Protective Nesting Associations

Condors and large falcons sometimes nest near each other.  Although falcons are smaller in size than condors, they are better defenders of their nests.  Consequently, when falcons aggressively drive away other predators from their nesting territories, they also drive away predators from nearby condor nests, and so can increase the chances that condor eggs and chicks survive (Snyder & Snyder 2000). 

In California, the Raven (Corvus corax) is the main predator of condor eggs, while the Golden Eagle is the main predator of condor chicks (Snyder & Snyder 2000).  One California Condor nesting territory was monitored for several years and, during one year, it was found that at least 5 pairs of Prairie Falcons nested "within a 2.4 kilometer radius of the territory center," driving away most Ravens and Golden Eagles that entered it (Snyder & Snyder 2000).  Not surprisingly, the condor egg and chick in this territory survived during that nesting season.  Two years later, however, prairie falcons nested further away from the condor nest and consequently did not provide nest defense for the condors. During that season, ravens invaded the territory and nested near the condors.  Not surprisingly, these ravens caused "two successive nesting failures of the condors (Snyder & Snyder 2000)." 

Of course, nesting near falcons is costly for the condors also, since falcons aggressively dive at condors and cause them to waste time and energy to avoid these attacks.  However, the cost is well worth it to the condors if eagles and ravens threaten their nests (Snyder & Snyder 2000).  For more information about how birds increase their breeding success by nesting near falcons and other birds of prey, see our special review:  Hawks, Owls and Falcons that Protect Nesting Birds.

Four California Condor nests have also been found located next to active nests of bumblebees (Bombus spp.) and honeybees (Apis melifera - Snyder et al. 1986).  It is unknown whether or not these bees protected the condor nests from predators, but such protection has been reported for many other bird species that nest with bees (Haemig 2001).

Food Habits

Condors will feed upon any size of dead mammal that they find.   For example, California Condors eat small mammals such as kangaroo rats, ground squirrels, pocket gophers and rabbits; medium-sized mammals such as Coyotes (Canis latrans), Gray foxes (Urocyon cinereoargentineus), and Puma (Puma concolor); and large mammals such as Mule Deer (Odocoileus hemionus), Wapiti, Grizzly Bears (Ursus arctos) and whales (Koford 1953; Collins et al. 2000).  Carrion of domestic livestock is also eaten extensively by condors since it is now so abundant.

From a cave in the Grand Canyon that was used by California Condors for nesting 9,000 to 13,000 years ago, bones have been found of the following prey species whose remains are believed to have been fed to condor chicks at that time:  bison (Bison sp.), horse (Equus sp.), mammoth (Mammuthus sp.), camel (Camelops sp.) and pygmy mountain goat (Oreamnos harringtoni; Emslie 1987).

Like the Pleistocene California Condors of the Grand Canyon, Andean Condors today feed upon the carrion of dead camelids, including the guanaco (Lama guanicoe) (Sarno et al. 2000), vicuña (Vicugna vicugna) and their domesticated descendants the llama (Lama glama) and alpaca (Vicugna pacos).  Andean Condors also feed on on a wide variety of other dead mammals (Houston 1994).

Exploitation of Marine Resources

Condors do not limit themselves to terrestrial food.  In coastal regions they feed extensively on marine life.  Marine carrion is especially important to condors living in arid regions, because in these areas grazing mammals are less abundant and the sea often produces more food for condors than the land.

For example, along the arid coasts of Peru and Chile, the Andean Condor feeds extensively on marine carrion washed ashore by the ocean waves.  Food recorded in its diet there includes the carcasses of whales and dolphins, maned sea lions (Otaria byronia), southern fur seals (Arctocephalus australis, Peruvian Diving-petrels (Pelecanoides garnotii), Humboldt Penguins (Spheniscus humboldti), green sea turtles (Chelonia mydas), fishes and kelp (Murphy 1936; Housse 1945; Wallace and Temple 1987a).

During El Niño years, when high mortality of marine vertebrates occurs, condors often benefit from an increased food supply if ocean currents deposit the carrion on beaches that they patrol (Murphy 1936).  If, however, the ocean currents wash the dead animals ashore in densely populated urban areas that condors are afraid to visit, this food will not be eaten by condors (Wallace & Temple 1988).

California Condors also feed on marine carrion.  For example, during the nineteenth century, when whales were more common than they are today, Gambel (1846) wrote that it was "not uncommon" to see California Condors feeding on the carcasses of whales that had been cast up on the beaches of California.  Near Monterey, Taylor (1859b)  also observed condors feeding "on the carcass of a whale on the sea shore."

