Haemig PD  (2012)  Ecology of Condors.  ECOLOGY.INFO 25

Ecology of Condors

Note: This online review is updated and revised continuously, as soon as results of new scientific research become available.  It therefore presents state-of-the-art information on the topic it covers.

Condors are giant raptorial birds found only in the western hemisphere. Two species are recognized: the California Condor (Gymnogyps californianus) of North America, and the Andean Condor (Vultur gryphus) of South America.

The Andean Condor is larger in size, with a wing span of up to 3.2 meters, compared to 2.7 meters for the California Condor (Houston 1994).  Although the condors differ enough to be classified into two genera, they are more closely related to each other than to other birds (Sibley and Alquist 1990) and their ecology is similar.

See color photos: Figure 1, Figure 2, Figure 3

Condors belong to the bird family Cathartidae (also called Vulturidae). This family is widely known as the "New World Vultures" because all of its living members are found only in the western hemisphere. 

The Cathartidae also include the familiar Turkey Vulture (Cathartes aura) and Black Vulture (Coragyps atratus), as well as three other species.  All are raptorial in appearance and specialized for finding and eating the meat of dead animals.  However, unlike the similar-looking Old World Vultures, which are related to hawks and eagles, the New World Vultures are related to storks (Sibley & Alquist 1990).

In this three-page report, we review the many ways that condors interact with other organisms and the environment, and explain why condors are endangered.

General Biology

Both condors feed primarily on mammalian carrion.  They usually nest on cliffs, but some exceptions occur (see below). The clutch size is one egg, however if it is lost a replacement egg will be laid.  Because it takes condor parents more than one year to raise a young condor, the rate of reproduction is extremely low: usually only one young, on average, every two years.

Breeding Andean Condors forage for food as far as 200 kilometers from their nests, while breeding California Condors forage as far as 180 kilometers (Wallace & Temple 1987b; Meretsky & Snyder 1992).  However, where food is concentrated in a small area, condor foraging ranges are smaller.  For example, on the arid coast of Peru, where the ocean washes ashore a "remarkably constant food supply" of dead marine mammals and seabirds, some Andean Condors limit their foraging to "stretches of beach several kilometers long (MP Wallace in Snyder & Snyder 2000)."

Snyder & Snyder (2000) list three habitat requirements for condors: (1) reasonably reliable winds or thermals upon which to soar, (2) foraging habitat that is sufficiently open to discover and access carrion food, and (3) adequate supplies of carrion.  A study of Andean Condors in southern Chile found that condors soared most frequently when winds were moderate (25-48 km/hr), and soared least when winds were strong, i.e. over 64 km/hr (Sarno et al. 2000).

Distribution

In the nineteenth century, the California Condor ranged along the west coast of North America from southern British Columbia south to the Sierra San Pedro Martir of northern Baja California (Snyder & Snyder 2000).  At this time, the bird was also found in Alberta, Montana, Idaho, Utah and Arizona, but it is unknown if the individuals observed were nesting in these inland states or simply wandering there (Snyder & Rea 1998; Snyder & Snyder 2000).  No attempts were ever made by early ornithologists to find California Condor nests north of San Francisco or outside California, so the exact breeding range of the species in the nineteenth century is unknown. 

Oral traditions of the Blackfoot Indians tell of occasional sightings and possible nestings of the California Condor in Montana and Alberta during the nineteenth century, and of this bird's visits to their bison kills on the plains (Schaeffer 1951).  Confirmation of condor occurrence in Alberta is provided by Fannin (1897), who observed two individuals between Calgary and the Rocky Mountains. In Idaho, the condor was reported to be "not uncommon" near Boise before cattleman began to "poison carcasses to kill wolves (TE Wilcox in Lyon 1918)." 

During spring along the Colombia River, the California Condor was "particularly attached to the vicinity of cascades and falls, being attracted by the great number of dead salmon," which it fed upon (Townsend in Audubon 1831-39) .  Along this same river, the condor was also seen "near [American] Indian villages, being attracted by the offal of the fish thrown around their habitations (Townsend in Audubon 1831-39)."  In Arizona, many distinguished ornithologists such as Elliott Coues observed California Condors between the years 1865 and 1924, and considered them to be nesting in the state (Snyder & Rea 1998). 

At the beginning of the nineteenth century, the Andean Condor bred along the entire chain of the Andes, from western Venezuela to Tierra del Fuego.  Although it is still found in much of this range, it has suffered intense persecution from humans and has been extirpated from many localities (Ridgely & Greenfield 2001).

According to Murphy (1932), the Andean Condor is "a mountain bird" that keeps to high-elevations in "rainy and forested parts of South America," but which "regularly descends to sea-level in desert districts," such as along the arid Pacific coast of Peru and northern Chile, and also along the arid Atlantic coast of Patagonia, from the Rio Negro south to the Strait of Magellan (Murphy 1936). 

In addition to occurring in the main ranges of the Andes, the Andean Condor is also found in some nearby mountain ranges.  For example, it occurs in temperate and paramo zones of the Sierra Nevada de Santa Marta on the Caribbean coast of Colombia (Norton 1975; Hilty & Brown 1986), in the Sierra de Perijá on the border of Colombia and Venezuela (Calchi & Viloria 1991; Hilty 2003), and in the Sierra de Córdoba of Central Argentina (Hendrickson et al. 2003).  It also enters Brazilian territory in the state of Mato Grosso, specifically in the "Rio Jauru region west of Cáceres (Sick 1993)."

During the late nineteenth and twentieth centuries, poisoning and shooting of condors caused massive declines of many condor populations, with the result that condors of both species disappeared from many parts of their former ranges.  The situation was especially bad for the California Condor, which became extinct in the wild from 1987 to 1992. 

