Archive for the ‘Ornithology’ Category

Late Miocene/Early Pliocene Climate Change Caused Sudden Burst of Warbler Speciation

February 18, 2018

I had a good birding day a few weeks ago.  I was walking alongside Woodbridge Lake in Evans, Georgia, and I saw many of the aquatic species I almost always see there–Canadian geese, mallard ducks, pied-billed grebes, cormorants, great blue heron, and great egret.  But much to my surprise, I also saw an immature bald eagle.  When I first spotted it, I assumed it was a black vulture because there was a flock of those scavengers soaring over the lake.  The eagle briefly flew low enough for me to identify it.  A couple osprey were soaring above the eagle, and I wonder if the young eagle was following them to supplement its diet.  Eagles are notorious for stealing fish from ospreys.  A lone Cooper’s hawk was another unexpected species to make my birding list that day.  Away from the water I saw a small flock of pine warblers (Setophaga pinus) roosting near the top of a pine tree.  Pine warblers are the only year round resident warbler species in southeastern North America.  Myrtle warblers (Dendroica coronata) spend winters in the south, and many warbler species either spend summers in the region or pass through during spring and fall on their migrations north and south.  This sighting made me curious about the fossil record of warblers, so I did an internet search.  As far as I could determine, fossil evidence of warblers is non-existent.  This is not surprising.  Warblers inhabit forest environments where their remains are not likely to be preserved.  However, I did come across an interesting genetic study that determined a sudden burst of warbler speciation occurred during the late Miocene/early Pliocene.

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I thought these were pine warblers, but a reader identified them as cedar waxwings, and I agree.  Nevertheless, my mistaken id inspired this blog entry.  I took this photo a few weeks ago.

This speciation event occurred between 4.5 million years BP-7 million years BP when climate became warmer and drier.  The authors of this study note this coincides with a time of faunal turnover.  Rhinos and species of 3-toed horses became extinct when warblers speciated into many different species.  They conclude the aridity fragmented forests, isolating many different populations of warblers that then evolved into unique species.  It’s a remarkable example of adaptive radiation, defined as the evolutionary lineage differentiation into a suite of closely related species differing in their use of ecological resources.  It resulted in the evolution of over 2 dozen species.  Warbler adaptive radiation differs from that of other species groups because there is little morphological difference between the species.  Darwin’s famous Galapagos Island finches evolved different bills depending upon which ecological niche they inhabited, but warblers remained very similar.

By the middle of the Pliocene, habitats began to resemble those that exist today (if left alone by man), and warbler speciation slowed down because existing species came into contact with each other and competed for all of the existing niches.  Still, the evolution of a few species may be linked to glacial/interglacial cycles.  Townsend’s warbler (D. townsendi), hermit warblers (D. occidentalis), and black-throated green warblers (D. virens) may have speciated during the Pleistocene.  Black-throated gray warblers (D. nigrescens ) and Grace’s warbler (D. gracae) may be the result of hybridization events.

The pine warblers of the south are closely related to the founder population of warblers.  The ancestors of all warblers likely were a more adaptable species, like the pine warbler, and less dependent upon migration for survival.  Pine warblers are 1 of the few warbler species that can feed upon seeds.  Most warbler species eat insects and fruit and thus require warmer temperatures.

Rapid adaptive radiation among mammals, like warbler speciation, followed a similar pattern after dinosaurs became extinct.  There was a sudden burst of speciation of mammals occupying newly available niches vacated by dinosaurs.  But the rate of speciation slowed down when enough species evolved that competition increased for those niches.


Lovette, I.; and E. Bermingham

“Explosive Speciation in the New World Dendroica Warblers”

Royal Society of Biological Sciences 1999


Pleistocene Wood Ducks (Aix sponsa)

January 4, 2018

Wood ducks differ from most other species of ducks because they nest in hollow trees, rather than in thick wetland vegetation.  Unlike migratory species of ducks that prefer to fly over open water or high in the sky, wood ducks comfortably fly between trees.  However, wood ducks do share a love of water with their kin.   Shortly after wood ducklings hatch, they jump out of their nest and follow their parent to water.  Oftentimes, their den tree is located in flooded terrain and the water guarantees a safe landing.  But the ducklings are so light they can land on solid ground without sustaining injury, though they are not yet able to fly.

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Male wood ducks are much more colorful than females.  I’ve only seen wood ducks on 1 occasion, while I was visiting Phinizy Swamp Park in Augusta, Georgia.

