The Contents of Pleistocene Condor Nests

The fossil remains of California condors (Gymnogyps californianus) have been found in at least 13 caves located in Arizona, New Mexico, and Texas.  The bones range in age from ~11,000-~25,000 calender years BP.  Apparently, packrats carried the condor bones, along with leftover bones from the bird’s meals, back to their nests where combined with sticks, they became an actual part of the nest itself.  I discussed how packrat urine acts as a preservative in the blog entry I wrote previous to this one.

California condor nest.  Although they often nest in rocky crevices, they also nest in hollow trees, explaining how they lived in the forested areas of eastern North America during the Pleistocene.  Condors can live to be 60 years old but reproduce slowly.

Most of the condor bones belonged to nestlings or individuals that died just prior to the time they would learn to fly and leave the nest.  Sandblast Cave in Arizona contained 64 specimens from 5 individuals as well as egg shells and feathers.  Stanton Cave, also within the Grand Canyon, produced even more–70 bones from 5 individual California condors, plus 1 bone from a teratorn, an extinct condor with a 12 foot wingspan.

The California condors living in the southwest during the Pleistocene scavenged dead mammoth, bison, horse, camel, and an extinct species of mountain goat (Oreomnos harringtoni).  The bones of all 5 species were associated in the packrat middens with the condor bones.  All 5 species are (or were) grass-eaters.  Some mammoth dung found in Bechan Cave (Bechan is an Indian word that literally means bullshit) was 85% dropseed grass by weight.  The environment in the Grand Canyon during the Ice Age must have consisted largely of grassland.

Skull of Harrington’s mountain goat.  It probably looked similar to a modern day mountain goat.  Condors scavenged goats.

Unlike mastodons which primarily ate twigs, aquatic plants, and fruit; mammoths mainly ate grass.  A dead mammoth or mastodon provided tons of meat for scavengers.

During the Pleistocene the California condor ranged all across North America where its fossils have been unearthed in Florida, New York, and even Cuba.  It’s larger extinct cousin, the teratorn, also lived as far east as Florida.  The extinction of the megafauna led to the extinction of the teratorn, and the extirpation of the California condor everywhere except the Pacific coast.  The population of condors living there survived by learning to scavenge dead whales that washed up on the beach.  The author of the below referenced study mentions that it is an ecological mystery why they didn’t survive on the Atlantic coast by scavenging whale carcasses there.  He also wonders why they didn’t persist on the Great Plains where they could have scavenged from the massive bison herds. I’ll offer my conjecture.

Eastern condors may simply never have learned to scavenge primarily on marine mammals.  Although an occasional individual may have fed upon a dead whale on an Atlantic beach, perchance not enough acquired the habit of cruising the beaches for dead marine mammals. Eastern condors may have even been a separate subspecies.  They were heavier and had wider bills.  I suspect they failed to adapt in the east due to sheer random chance.  The explanation for the condor’s extirpation from the prairie region is more complex.  Perhaps, bison populations became scattered and rare following the extinction of the rest of the megafauna.  Forest may have covered much of the prairie region early during the Holocene.  Indian-set fires probably created much of the prairie land, and bison herds later expanded as a result but not til after the condors were gone.  Still, it’s an enigma why they never recolonized the southwest, though a few were sighted there in the 19th century after European livestock were introduced, augmenting the potential food supply.  Man has re-introduced condors to the Grand Canyon, and a few live there today.

Reference:

Emslie, Steven

“Age and Diet of Fossil California Condors in Grand Canyon, Arizona”

Science, New Series 237 (4816) 1987

See also: https://markgelbart.wordpress.com/2011/07/13/pleistocene-vultures-of-southeastern-north-america/

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Pleistocene Vultures of Southeastern North America

It seems fitting to follow last week’s blog entry about saber-tooths with one about vultures, a whole class of birds that benefited from the big carnivore’s work.  The extinction of the megafauna led to the extinction of several vulture and condor-like species.  Other species of scavenging birds became less widespread and more local in distribution.

Teratorn

Teratorn–Teratornis merriami

This huge condor-like bird stood 2.5 feet tall but had a wingspan of 12 feet–the length of 2 average-sized men spread from head to foot.  Fossils of this species have been excavated in Florida, California, and several western states, so it likely ranged throughout most of the southeast.  An even larger species, Aiolornis incredibilis, had a wing span of 17 feet, but this may have been an early Pleistocene species, not present in the late Pleistocene.  The teratorn’s bill was much larger than other vultures, suggesting it often took live prey such as rabbits and bird nestlings which it swallowed whole.