Fortunately, captive breeding and release programs have begun to return condors to the wild in some areas of their former ranges (eg. California, Arizona, Baja California, Colombia, Venezuela).  However, because nesting condor pairs of both species raise, on average, only one young every two years, and also because poisoning and shooting continue to cause condor deaths at alarming rates, it will take many years before the number of wild condors returns to nineteenth century levels.  Until then, populations of both condor species will remain endangered.

Prehistoric Distributions

Both species of condors were more widespread in prehistoric times than in the nineteenth century.  For example, during the Pleistocene in North and South America, condors appear to have ranged across both continents, from the Atlantic to the Pacific, occurring in many areas where they do not occur today.

One possible explanation for the flourishing of condors during this time is that great herds of ungulates as well as other large mammals, such as sloths and elephants, roamed the Americas then, providing condors with a rich supply of carrion to eat.  Many of these prehistoric mammals are now extinct, so the subsequent contraction of condor ranges may in some way be related to this fact (Emslie 1987; Steadman & Miller 1987).

However, other explanations are also possible.  For example, killing of condors for ceremonial purposes by indigenous human cultures (McMillan 1968; Snyder & Snyder 2000) may have increased since the Pleistocene, and this activity alone could have led to extirpation of condors from significant parts of their ranges.  Alternatively, the wind conditions that enable condors to soar may have become less favorable in some regions, causing condors to abandon those areas (Tonny & Noriega 1998).

Condor fossils from the Pleistocene have been found in many localities outside the nineteenth-century ranges of both species.  For example, Andean Condor remains 13,000 years old have been found in caves at Lagoa Santa, Minas Gerais, Brazil (Alvarenga in Sick 1993), and California Condor remains 9,500 to 16,000 years old have been found in New York, Florida, Texas, New Mexico and Arizona, as well as in California and other western states (Emslie 1987; Snyder & Snyder 2000; Brasso & Emslie 2006). 

The California Condor fossils discovered in western New York state, near the village of Byron in Genesee County, are especially interesting because they date from a time (9000 B.C.) when flora and fauna were reoccupying the land following the melting of Ice Age glaciers.  Boreal, coniferous vegetation, characterized by spruce (Picea sp.) and jack pine (Pinus banksiana), dominated the area at this time, and the climate is believed to have been cold.  Fossils found in association with those of the California Condor at this site include extinct mastodonts (Mammut americanum), caribou (Rangifer sp.) and wapiti (Cervus elaphus).

These findings demonstrate that the California Condor was "able to live in a colder climate and in a boreal, coniferous setting at a time when appropriate food (large mammal carrion) was available (Steadman & Miller 1987)."  Synder & Snyder (2000) point out that the presence of California Condors fossils in such far-flung localities as New York, Florida, the Southwest and the Pacific Northwest suggests that this species has "very wide habitat and climatic tolerances."  Their conclusion is also supported by the wide distribution of the California Condor in western North America at the beginning of the nineteenth century, a range that included the Pacific coast region from British Colombia to Baja California, and inland to the Grand Canyon and Rocky Mountain regions (see previous section).

Nest Site Selection

Both species of condors nest primarily on cliffs.  However, detailed information on nest-site characteristics is currently available only for the California Condor.

California Condors nest from near sea-level to an altitude of 1830 meters (Snyder et al. 1986).  High elevation nest-sites differ from those at lower elevations in that they more frequently face south, but it is unknown if south-facing cliffs are used more frequently because they are warmer or simply because they are more abundant (Snyder et al. 1986).

While most California Condor nests are made on cliffs (in potholes, crevices, cracks or on overhung ledges), some are also made in crevices among boulder piles on steep slopes, and in natural cavities of large trees (Snyder et al. 1986).  For example, in the Sierra Nevada, condors not only nest on cliffs, but in cavities of the Giant Sequoia (Sequoiadendron giganteum), the largest species of tree in the world (Koford 1953; Snyder et al. 1986).  One nest placed in a Sequoia was 29 meters above the ground, while another placed in a different Sequoia was 30 meters above the ground (Snyder et al. 1986).  Both were placed in cavities that had been "produced by burn-outs of limbs into the main trunks of the trees (Snyder et al. 1986)." 

In a survey of 96 Giant Sequoias, Snyder et al. (1986) found that 20% of these trees had natural cavities, all produced by similar burn-outs, demonstrating the dependence of California Condors on wildfire for producing nest cavities in Giant Sequoia trees.  In the Santa Lucia Mountains of the Central California Coast, a condor nest was found "in the hollow of a tall, old robles-oak, in a steep barranca, near the summit of one of the highest peaks (Taylor 1859)."  

The male of one California Condor pair found nesting in a cavity of a Giant Sequoia had, the year before, nested with another female 150 kilometers away in a pothole on a cliff, demonstrating that at least some individual condors show variability in choosing nesting sites (Snyder and Johnson 1985). 

California Condors appear to avoid nesting in areas where Golden Eagles (Aquila chrysaetos) are common (Snyder & Snyder 2000).  Of the many nesting sites studied in the 1980's, only one was located in a territory where Golden Eagle sightings were frequent (Snyder & Snyder 2000).  Fortunately for the condors, this territory also had numerous nesting Prairie Falcons (Falco mexicanus), which protected the condor nest from eagle predation by driving the eagles away (For more information, see the next section: Protective Nesting Associations).

As mention earlier, the Andean Condor also nests primarily on cliffs, but like the California Condor it is adaptable and can nest elsewhere.  For example, along the arid coast of Peru where the terrain is relatively flat, some nest sites of this species are "little more than partially shaded crannies tucked against boulders on modest slopes (MP Wallace in Snyder & Snyder 2000)."  Caves are also used for nesting, especially when located on cliffs (Lambertucci et al. 2008).