Wood ducks probably first speciated during the early Pliocene when Ice Ages began occurring, and glaciers caused a divergence in the Holarctic ancestral population that also gave rise to their closest living relative, the mandarin duck (Aix galericulata) of east Asia–the only other species of duck in the Aix genus.  Fossil evidence of wood ducks dating to the late Pliocene and Pleistocene has been found at 6 sites in Florida and 1 each in Oregon, New Mexico, and Georgia; suggesting the species has been widespread for millions of years.  (Pleistocene wood duck remains in Georgia were excavated from Kingston Saltpeter Cave, Bartow County.)  Wood ducks were likely most common during interglacials and interstadials when their favored habitat–beaver ponds and woodlands with abundant streams–expanded.  Wood ducks eat acorns, seeds, berries, and insects.  Oaks increased in abundance during wetter climate phases, therefore providing more acorns for wood ducks to eat.

There are eastern and western populations of wood ducks.

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Wood duck range map.

Genetic evidence suggests these populations diverged ~34,000 years ago.  This is consistent with the record of climate change.  The stage 2 stadial that included the Last Glacial Maximum started about 29,000 years ago and before this climate frequently fluctuated between stadial and interstadial. Any 1 of the previous stadials preceding stage 2 or stage 2 itself could have caused the ecological changes isolating the 2 populations.  Dry grassland habitat expanded and streams dried up, so that eastern and western populations were separated into different refugia.  They still haven’t reconnected, even though the 2 populations come so close to each other in the midwest.


Peters, J.L.; W. Gretes, and K. Omland

“Late Pleistocene Divergence between Eastern and Western Populations of Wood Ducks (Aix sponsa) inferred by the ‘Isolation with Migration’ Coalescent Method”

Molecular Ecology (11) October 2005

Ice Age Western Lakes and Altered Bird Migrations

April 9, 2017

I photographed a lesser yellowlegs (Tringa flavipes) at Woodbridge Lake, Evans, Georgia last weekend.  I was thrilled to see this transient species in such an unexpected locality.  Lesser yellowlegs and many other species of sandpipers spend the winter in South America, Florida, and the coasts of Georgia and South Carolina, but they migrate to their summer breeding grounds in western Canada during spring.  The present day breeding grounds of 22 American species of sandpipers, plovers, curlews, and dowitchers were mostly or completely under glacial ice during Ice Ages.  One might ask where these species bred during Ice Age summers.  Weather patterns were much different then.  Today, much of the west is arid desert, but during Ice Ages the region enjoyed a cooler and much wetter climate.  Many large lakes existed in western North America, and they provided beach, reedy marsh, and open water habitats for aquatic birds.  A large prehistoric body of water, known as Pleistocene Lake Manix, covered what today is the Mojave Desert, and Pleistocene Fossil Lake inundated the modern day site of a desert in central Oregon.  Both of these sites yield abundant remains of the aquatic bird species that formerly spent all or part of their lives there.

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Map of western North America during the Ice Age.  More precipitation and cooler weather patterns resulted in large lakes in place of present day arid landscapes.

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Lesser yellowlegs in Evans, Georgia.  This species is a transient here.  It spends winters in South America, Florida, and the southeastern Atlantic Coast, but breeds during summer in western Canada.

Lesser Yellowlegs Range Map

Range map for a lesser yellowlegs.  Many species of sandpipers have similar ranges.  Almost their entire breeding range was under glacial ice during Ice Ages.  They shifted their breeding ranges to the lakes in western North America that no longer exist and are deserts today.

The entire breeding range of the white fronted goose, the blue goose, and 10 species of ducks was also under glacial ice during the late Pleistocene.  The geese and some species of ducks shifted their breeding ranges to these western lakes.  However, harlequin, eider, king eider, and the extinct Labrador duck have/had more easterly distributions and likely bred near the Atlantic coast south of the ice sheet.  Other migratory species of birds that bred on western lakes during Ice Ages include whooping cranes, northern skuas, and arctic loons.

Many species of aquatic birds that breed in western Canada during summer still breed in western states as well wherever wetlands still exist.  Instead of shifting their breeding ground migration north, these species expanded their summer breeding grounds but still also nest within their Pleistocene range.  This list of species includes 2 loons, 2 grebes, white pelicans, 2 swans, 10 ducks, sandhill cranes, Virginia rails, Hudsonian godwits, American avocets, 3 phalaropes, and 3 jaegers.

The abundant large lakes of Pleistocene western North America attracted some species of non-migratory birds that no longer occur in the region.  Anhingas are fish-eating birds confined to southeastern North America today, but fossil evidence shows they lived in Oregon during the Ice Age.  The beautiful scarlet ibis no longer occurs north of Central America but ranged to Oregon then also.

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The scarlet ibis no longer occurs north of Central America but did live as far north as Oregon during Ice Ages.

