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Overview

Brief Summary

Cardellina canadensis

A small (5-5 ¾ inches) wood warbler, the Canada Warbler is most easily identified by its bright yellow breast, blue-gray back, and black streaky “necklace. ” Other field marks include large black eyes with yellow eye-rings, a thin black bill, and orange legs. Female Canada Warblers are duller gray above with less well-defined necklaces than males. Appropriately enough, the Canada Warbler’s breeding range is centered on southern Canada from Nova Scotia west to British Columbia. Smaller numbers breed in the northeastern United States and at higher elevations in the Appalachian Mountains south to Georgia. The Canada Warbler is a long-distance migrant, wintering in northern South America. In summer, the Canada Warbler breeds in a variety of deciduous and mixed deciduous and evergreen forest types. In winter, this species inhabits tropical mountain forests. On migration, Canada Warblers may be found in shrubs along woodland edges as well as in thickets along rivers and streams. This species eats small invertebrates, primarily insects and spiders. Despite its bright colors, the Canada Warbler is often difficult to observe due to its small size and preference for habitats with thick vegetation. With the aid of binoculars, Canada Warblers may be seen high in the forest canopy or deep in the undergrowth gleaning insects from branches. The Canada Warbler is most active during the day, but, like many migratory songbirds, this species migrates at night.

Threat Status: Least concern

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Distribution

Wilsonia canadensis (Canada warblers) has a diverse range that includes both North and South America at various times during the year. They breed in the southern boreal forest and in a large portion of southeastern Canada in the Nearctic region and migrate during the spring and fall to their South American winter range in the Neotropical region. Canada warblers breed in the southern part of the boreal region in North America, from the southeastern Yukon territory, northeastern portion of British Columbia, and parts of northern Alberta across southern Canada as far east as Nova Scotia down to central Minnesota, New York and New England. Canada warblers also breed in the Great Lakes region. The range of Canada warblers extends south in areas of higher elevation through the Appalachian Mountains. To date, it has been determined that Canada warblers only winter in the northern region of South America in the Andes Mountains and in the region to the east of the Andes. “Accidental” occurrences of Wilsonia canadensis have been recorded in Greenland and Iceland.

Biogeographic Regions: nearctic (Native ); neotropical (Native )

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occurs (regularly, as a native taxon) in multiple nations

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National Distribution

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Breeding range extends from southeastern Yukon, northeastern British Columbia, and northern Alberta across southern Canada to Nova Scotia, and south to southern Manitoba, northern Minnesota, Great Lakes region, southern Appalachians (to northern Georgia), northern New Jersey, southeastern New York, and southern New England (AOU 1998, Conway 1999).

Range during the boreal winter extends from Venezuela and northern Colombia south to Ecuador, southern Peru, and the Tepui region of northern Brazil, mostly in and east of the Andes, and rarely northward to Central America (AOU 1998, Conway 1999).

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Range

E North America; winters Panama and mts. of nw South America.
  • Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2014. The eBird/Clements checklist of birds of the world: Version 6.9. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/

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Physical Description

Morphology

Canada warblers are bright, vividly colored birds. The species is nicknamed “the necklaced warbler” because of the unique ring of bluish-black markings around an otherwise yellow breast and throat. Canada warblers have no wing bars and have white under-tail coverts. They feature a yellowish-white ring of color around the eye that creates a spectacle-like marking that is very distinguishable. Canada warblers are remarked to always have a surprised look because of these spectacle markings. They have gray backs and matching wings that fade to black around the crown. They are a small warbler, weighing 9.5 to 12.5 g and measuring 12 to 15 cm in length. Their wingspans measure 20 to 22 cm.

