Swainson's Thrush
Encyclopedia
Swainson's Thrush also called Olive-backed Thrush, is a medium-sized thrush
. This species is 16–18 cm in length, and has the white-dark-white underwing pattern characteristic of Catharus thrushes. Swainson's Thrush was named after William Swainson, an English
ornithologist.
The breeding habitat
of Swainson's Thrush is coniferous woods with dense undergrowth across Canada
, Alaska
and the northern United States
, also deciduous
wooded areas on the Pacific coast of North America
.
These birds migrate
to southern Mexico
and as far south as Argentina
. The coastal subspecies
migrate down the Pacific coast of North America and winter from Mexico
to Costa Rica
, whereas the continental birds migrate eastwards within North America (a substantial detour) and then travel southwards via Florida
to winter from Panama
to Bolivia
. Swainson's Thrush is a very rare vagrant to western Europe
. It has also occurred as a vagrant in northeast Asia.
This species may be displaced by the Hermit Thrush
where their ranges overlap. Possibly, the latter species adapts more readily to human encroachment upon its habitat. At least in the winter quarters, Swainson's Thrush tends to keep away from areas of human construction and other activity.
n Coast Mountains
, the Cascades
and the Sierra Nevada, and C. u. ustulatus and C. u. oedicus summer west of these ranges. There is a small area of overlap in the Coast Mountains. Recent molecular systematics work confirms that these two pairs of subspecies form two genetically distinct clade
s, referred to as the continental and coastal clades, which diverged during the Late Pleistocene
era, probably about 10,000 years ago as the last ice age came to its end and habitats shifted across North America.
The genetic differences between the subspecies, and the circuitous migratory route of the continental birds, strongly suggest that these species underwent a rapid range expansion following the end of the last ice age
, with populations originally summering in the south-east of North America expanding their ranges northwards and westwards as the ice retreated. Details of the molecular genetic analysis support the hypothesis of rapid expansion of both coastal and continental populations. The current migratory routes of the continental birds, especially the western populations, are not optimal in ecological terms, and presumably represent an inherited, historical route pattern that has not yet adapted to the birds' modern population locations.
These results notwithstanding, analysis of mtDNA cytochrome b
and NADH dehydrogenase
subunit
2 as well as nuclear
β-fibrinogen
intron
7 sequence
data shows that Swainson's Thrush is the most ancient North American species of its genus; it is not closely related to other Catharus and the outward similarities with the other North American species are due to convergent evolution
.
Thrush (bird)
The thrushes, family Turdidae, are a group of passerine birds that occur worldwide.-Characteristics:Thrushes are plump, soft-plumaged, small to medium-sized birds, inhabiting wooded areas, and often feed on the ground or eat small fruit. The smallest thrush may be the Forest Rock-thrush, at and...
. This species is 16–18 cm in length, and has the white-dark-white underwing pattern characteristic of Catharus thrushes. Swainson's Thrush was named after William Swainson, an English
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
ornithologist.
The breeding habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
of Swainson's Thrush is coniferous woods with dense undergrowth across Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and the northern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, also deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...
wooded areas on the Pacific coast of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
These birds migrate
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
to southern Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
and as far south as Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. The coastal subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
migrate down the Pacific coast of North America and winter from Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
to Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
, whereas the continental birds migrate eastwards within North America (a substantial detour) and then travel southwards via Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
to winter from Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
to Bolivia
Bolivia
Bolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
. Swainson's Thrush is a very rare vagrant to western Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. It has also occurred as a vagrant in northeast Asia.
This species may be displaced by the Hermit Thrush
Hermit Thrush
The Hermit Thrush is a medium-sized North American thrush. It is not very closely related to the other North American migrant species of Catharus, but rather to the Mexican Russet Nightingale-thrush.-Description:...
where their ranges overlap. Possibly, the latter species adapts more readily to human encroachment upon its habitat. At least in the winter quarters, Swainson's Thrush tends to keep away from areas of human construction and other activity.
Description
Adults are brown on the upperparts. The underparts are white with brown on the flanks; the breast is lighter brown with darker spots. They have pink legs and a light brown eye ring. Birds in the east are more olive-brown on the upperparts; western birds are more reddish-brown. This bird's song is a hurried series of flute-like tones spiralling upwards.Diet
They forage on the forest floor, also in trees. Swainson's Thrushes mainly eat insects, fruits and berries. They make a cup nest on a horizontal tree branch.Subspecies
Four subspecies are recognised, Cathartus ustulatus alame, C. u. swainsoni, C. u. ustulatus and C. u. oedicus. Subspecies Cathartus ustulatus alame and C. u. swainsoni summer east of the British ColumbiaBritish Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
n Coast Mountains
Coast Mountains
The Coast Mountains are a major mountain range, in the Pacific Coast Ranges, of western North America, extending from southwestern Yukon through the Alaska Panhandle and virtually all of the Coast of British Columbia. They are so-named because of their proximity to the sea coast, and are often...
, the Cascades
Cascade Range
The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...
and the Sierra Nevada, and C. u. ustulatus and C. u. oedicus summer west of these ranges. There is a small area of overlap in the Coast Mountains. Recent molecular systematics work confirms that these two pairs of subspecies form two genetically distinct clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s, referred to as the continental and coastal clades, which diverged during the Late Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
era, probably about 10,000 years ago as the last ice age came to its end and habitats shifted across North America.
The genetic differences between the subspecies, and the circuitous migratory route of the continental birds, strongly suggest that these species underwent a rapid range expansion following the end of the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
, with populations originally summering in the south-east of North America expanding their ranges northwards and westwards as the ice retreated. Details of the molecular genetic analysis support the hypothesis of rapid expansion of both coastal and continental populations. The current migratory routes of the continental birds, especially the western populations, are not optimal in ecological terms, and presumably represent an inherited, historical route pattern that has not yet adapted to the birds' modern population locations.
These results notwithstanding, analysis of mtDNA cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...
and NADH dehydrogenase
NADH dehydrogenase
NADH dehydrogenase is an enzyme located in the inner mitochondrial membrane that catalyzes the transfer of electrons from NADH to coenzyme Q...
subunit
Protein subunit
In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles with other protein molecules to form a protein complex: a multimeric or oligomeric protein. Many naturally occurring proteins and enzymes are multimeric...
2 as well as nuclear
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
β-fibrinogen
Fibrinogen
Fibrinogen is a soluble plasma glycoprotein, synthesised by the liver, that is converted by thrombin into fibrin during blood coagulation. This is achieved through processes in the coagulation cascade that activate the zymogen prothrombin to the serine protease thrombin, which is responsible for...
intron
Intron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
7 sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
data shows that Swainson's Thrush is the most ancient North American species of its genus; it is not closely related to other Catharus and the outward similarities with the other North American species are due to convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
.
External links
- Swainson's Thrush Species Account - Cornell Lab of Ornithology
- Swainson's Thrush Information and Photos - South Dakota Birds and Birding
- Swainson's Thrush - Catharus ustulatus - USGS Patuxent Bird Identification InfoCenter
- Example of call Turdidae: Thrushes- naturesongs.com