Archive for the ‘Ornithology’ Category

Pleistocene Cuckoos (Coccyzus sp.)

June 8, 2019

I frequently hear yellow-billed cuckoos (C. americanus) during summer, but I almost never see them.  They spend most of their time perched in tree tops and they blend in well, so they are difficult to spot.  I’ve never even seen this species perched, but I have occasionally spotted them flying in front of me, while I’m jogging or driving.  They are long birds with reddish brown wings and a checkered tail.  I discovered this species lives in my neighborhood a few years ago when I was learning bird calls from the Cornell University ornithology website.  I searched for yellow-billed cuckoos on this site and was pleasantly surprised to recognize their distinctive call.  Here’s a link.

Video of a perched cuckoo.  I’ve never seen one perched. Old timers called these birds rain crows because they will sometimes call in response to thunder.

Yellow-billed cuckoos spend summers in North America and winter in South America.  Caterpillars are the most important item in their diet, and they specialize in eating large spiny caterpillars that taste bad to most other species of birds.  They are so well-adapted to eating caterpillars that when their stomachs become clogged with spines, they vomit up their stomach lining and grow a new one.  They also feed on other large insects such as cicadas, locusts, and dragonflies.  Fruit balances out the rest of their diet.  They lay their eggs at intervals, and their nests often contain different aged nestlings.  The young are covered in porcupine like quills, and they are capable of climbing trees to avoid predators.  They leave the nest just 17 days after hatching.

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Yellow-billed cuckoo range map.

2 other species of cuckoos in the coccyzus genus live in North America–the black-billed cuckoo (C. erythropthalmus) and the mangrove cuckoo (C. minor).  Surprisingly, genetic evidence suggests the black-billed cuckoo is not a sister species of the yellow-billed cuckoo.  The black-billed cuckoo also summers in North America and winters in South America, but it breeds in more northerly locations.  These species independently evolved the habit of migrating north to find summer breeding ranges.  The pearly-breasted cuckoo (C. euleri), restricted to South America, is a sister species to the yellow-billed.  I looked at a photo of this species and I can’t tell the difference between the 2.  The mangrove cuckoo ranges from South Florida and the Bahamas to the coasts of Mexico and Central America.

Fossil evidence of cuckoos in the coccyzus genus has been excavated from sites in Florida, Virginia, the Bahamas, Dominican Republic, and Bolivia.  They are a bird of deep forest and therefore the process of preservation is rare in their habitat, explaining why they are absent in much of the fossil record.  Coccyzus cuckoos likely increased in abundance during warmer wetter stages of climate.

Cuckoos belong to the Cucilidae family which includes 135-147 species, depending upon the taxonomist’s opinion.  All Eurasian species are parasitic–they lay their eggs in other birds nests.  (These are the species depicted in cuckoo clocks.)  Yellow-billed cuckoos are occasionally parasitic.  During times of plenty when there are outbreaks of fall webworms or tent caterpillars, they will lay an egg in the nests of other cuckoos, robins, catbirds, or woodthrushes.  The cuculidae family also includes anis of South America and Mexico, coucals of Melanesia and Australia, and New World ground cuckoos.  Roadrunners belong to the New World ground cuckoos.  Most other species of New World ground cuckoos are parasitic, and 1 species specializes in preying upon army ants.


Forbush, Ed

A Natural History of American Birds of Eastern and Central North America

Bramhall House 1955

Hughes, Janice

“Phylogeny of the Cuckoo Genus Coccyzus (Aves: Cuculidae): a test of monophyly”

Systematics and Biochemistry 2006


2 Additional Extralimital Bird Species found in Florida’s Fossil Record

December 22, 2018

Some species of birds that lived in Florida during the Pleistocene no longer occur in state or even the region.  A few of the more notable species include the California condor, magpie, and trumpeter swan.  The extinction of the Pleistocene megafauna caused the extirpation of condors and magpies because they depended upon scavenging these animals as their most important food source.  Other species of birds periodically disappeared from the state due to sea level rise when their nesting habitat became inundated.  During some climate phases most of Florida became submerged, and a number of bird species simply never recolonized the state.  I was reading through an article on the University of Florida Museum website the other day and learned of 2 additional species that lived in Florida during the Pleistocene but no longer occur in state–the Manx shearwater (Puffinus puffinus) and the northern jacana (Jacana spinosa).