Though females are always observed as having significantly less vivid coloring than males, females generally still exhibit at least a faint necklace marking. This color difference between sexes is typical of warblers, as they usually exhibit sexual dimorphism. There is also a wide variation of the necklace pattern that is independent of age differences. This distinct pattern may be considered a unique marking of individuals. Seasonal variation of a male's markings is typical, with the black markings being much less distinct in the fall than in the spring. In winter, the black coloring turns to more of an inky, bluish-dark gray color. Juveniles are usually a brownish color on their head and upper body parts, with lighter brown coloring on their under-parts. Any markings on juveniles are far less distinct than adults.

Canada warblers are often confused with other wood warbler species. They look similar to Kentucky warblers, which have a similar body color pattern but no “necklace” markings. Kentucky warblers also have a yellow breast and black cheeks similar to Canada warblers. Magnolia warblers are also similar in appearance to Canada warblers. They are also yellow-breasted with black stripes, but have a gray head and are more mottled with less distinct coloration than Canada warblers.

Range mass: 9.5 to 12.5 g.

Range length: 12 to 15 cm.

Range wingspan: 20 to 22 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes colored or patterned differently; male more colorful

  • 1989. American Warblers : An Ecological and Behavioral Perspective. Cambridge, Massachusetts and London, England: Harvard University Press.
  • 2003. Warblers of the Great Lakes Region & Eastern North America. Buffalo, NY: Firefly Books Ltd..
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Size

Length: 13 cm

Weight: 11 grams

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Ecology

Habitat

Canada warblers utilize a mixed woodland habitat. They are found nesting in areas that contain nearly-mature tree stands and an abundance of wet forest floor-cover and understory. Canada warblers will often inhabit areas at higher elevations, near open water. The eastern slopes of mountains where the forest composition is significantly deciduous are preferred. They are found at elevations ranging from 457 to 2500 m. In areas of lower elevation, they reside in bogs, clearings, woodland edges, and open areas created by human disturbance. This species has been found to show preference to mossy areas and it nests near wet habitats. Moss-covered stumps within a foot of water have been noted as extremely favorable nesting spots for Canada warblers.

Canada warblers also occur in riparian shrub forest on slopes, in deep ravines rich with hemlocks, moss-covered boulders and rhododendron thickets. They have also been recorded nesting in more exposed situations, such as in and around birch roots covered with moss and dead leaves, or under bank overhangs of streams. This species chooses very fine, delicate materials with which to construct its nest, so moss is often a key habitat component. In their wintering range, Canada warblers are found in mature cloud rainforests as well as some coffee plantations and agricultural areas.

Range elevation: 457 to 2500 m.

Average elevation: 1800-2000 m.

Habitat Regions: temperate ; tropical ; terrestrial

Terrestrial Biomes: taiga ; forest ; rainforest ; scrub forest ; mountains

Aquatic Biomes: lakes and ponds; rivers and streams

Wetlands: swamp ; bog

Other Habitat Features: agricultural ; riparian

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Habitat and Ecology

Systems
  • Terrestrial
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Comments: Breeding habitat includes moist thickets of woodland undergrowth (especially aspen-poplar), bogs, tall shrubbery along streams or near swamps, and deciduous second growth. Habitat is more specific in localized regions. For example, the species is limited to forested wetlands in Rhode Island (Miller 1999) and hemlock-dominated ravines in Ohio (Mitchell 1999). Habitat predictors in western Maryland included limited ground cover but high foliage density between 0.3 and 1 meter (Robbins et al. 1989). Habitat in Rhode Island also included limited ground cover (a negative correlation with deciduous foliage cover within 0.5 meter of the ground) and a thick shrub layer (a positive correlation with foliage cover between 2 and 4 meters; Mitchell 1999). In northeastern British Columbia this warbler is associated with wet, usually unstable slopes in deciduous or mixed forests with a well-developed shrub layer and considerable amounts of woody debris (Campbell et al. 2001). Nests are on or near the ground, among roots of fallen trees, in cavities in banks, or on ledges, sides of rocks, hummocks, stumps, or fallen logs, or on the ground under shrubbery (Harrison 1978).

In migration, this warbler uses various forest, woodland, scrub, and thicket habitats, mostly in humid areas. In winter, it occurs in forested areas of foothills and mountains.