Western lakes evaporated and turned into desert following the end of the Ice Age.  A number of species failed to adapt by shifting their ranges to newly available Canadian habitat, and they became extinct.  The extinct species include a flamingo, 2 gulls, a jaeger, a cormorant, a grebe, a swan, a goose, and a shelduck.

Breeding colonies of aquatic birds attract predatory species such as bald eagles and great horned owls.  Fossil evidence of both these species is found at most of the sites of these former Pleistocene lakes.

The extinct western lakes would have been a birder’s paradise. Paleo-indians saw the wealth of avifauna as a food source.  Paleo-indians had no television, radio, and little in the way of entertainment, so perhaps bird-watching was a leisure activity for them after they filled their bellies with spit-roasted duck.


Jefferson, George

“Remains of the Late Pleistocene Avifauna from Lake Manix, Central Mojave Desert, California”

Bulletin of the Natural History Museum of Los Angeles County June 1985

The Disappearance of the Dickcissel (Spiza americana) from the Mid-Atlantic States

April 4, 2017

The dickcissel is a cyclically abundant grassland bird that spends its summers in North America and flies to South America during winter.  They feed upon grass seeds, though they give their young high protein insects in spring.  Their nests are hidden in tall grass.  Dickcissels are found associated with other grassland species of birds such as meadowlarks, red-winged blackbirds, vesper sparrows, grasshopper sparrows, and savannah sparrows.  Dickcissels prefer clover and alfalfa pastures and old abandoned fields, but they don’t like suburban habitat.  The heart of dickcissel range is the agricultural Midwest.  Migrating stragglers may occur on the Atlantic coast today, but mysteriously, large breeding populations of dickcissels invaded the mid-Atlantic during the middle of the 19th century and just as mysteriously they disappeared from this part of their range by 1900.  Maybe farmers in this region planted more corn and less wheat and clover fields.  Corn rows don’t offer usable habitat for dickcissels.

Summer range map of the dickcissel.  It breeds in the dark red area but vagrants are found within the dotted lines.  They formerly bred in the mid-Atlantic states from South Carolina to Massachusetts.  Stragglers migrate south along the Atlantic coast.

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A pair of dickcissels.  They are a type of finch.

Dickcissels likely were cyclically abundant during the Pleistocene as well with widely changing geographic ranges.  Studies show dickcissels are eliminated from ranges that are burned, and their numbers decline in areas where bison graze.  This suggests they bred on grasslands temporarily abandoned by grazing megafauna herds and left untouched by fire for at least a year.  Lightning-ignited wild fires were less frequent during colder climate phases of Ice Ages.

As far as I can determine, dickcissel remains have been excavated from only 1 Pleistocene-aged fossil site–Little Box Elder Cave in Wyoming, a site just outside the periphery of their modern day range.  (Little Box Elder deserves a blog entry of its own.  Remains of at least 62 mammalian species were recovered here including horse and the only known association of grizzly and short-faced bears south of the former ice sheet.)  Although dickcissels are known from just this 1 fossil site, they may have been common during some climatic stages of the Pleistocene.  I believe they are rare in the fossil records because they inhabit open grassy areas where their remains are not likely to be preserved.

Little is known abut the dickcissel’s past.  Scientists could use genetic analysis to determine historic and pre-historic population dynamics and their evolutionary relationships to other members of the Cardinalidae family which includes cardinals, grosbeaks, finches, and buntings.  Maybe some day, they will be able to explain why the dickcissel disappeared from mid-Atlantic sites.

A Pleistocene-age Carolina Parakeet (Conuropsis carolinensis) Fossil Finally Discovered

December 29, 2016

The Carolina parakeet was a common species living in old growth bottomland forests until Europeans settled eastern North America.  Overhunting and deforestation doomed this only temperate species of parakeet. The colorful noisy birds were an agricultural pest that destroyed ripening fruit when they fed upon the seeds inside the pulp.  Orchardists wiped out entire flocks.  Though parakeets are supposed to be intelligent, they were not well adapted to avoiding patient men with guns.  A farmer firing his weapon into a flock (the birds routinely congregated in flocks of 200-300) caused the survivors to fly in a wide circle and return to the same place where their feathered comrades had just been killed.  A farmer could slaughter the entire flock in an afternoon without moving from the same spot.  Carolina parakeets nested in large hollow trees, but lumbering operations during the late 19th century eliminated their homes as well.  The last population of Carolina parakeets was probably rubbed out by market hunters seeking red and green and yellow feathers, then fashionable in women’s hats.  The last wild specimen was taken near Lake Okeechobee, Florida in 1904, and the last captive specimen died in the Cincinnati Zoo in 1918, coincidentally the same place and year where the last passenger pigeon died.