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The Manx shearwater is an oceanic bird that nests in burrows on islands.

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Manx shearwater range map.

The Manx shearwater is an oceanic bird that nests in burrows on rocky islands off the coasts of Canada and Europe.  They migrate to the South Atlantic during winter, flying over open ocean where they prey on small fish schooling near the surface.  They rest by floating on top of the water.  Scientists don’t know how they navigate to the same island colonies year after year.  During Ice Ages when sea level fell and the land area around Florida expanded there must have been some offshore islands that emerged and provided nesting sites for colonies of Manx shearwaters.  Islands emerged above sea level off the coasts of Georgia and South Carolina as well, and Ice Age oceans probably hosted higher populations of Manx shearwaters than exist today.  I couldn’t determine from the available information where fossil remains of this species were found in Florida.  It’s not listed in the Florida Museum of Natural History database and neither is the northern jacana, though I did find a paper that notes the presence of this species at 2 fossil sites.

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Northern jacana.

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Northern jacana range map.  Inundation by rising sea levels probably caused the extirpation of this species from Florida.

The northern jacana inhabits marshes.  This species of bird often walks on floating mats of vegetation while it hunts the small fish and insects it preys upon. Because it appears to walk on water, it is sometimes referred to as the Jesus bird. Fossils of this species have been found at 2 sites in Florida–Lecanto 2A and Leisey Shell Pit.  It likely became extirpated from Florida when rising sea levels eliminated its favored habitat.



Pleistocene Anhingas

December 3, 2018

I saw an anhinga (Anhinga anhinga) on my trip to Florida last week.  It was on the edge of a pond on the golf course behind my sister’s house.  I always see more wildlife there than I do in Florida’s much vaunted preserves and parks.  Anhingas belong to the Anhingidae family which includes just 1 genus and 4 species, but they have a wide distribution in the tropical to warm temperate regions of North America, South America, Africa, India, and Australia.  The Anhingidae family diverged from the cormorant family (Phalacrocoridae) early during the Miocene about 25 million years ago, and there is fossil evidence of anhingas in Florida during the late Miocene.  This early Florida anhinga goes by the scientific name of Anhinga grandis.  Anhingas probably originated in South America and later spread throughout the world.  There were 2 species of anhinga that co-existed in Florida during the Pleistocene–the extant A. anhinga and the extinct A. beckeri.  Anhinga remains have been recovered from 15 sites in Florida but A. beckeri fossils are known from just 4 sites.  Little is known about this extinct species, but it probably became extinct following the end of the last Ice Age when rising sea levels inundated important rookeries.  Anhingas often nest in colonies with herons and egrets, and the extinct species likely just never moved its breeding range to higher land as other species did.

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Anhinga range map.

Video of an anhinga swimming.

Anhingas are often seen drying their wings after swimming in the water while hunting for fish.  

Anhingas are also known as darters or snakebirds.  Note the snake-like head.

Anhingas hunt fish, amphibians, reptiles, and large invertebrates.  They swim underwater and impale their prey with their long bills.  When they return to shore they toss their prey up in the air and swallow it whole.  Crocodilians prey upon anhingas, but the birds are a dangerous adversary.  They aggressively fight predators with their bills, aiming for the eye.  A scout who guided the first academic ornithological expedition to the Okefenokee Swamp was blind in 1 eye because his pet anhinga had gouged it.  The anhinga is another amazing adaptable animal that has survived for millions of years.