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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Migration through Central America and eastern Mexico occurs in both fall and spring. This species is a common migrant in Costa Rica in early September-early November; uncommon transient in April-early May (Stiles and Skutch 1989). It is present in South America mostly in October-April (Ridgely and Tudor 1989). On Appledore Island, Maine, individuals have significantly longer stopovers in fall than in spring (Morris et al. 1994).

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Trophic Strategy

Canada warblers are excellent foragers and are well-adapted for catching flying insects. They can be found foraging in lower vegetation like shrubs and tree branches, and occasionally on the ground. Canada warblers use red-osier dogwood and young birch when it forages, as well as shrubs, saplings and the inner, entangled branches of trees. This enforces its niche requirements for substantial understory vegetation. It uses flight during foraging and gleaning in foliage while it hops along branches. In foraging, Canada warblers are similar to magnolia warblers in that they use deciduous and coniferous mixed-wood habitat equally. Others, like black-throated green warblers, may specialize and differ in habitat use throughout their range.

The diet of Canada warblers consists primarily of flying insects which may include mosquitoes, flies, moths and beetles. At one time, 5 locusts and 29 other insects were found in a Canada warbler's stomach in Nebraska. Canada warblers may also eat small (hairless) caterpillars and spiders as well as insect larvae. They feed heavily on spruce budworm during outbreaks, though it is not considered to be a spruce budworm specialist.

Canada warblers have some specialized physical structures and techniques for catching and eating flying insects. They have sensitive bristles surrounding the beak to aid in sensing and catching flying insects. Once a bird has caught its prey, the flying insects are sometimes held in the warbler’s beak and tossed against a tree branch before being eaten.

Animal Foods: insects; terrestrial non-insect arthropods

Primary Diet: carnivore (Insectivore )

  • Sleep, D., M. Drever, K. Szuba. 2009. Potential Role of Spruce Budworm in Range-Wide Decline. The Journal of wildlife management, Volume 73 no.4: 546-555.
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Comments: Diet includes beetles, mosquitoes, flies, moths, smooth caterpillars, etc.

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Associations

Canada warblers are considered to be territorial during the breeding season; however they can occur in small mixed-species flocks and with other warbler groups during migration and wintering season. In winter habitats these birds utilize such sites as coffee plantations and may positively impact the crops by consuming pest insects.

Canada warbler nests are frequently parasitized by brown-headed cowbirds in areas of habitat overlaps like Saskatchewan, Ontario, New Brunswick, New York, Indiana, Michigan, and Minnesota. It has been reported that some female Canada warblers will accept these parasitic cowbird eggs and later hatch them successfully. Cowbirds will sometimes remove Canada warbler eggs from the nest so that the parasitic eggs receive priority incubation.

Commensal/Parasitic Species:

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Canada warblers are subject at some stage of maturity to predation by blue jays and milk snakes. Blue jays have been reported as successful predators on Canada warbler nests, while milk snakes are reported predators of fledglings.

Females stay on the nest until a predator is within very close range in order to camouflage and protect the eggs. If a predator descends on a Canada warbler nest, the female will launch into a dramatic display and feign an injury on the ground, away from the nest. She does this with her wings cocked out and dragging, fluttering around and with feathers fanned and ruffled. Males will also conduct this display. Purple martins will also imitate a fledgling on the ground if the eggs are already hatched to distract predators from the actual fledglings in the nest.

Known Predators:

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: This species is represented by a large number of occurrences (subpopulations).

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Global Abundance

>1,000,000 individuals

Comments: Total population size is unknown but certainly exceeds 100,000 and probably exceeds 1,000,000. Rich et al. (2004) estimated population size at 1,400,000.

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General Ecology

This species appears to show positive numerical response to outbreaks of the spruce budworm (Crawford and Jennings 1989, Patten and Burger 1998), though it is not generally considered to be a "budworm specialist."

