Swainson’s thrushes (Catharus ustulatus) are found primarily in forested areas of the Americas. The northernmost extent is southern Canada, and their range extends southward through the United States, Central America, and into western South America.
Their summer breeding range includes central Canada south of Great Bear Lake and eastern and western Canada in their entirety. They are absent in southern portions of Saskatchewan, Alberta, and southwestern Manitoba. Their summer range extends to the southern two-thirds of Alaska. The distribution in the continental United States includes California and follows the Rocky Mountains as far south as New Mexico and Utah. Their summer range also includes northern Minnesota, Wisconsin, and continues eastward to New York and Maine.
During winter, Swainson's thrushes live in western South America from Venezuela continuing south to northern Argentina. Migratory pathways differ for two groups of subspecies. Russet-backed Swainson’s thrushes (Catharus ustulatus ustulatus, Catharus ustulatus oedicus, and Catharus ustulatus phillipsi) typically follow coastal routes both on the east and west coasts of the continental United States. However, olive-backed Swainson’s thrushes (Catharus ustulatus swainsoni, Catharus ustulatus incanus, and Catharus ustulatus appalachiensis) migrate throughout the interior continental United States and Mexico.
They are occasional visitors in western Europe and the Caribbean. (BirdLife International, 2018; Mack and Yong, 2020)
Swainson's thrushes in the western regions commonly live in riparian woodland forests and conifer forests. In eastern regions, Swainson’s thrushes live in a combination of coniferous and hardwood forests. The elevation range of their habitat is from sea level to 3000m.
During their breeding season, Swainson’s thrushes choose mature coniferous forests but have been found to live in early successional forests and riparian forested habitats. Areas with higher tree density and complete canopy cover harbor more significantly more thrushes than those that are widely-spaced and open-canopied. In California, they more often inhabit shrubby sites that include willow (Salix) and alder (Alnus) bushes.
In the non-breeding seasons, these thrushes live in a wide variety of habitats including desert habitats, rainforests, and upland hardwood forests. They can be found in pastures with forest edges.
Mostly rainforests, mature forests, and forest edges. They are associated with younger forests with dense shrubs and an abundance of food sources. They can be associated with ornamental shrubs, as well, and are more common at mid-range elevations (ca. 1000m) rather than coasts or mountains (1900 m or higher).
Swainson’s thrushes typically build nests in dense shrubs and dense forests using a variety of tree and shrub species. They nest generally 3m off the ground if in trees. Twigs, moss, pieces of bark, and dead leaves are some of the materials used in nest making. ("Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004; Mack and Yong, 2020; McElaney, 2019; )
Swainson’s thrushes have an olive-brown dorsal side and brown spotting on a white chest and throat. Their beak is described as straight and their legs are a brownish-pink color. There are no distinct seasonal changes in plumage. Both sexes have the same plumage. Their wings and tail are slightly darker brown than the rest of their body. Body measurements are similar between sexes at 16.1 to 19.3cm in total length and a mass of 23 to 25g. Although reported wingspans are typically 30cm, male wings lengths are slightly longer than female wings (USDA, 2004).
Of the two major groupings of subspecies, russet-backed thrushes (comprised of three subspecies) have a redder plumage than olive-backed thrushes (also comprised of three subspecies). All six subspecies have the same color patterns and body size.
Juvenile thrushes have distinct light brownish-yellow eye-rings and brown spotting on the sides of a white and light brown head.
Swainson’s thrush eggs are blue and speckled with red and brown spots. Egg size is around 2.3 cm in length and 1.7 cm in width. Hatchlings are partially covered with feathers at birth. (BirdLife International, 2018; Carnes, 2017; "Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004; Covino, 2015; Mack and Yong, 2020)
Males usually arrive first to breeding territories, typically from late April until mid-May.
Mating systems usually form out when males defend a territory and females choose to remain in it. Males sing to females and a bond is formed. One male thrush accepts one female thrush as a mate after about 3 to 4 days in the territory.
