotripper's California Birds spills over into areas that may be of interest to those interested in the geology I cover at Geotripper. This is one of them, so I've re-posted it here:
California has precious few endemic species of birds. In one sense, this fact seems odd, given the many ecological "islands" in California, isolated environments where evolutionary pressures are the greatest. There are high alpine environments, desert mountain ranges with relict conifer forests, and valleys isolated by high mountain ranges, for instance. I have a feeling that the geology of the state has something to do with it the distribution of birds. There are many environments, but the orientation of the geological provinces is mostly north-south, and routes exist for birds to spread far and wide, crossing political borders into Baja and the Pacific Northwest. There are low exit points from places like the Great Valley and low passes over the margins of the Sierra Nevada. Other vertebrates can't surmount these boundaries the way flying birds can, so the trapped reptiles, amphibians and mammals show a great deal more species variation and endemism (is that a word?).
some research suggested that the population had been halved again. Only 5% of the living birds tested displayed any kind of antibody response to the virus. That's an extinction threat.