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Life History and Behavior

Behavior

Canada warblers have a very distinct song, though it follows no rules and is characteristically irregular and variant in pitch. It has been described as a rapid, sputtering warble. A common dictation is “chip-chupety swee-ditchety”, or another is “te-widdle-te-widdle-te-widdle-te-wip”. Canada warblers' songs are notoriously difficult to define, thus the variation in interpretations. The song of this species is different from other warblers; it does not have the same buzzing elements of other warblers’ songs, or the same husky notes. Some say it is a similar, longer version of the song of magnolia warblers. The call by both sexes is a “chyup” sound, while their alarm call is “check” or “chip” in a loud, sharp tone. They have a flight song in addition to a regular song that sounds the same but is generally longer. Canada warblers sing more after they have completed molting than any other wood warbler species.

Like all birds, they perceive their environments through visual, auditory, tactile and chemical stimuli. Their plumage differences serve to visually communicate gender, age, and breeding status to other individuals.

Communication Channels: visual ; acoustic

Perception Channels: visual ; tactile ; acoustic ; chemical

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Life Expectancy

The maximum recorded age for a Canada warbler is 7 years and 11 months old. Their estimated lifespan is 8 years.

Range lifespan

Status: wild:
7.92 (high) years.

Typical lifespan

Status: wild:
8 (high) years.

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Lifespan, longevity, and ageing

Maximum longevity: 8 years (wild)
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Reproduction

Canada warblers are considered to be socially monogamous, but sometimes extra-pair copulations may occur during breeding season. Individuals will either arrive at the breeding grounds already in a breeding pair or will form breeding pairs quickly upon arrival. It was previously thought that Canada warblers maintained pair bonds year-round, however there has been research in the winter ranges that showed solitary birds as well as pair-bonded birds. Individuals of this species often return to the same site to nest, and often remain with the same mate year after year.

Mating System: monogamous

Canada warblers have 2 broods a year on average. Canada warblers construct nests in the shape of a loosely built cup, and they are composed of a huge variety of material including grass, bark, leaf matter, moss, pine needles, twigs and animal hair. Canada warblers can make nests in 3 to 5 days using dried leaves and grass, close to the ground and often at the base of tree stumps or in clumps of ferns. Nest size is approximately 2 inches wide (4.5 inches outside diameter, 2.5 inches inside diameter), and 1.5 inches in depth. In the rare event that they re-use a nest, it will only take the birds about a day to make the nest, as they will likely just add more lining using the previously mentioned nest-construction materials. Optimal nesting areas contain dense shrubbery with abundant cover and protection.

Females usually lay 4 to 5 eggs and incubation lasts approximately 12 days. The eggs are creamy white in color with a slightly glossy finish. They are also speckled with brownish dots in a wreath formation. Average fresh-laid egg mass is 1.56 grams and they are 17.33 mm long. All eggs usually hatch within 24 hours once hatching begins, and if not, then the remaining eggs are likely infertile.

Canada warbler young are very dependent on their parents until they leave the nest. When the chicks are born, they have no feathers and their eyes are closed; they have very poor motor skills but are able to lift their heads for food. By day five, the feather sheaths are visibly prominent, and the chicks may start to stand and stretch their legs. It is estimated that the fledglings leave the nest at ten days old, and Canada warbler parents have been observed feeding their young after their departure from the nest. This species uses direct feeding methods and may regurgitate food for the young. Nestling period lasts an average of 8.1 days. Asymmetry is not uncommon in Canada warbler nests as one chick may be up to 2 times the size of another. The chicks remain dependent on their parents for two to three weeks after leaving the nest.

Breeding interval: Canada warblers produce one clutch of eggs per year.

Breeding season: Canada warblers breed from May through August.

Average eggs per season: 4 to 5.

Average time to hatching: 12 days.

Average fledging age: 10 days.

