Posts Tagged ‘Bubo virginianus’

The Unknown Owl of Pleistocene Georgia

April 22, 2013

A few scraps of bone found at just 2 fossil sites in Georgia indicate a now extinct species of owl, larger than any present day owl species, used to live in the region.  Starrs Olson compared a mandibular symphysis discovered on Ladds Mountain, Bartow County with those from a great horned owl (Bubo virginianus), a snowy owl (Nyctea scandiaca), and a great gray owl (Strix nebulosa).  On a human the mandibular symphysis is the cartilage in the front dimple of the chin that connects the left jaw bone with the right jaw bone, but on a bird it’s the lower bill.  The unknown species of owl’s lower bill was significantly larger than those from the extant largest species of owls.

Marshall Forest

Photo comparing the mandibular symphysis of the unknown Pleistocene species with those from the 3 largest species of extant owls.  It’s the largest lower bill, suggesting this extinct species was larger than any North American owl species still extant.

David Steadman examined all the bird fossils excavated from Kingston Saltpeter Cave, also located in Bartow County, and he came across 2 unusually stout tarsometatarsii from juvenile owls that didn’t match the measurements from any known species of owl.  The tarsometatarsi is a bird’s equivalent of an ankle bone.

Tarsometatarsii from vultures and condors.  I couldn’t find any photos on the web of owl tarsometatarsi.

Those 2 specimens from Kingston Saltpeter Cave either belong to the same species that Starrs Olson examined, or they belong to yet another unknown extinct species.  Neither paleo-ornithologist was willing to describe a new species based on such scant evidence, even though it’s fairly certain a large unique owl did exist here during the Pleistocene.  This case reminds us of why the La Brea Tar Pits are of such value to science.  A different extinct Pleistocene owl also used to live in the American southwest.  It’s known as the Brea owl and was recently given the new scientific name Oraristrix brea.  At least 23 individual Brea owls became trapped in the tarpits, leaving scientists with many specimens to examine.  But if it wasn’t for the tarpits, there’s barely enough evidence to recognize this animal as a species because just a few fossil specimens of this owl have been found at 2 other sites in Arizona and Mexico.

The unknown Georgia species was likely a spectacular bird that would have impressed any human who had a chance to see it.  Like most large predatory birds, it probably lived in low population densities.  Let’s assume an average of 1 individual lived per 10 square miles, and that an average owl’s lifespan was 3 years.  Let’s also assume this bird had a limited geographical range of about 60,000 square miles ( the area of present day Georgia).  And suppose this animal existed as a species for 1 million years.  I did the math: 1.8 billion individuals of this undescribed species of owl lived on earth, and the only evidence we can find is a lower bill and a couple ankles.  Moreover, there’s no evidence at all of its immediate evolutionary ancestor.  My calculations show just how low the odds of an organism becoming a fossil can be, especially for a forest bird that successfully can avoid dying in a flood when the possibility of being covered by sediment and preserved is higher.  No Pleistocene fossils of ivory-billed woodpeckers or Carolina parakeets have ever been found either, though parakeet fossils from the Pliocene have been unearthed in Nebraska.

Scientists are interested in finding more fossils of this owl.  Besides earning the honor of naming a new species, they want to unravel the possible evolutionary relationship between this large owl, and the extinct giant Cuban owl (Ornimegalonyx), a flightless owl that served as top predator there until its extinction when man disrupted the environment.  The unknown Georgia owl was probably not flightless because it would have faced too much competition from large mammalian predators.  Its shorter, stouter legs suggest it was also not likely a ground dweller, like the Brea owl of the southwest.  Nevertheless, it undoubtedly was at least a fearsome predator as the 3 large owls below.

Great horned owl with captured skunk.  The great horned owl is the heaviest extant species.  They’ve been known to prey on tom cats and they regularly prey on skunks, squirrels, rabbits, turkeys, and grouse.

The lower bill of the unknown extinct species was 25% larger than that of this species, the great gray owl.  If the overall body proportions were the same, than the extinct Pleistocene owl of Georgia was probably about 25% larger  than this species as well.

Snowy owls have been known to attack small house dogs.  The extinct Pleistocene species that used to live in Georgia was also likely a fearsome predator of small mammals.