African scavenging birds occupy different niches described as rippers, grabbers, and scrappers.   Rippers rip open thick-skinned, large, carcasses and eat hide and the tougher parts of the animal.  Grabbers eat the soft meat; scrappers eat the bits of meat that get scattered around the carcass.  Scientists believe the same holds true for scavenging birds in Pleistocene North America.  Teratorns were the rippers, capable of opening dead thick-skinned mammoths or ground sloths, helping make the meat available for other scavengers.

California Condor—Gymnogyps californianus

Photo from google images of a California condor.  Man, are they ugly.

I say this bird should be known as the North American condor because Pleistocene age bones of this bird have been found as far east as New York (the Hiscock site) and Florida.  Obviously, it lived throughout the southeast.  Scientists know from an analysis of its fossil bone chemistry that California condors survived the extinction of the megafauna because a local population of the birds learned to scavenge whale carcasses off the California coast.  Ranchers attempting to kill coyotes with ill-conceived poison control programs, instead nearly extirminated the beneficial condors.  Now, they’re back from the brink, feeding mostly on the abundant dead livestock on western ranges.

American griffin vulture?  No common name–Neophrontops americanus

An extinct American vulture related to old world vultures.  No representatives from the old world vulture family still occur in North America.

The accipitrids are old world vultures today found in Africa and Eurasia.  They’re more closely related to hawks than to extant new world vultures which are related to storks.  The physical similarity between old and new world vultures is a case of convergent evolution when unrelated species develop similar characteristics to adapt to similar conditions.  Both old and new world vultures have featherless necks to prevent the build-up of toxic bacteria.  Both are capable of digesting well-rotted food without getting sick, and they are adapted to tearing open carcasses.

American old world vulture.  No common name–Neogyps errans

This is another old world type vulture that became extinct with the megafauna.

King Vulture–Sarcaramphus papa

William Bartram described this vulture in north Florida during the 18th century.  For over a century ornithologists doubted the veracity of Bartram’s account, thinking he either had the bird confused with a mythical creature or a caracara, because no specimens of this still living species were known to occur north of Central America.  Then in 1932, Frances Harper reviewed Bartram’s field notes and discovered that Bartram actually had obtained a specimen.  The description in the field notes matched the king vulture even better than his account in his book, Travels, which was written years later apparently from imperfect memory.  Mr. Harper theorized the king vulture occurred in Florida until the great freeze of 1835.  Bartram also reported royal palms in north Florida which were extirpated from all but the southernmost region of the state after that freeze.  King vultures probably colonized and recolonized the south during warm interglacials.

Bartram noted an interesting habit of this species in Florida.  King vultures followed the frequent fires in the longleaf pine savannahs and ate the “roasted” reptiles that failed to escape the flames.

Black Vulture–Coragyps atratus

Photo from google images of a black vulture–still common.

It’s no coincidence that drivers often spy these still extant birds soaring over highways.  They’ve adapted well to the roadkilled supermarkets of our modern highways which offer a buffet of dead deer and dogs.  Two fossil specimens of black vulture nestlings found at Kingston Saltpeter Cave, Bartow County prove this bird lived here during the Pleistocene as well.

Turkey vulture–Cathartes aura

Photo of google images of a turkey vulture.  They’re easy to distinguish from black vultures even if one can’t see the red head because they’re flying high in the sky.  Note the tail is much narrower on a turkey vulture than a black vulture.

Turkey vultures are still common but don’t congregate in large flocks like black vultures do.  Their niche differs too–they subsist on smaller carrion such as dead possums, flattened road-killed snakes and squirrels, etc.

Eagles also benefited from the deaths of Pleistocene megafauna.  Grinell’s crested eagle and hawk eagles, now extinct, probably relied on carrion for an important part of their diet.  Golden eagles and bald eagles were probably more comman then, thanks to the abundance of meat on the range.

Caracaras, ravens, and magpies were also more widespread during the Pleistocene because of the greater supply of meat.

References:

Harper, Frances

“Vultura sacra of William Bartram”

The Auk October 1932

Hertz, Fritz

“Diversity in Body Size and Feeding Morphology within Past and Present Vulture Assemblages”

Ecology 75 (4) June 1994