Until recently, the only North American fossil remains of a parakeet was a specimen found in Nebraska, dating to the mid-Miocene (about 16 million years BP).  Scientists are uncertain if this specimen represents a species ancestral to the Carolina parakeet, the same species, or a different lineage.  In any case no fossil remains of a parakeet dating to the Pleistocene age (~2 million years BP-11,000 years BP) had ever been found in North America.  Carolina parakeets lived in habitat where preservational processes don’t often occur.  Most bird remains are found in caves where they were carried by roosting owls or hawks.  There aren’t many caves in the lowland habitats favored by parakeets.  Moreover, the flesh of parakeets was toxic to many predators because they fed on poisonous cocklebur seeds.  Their colorful plumage may have worked as a deterrent to predators who learned to avoid the well-marked prey that may have sickened them previously.  Although preservational bias was the probable reason why remains of this species had never been found, it was possible Carolina parakeets were a recently evolved species that colonized North America, following the end of the most recent glacial-interglacial transition.  But finally, just a few years ago, the remains of a Pleistocene-age Carolina parakeet were unearthed at the Dickerson Coquina sand pit in St. Lucie County, Florida.  Fossils found at this site are estimated to be somewhat younger than 730,000 years BP-430,000 years BP, proving that Carolina parakeets had a very long history in North America.

Map of Florida highlighting St. Lucie County

St. Lucie County, Florida.  The Dickerson Coquina Pit fossil site, located in this county, yielded the first known Pleistocene-age remains of a Carolina parakeet.

The extinct Carolina parakeet.

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Range map of the formerly widespread Carolina parakeet.  It was doomed by overhunting and deforestation.

Sand is mined from the Dickerson Coquina sand pit to replace sand lost on Hutchinson Island to erosion.  Hutchinson Island is located in the same county as the sand pit.  Pleistocene-age fossils have been found in the sand pit and on the sand dumped on Hutchinson Island Beach.  Electron spin resonance dating determined the specimens excavated from the sand pit were above a layer dated to 730,000 years BP-430,000 years BP.  The species found are consistent with this dating and were common during the late Pleistocene including giant tortoise ( Hesperostestudo crassicutata ), box turtle, snakes, sharks, rays, fish, mammoth, paleollama, tapir, horse, pampathere, dire wolf, and jaguar.  No bison fossils were found.  Bison didn’t colonize North America until 300,000 years ago, so the absence of this species is consistent with an estimated date of 400,000 years BP for the fossils found here.

The remains of at least 24 species of birds have been excavated from these sands including a number of interesting extinct or extralimital species aside from the Carolina parakeet.  (The complete list of species found is described in the paper linked below as a reference).  Ornithologists have identified the remains of great auk ( Pinguinus impennis ), short-tailed albatross (  Phoebastrea albatrus ), northern gannet ( Morus bassanus ), an extinct stork ( Ciconia maltha ), and an unnamed extinct crane ( Grus sp. ).

Today, the short-tailed albatross nests on just 4 islands in the North Pacific between Hawaii and Japan (including Midway near where the famous WWII battle took place). But the presence of their bones in Florida means this species formerly ranged throughout the North Atlantic Ocean.  They probably nested on islands that were inundated by rising sea levels about 400,000 years ago, causing their extirpation here, but they didn’t necessarily nest in Florida.  Storms may have blown flocks inland.

Short tailed Albatross1.jpg

Today, the short-tailed albatross is a rare bird that nests on 4 islands in the North Pacific, but it also lived in the Atlantic Ocean during the middle Pleistocene.

The great auk was a denizen of rocky islands off the coast of Maine and Canada until 1852 when it was overhunted to extinction.  I hypothesize they nested on a rocky island off the coast of South Carolina, known as Bulls Scarp, that was above sea level during Glacial Maximums.  This possible nesting site may explain why they were close enough to have fished waters off the coast of Florida.  It’s likely storms blew this species inland as well.

A large, stuffed bird with a black back, white belly, heavy bill, and white eye patch stands, amongst display cases and an orange wall.

The great auk was overhunted to extinction by 1852.  Remains of this species were also found at this site.  I hypothesize that during Glacial Maximums this species may have nested as far south as South Carolina.

Northern gannets nest on subarctic islands in the North Atlantic but range throughout most of the Atlantic when seeking fish.  They too may have nested on Bulls Scarp.  The extinct species of stork probably ate carrion and depended upon the existence of large herds of megafauna for a major part of its food supply.  Not enough skeletal material has been found here from the large extinct species of crane to officially name it.  The fossil bone recovered from the sand pit resembles that from an extinct flightless crane that formerly lived in Cuba, but it is not an exact match.  This species was probably not flightless, like its Cuban cousin, because there were too many predators on the mainland.