Females construct nests, about 3 weeks after males' arrival. It takes females about 4 days to solely construct a nest.
Swainson's thrushes are presumed to be monogamous but polygynandry has been observed in closely-related Bicknell's thrushes (Catharus bicknelli). So, it is possible that Swainson's thrushes are polygynandrous, especially across seasons. (Mack and Yong, 2020)
Swainson's thrushes have one breeding season per year between mid-April and late-June. They typically do not reuse nests and begin building them after 2-3 weeks after arriving in the breeding area. Females lay an average of 4 eggs per clutch (range 1-5) and average one egg per day until complete. They typically lay just one clutch per season, unless the nest fails early in the season. In this case, they may lay a second, smaller clutch. Eggs take around 12 days (range 10-14) to hatch. Hatchlings weigh around 3.9g. They fledge and are independent after 12 days (range 10-14 days). Sexual maturity for both sexes is reach at about 1 year of age. (Blumstein and Moller, 2008)
Females Swainson's thrushes prepare new nests typically every breeding season. Female thrushes sit on their eggs for around 9-14 days before they hatch, and the adult males will bring food to the females. Male and female thrushes typically share feeding responsibilities. However, there is no research on the proportion in which males and females feed their young. Female thrushes will remain with the altricial young for the first 3-4 days post-hatching, and then then begin to leave the nest more frequently to provide food. Females also groom their young and clean their nest using their bill. After thrushes become independent at ca. 12 days post-hatching, parental investment ends and post-independence association does not occur. (Mack and Yong, 2020)
Swainson's thrush lifespan is measured primarily using recapture methods or records from banding efforts. The expected lifespan of Swainson's thrushes in the wild ranges from 2 to 10 years. Limits to lifespan include predation, lack of food resources, and human impacts like architectural design and communication towers. The expected lifespan has not been reported because lifespan assessment relies on banding data. Several studies summarized by Mack and Yong (2000) estimated that the probability of yearly survival is between 0.44 to 0.65, but it can be higher for male thrushes. (Blumstein and Moller, 2008; Borden, et al., 2010; Bracey, et al., 2016; Mack and Yong, 2020)
Swainson's thrushes are diurnal, typically moving in hops on the ground and flying short flights from branches. They typically forage in trees. Intraspecific aggression is usually limited to the mating season. In these cases, males combat by singing to one another, and rarely escalate to physically aggression. Occasionally, the aggressive male may pull feathers out of the fleeing male.
Swainson's thrushes have a variety of songs and calls. Mack and Yong (2020) noted that Swainson's thrushes respond to predators by repeated "whit" calls and flying around from perch to perch. Female thrushes freeze in place while protecting the nest. Sometimes neighboring thrushes may help with vocal defense against potential predators.
There are non-vocal gestures that Swainson’s thrushes use to communicate, including upright body gesturing and puffing up of feathers, tail-flicking, and opening their beaks. There is some genetic variation in mating calls due to variations in environment, but not enough for calls and songs to be distinctly different. “Whit” and “whit-burr” (Mack and Yong, 2020) are calls made by both sexes when the nest is threatened. During migration periods, “peep” calls by both sexes are most common.
Swainson's thrushes migrate during warmer months (early March-late May) to the continental United States including California, the Rocky Mountains, as far south as New Mexico and Utah. Their summer range also includes northern Minnesota, Wisconsin, and continues eastward to New York and Maine. Swainson's thrushes migrate through western South America from Venezuela continuing south to northern Argentina in colder months (September-early December). Swainson's thrushes migrate during the night, but some stopover behavior has been reported during the day (Mack and Yong, 2020). Males arrive first to breeding grounds.
