Posts Tagged ‘ivory-billed woodpecker’

Pleistocene Tornadoes and Windthrow Ecology

February 18, 2017

Unstable weather conditions spawn outbreaks of tornadoes.  Cold fronts collide with warm air causing the chilled air from the upper layer of the atmosphere to plummet, creating swirling winds of great destructive force.  Tornado intensity is classified according to the Fujita scale or F scale for short.  Tornado wind speeds range from less than 73 mph (an F0 tornado) to estimated wind speeds of 261 mph-318 mph (an F5 tornado).  One of the largest outbreaks of tornadoes in recorded history occurred in early April, 1936.  At least 12 tornadoes struck the south from Tupelo, Mississippi to Anderson, South Carolina.  A tornado from this system that hit Tupelo left a path of destruction 15 miles long.  Another tornado from this storm traveled 50 miles from Alabama to Tennessee.  Two tornadoes merged in Gainesville, Georgia, killing 200 people in a factory and a department store.  Overall, this storm system wiped out 454 human lives.

Image result for F5 tornado

F5 tornado in Oklahoma.  I hypothesize storms and tornadoes were much more frequent and severe during some Pleistocene climate phases than they are today, but they may have been less severe during others.

I hypothesize tornado frequency and intensity was greater during some climatic phases of the Pleistocene than it is today.  As far as I can determine, no scientist has ever published a study of paleotornado frequency, probably because there just isn’t any method to collect data about past transient phenomena. Incidentally, I invented the term, paleotornado, in case a scientist figures how to study them.  My hypothesis is conjecture, but I am confident it is correct.  I base it on 3 lines of indirect evidence.

a) Data from ice cores in Greenland shows average annual temperatures fluctuated dramatically during Ice Ages.  There was an alternating cycle of sudden warm spikes in temperature that melted ice dams which in turn released glacial meltwater and icebergs into the ocean, shutting down the gulf stream.  This caused an equally sudden reversal in temperatures.   By comparison today’s climate is relatively stable, yet even with a stable climate, tornadoes form with regularity. When climate changed more rapidly in the past, it seems logical to assume there was an increased frequency of colliding warm and cold weather fronts.  I believe the middle south was an Ice Age tornado alley.  Temperatures in south Florida and the Gulf Coast were warmer than they are today because oceanic circulation ceased and warm water stayed in the Caribbean, but the upper south was only a few hundred miles from the Laurentide Ice Sheet that covered Canada and New England.  Cold fronts blowing off the Ice Sheet met warm fronts originating from the Gulf of Mexico in what must have been an exceptionally stormy transition zone.

b) An unusually cold phase of climate, known as The Little Ice Age, occurred between 1310-1850.  Anecdotal historical references suggest storms were more frequent and intense during this time period.  In Europe several storms killed hundreds of thousands of people.  The Little Ice Age is a tiny blip compared to the climate fluctuations of the Wisconsinian Ice Age as recorded from Greenland ice core data.

c) Geological evidence suggests river flooding in southeastern North America was much more severe during the early Holocene (11,000 BP-6,000 BP).  These massive floods caused supermeandering river patterns.  An increase in river flooding indicates an increase in storm activity and hence tornadoes.

Image result for windthrow in Arkansas

Windthrows open up the forest canopy and dramatically change the local ecology.

Tornadoes, thunderstorm downbursts, and hurricanes have a profound impact on forest ecosystems and may be a primary driver of evolutionary relationships.  Areas of forest felled by wind are known as windthrows among ecologists.  Tornadoes can travel for many miles, and they leave long scars of fallen and splintered trees that can be seen in satellite and aerial photographs.  These long windthrows create gaps in the canopy where shade intolerant species can thrive.  In southeastern North America canopy gap formation is beneficial for oak, pine, persimmon, sumac, grapevine, blackberry, composites, and grasses.  Windthrows can become tangles of luxuriant vegetation that provide forage and cover for forest edge species such as whitetail deer, cottontail rabbits, and ruffed grouse.  Fallen rotting timber attracts beetles, food for woodpeckers and other birds.  The extinct ivory-billed woodpecker formerly relied on vast tracts of timber with freshly created windthrows from annual storms.  Unlike extant woodpeckers, they depended upon early colonizing, shallow burrowing beetles.  Snakes and lizards lay their eggs in rotting timber.  Bears tear up these logs, looking for beetle larva, termites, and reptile eggs.  The pits created when trees are uprooted fill with water following heavy rains, and they serve as breeding pools for amphibians.  Most of the organisms that live in southeastern North America evolved to thrive in canopy gaps resulting from wind storms.  Plants able to resprout after sustaining wind damage have a competitive advantage over those species easily uprooted and killed, and the animals that browse and can digest those plants also enjoy a competitive advantage.

One study estimated wind felled 20 square miles of forest per year in pre-settlement forests of Wisconsin.  They also estimated the recovery time for northern hardwood-hemlock forests to erase the windthrow scar is 1210 years.  The recovery time in southeastern forests is probably quicker due to the longer growing season. A tornado can leave a long-lasting impact on the landscape, and wind may be a critical element, along with megafauna foraging and fire, that may explain why Ice Age environments were so much more open than they were in late Holocene environments.