Kilmer, John; and David Steadman

“A Middle Pleistocene Bird Community from Saint Lucie County, Florida”

Bulletin of the Florida Museum of Natural History 2016

Forest Succession and Changing Song Bird Species Composition in Central Georgia

November 13, 2016

Cotton and corn cultivation were important in central Georgia until the boll weevil struck in the 1920’s.  Then the depression bankrupted many farmers who tried to persevere, despite this agricultural pest.  This economic calamity gave ecologists the opportunity to study forest succession as fallow fields eventually were transformed into climax forests.  In less than a year bare soil becomes covered in grass and weeds 2 feet tall.  Ragweed, asters, and broomsedge (a type of bunch grass) take over in the 2nd year, and by the 3rd year broomsedge and pine saplings up to 3 feet tall predominate.  These 1st three years are known as the “grassland stage.”

If left unmodified, years 3-10 are known as the “grass and shrub stage.”  Broomsedge and pine saplings are joined by blackberry, blueberry, sumac, greenbrier, and persimmon often covered by grape vines, Virginia creeper, Carolina jessamine, and honeysuckle–all plants that thrive in the sun.  Eventually, pine trees emerge above this tangled mess.  During years 11-30 the landscape is known as a “young pine forest.”  An “old pine forest,” years 31-60, hosts tall pine trees but with a dense oak understory.  This mixed pine/oak forest is habitat for more species of birds than any other stage.  Lightning strikes, red heart disease, and pine beetles kill many pine trees during this stage, opening up the forest canopy and creating uneven-aged stands of trees beneficial for many different species of birds.  After 60 years left fallow the land becomes a climax oak/hickory forest.

Below is a chart interspersed with photos showing the association of bird species with each stage of forest succession.

Years 1-3 (Grassland Stage)–grasshopper sparrow, field sparrow, song sparrow, meadowlark, killdeer plover, quail, junco, horned lark.

Female grasshopper sparrow returning to nest with prey in beak

Grasshopper sparrows (Ammodramus summurum) are abundant in old fields.

Years 3-10 (Grass and Shrub Stage)–Add white-throated sparrow, rufus-sided towhee, cardinal, catbird, mockingbird, mourning dove, Carolina wren, and brown thrasher.

bobwhite quail covey












Covey of quail.  This species becomes most abundant 3-5 years after cleared land is left fallow.

Years 11-30 (Young Pine Forest)–Subtract most of the grassland species but add flicker, blue jay, chickadee, titmice, pine warbler, and white-eyed vireo.

Eastern Towhee














Rufus sided towhees move into young pine forests.

Years 31-60 (Old Pine Forest Stage)–Subtract mourning dove, catbird, mockingbird, brown thrasher, and white-eyed vireo, but add summer tanager, woodpeckers, yellow-throated warbler, black and white warbler, wood thrush, flycatchers, red-eyed vireo, and kinglets.

Carolina Wren Photo

Carolina wrens are abundant in old pine forests with an hardwood understory.

> 60 years (Climax Oak/Hickory Forest) Subtract towhee, pine warbler, and tanager, but add white breasted nuthatch.

White-breasted nuthatch foraging in tree

White breasted nuthatches won’t move into a forest until it is at least 50 years old.  Last time I saw this species was when I visited Marshall Forest in Rome, Georgia which is a virgin forest.

Forest succession from bare soil to climax forest has occurred in Georgia ever since Indians began cultivating the land here over 1000 years ago.  However, habitat including each successional stage is much older than this because our present day species of song birds, especially habitat specialists, have existed for over 1 million years.  Before man impacted the environment, changes in the landscape depended upon natural disturbances.  Heavy acorn consumption by megafauna along with trampling and bark-stripping suppressed tree recruitment and growth.  Lightning-ignited fires thinned forest into open woodlands.  Tornadoes and downbursts flattened wide swaths of trees.  Drought, ice storms, floods, and fluctuating climate cycles also changed forest structure and tree species composition.  Landscapes are never eternally permanent.