Migratory pathways differ for two groups of subspecies. Russet-backed Swainson’s thrushes (Catharus ustulatus ustulatus, Catharus ustulatus oedicus, and Catharus ustulatus phillipsi) typically follow coastal routes both on the east and west coasts of the continental United States. However, olive-backed Swainson’s thrushes (Catharus ustulatus swainsoni, Catharus ustulatus incanus, and Catharus ustulatus appalachiensis) migrate throughout the interior continental United States and Mexico. (BirdLife International, 2018; Carnes, 2017; "Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004; Covino, 2015; Mack and Yong, 2020; Ruegg, et al., 2006)
Home ranges typically are quantified only during the breeding season, and vary widely across geographic areas. For example, in New Hampshire, Ontario, and Idaho, breeding home range varied from 1 ha to 2.1 ha. Ontario territory dimensions ranged from 0.12 ha to 5.14 ha. ("Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004). The same source even reported that territory height can reach 6.1 m above ground level. However, defended territories rarely extended past the immediate vicinity of the nest. This territory size has not been quantified. Mack and Yong (2020) report that these thrushes may defend territories on wintering grounds, but no quantifiable areas were reported. (BirdLife International, 2018; "Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004; Mack and Yong, 2020)
Swainson's thrushes have a variety of songs and calls. Male primary songs, also known as advertisement calls, are described phonetically as “whip-poor-will-a-will-e-zee-zee-zee” (Mack and Yong, 2000). This song is meant to communicate territory defense and also attract mates. “Whit” and “whit-burr” (Mack and Yong, 2020) are calls made by both sexes when the nest is threatened. During migration periods, “peep” calls by both sexes are most common. There are multiple non-vocal actions that are known to be used in communication for Swainson’s thrushes. These include sitting erect and fluffing up feathers, tail-flicking, and beak-opening. These are mainly visual signals to conspecifics.
Russet-backed thrushes (Catharus ustulatus ustulatus, Catharus ustulatus oedicus, and Catharus ustulatus phillipsi) tend to have a slightly more liquid "whit-burr" call while olive-backed thrushes (Catharus ustulatus swainsoni, Catharus ustulatus incanus, and Catharus ustulatus appalachiensis) deliver a sharper call.
Like all birds, Swainson’s thrushes have color vision and use color patterns to attract mates, find food, and avoid predators. They use tactile senses frequently to communicate with mates and with young. Occasional aggressive acts in the breeding season may involve direct contact and even feather-pulling. (Carnes, 2017; Covino, 2015; Mack and Yong, 2020; Ruegg, et al., 2006)
Swainson's thrushes commonly eat insects or berries. Swainson’s thrushes get their food by extracting them from bushes or the ground (Mack and Yong, 2000). Their food choices depend on availability. For example, a diet study of Swainson’s thrushes in the eastern United States found that insects made up 63.5% of stomach contents (USDA, 2004). Specifically, the orders Coleoptera (beetles, 16%), Hymenoptera (ants, 15%; bees and wasps, 6%), Hemiptera (true bugs, 11%), Lepidoptera (caterpillars, 10%) and Diptera (flies, 6%). The remaining 36.5% of their diet was fruits, including berries in the family Ericaceae, and other soft fruits. These birds have been known to consume significantly more caterpillars when they are in extremely high densities.
Locations that house Swainson's thrushes report an increase, then decline, in insect densities, suggesting that insects are main source of food (USDA, 2004). ("Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004; Mack and Yong, 2020; Wiley, et al., 2015)
Swainson's thrushes have few instances of predation in adults. The most frequent predators during migration are hawks and falcons. Sharp-shinned hawks (Accipiter striatus) are frequent predators during the migration period. Additional raptor predators include merlins (Falco columbarius), northern goshawks (Accipiter gentilis), Cooper's hawks (Accipiter cooperii), and great gray owls (Strix nebulosa).
Common nesting predators include red squirrels (Tamiasciurus hudsonicus), American martens (Martes americana), Stellars jays (Cyanocitta stelleri), and gray jays (Perisoreus canadensis). Most predation events occur in nests. Predators commonly puncture eggs and remove the contents of the nest, including hatchlings. Red squirrels are known to tear apart nests.