Further north, along the coast of Oregon during the winter of 1805-1806, Meriwether Lewis and William Clark observed California Condors feeding upon the remains of a whale and on fishes that had been "thrown up by the waves on the seacoast."  During the winter months that these renowned explorers spent near the Columbia River estuary, they found the condor "more abundant below tidewater than above (Lewis & Clark [1804-1806] 1990)." 

Even during the late twentieth century, when the California Condor was almost extinct in the wild, fragments of marine molluscs, including the Pismo Clam (Tivela stultorum), Common California Venus (Chione californiensis), and Moon Shell (Polinices sp.) were frequently found in condor nest caves in southern California (Collins et al. 2000), suggesting some foraging by parent condors in the inter-tidal zone.

Condors living along arid coasts also fly out to offshore islands to raid seabird colonies of eggs and young.  For example, when Murphy (1925) visited Asia Island off the coast of central Peru, he found Andean Condors, Turkey Vultures and gulls feeding on eggs at a large colony of the Guanay Cormorant (Phalacrocorax bougainvilli) that contained "countless eggs and young."  According to Murphy, the condors, vultures and gulls were all "more abundant and rapacious" there than anywhere else he had visited.  One condor stood in the middle of the cormorant colony, "with a circle of abandoned and rifled nests roundabout."  When this condor was shot and picked up by its feet, "the albumen and mostly unbroken yolks of a round dozen of fresh eggs slid out of its gullet." Because virtually no shell fragments were visible in this meal, Murphy suggested that "condors must suck the contents of the eggs through their trough-shaped tongues."

During his visit to Asia Island, Murphy observed a minimum of 18 condors "flying back and forth slowly" over the cormorant colony and, before noon, watched them all fly back to the mainland.  He added that at Santa Rosita, a nearby island, a reliable informant observed 36 condors descend together upon a Guanay Cormorant colony.  On San Gallan, another island off the coast of Peru, Murphy (1925) found that Andean Condors walked around outside the burrows of Peruvian Diving Petrels and snatched exiting birds to eat.  Thus, the Andean Condor is not just a scavenger on these islands, but a bird of prey as well, eating adult seabirds and eggs as well as carrion (Murphy 1925).  Fortunately for the nesting seabirds, if a condor eats their eggs and young, they can just lay new eggs to replace the lost ones.

It appears that the California Condor also foraged on offshore islands.  For example, during the twentieth century, a resident of Oxnard, California who was a close friend of Professor Barbara B. DeWolfe (University of California, Santa Barbara), told DeWolfe that she often saw California Condors flying out to the nearby Channel Islands, presumably to raid seabird nests, forage for carrion of marine vertebrates, or eat the carrion of domestic livestock raised there (Barbara B. DeWolfe, personal comment to the author in the 1980s).  Fossils of California Condors have also been found on these islands, suggesting that condors exploited marine resources there for thousands of years (Orr 1968; Guthrie 1992, 1993).

Interactions with other Scavenger Birds

When condors descend to feed on a carcass, they often meet other species of scavengers there that are already feeding.  Sometimes condors peacefully join these other scavengers in feeding, but other times they must fight to displace them or else wait until they have finished eating and leave.  Fortunately for condors, their larger body size helps them win encounters with other vultures.

For example, in Peru, Wallace and Temple (1987a) studied interactions of Andean Condors with other vulture species at carcasses, and found that the larger species dominated the smaller species.  Since condors had the largest body size, they occupied the top of the dominance hierarchy and the other vultures yielded to them.  Turkey vultures were usually the first to arrive at a carcass, Black Vultures second, and condors third.  Yet, when the condors arrived, the other vulture species generally yielded to them.  Condors won 100% of aggressive interactions with Turkey Vultures, 94% with Black Vultures and 100% with King Vultures (Sarcoramphus papa).  At no time did a King Vulture (the second largest species) initiate an encounter with a condor.

In North America, the Turkey Vulture also arrives early to carcasses, often first because of its well-developed sense of smell.  However, in some regions ravens are more abundant than Turkey Vultures and so often arrive first at a carcass, followed by Golden Eagles and then California Condors (Snyder & Snyder 2000).  The much larger condor dominates both the Turkey Vulture and the Raven, causing them to yield during encounters. 

However, interactions between the California Condor and the Golden Eagle are more complex and do not simply follow the dominance hierarchy based on size.   California Condors weigh approximately twice as much as Golden Eagles, yet usually wait for the latter to finish eating and leave before stepping up to a carcass, perhaps fearing the eagles' dangerous talons (Snyder & Snyder 2000).  On some occasions, perhaps when very hungry, adult California Condors do challenge eagles and displace them from carcasses, however juvenile condors have not been seen to do so (Snyder & Snyder 2000).