Johnson and Odum

“Breeding Bird Populations in Relation to Plant Succession on the Piedmont of Georgia”

Ecology 37 1956

Meyers, J.M. and A.S. Johnson

“Bird Communities Associated with Succession and Management of Loblolly-Shortleaf Pine Forests”

U.S. Forest Service General Technical Report


Pleistocene Roadrunners (Geococcyx californianus)

August 5, 2016

Roadrunners are neotropical invaders that spread across North America, probably no earlier than the late Pleistocene.  Fossil remains of roadrunners dating to this time period have been excavated from sites in Arizona, New Mexico, and California.  Roadrunners are ground foraging birds in the cuckoo (Cuculidae) family.  All other members of this family prefer the tree canopy.  There are just 2 species of roadrunner–Geococcyx californianus ranges from central Mexico west to California and east to Arkansas and Louisiana and G. velox occurs in tropical deciduous forests from southern Mexico to Nicaragua.  The ancestor of these species likely diverged during an arid climate cycle of the Pleistocene.  G. californianus evolved a preference for desert scrub and cactus environments and moved north across the Rio Grande.  I think they are a fairly recent colonizer of this region because desert grassland and scrub habitat was widespread across southeastern North America during the late Pliocene/early Pleistocene about 2 million years ago, yet there is no fossil evidence of roadrunners in this region from that time period.    If roadrunners lived in southwestern North America during this early time period when their ideal habitat was so widespread, I believe they would have colonized the southeast.  And they would still persist in some areas of the southeast where favorable habitat exists.  There’s no shortage of thickets mixed with clearings in the southeast.  In Arkansas, the easternmost part of their modern range, roadrunners occur in farms and clearings, cedar glades, scrubby woods, and rocky outcroppings.  Currently, the Mississippi river appears to be a barrier that prevents them from expanding their range east.  They haven’t crossed the river yet because they are weak flyers and prefer to run in zigzag patterns between thickets.  They are the fastest runners among birds capable of flight, reaching speeds of 25 mph–about the speed of an Olympic male sprinter.

Roadrunner and Snake









Roadrunner killing snake.  They kill their prey by bashing it against the ground until it is senseless.

Geococcyx californianus map.svg

Roadrunner range map.  I believe the Mississippi River is the barrier that keeps them from expanding their range east.

Video of a roadrunner ambushing an hummingbird at a feeder.


Real life roadrunners are smart like their cartoon imitation.

Pleistocene roadrunners were slightly larger than modern roadrunners but are considered to be the same species.  Scientists believe they grew to a larger size due to cooler Ice Age summers.  The modern smaller birds have more endurance in warmer conditions than larger birds and can chase down their favored prey (lizards, snakes, mice, scorpions, insects, and other birds) for longer periods.

Roadrunners are poorly studied.  I searched The Auk and The Condor, 2 ornithology journals, for more information about them and found very few articles..  They are an intelligent bird, not unlike their cartoon counterpart, and this makes them hard to study because they are smart enough to avoid traps.  This is 1 case when the cartoon imitation of an animal matches its real personality.


Passenger Pigeons (Ectopistes migratorius) and Forest Succession

August 1, 2016

The former abundance of the now extinct passenger pigeon amazed all of the pioneers who witnessed their migration and roosts.  Some researchers estimate passenger pigeons composed 25% of the total bird population in eastern North America during colonial times.  Their migrations consisted of billions of birds that could eclipse the sun for as long as 14 hours.  Pigeon dung fell like “snowflakes” underneath this eclipse.  They nested in enormous colonies, covering many square miles.  Their survival strategy was predator satiation.  With synchronized hatching there were billions of squabs on the forest floor during the week they left the nest and were learning how to fly.  There were just too many for predators to eat all at once. They nested and reproduced in the great deciduous and coniferous forests of the Midwest, then migrated to the middle south during the winter where they still roosted in large colonies.  Passenger pigeon roosts destroyed vast areas of the forest.  The weight of all those birds broke limbs off trees and even busted thick tree trunks in half.  The armies of pigeons vacuumed all the acorns, beechnuts, and chestnuts off the forest floor, leaving no mast for other animals.  But their dung was the most detrimental element of their roosts–overfertilizing the soil and killing all the trees in the vicinity.  Yet, ecologists believe passenger pigeons played a critical role in creating habitat diversity across the landscape.

Illustration showing how passenger pigeons created more diverse habitats.

Flocks of migrating passenger pigeons could eclipse the sun for as long as 14 hours.  Areas of the forest where they roosted were devastated.

Stuffed specimen of a male passenger pigeon.

The response of the environment following the aftermath of a cataclysmic pigeon occupation would have been interesting to study.  Unfortunately, passenger pigeons were overhunted to extinction before scientific studies of their ecological impact could be conducted.  However, we can safely assume the environment recovered in stages.  First, plants; such as ginseng, pokeberry, and Virginia creeper; that thrive in soils rich in nitrogen were the initial species to grow in the open conditions strewn with fallen dead trees and limbs.  Second, as rain reduced the concentration of nitrogen in the soil over the years; ragweed, grasses, sedges, and composites returned.  A shrubby stage with pioneer trees including cedar and pine gradually replaced the grassy stage.  Acorns carried by jays and squirrels sprouted into oaks that grew with the pioneer trees before eventually outcompeting them.  If undisturbed for centuries, shade tolerant species such as maple and beech took over from the oaks. The dead wood from the original pigeon roosts was flammable during dry weather, and wild fires were likely more common, explaining why fire-tolerant species of oaks (burr, white, and black) predominated in the Midwest.