Average time to independence: 2 to 3 weeks.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous

For Canada warblers, both parents are very invested in rearing their young. When a nesting site has been chosen, they both work on the construction of the nest. Female Canada warblers are known as “close-sitters” and will remain on the nest for a large majority of the incubation period unless intruders are immediately present. Males have been observed exhibiting anticipatory feeding where they bring food to eggs that have not yet hatched. This behavior may increase during the incubation period.

The male is a frequent presence during the entirety of nesting, and both parents clean out the nest once the chicks have hatched, ridding it of any eggshell or embryonic sac waste. Females remove unwanted pest insects from the nest, which tend to accumulate under the young if the nest is left for a relatively extended period of time. Males will often protect the nesting mother and chicks from a close range and feed the chicks often, sometimes 2 times more frequently than females do. The young are fed very frequently, anywhere from once per minute to every 20 minutes.

Parental Investment: altricial ; male parental care ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female)

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Eggs are laid in May-June. Clutch size is three to five (usually four). Young are tended by both parents (Terres 1980, Harrison 1978).

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Wilsonia canadensis

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 9 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNGGNCCNNGNATTCNTNNNANTTTTNNTTATNNNNNTGCNAATTANANNNGNNNGGNTCGGTANCNNANNNGTCCNTCTAANAANNNAAGCCCCAGACATAGCATTCCCACGTATAAACAACATANGNTTCTGACTACTCCCTCCATCATTCCTTCTACTACTAGCATCTTCCACAGTTGAAGCAGGCGTCGGCACAGGCTGAACAGTGTACCCCCCACTAGCCGGCAACCTAGCCCACGCCGGAGCCTCAGTCGACCTAGCAATCTTCTCTCTNCACCTAGCCGGTATTTCATCAATCTTAGGAGCTATCAACTTCATTACAACGGCAATCAACATAAAACCTCCTGCCCTCTCACAATACCAAACCCCCCTATTCGTCTGATCCGTCCTAATCACTGCAGTTCTCCTACTCCTCTCTCTACCAGTCCTAGCCGCAGGAATCACAATGCTCCTAACAGACCGCAACCTCAACACNACATTCTTCGACCCTGCCGGAGGAGGAGATCCAGTCCTATATCAACATCTCTTCTGATTTTTCGGCCACCCAGAAGTCTACATCTTAATCCTC
-- end --

Download FASTA File

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Statistics of barcoding coverage: Wilsonia canadensis

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 10
Specimens with Barcodes: 11
Species With Barcodes: 1
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Conservation

Conservation Status

The conservation status of Canada warblers was designated as “threatened” in Canada as of April 1998. This means, under the Committee on the Status of Endangered Wildlife In Canada (OSEWIC) definition, that the species may become endangered if limiting factors are not reduced. Canada warblers have low population densities across their range and deforestation has affected their wintering grounds. As they are migratory birds, Canada warblers are protected under the Migratory Birds Convention Act 1994. Canada warblers have been designated a Highest Priority Landbird under the North American Bird Conservation Initiative, and Partners in Flight has listed Canada warblers as being continentally important.

Historically, Canada warblers, black-and-white warblers, and American redstarts have shared one of the highest yearly survival rates at 71%, however Canada warblers have experienced a 40% decline overall since 1966. While this species appears to be mildly resilient to disturbances like forestry practices, Canada warblers are threatened by increasing habitat fragmentation.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

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IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
BirdLife International

Reviewer/s
Butchart, S. & Symes, A.

Contributor/s

Justification
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
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National NatureServe Conservation Status

Canada

Rounded National Status Rank: N5B - Secure

United States

Rounded National Status Rank: N5B - Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

Reasons: Large breeding range in North America; large population size; many occurrences; apparently has declined over the past several decades, probably as a result of forest maturation/fragmentation and loss of forested wetlands in the breeding range and habitat loss in the nonbreeding range.

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Population

Population
The global population has been estimated at 1,400,000 individuals.

Population Trend
Decreasing
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Global Short Term Trend: Relatively stable (=10% change)

Comments: Breeding Bird Survey (BBS) data indicate a very slow decline or relatively stable trend over the past 10 years or three generations.

