The recent finding of California condors in a hole in a coast redwood (Sequoia sempervirens) in Monterey County apparently is not a nesting record, as originally thought. Nevertheless, I think it would be extremely unusual if the use of the hole by condors did not represent potential nest site inspection, rather than just roosting. With that in mind, we might consider the question of just how often condors nested in trees in the past. There are only two positive records:
1950 - a nest from which a condor was successfully fledged, 95 feet above the ground in a cavity in a Big Tree (Sequoiadendron giganteum), in the Sierra Nevada of Tulare County, California. [Koford, Audubon Research Report No. 4, 1953, page 83]
1984 -another nest in a Big Tree in Sequoia National Forest, in the same general area as the 1950 nest, and approximately the same distance off the ground in a similar cavity. The researchers who examined the site felt it had been used in previous nesting attempts. [Snyder, Ramey and Sibley, Condor 88:228-241 (1986)]
There were numerous summer records of condors in the general area of the known Sierra Nevada tree nests [see a selection of these records in Koford, op.cit., page 146, and in Wilbur, North American Fauna 72, 1978, pp. 68-69]. Interpreting the information is complicated because condors had some regularly used late summer roosts in the same general area, so likely very few of the records indicate nesting birds. Also, spotting a condor around a cliff face is a lot easier than spotting one diving into a forest, so finding a tree nest under the best of circumstances would be serendipitous. [Both of the Sierra nests were discovered during logging operations.] All that can be legitimately said is that there is a "good chance" condors nested regularly in the Big Tree groves of the western Sierra Nevada.
This year's Monterey County tree hole use is the first such record from the Coast Ranges. From what I can see from a couple of photos sent to me, the situation is quite similar to the Sierra nests, and would seem to be very suitable for a nest. The Coast Range redwood groves stretching from Monterey County north into southern Oregon offered many opportunities for nests. There are a number of records of condors associated with remote redwood groves. For example:
1855 - A. C. Taylor gave the California Academy of Sciences some condor feathers taken from a dead bird "in the vicinity of the redwoods of Contra Costa (County) [Proc. Cal. Acad. Sci. 1:70-71 (1855)]. There are some great looking cliffs in eastern Contra Costa and Alameda counties that might have had condor nests (none ever confirmed), but there are very few cliffs and rock outcrops "in the vicinity of the redwoods" in these counties.
1856 or 1857 -- Alexander S. Taylor wrote in 1859: "One of these (old hunters and trappers) informs me that three years ago he caught two young condors in the Redwoods of Santa Cruz county, and kept them over a month. When young, they are covered with a dirty white down, and have a strong smell; and are three months old before they fly" [Hutching's California Magazine 3:542]. Taylor's observations are often not reliable, and this description is not particularly diagnostic, but the record is interesting in light of the following record.
July 1879 - 2 condor eggs collected in Santa Cruz County, California [eggs now in the collection of the Chicago Field Museum of Natural History]. There was rumor that they were from the redwood areas (not necessarily from trees), but I haven't located all my original notes on these records.
1901 -- Rumored that "a few (condors) still breed in the wild mountains north of Santa Cruz" [McGregor, Pacific Coast Avifauna 2, 1-22 (1901). Again, a redwood area, but not necessarily a tree nesting rumor.
July 1905 - 8 or 10 condors roosting in a redwood grove near the Big Sur coast of Monterey County, in the same general area as this year's hole occupation [Jenkins, Condor 8:122-130 (1906)].
There is one other tree nesting record that has been discounted because (1) it was a tree record when there weren't other tree records, (2) it was in an oak tree, and (3) it was described in a paper by Alexander S. Taylor, who was noted for getting his facts wrong. However, the egg in question does exist (now in the British Museum of Natural History), reportedly collected in the Tularacitos Mountains, Monterey County. As described by Taylor, the collector " brought away a young bird of six or seven days old, and also an egg - the egg from one tree, and the chick from another. There was, properly speaking, no nest; but the egg was laid in the hollow of a tall old robles-oak, in a steep barranca" [Taylor, Hutching's Calif. Mag. 3:540-543, 4:17-22, 61-64 (1859)]. Some of the largest of the California oaks could have had a "hollow" large enough to support a condor nest, although having two oak tree nests in one year (as the narrative describes) seems pretty unlikely. But knowing what we know now about condor tree cavity nesting, perhaps we shouldn't write that one off completely.
In describing the 1950 Big Tree nest, Koford (op. cit., page 83) noted: "Except for being made of wood, this nest site has all the essential features, such as steadiness, accessibility to condors, ease of take-off, protection of nestling, and presence of perches, found in cliff nests." So, how common are suitable tree cavities? Snyder, Ramey and Sibley (op. cit, page 236) found that 20% of 96 large Big Trees checked had fire-created cavities that might be used as nest sites. Because the Big Tree is a species found in areas that have burned regularly (in fact, has been experiencing low regeneration in recent years because of fire control that allows other species to crowd out Big Tree seedlings), it is probable that potential nest sites exist all along the Sierra Nevada western front. The coast redwoods, on the other hand, are not a fire-maintained species, so one might expect the percentage of trees with suitable cavities to be much lower. But with coast redwoods found in a 400 mile long band from Monterey County to southern Oregon, the actual number of sites might be significant.
Condors almost certainly nested north in the coastal mountains into Oregon in the 1800s, and perhaps into the early 1900s (Wilbur, Auk 90:196-198, 1973). No nests were ever found, and there are not a lot of areas in northwestern California and southwestern Oregon that look like "typical" southern California condor habitat. On the other hand, there are lots of coast redwoods, and north of the redwood belt there are other massive conifers that might provide the same sort of nest sites. In considering introducing captive-reared condors into areas north of San Francisco, we should not lose sight of the possible significance of trees for nesting.