On 8 November 2005, the New York Times carried a brief article, titled "Advice to California Condors: Change Your Diet." Later, I found a longer discussion on a Stanford University web site. Both noted that a study had been done of past and present condor food habits, measuring isotopes of nitrogen and carbon in condor bones and feathers. According to the reviews, the researchers had concluded that it would be much safer for condors to revert back to an historical food source - sea lions, seals and whales - than in would be to keep eating lead-contaminated land mammals. I had an immediate objection to that idea, but thought I better check the real study, first. Kelly Sorenson, one of the co-authors, supplied me with a copy of the paper (1).

STUDY DETAILS
The researchers obtained feather samples from 12 "modern" condors (birds that died between 1993 and 2001) and 50 "historical" condors (museum specimens collected 1797 to 1965), and analyzed these for changes in carbon and nitrogen isotopes. They analyzed bone collagen from 10 Pleistocene condors, 10 historical birds (1904-1965), and 10 modern ones (1993-2001). From their samples, they felt they could tell differences between the relative amounts of land-based and ocean-based food that the condors had been eating. Not having even a remote schooling in their methodology, I can only say it "looks good to me."

The authors concluded (page 16709) "that marine mammals were an important component of the diets of Pleistocene condors, and that historical condors ate terrestrial land mammals." They felt this conclusion supports their hypothesis "that the restriction of the range of condors to the Pacific coast after the Pleistocene megafaunal extinction was largely controlled by the presence of a 'fall-back' food source, marine mammals," and that "the switch to terrestrial foods in historical condor populations may reflect the reduction in pinnipeds and whale populations due to commercial hunting."

OBJECTIONS TO THEIR CONCLUSIONS
Considered at face value, it seems safe to say that marine mammals were an important component of the diets of some Pleistocene condors (say, those living within 100 miles or so of the seacoast). However, the research does not support the conclusion that the diet of condors changed markedly from marine to terrestrial mammals from Pleistocene to Recent times. Neither does it show that the marine mammal food supply in any way controlled the post-Pleistocene distribution of condors, nor that the presumed switch from marine to terrestrial foods was a function of fewer marine mammals.

All the researchers' Pleistocene samples came from Rancho La Brea, in what is now the western portion of the Los Angeles metropolitan area. The sample results of four birds (bones) that showed strong marine food characteristics, and six with strong terrestrial affinities seems logical, in that Rancho La Brea is only a few miles from the Pacific Ocean, but in the Pleistocene was also in the midst of an abundant supply of land mammals. Condors were found in the tar pits because they came to feed on land mammals that were trapped there, and they in turn became mired. Some likely came to the pits from great distances, and we have no way of knowing whether individual birds flew in from the coast (where marine mammals would have been available), or came from the interior (where land mammals would be their main food). The data only tell us that Pleistocene condors near the coast were feeding on both marine and terrestrial mammals. It would be interesting to sample Pleistocene and early Recent bones from other coastal and near-coastal locations (Carpenteria and Emeryville in California, Brookings and The Dalles in Oregon) to see how they compare to the tar pit bones.

The extinction of much of the Pleistocene megafauna almost certainly had a major effect on the distribution of condors and other scavengers, but large land mammals did not entirely disappear from condor habitat. I suspect food could have become very difficult to find in the increasingly arid interior Southwest, parts of which one researcher hypothesized once looked much like the current oak savannah country of central California (7). However, in what is now western California, the habitat changes were not so drastic, and there were apparently large numbers of tule elk, pronghorn antelope, and black-tailed deer that - along with marine mammals - would have provided a reliable food source between the post-Pleistocene condor range contractions and the development of large herds of domestic livestock after 1800. Rather than thinking of marine mammals as a "fall-back" food that was responsible for the condors' continued existence on the Pacific Coast, I think it is more reasonable to assume that condors -- from both Pleistocene and Recent times -- that lived near the ocean ate pinnipeds and whales, and those that didn't ate other large mammals.

To reach the conclusions that condor food habits changed significantly from Pleistocene to "historical," the researchers must have assumed that their sample of condor materials adequately covered all aspects of condor distribution and behavior that would have affected their food use. That assumption is clearly incorrect. The range of "historical" specimens (1797 to 1965 for feathers, and 1904 to 1965 for bones) is just too broad to take in many aspects of condor distribution, and the available samples of feather and bone are not adequate to measure each of the known historical changes in distribution. For example, only one condor specimen is available from before 1805 (and that was collected in 1792, not 1797 as noted in the publication). It was collected near the coast. I think there is only specimen in existence from Oregon that could have been in their sample, collected in 1835 in Clackamas County, which could have been either a "coastal" or an "inland" bird. [The reported sampling of one or more condor specimens from the Columbia River between 1877 and 1885 (page 16710) is almost certainly an error. There are only a few condor records from north of California after 1835, and none that I know of involved specimens.] From 1836 to 1890, there are approximately 35 condor specimens preserved. At least 24 of those were collected near the coast; the other eleven are from unknown locations, or from far enough inland that they might or might not have had access to marine life. Between 1890 and 1900, perhaps a third to a half of the 60 existing specimens were from coastal counties. After 1900, there were few California condors left near the Pacific Ocean, and only a few of 85 condors now available as specimens would have had regular access to marine mammals. [This specimen information is from my compilations (2). I have no idea which of these specimens the researchers used in their study.] Once again, rather than showing marine mammals to be a "fall-back" food supply, the researchers may only be showing that marine mammals were a greater or lesser part of the diet of those condors that occurred within a moderate distance of the sea coast. The "switch" from marine mammals to terrestrial mammals could be that there were few condors left in the seacoast areas when the majority of "historical" samples were taken.