In Defense of House Sparrows

September 18, 2018

Jessica Neal and Virginie Rolland, scientists from Arkansas State, published a paper in Southeastern Naturalist about their research of bluebird nesting boxes, and they mentioned “euthanizing” non-native house sparrow nestlings that they found occupying the nest boxes intended for bluebirds.  This irritates me for several reasons.  I hate the use of the word, euthanize, because it was used to sanitize what they actually did.  They killed helpless baby birds.  Many people kill house sparrows because this species outcompetes native birds such as bluebirds, swallows, woodpeckers, and unestablished purple martins.  It is too bad these species may be in decline, but when she killed the house sparrows that were occupying that site there were then fewer  birds occupying that area.  Bluebirds probably weren’t going to return to that site during that nesting season, and there is no guarantee they ever will.  Without the house sparrows there was less avifauna for bird watchers to enjoy.  I also don’t like the way they played God by deciding which species they wanted to live there.  Some may say humans already decided to play God by introducing house sparrows to North America in 1852 when ironically they were brought to New York to control native linden moths.  I reject this argument.  Humans shouldn’t pick an animal to introduce, then decide they don’t want it any more and try to eradicate it.  Not only are humans playing God, they are playing a fickle God in this case.  Not even the worst Old Testament version of God was this monstrous.

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House sparrows are a commensal species with humans.

I love house sparrows because they thrive where few other birds can.  Every grocery store shopping center hosts a colony of house sparrows, and they often live in the patio section of big chain lawn and garden centers.  This habitat is completely unsuitable for native songbirds.  The only other bird species I see in suburban parking lots are city pigeons (also non-native) and ring-billed gulls during winter.  But house sparrows are abundant in these otherwise barren urban environments where they feast on discarded junk foods and fill the atmosphere with their delightful singing.

The house sparrow (Passer domesticus) originated in the Middle East having evolved from P. predomesticus following the development of agriculture.  Fossil remains of P. predomesticus have been unearthed from Qumm-Quatufa Cave in Israel that date to the mid-Pleistocene.  House sparrows may have already been a commensal species with archaic humans, hanging around their garbage middens.  Late Pleistocene remains have also been discovered from Kebara Cave in Israel.  Genetic evidence suggests P. predomestica diverged from the Spanish sparrow (P. hispaniolensis) about 100,000 years ago.  Another genetic study suggests P. domesticus evolved larger skulls and an improved ability to digest starch 11,000 years ago–the dawn of the agricultural era.  The larger skulls helped them crack human-grown grains, and the improved ability to digest starch let them survive on an heavy diet of wheat, rye, and oats.  They became less dependent upon insects than their wildest remaining subspecies P. domesticus bactranius. Unfortunately for other songbirds, their larger skulls gave them greater biting and piercing force, and this allows house sparrows to outcompete them.

House sparrows followed humans throughout Europe and Asia where they continued to feast on grain spillage and nest on housing structures.  This close association with humans let house sparrows conquer the world wherever humans became established.  House sparrows were formerly even more abundant when the horse and buggy were the most common mode of transportation.  In addition to excess grain spillage house sparrows ate the undigested grains in horse manure.  But the introduction of the automobile dealt a little setback to house sparrow populations, reducing the amount of grain and manure in the environment.  Nevertheless, a trip to the local grocery store is all it takes to see them.


Schans, Franke

“How the Sparrow Made Its Home with Humans”

Science August 24, 2018

Neal, Jessica; and Virginie Rolland

“A Potential Case of Brood Parasitism by Eastern Bluebirds on House Sparrows”

Southeastern Naturalist (14) 2 2015

Pleistocene Mockingbirds (Mimus polyglottos)

June 9, 2018

Mockingbirds are swingers.  Most suburban yards in southeastern North America host a pair of mated mockingbirds, but they might not remain the same pair throughout the breeding season because both males and females often switch mates.  Male mockingbirds sit on the top of trees and sing long melodious songs to attract female mockingbirds from adjacent territories, not unlike the way human pop singers attract groupies.  Female mockingbirds may leave their mates for better singers.  Males also flash their wings, and this entices female mockingbirds as well.  It doesn’t matter if a male already has a mate because they will continue to try and attract other females.  Constant mate switching ensures the genetic vigor of this species.  Despite this competition, mockingbirds from adjacent territories respond to their neighbor’s distress calls and will help drive away predators, such as crows.  Each territory of swinging and singing mockingbird mates can produce 2-4 broods per year.  Mockingbirds are an intelligent bird able to recognize individual humans, and they can imitate the calls of at least 14 other bird species as well as the vocalizations of cats, dogs, frogs, and crickets.