Global Long Term Trend: Unknown

Comments: Long-term trend (past 200 years) is unknown, but this species may have undergone a decline over the past several decades. Breeding Bird Survey (BBS) data indicate a significant survey-wide decline averaging 2.3% per year during 1966-2007; this amounts to a 61% decline over this time period. However, this species is detected in relatively low numbers during these surveys. For example, BBS abundance (average number of individuals per route) declined from 0.9 to 1.3 in the 1960s and early 1970s to 0.5 to 0.6 in 2000-2007. So although the percentage decline is high, the decline in absolute terms is only 0.3-0.8 individuals per route.

BBS data for 1966-2003 indicate that most declines were in the northern part of the range, whereas increasing trends occurred in much of the Great Lakes region and Appalachian Mountains.

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Threats

Degree of Threat: Medium

Comments: Declines evident in Breeding Bird Survey data may be related to change in forest structure over the past century, combined with loss of forested wetlands (Conway 1999). Forest regeneration of previously farmed lands in the Northeast probably provided optimal habitat (forest with dense understory) in the early and mid-1900s, but continued forest maturation probably eliminated the understory, and habitat became less suitable for the Canada Warbler (Conway 1999). Additionally, a large area of forested wetlands in the Northeast were drained, filled, and developed between 1950 and 1980 (Tiner 1984). Infestations of the hemlock woolly adelgid have degraded or eliminated habitat in some areas. Miller (1999) reported that declines in Rhode Island may be related to the impingement of urban development on heavily forested landscapes. This species appears to be sensitive to forest fragmentation; density and probability of occurrence in a forest decline with forest area (reviewed by Conway 1999).

Loss of wintering habitat in the northern Andes region of South America may have contributed to the decline (Robinson 1997, Faccio et al. 1997). Diamond (1991) projected that from 1985 to 2000, 28 percent of wintering habitat would be lost. Declines in undisturbed breeding habitats in Vermont (Faccio et al. 1997) suggest the problem is more than loss of breeding habitat, unless there is an undiscovered link between the advancement of succession on those monitoring sites and the reported declines.

Regardless of location, habitat loss is a primary concern. No other major threats have been identified.

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Management

Restoration Potential: Moderate, assuming threats can be fully understood. Habitat loss in South America may prove to be more difficult to address than habitat problems in North America due to economic and population pressures there.

Preserve Selection and Design Considerations: Miller (1999) determined that landscape predictors are stronger than habitat predictors in Rhode Island. Warbler presence was more significantly correlated with distance from paved roads and total length of paved roads in nearby forests than with habitat variables. This suggests that preserves should be established in heavily forested landscapes that are relatively undisturbed by human activity. Robbins et al. (1989) found that forest size was positively correlated with warbler presence, and they implied a minimum preserve size of 400 hectares. Miller (1999), however, found that poorly drained forest wetland patches as small as 6 hectares were used if they had sufficient upland forest buffer; suitable preserves could be based on these small tracts of appropriate habitat if the surrounding area excludes human disturbance.

Preserves should include well-developed shrub layers (high densities of foliage between 0.5 and 4 meters) and minimal ground cover. Mesic sites, especially those with sphagnum moss, are preferred. Studies suggest that some recent disturbance is preferable to undisturbed, mature forests (Titterington et al. 1979, Maurer et al. 1981, Adams and Hammond 1991, Christian et al. 1996, King and DeGraaf, in press; King, pers. comm.), although at least two produced conflicting evidence (Johnson and Brown 1990, DeGraaf et al. 1991). Less information is available to guide preserve design in wintering areas. Thick, shrubby habitat structure is similar to that of breeding areas, suggesting that preserves incorporate some disturbance, but no data are available to quantify this.