Reference:

Canham, Charles; and Orie Loucks

“Catastrophic Windthrow in the Presettlement Forests of Wisconsin”

Ecology 1988

Advertisements

The First Ever Ornithological Expedition to the Okefenokee Swamp in 1912

February 6, 2016

In 1912 an expedition composed of 4 Cornell University professors, 2 graduate assistants, the principle of Ithaca High School, 2 Georgia state entomologists, and 4 local guides conducted an ornithological survey of the Okefenokee Swamp.  The expedition lasted from May 6th-July 13th.  They found 75 species of birds, and 19 species were added to their list based on descriptions of the local guides who were considered reliable sources.  At the time of the expedition the Okefenokee was still a vast wilderness of cypress swamps, flooded marshes, hardwood hammocks, and larger islands topped by open pine savannahs.  River bottomland forests grew along the Suwanee River.  A few families lived on the edges of the swamp and within it, but a lumber company was making inroads at the time because they were felling much of the best timber.  The expedition wrongly assumed the swamp was going to be destroyed, like so many other remnants of wilderness left in North America then.  They did not know Franklin Roosevelt would eventually make it a protected wildlife refuge.

The most abundant bird in the swamp was the red-bellied woodpecker followed closely by the crested flycatcher.  Old growth forests provide plenty of food for woodpeckers.  Bobwhite quail were abundant on the larger islands where “pine barrens” prevailed.   Prothonotory warblers were also considered abundant.  The expedition found a rookery consisting of 500 little blue heron nests with eggs.  However, they saw just a few egrets because a recent fashion craze for egret feathers on women’s hats had led to the decimation of this species.  Georgia outlawed egret hunting in 1910.

037

The information for this blog entry comes from an article published in The Auk from October 1913.  I purchased this vintage scientific journal from paleopublications.com .

The red-bellied woodpecker was the most abundant bird in the Okefenokee Swamp during Frances Harper’s survey of 1912.

The crested flycatcher was the 2nd most abundant bird during his survey.

File:Everglades Little Blue Heron.jpg

Harper found an active rookery of 500 little blue heron nests in the Okefenokee during his 1912 survey.

The expedition saw 150-200 wood storks feeding in shallow water, and 1 day a flock of 40 bobolinks flew over their heads.  Carolina wrens and brown-headed nuthatches were also considered very common/abundant in the swamp.

Woodpeckers in order of abundance were; 1. red-bellied, 2. pileated, 3. red-cockaded.  Hairy, downy, and red-headed woodpeckers were present but considered uncommon.  Ivory-billed woodpeckers, extinct since ~1945, still occurred in the northwestern part of the swamp on Minne Island then.  A guide heard an ivory-billed call during the expedition, and they found some recently used nests.  Red-cockaded woodpeckers, rare and endangered today, were still common here in 1912.

Ivory-billed woodpecker and nest.  Frances Harper found ivory-billed woodpecker nests in the Okefenokee that had been in use within 3 years of his survey.  One of his guides heard the call of an ivory-billed woodpecker during the survey, but Harper did not see or hear any.

Swainson’s warbler, considered uncommon now, were reported to be “not uncommon” in the swamp during the expedition.  Chimney swifts were a common bird seen hunting for mosquitoes over the water.  Evidentally, large colonies of this bird nested in hollow cypress trees for the local guides said they did not nest in their homestead chimneys.  Other common song birds included grackles, yellow-billed cuckoos, yellow throats, pine warblers, bluebirds, tufted titmice, eastern meadowlarks, and cardinals.

Red-shouldered hawks were the most common bird of prey during the day, while barred owls dominated the night.  Turkey vultures and black vultures were both common and made quick work of skinned alligators killed by hunters.  The expedition found 15 osprey nests.  They also often enjoyed seeing the aerial acrobatics of swallow-tailed kites.

Swallow-tailed Kites

Harper saw flocks of swallow-tailed kites summersaulting above the tree line.

Wood ducks were common year round residents, but the expedition came at the wrong time of the year to see winter migrants.  However, the local guides informed them that hooded mergansers, mallards, and coots commonly wintered in the swamp.  Shy sand hill cranes were  more often heard than seen because the local people hunted the delicious birds whenever they could.  The locals also relished wood ducks.  Oddly enough, white ibises were on the local menu.  I would suppose a fish-eating bird would taste too strong.

Anhingas could be found along the Suwanee River and in some of the larger bodies of water.  One of the guides was blind in 1 eye because his pet anhinga had stabbed it with its bill.

A single loggerhead shrike was seen chasing a bluebird.  A dead bluebird impaled by a shrike was further evidence of this species.

The only species the expedition was surprised to find was the spotted sandpiper.  This bird prefers open shore type habitat, but apparently some individuals were content to forage around fallen logs adjacent to marshes.  Spotted sandpipers winter south of this region and spend summers to the north.  The birds the expedition saw were probably in the process of migrating north.

Remarkably, not a single common crow was seen in the swamp.  The crow is 1 of the most common birds in my neighborhood in Augusta, Georgia, and I always see them wherever a travel.  This demonstrates just how attached crows are to the neighborhoods of man.  They thrive in manmade environments but avoid deep wilderness.  They like to eat human agricultural waste and garbage–a rich source of food compared to what they can forage in deep wilderness.  The expedition did identify a few fish crows along the Suwannee River.

Carolina parakeets became extinct in 1914.  Sadly, this species had been gone for so long from the Okefenokee that none of the old-timers were able to give any personal accounts of their encounters with them.

Reference:

Wright, Albert; and Frances Harper

“A Biological Reconnaissance of the Okefinokee Swamp: the birds”

The Auk 30 (4) October 1913