THE ACTUAL RECORD
While it is logical to think that condors with access to the seacoast ate pinnipeds and whales regularly, the actual records are sparse - perhaps there are only two that are entirely reliable.
The most quoted "record," attributed to Fr. Antonio de la Ascension in California in 1602, turns out to be no record at all. Harry Harris (3) took two quotes from Ascension's journals - one about a whale on a beach, another about seeing what were obviously condors - and put them together to make a romantic comment about what those early explorers might have seen (4).
We have to wait until the winter of 1805-1806 before we get our first real observation, that of the Lewis and Clark expedition seeing condors feeding on "the whale and other fish" at the mouth of the Columbia (5). From the journals, it isn't clear how often such feeding behavior was observed. In fact, no specific sighting is recorded, the 16 February 1806 record from Capt. Clark's journal being a general statement that they had seen condors feeding on whales and fish on some date(s). "The whale," as written by Capt. Clark. would seem to relate to the species (i.e., more than one whale), not an individual whale, and his stated opinion that marine species "constitute their principal food," would seem to suggest that they had seen the behavior more than once. The party had not recorded any other feeding by condors before February 1806, and Clark could only assume that they "also feed on flesh." In fact, on 28 March 1806, condors ate most of four black-tailed deer killed by the explorers. If Clark had written his summary statement in April rather than February, he might not have been as confident that whales and fish were their "principal food."
Next come the observations of Alexander S. Taylor, published in Hutching's California Magazine in 1859 and 1860 (6). But were they really observations? Taylor was renowned for his hodgepodges of fact and fiction, blended together in such a way that, while the most outlandish statements and a few facts were identifiable, the validity of most of his information remains questionable (4). Look at his entire food section in context:
Volume 3, Page 541 --"It [the condor] is particularly fond of fish, and is often found on the sea-shore watching for fish thrown on the beach, or even steals from the Indians when catching salmon and mountain trout in the lakes and rivers of the Great Plains and of the Coast. A dead whale thrown ashore is sure to bring some of them in sight, and a hunter killing a deer in the mountains is confident of their appearance as soon as the beast is wounded. They are also said to attack wounded deer and other animals, and kill them, and sometimes carry off alive smaller creatures. They are also stated to carry off fish caught in river, sea and lake shallows; and though they will eat dead meat, they will not, like a buzzard, eat carrion - but the last is a mistake."

Volume 4, Page 19 - "During the early part of the present month (July), large quantities of sea lions have been killed on the southern coasts for the oil; the carcasses of those animals on the beach may be seen at times surrounded by hundreds of the Condor. A friend of our informed us that he saw a few days ago, as many as three hundred of these creatures near such feeding ground, within the distance of a league.
The voracity of these birds is astonishing A friend of ours engaged in the cattle trade, informs us, that in going from the Mission of Santa Clara towards San Francisco, in 1850, he accidentally dropped a quarter of fat beef from his cart, while a number of the Condor were in sight. On discovering his loss, after a few minutes, he turned back and observed the Condor in numbers, which he estimated at over three hundred, hovering over and near his lost beef. On coming up with it, he was surprised to find that the fat and kidneys of the quarter, with all the inner meat, had completely cleaned off the bones, and the piece of meat had lost more than half its weight."
Taylor goes on to cite another anecdote where "a vaquero" left a large grizzly bear by the seashore, and went to get help cleaning it. When he returned two hours later, the condors had completely cleaned it, and only the bones and skin remained.
All the above appears to be hearsay. If we throw out the more outlandish reports, and reduce the estimates of hundreds of condors in a flock (which were never reported reliably by anyone, ever) to "some," then the sea lion record might be valid. It perhaps gains some respectability later in the article when Taylor reports what seems to be a personal observation: "A few days ago we got within about seventy yards of a number of the male and female [sic] Condor. They were feeding on the carcass of a whale on the sea shore."

The current authors cite J. G. Cooper (7) as reporting condors feeding on seals and whales in the 1850s, but note correctly that Cooper did not observe this, himself. His hearsay evidence appears to be traceable back to Alexander Taylor.