What caused the extinction of this mystery owl?  I believe a large fearless owl living in low population densities was easily overhunted by men.  According to George Leonard Herter, owl meat is as white and flavorful as chicken.  They reportedly have large drumsticks.  There’s also the possibility that this owl scavenged meat for part of its diet, and the extinction of the megafauna reduced its food supply.  Or this owl may have had a narrow ecological niche that disappeared at the end of the Pleistocene.  Whatever the reason for its extinction, it’s a shame that we know so little about this animal.

References:

Campbell, Kenneth; and Zbigniew Dochinski

“A New Genus for the Extinct Late Pleistocene Owl Strix brea (Aves: Strigiformes) from Rancho La Brea”

Australian Museum of Natural History 62 (1) 2010

Olson, Starrs

“A Very Large and Enigmatic Owl from the late Pleistocene at Ladds”

Special publication of the Carnegie Museum of Natural History 1984

Steadman, David

“Fossil Birds from Kingston Saltpeter Cave, Bartow County, Georgia”

The Late Pleistocene Record of Kingston Saltpeter Cave, Bartow County, Georgia edited by Joel Sneed and Larry O. Blair

Pleistocene Skunks

April 7, 2013

The skunk’s black and white markings warn predators, even those lacking color vision, to beware of the noxious spray this animal is capable of unleashing.  The skunk’s defense mechanism is so effective they seem to fear no other animal.  When threatened they often run toward much larger animals and chase them away.  Nevertheless, skunks do suffer predation.  Most notably, great horned owls (Bubo virginianus) specialize in taking skunks, and the owls seem to be immune to the spray.  For this reason some great horned owls smell like skunk.  Cougars stalk and kill skunks before the skunk has time to respond.  Formerly, some Native Americans preferred skunk to other types of meat such as turkey.

Scientists no longer consider skunks to be members of the weasel family, the mustelidae.  Instead, skunks and old world stink badgers belong to a family all their own known as the mephitidae.  Today, Georgia is h0me to 2 species of skunks–the striped (Mephitis mephitis) and the spotted (Spilogale putorious).  During the Pleistocene hog-nosed skunks (Conepatus leuconotus) lived throughout the south as well, leaving fossils at Ladds Mountain, Bartow County, Georgia and several sites in Florida.  The extinct short-faced skunk (Brachyprotoma obtusata)  may have extended its range into the upper south but was more of a boreal species.  Fossils of this species have been found as far south as Arkansas.

Striped skunk–the most common species found in Georgia today and probably during the Pleistocene.

Striped skunks are the most common skunk in Georgia today, and are the only species found in more than 1 fossil site in state, so they likely were the most common species throughout the Pleistocene.  Striped skunks are omnivorous, feeding on small mammals, reptiles, birds, insects, and fruit.  I’ve never seen a live individual, but I have frequently seen road-killed skunks in rural areas of north Georgia.  They prefer broken country with a mix of fields and woods.  Curiously, they’re rare near Augusta, Georgia, perhaps because there aren’t many farms with stores of grain that attract enough mice to entice skunks.

Spotted skunk.  When a spotted skunk displays a handstand flee the scene immediately…it’s about to spray.

I did see a live spotted skunk once in 1990, while I was throwing a paper route at about 5:00 am on Sand Bar Ferry Road located east of downtown Augusta.  Spotted skunks are attractive little animals that climb trees–an unusual behavior for a skunk.  Spotted skunks prefer forest edge and prairie habitats and are common in the middle part of North America but less abundant on the edges.

Hog-nosed skunk.  Note the claws for digging up grubs.

Current range of hog-nosed skunk and closely related South American species.  During the Ice Age its range expanded into the southeast of North America because there was more brushy arid habitat then.

Hog-nosed skunks prefer arid brush and grassland habitats, thus explaining why they occupied the south during the Ice Age but no longer occur here.  Arid scrub habitat expanded across the southeast during the Ice Age because the climate was drier then.  Like striped and spotted skunks, hog-nosed skunks are omnivorous but rely more on insects for a greater part of their diet than other skunk species.

Little is known about the extinct short-faced skunk.  It was a small skunk, more like the spotted skunk than any other extant species.  Based on its fossil distribution, it was an animal of the boreal forests that predominated south of the ice sheet.  It co-existed with the other 3 species of skunks, but unlike them, it failed to adapt to the environmental changes that occurred ~8,000 years BP.  Perhaps, they were more vulnerable to diseases carried by an increased population of parasites in the warming climate.