In many areas of the Midwest some species of oaks are in decline, especially white oak, while red oak is increasing.  White oak germinates during the fall when passenger pigeons were absent in this region.  But the pigeons were able to consume spring-germinating red oak acorns after the snow melted.  Moreover, red oaks are less fire tolerant than white oaks.  Oaks are also shade-intolerant and are being replaced by shade tolerant maples.  Ecologists think white oaks are missing the passenger pigeon invasions that created the natural disturbance they need and reduced the competition they now face from red oaks.

Scientists with the Revive and Restore Project hope to genetically engineer the passenger pigeon by cutting and pasting their genes into the embryos of their closest living relative, the band-tailed pigeon.  I doubt they will successfully be able to re-establish passenger pigeons in the wild.  Passenger pigeons fail to breed unless they live in enormous colonies.  To survive predation, they must exist in large numbers…the sheer size of their population was the survival mechanism they required.  Researchers would need to release at least 10,000 birds to establish a successful breeding population in the wild.  Passenger pigeons evolved their survival strategy millions of years ago.  Though 1 genetic study suggests their overall numbers fluctuated with changes in climate phases, I am convinced they always occurred in large colonies. The task of re-establishing these numbers is probably an impossible one.

See also:

Pleistocene chickens (Gallus sp.)

July 4, 2016

Some of my wife’s relatives are chicken farmers.  Modern day poultry farmers raise chickens in long metal warehouses containing as many as 30,000 birds.  The warehouses smell like the inside of a toilet bowl that hasn’t been flushed or cleaned in a year.  Chicken farmers have to walk through each of their warehouses twice a day to collect and dispose of dead chicks.  This task prevents the spread of infectious diseases.  Agricultural catalogues sell Israeli gas masks for poultry farmers, so they won’t get sick from working inside their warehouses.  Wild chickens have a better quality of life than the birds that spend their entire lives inside these awful concentration camps.  At least they get to breathe fresh air and live naturally.

According to the paleobiology database, chickens formerly lived all across Eurasia.  The bones of extinct species of chickens have been unearthed at 8 sites in Europe.  These extinct species lived from the late Miocene to the early Pleistocene.  But when Ice Ages began occurring, the range of the chicken was reduced to southeast Asia.  Now, there are 4 or 5 species of chickens, but many additional species existed when earth’s overall climate was warmer.  Chickens require warm tropical/semi-tropical river valley forests where they can forage for seeds, fruits, and insects on the ground.  They can’t endure harsh temperatures.  Curiously, there are no known Pleistocene-aged fossils of chickens from their current range, though they undoubtedly abounded in the region then.  Bone preservation is uncommon in lowland tropical forests because of the acid soils.

Distribution map of the red jungle fowl, 1 of the ancestors of the domesticated chicken.

Research of the origin of chicken domestication is confused and contradictory.  Zooarchaeological and genetic evidence suggests chickens were first domesticated in northern China about 8,000 years ago.  However, some scientists re-examined the zooarchaeological evidence and determined the chicken bones were misidentified.  Instead, these supposed chicken remains are actually pheasant bones.  They also note that chickens are and were not native to northern China, a temperate zone region.  The fauna associated with the pheasant bones consisted of temperate species such as red deer, sika deer, and wild boar.  The species of mammals that co-occur with wild chickens including rhesus macaques, Asian elephants, and rhinos were absent from this region.  Northern China is just too cold for chickens, and it’s far more likely they were first domesticated in their native range of southern China.  By 3000 BP chicken farming had spread to northern China where the birds could survive winter with human help.

The modern farm-raised chicken is a hybrid cross between 2 species–the red jungle fowl (Gallus gallus) and the gray jungle fowl (G. sonneratii). Genetic evidence suggests the yellow skin pigment descends from the latter species.  Feral chickens occur locally in many towns and cities across southeastern North America including Miami, Key West, St. Augustine, Houston, New Orleans, and Fitzgerald, Georgia.  Chickens living in Fitzgerald descend from a population released along the Ocmulgee River.  The Georgia State Fish and Game Department hoped the birds would become a popular target for hunters.  Instead, the chickens abandoned the river bottomland forest and moved into suburban areas of the nearby town where they have thrived for decades.  Their preference for human-modified habitats may mirror their close ties to habitats modified by elephant foraging in their native range.  Elephants expand and maintain open areas, and they knock fruit to the ground.  Their manure attracts insects and contains undigested seeds.  Wild chickens benefit from the presence of elephants.  In suburbs humans maintain the open areas and accidentally provide food for chickens.