H. R. Taylor, well acquainted with condors and likely to pass on reliable information, had two reportsof condors feeding on sea lions in the late 1800s near San Francisco. In a letter to Lee Chambers on 6 April 1905, Taylor wrote that J. E. Roadhouse of Berkeley, California (Taylor's cousin) reported seeing condors feeding on dead seals or sea lions near the Cliff House, San Francisco. Also: "My collector [Taylor dealt in birds' eggs] tells me they (condors) feed now on young seals in July in caves on the coast further south (from San Francisco."

Finally, I've just heard that condors were seen in April this year (2006) feeding on a beached gray whale on the central California coast. So, all together, the total is two positive reports of condors feeding on marine mammals, three probables, and one (if you ignore the numbers of condors given) maybe. This meager accounting doesn't mean that condors in coastal situations didn't feed regularly on marine mammals, just that few observers saw them and documented their observations.

A POSSIBLE REASON NOT TO ENCOURAGE USE OF SEA MAMMALS?
Currently, there is a lot of concern about condors being poisoned by lead, which they are presumably getting in their terrestrial food sources. Because of this worry, the authors of the bone and feather analysis study suggested it might be safer to encourage condors to feed on marine mammals than to have them continue to eat land mammals. A basic impracticality of that suggestion is that only one of the condor populations currently being established occurs close enough to the ocean to expect more than rare and incidental use of the shoreline resources. There might be the possibility of future ocean-oriented condor populations farther north in California or in Oregon, but that is likely a long way in the future, if at all.
Probably there is no practical way to keep condors from feeding on marine mammals if they happen to find them, but there is a practical question that should be taken into account in any scheme to provide or encourage the use of sea life in lieu of terrestrial animals. Lead may be a threat to condors, but marine mammals have some of the highest levels of DDT, PCBs and other pesticides of any group of animals. For example, a study of pesticide residues in California sea lions along the central California coast in 2000 found that, although DDT levels have decreased markedly in the past three decades, the levels of DDT metabolites "are higher (up to 2 orders of magnitude) than current levels reported in other marine mammal species Similarly, PCB levels also appear to be higher than in several other species and geographical areas, although the difference is more moderate. In general, marine mammals from the West Coast of North America display among the highest DDT and PCB loads observed." (8). Another recent study concluded that killer whales off the central California coast "appear to be the most contaminated animals on earth," carrying high levels of both PCBs and DDT (9). We know that condors from non-marine feeding environments accumulated enough DDT metabolites by the 1960s to thin eggshells by a third over earlier samples, and to spectacularly disrupt calcium deposition in the shells. The amount of residue we found might have been enough to disrupt condor behavior (10). With contaminant levels still so high in the marine environment, we shouldn't be too quick in exchanging one problem for another.

LITERATURE CITED
1. C. P. Chamberlain, J. R. Waldbauer, K. Fox-Dobbs, S. D. Newsome, P. L. Koch, D. R. Smith, M. E. Church, K. L. Sorenson, and R. Risebrough. (2005), Pleistocene to recent dietary shifts in California condors. Proc. Natl. Acad. Sci. 102(46):16707-16711.

2. S. R. Wilbur (1978), The California condor, 1966-76, a look at its past and future.
U. S. Fish and Wildlife Service, North American Fauna 72..

3.H. Harris (1941) Annals of Gymnogyps to 1900. Condor 43:2-55.

4. S. R. Wilbur (2004), Condor Tales: What I Learned in Twelve Years with the Big Birds. Gresham, OR: Symbios. Pages 29-30].

5.R. G. Thwaites, editor (1905), Original Journals of the Lewis and Clark Expedition 1804-1806. New York: Dodd, Mead and Co.

6. A. S. Taylor (1859-1860), The Great Condor of California. Hutching's California Magazine 3:537-543; 4:17-22, 61-64.

7. P. J. Mehringer Jr. (1967), The environment of extinction of the late-Pleistocene megafauna in the arid southwestern United States. Pp. 247-266 in P. S. Martin and H. E. Wright Jr., eds., Pleistocene Extinction. Yale University Press.

8. B. J. Le Boeuf, J. P. Giesy, K. Kannan, N., Kajiwara, S. Tanabe, and C. Debier (2002), Organochloride pesticides in California sea lions revisited. BMC Ecology 2:11- [Note: I reviewed the electronic version of the article at http://www.biomedcentral.com/1472-6785/2/11 ]

9. N. Black, R. Ternullo, and M. Dahlheim (2003), Killer whales have extremely high levels of PCBs and DDT. Ecological Observations for the Monterey Bay National Marine Sanctuary. Electronic version: http://montereybay.noaa.gov/reports/2003/eco/mammals.html

10. L. F. Kiff, D. B. Peakall and S. R. Wilbur (1979), Recent changes in California condor eggshells. Condor 81:166-172.