Photo of a mockingbird in my front yard.  Click to enlarge.

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Northern mockingbird range.

I wonder how common mockingbirds were during the Pleistocene compared to today.  Studies show mockingbirds enjoy longer lives in suburban areas than they do in wilderness refuges.  Scientists believe mockingbirds prefer the stability of manmade habitats where they can find the same nesting sites, fruit trees, and insect species year after year.  They don’t have to travel far to find favorable habitat that might be dispersed in a wilderness.  I hypothesize mockingbirds were common in the south during most climate phases of the Pleistocene, but were not as common as they are today.  Mockingbirds probably occurred in forest edge habitat along megafauna trails maintained by the regular migration of herds.  Mockingbirds could rely on fruits originating from trees sprouting in seed-filled dung, and they fed on insects stirred up by roaming large animals.  Northern mockingbirds are uncommon in the fossil record.  They are known from just 3 specimens excavated from Reddick and 1 in Haile–both located in Florida.  Bahamian mockingbirds (M. gundlachii) left fossil evidence at the Banana Hole site in the Bahamas.  This paucity of fossil evidence doesn’t mean mockingbirds were an uncommon bird in the past.  Potential sites of fossil preservation in their favored forest edge habitat just didn’t exist to any great degree.

Genetic evidence does suggest mockingbirds have an ancient origin somewhere in South America where the most species of mockingbirds occur.  Mockingbirds belong to the Mimidae family which also includes thrashers and catbirds.  There are 14 species of mockingbirds: northern, tropical (M. gilvus), brown-backed (M. dorsalis), Bahama, long-tailed (M. longicauda), Patagonian (M. patagonicus), Chilean (M. thenca), white-banded (M. triuris), Socorro (M. graysonii), chalk-browed (M. saturninus), Floreana (M. trifusciatus), San Cristobal (M. melanotis), Hood (M. macdonaldi), and Galapagos (M. parvalus).  The northern mockingbird is a sister species to the tropical mockingbird, and they are so closely related they interbreed on the border region where their ranges overlap in southern Mexico.  The Chilean mockingbird is a sister species of the Patagonian mockingbird.  The uplift of the Andes mountains separated the founding population of these mockingbirds into 2 species.  Oddly enough, the Bahama mockingbird is a sister species to the 4 kinds of mockingbirds found on the Galapagos Islands including the San Cristobal, Galapagos, Hood, and Floreana.  Each of these species occupies just 1 or 2 Galapagos Islands.  Darwin wrongly assumed they were most closely related to South American species of mockingbirds due to the relative proximity.  But genetic evidence shows the mockingbirds that traveled over the Pacific Ocean to the Galapagos Islands came from even further away.  It seems likely this occurred before a land bridge connected North and South America.  Otherwise, the exhausted birds would’ve landed on Central America instead.  Unlike Darwin’s famous finches, mockingbirds didn’t evolve into different species that occupied different niches on each island, but instead remained habitat generalists, though each became a different species unique to the island they landed upon.


Hoeck, P; et al

“Differentiation with Drift: A Spatio-Temporal Genetic Analysis of Galapagos Mockingbird Populations (Mimus spp.)”