Feral chickens in Fitzgerald, Georgia.

Some people love suburban wild chickens, while others (the get-off-my-lawn assholes) resent the crowing and droppings.  I like free-ranging chickens better than grouchy old people.


Eriksson, J; and et. al.

“Identification of the Yellow Skin Gene Reveals a Hybrid Origin of the Domestic Chicken”

PLOS Genetics 2008

Peter, Joris; and Ophelia Librasseum, Hai Deng, and Gregor Larsh

“Holocene Cultural History of Red Jungle Fowl (Gallus gallus) and its Domestic Descendent in East Asia”

Quaternary Science Reviews   June 2016

Pleistocene Chickadees

March 27, 2016

It is difficult to discern the difference between a black-capped chickadee (Poecile atricapillus) and a Carolina chickadee (P. carolinensis).  The former has a longer tail and is a little heavier on average, but as the below photos show, they are hard to distinguish, even if examined side-by-side.  Moreover, the 2 species hybridize in regions where their ranges overlap.  The hybrid zone extends from New Jersey to Kansas with an outlying zone in the Appalachian Mountains.  In captivity male Carolina chickadees outcompete black-capped chickadees for mates, and scientists know female black-capped chickadees will choose male Carolina chickadees in the wild, often as “extra pair sires.”  Supposedly Carolina chickadees have a 4 note song, while black-capped chickadees have a 2 note song.  (See: ) In the hybrid zone chickadees use both songs.  However, I live in Augusta, Georgia; far from the hybrid zone, and I discovered Carolina chickadees here use both the 2 note and the 4 note song.  I conclude the 2 species can’t be distinguished by which song they use.

bcchcach.gif (8294 bytes)

Partial range map for Carolina and Black-capped Chickadees.  

Black-capped chickadee

Black-capped chickadee.

Carolina Chickadee

Carolina chickadee.


The chickadees are tough Pleistocene survivors.  They are a year round resident of forest and woodland, capable of enduring harsh winters because they stash caches of seeds utilized during lean times.  Chickadees belong to the Paridae family that also includes tits and titmice.  Genetic evidence suggests the ancestors of all American Paridae originated in Asia and then colonized North America about 3.5 million years ago.  Cyclical climate change caused corresponding changes in the environment over time.  The founding population of these forest-dwelling birds became isolated into different populations by expanding desert grassland or in some cases by glaciers, resulting in the evolution of different species.

I was surprised to learn Carolina chickadees and black-capped chickadees are not sister species, even though they appear so similar and hybridize.  (Sister species are organisms that most recently evolved from the same common ancestor.  The official definition is “taxa derived from a common ancestral node.”)  Instead, the genetic evidence suggests the black-capped chickadee is a sister species of the mountain chickadee (P. gambeli), a bird that ranges throughout the Rocky Mountains, and the Carolina chickadee is a sister species of the Mexican chickadee (P. sclateri).  The chestnut-backed chickadee (P. rufescens) of the Pacific northwest, the boreal chickadee (P. hudsonicus) of Canada, and the gray-backed chickadee (P. cinctus) of Alaska and Scandinavia are sister species with each other.  Genetic evidence also shows black-capped chickadees and boreal chickadees have greatly expanded their ranges from single source populations, since the end of the last Ice Ages after the massive glaciers that covered their present day ranges melted.

Chickadees have likely been a common bird in southeastern North America for over 2 million years.  Yet, I’m aware of just a single specimen found in this region dating to the Pleistocene.  This specimen belongs to the University of Florida Museum of Natural History and was found at the Inglis fossil site in Florida.  It is early Pleistocene/late Pliocene in age (~1.9 million years old).  It was identified as a boreal chickadee, a species restricted to Canada today.  I can’t find the scientific journal within which this specimen was described.  Considering how hard it is to distinguish between species of chickadees, I’m uncertain how accurate this species diagnosis is.  However, boreal chickadees may have once been more widespread in North America before other chickadees, such as the Carolina, evolved and outcompeted them in various regions. The rarity in the fossil record of a species that was probably abundant for millions of years shows how fleeting evidence of an organism’s existence is.


Gill, FB; B. Slikas and F.H. Shulde

“Phylogeny of titmice (Paridae): 11 Species Relationships Based on Sequences of the Mitochondrial Cytochrome Gene”

The Auk 122 Jan 2005

Reudink, Matthew; et. al.

“Structure and Dynamics of the Hybrid Zone between Black-Capped Chickadee (Poecile atricapullus) and Carolina Chickadee (P. carolinensis) in Southeastern Pennsylvania”

The Auk 124 (2) 2007