Swainson's thrushes respond to predators by repeated "whit" calls and flying around from perch to perch (Mack and Yong, 2020). Female thrushes freeze in place while protecting the nest and males let out these calls. Sometimes neighboring thrushes may help with vocal defense against predators like gray jays and red squirrels. Nesting predation negatively impacts reproductive success.
Swainson's thrushes are cryptic, with brown backs, allowing them to blend in with leaves and shrubs on the ground. ("Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004; Mack and Yong, 2020)
Swainson’s thrushes generally eat small insects and berries and are preyed upon by small mammals.
Brown-headed cowbirds (Molothrus ater) are common brood parasites to Swainson's thrush nests. In central California, White and Gardali (2004) reported that 4% of Swainson's thrushes' nests were parasitized by cowbirds. Hemosporidian parasites (protozoans in the Phylum Apicomplexa) are blood parasites commonly found in Swainson's thrushes. Common protozoans found in Swainson's thrushes includes members of the genera Leucocytozoon and Haemoproteus. Some Swainson's thrushes have been documented to have a trypanosome (Trypanosoma) parasite. Trematodes (Capillaria exile) and roundworms (Dyspharynx nasuta) also have been documented as endoparasites. Swainson's thrushes also carry external parasites such as lice (Myrsidea incerta) and ticks. (BirdLife International, 2018; "Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004; Dodge, et al., 2013; White and Gardali, 2004)
Bird-watching, which includes migratory Swainson's thrushes, poses an economic benefit to humans. For example, in 2011, bird-watchers spent around 41 billion dollars a year on travel expenses and equipment in the United States. Bird-watchers were estimated to spend ca. 14.9 billion dollars on food and lodging (U.S Fish and Wildlife Service, 2014). ("Birding in the United States: A demographic and economic analysis addendum to the 2011 national survey of fishing, hunting, and wildlife-associated recreation", 2013; "Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004)
There are no known adverse economic effects of Swainson's thrush on humans.
Swainson's thrushes (including all subspecies) are considered a species of "Least Concern" on the IUCN Red List. These thrushes are "Protected" under the US Migratory Bird Act, meaning that it is illegal to capture, kill, sell, transport, or trade them (alive or dead, whole or in part). Swainson's thrushes have no special status on the US Federal List, CITES appendices, or State of Michigan List.
Collisions with windows and other anthropogenic structures, like communication towers, are a primary cause of death with these thrushes. For example, Borden et al. (2010) reported that Swainson’s thrushes represented nearly 3% of all birds in a year-long bird-window collision study. Similarly, Gehring et al. (2011) reported that these birds comprised 3% of all deaths from communication towers. Bracey et al. (2016) reported that Swainson's thrushes comprised 32% of the long-distance migrants that died from collisions, and 13% of the total observed bird-window collisions.
Habitat loss and fragmentation are additional threats to Swainson's thrushes, as urbanization and deforestation increase on the landscape. Lastly, predation, primarily in nests, is a potential threat to the longevity of young offspring of Swainson's thrushes.
Conservation efforts include national protection from hunting and capture via the U.S. Migratory Bird Act. Bird-friendly window films are also helpful in preventing or reducing window collisions. Gehring et al. (2011) suggests that guy wires can be removed, shorter towers can be made, and issues with lighting can be adjusted to reduce the number of deaths. (Borden, et al., 2010; Bracey, et al., 2016; "Conservation assessment for Swainson's thrush (Catharus ustulatus)", 2004; Gehring, et al., 2010; Kahle, et al., 2016; Mack and Yong, 2020)
Justin McLaughlin (author), Radford University, Logan Platt (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats fruit
An animal that eats mainly plants or parts of plants.
An animal that eats mainly insects or spiders.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
makes seasonal movements between breeding and wintering grounds
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
scrub forests develop in areas that experience dry seasons.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
uses sight to communicate
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