Philosophical Transactions of the Royal Society of Biological Science 365 (1543) 2010

Lovette, I; et al

“Philogenetic Relationships of the Mockingbrids and Thrashers (Aves: Mimidae)”

Molecular Phylogenetics 2011


The Secretary Bird of Pleistocene North America (Buteogallus daggetti)

March 28, 2018

Most species of birds that became extinct at the end of the Pleistocene were dependent upon the megafauna in some way.  The list of extinct species includes 2 relatives of the extant cowbird.  These birds likely followed herds of mammoths and horses around, just like their living cousins follow herds of bison and introduced cattle to feed on stirred-up insects and dislodged grass seeds.  Several species of extinct vultures, condors, and eagles obviously disappeared when there were no longer any carcasses of mammoths, ground sloths, llamas, etc. to feed upon.  Extant California condors, golden eagles, and magpies suffered reduced ranges for the same reason.  There were several species of raptors in the Buteogallus genus living in the southern region of North America during the late Pleistocene.  The Buteogallus genus is classified within the Accipitritidae family which includes the well known Cooper’s hawk and goshawk of North America.  However, the 9 extant species in the Buteogallus genus are restricted to South American and Mexico.  3 extinct species of late Pleistocene Buteogallus ranged into Florida and California.  Perhaps the most interesting was the walking eagle (Buteogallus daggetti).

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Savannah hawk.  The walking eagle was a close relative of the savannah hawk but had even longer legs.

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Secretary bird.  The savannah hawk and walking eagle occupy (ied) a convergent ecological niche with this species–grassland birds that feed upon rodents, reptiles, and large insects stirred up by fire or megafauna.

The walking eagle most closely resembled the living savannah hawk (B. meridionalis) of South America, but it had even longer legs.  It hunted small animals from the air and the ground, like its living relative.  Both species occupy (or occupied in the case of the extinct species) a similar niche exploited by the secretary bird (Sagittarius serpentarius) of Africa today.  All 3 of these tall grassland birds use (or used) their long legs to pummel small vertebrates.  The walking eagle likely preyed on small animals escaping grass fires, like savannah hawks and scissor-tailed swallows do today.  Walking eagles may have preyed upon rodents, reptiles, and large insects forced to come out of hiding in tall grass and reveal themselves when herds of megafauna threatened to trample them.  Subfossil remains of walking eagles have been excavated from northern Mexico and southern California, but they may have been more widespread.  They may have lived in habitats where geological preservation of bird bones is rare.  The dhole (Cuon alpinus) crossed the Bering land bridge and colonized North America during the Pleistocene, but its remains have only been found at 1 site in Mexico. The walking eagle may be another example of a once common animal that left scant fossil evidence of its existence.

Another extinct species in the Buteogallus genus, the fragile eagle (B. fragilis), lived in California until the late Pleistocene–its remains are relatively common from the La Brea Tar Pits.  Remains of the fragile eagle are also known from the mid-Pleistocene of Florida.  Subsequent sea level rise may have inundated fragile eagle habitat in Florida, causing its extirpation there, but it may have continued to occur elsewhere in southeastern North America where it remains undetected in the fossil record.

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Great black hawk.  This species currently inhabits wetlands in the tropics of South America and along both Mexican coasts.  It lived in Florida during the mid-Pleistocene.

The great black hawk (B. urbutinga) occurs today in South America and along both coasts of Mexico.  Remains of this species dating to the mid-Pleistocene have also been found in Florida.  Sea level rise probably caused the extirpation of this species from peninsular Florida too, and it is not known from any other site north of Mexico.  An extinct close relative of the great black hawk (B. borrasi) inhabited Cuba during the late Pleistocene.  It was 33% larger than its living close relative.  B. borrasi probably evolved from a population of B. urbutinga that found their way to Cuba, but it may have been more widespread in the West Indies and maybe even Florida earlier during the Pleistocene.  A less likely but possible explanation is that B. borrasi was formerly more common across southeastern North America but by the late Pleistocene there was just a relic population living on Cuba.  A genetic study could probably solve this mystery.


Olson, Storrs

“The Walking Eagle Wetmorgyps daggetti: A scaled up version of the Savannah Hawk”

Ornithological Monographs 63 2007

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.