Management Requirements: Management treatments that increase shrub density while limiting ground cover will be most effective. Clearcuts and shelterwood cuts received more use than mature forest in northern New Hampshire (King and DeGraaf, in press). In general, populations decrease at the time of disturbance but expand as regeneration of the shrub layer occurs. In New York, abundance peaked 5-15 years after heavy logging (Webb et al. 1977). Selective thinning of the forest canopy, whether by natural events like insect infestations (Adams and Hammond 1991) or blowdown (Hall 1984), or by human activities like mechanical strip thinning of aspen stands (Christian et al. 1996), appear to be beneficial, at least until the return of canopy closure. Where clearcuts are done, the leaving of residual patches of trees may provide some benefits (Merrill et al. 1998). Probably because they reduce vegetation in the shrubby understory, large numbers of deer have a negative effect on populations (DeGraaf et al. 1991). Managers should permit deer harvest in order to prevent high ungulate densities.

Management Research Needs: The greatest need for information occurs on the wintering grounds, where habitat is rapidly disappearing but remains poorly understood. Population trends, important concentration areas for wintering birds, exact habitat requirements, and sensitivity to disturbance all require study (Conway 1999). More study should be undertaken of factors influencing breeding success, including the impacts of forested wetland losses, the effects of management treatments, and the impacts of predation and brood parasitism. Evidence that abundance is negatively correlated with the proximity of paved roads raises questions about what the ultimate cause(s) is of this negative effect (Miller 1999). Conway (1999) notes a need for basic information about biology, especially all aspects of breeding biology.

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Global Protection: Very many (>40) occurrences appropriately protected and managed

Comments: Many occurrences are in protected areas.

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Relevance to Humans and Ecosystems

Benefits

There are no known adverse effects of Canada warblers on humans.

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There are no known positive effects of Canada warblers on humans.

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Risks

Stewardship Overview: Several decades of population declines have led to increasing concern. Habitat loss appears to be the major problem, both on breeding and wintering grounds. Preserves will need to protect large areas, whether they are sizable tracts of good habitat or smaller tracts of good habitat surrounded by forested buffer zones to limit the encroachment of development. Some site disturbance, to the extent that it promotes development of a dense shrub layer, may have positive effects in both breeding and non-breeding areas. Much basic research remains to be done.

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Wikipedia

Canada warbler

The Canada warbler (Cardellina canadensis) is a small 13 cm (5.1 in) long songbird of the New World warbler family.

Description[edit]

These birds have yellow underparts, blue-grey upperparts and pink legs; they also have yellow eye-rings and thin, pointed bills. Adult males have black foreheads and black necklaces. Females and immatures have faint grey necklaces. They have yellow “spectacles” round the eyes.

The Canada warbler is the host to the parasite Apororhynchus amphistomi.[2]

Female Canada warbler showing characteristic lighter neck markings and grey top plumage

Ecology[edit]

Breeding[edit]

They breed generally in dense secondary growth forests, red maple swamps or high elevation alpine forests. These forests are located across Canada, east of the Rockies, and in the eastern United States. The nests are shaped like open cups and are placed on the ground in a damp, heavily wooded location, generally characterized by a sphagnum hummock, tree stumps or other woody debris. The female lays four to five eggs and incubates for about 12 days. The chicks remain in the nest for about 10 days after hatching and are dependent on their parents for two to three weeks after they leave the nest.[3]

These birds migrate to northern South America, and are very rare vagrants to Western Europe.

Feeding[edit]

They forage actively in vegetation or on the ground, and they often catch insects in flight. These birds mainly eat insects. They forage in flocks in their winter habitat.

Song[edit]

The song of this bird is loud and highly variable, resembling chip chewy sweet dichetty. Their calls are low chup's.

Status[edit]

Canada warblers' numbers have declined due to loss of suitable habitat and the species has been assessed as "threatened" by the Committee on the Status of Endangered Wildlife in Canada.[4] The IUCN, however, ranks the Canada warbler as a species of least concern.[1]

The Canadian population, which accounts for 85% of the global population, is estimated at roughly 2.7 million individuals.[3]

The Canada warbler is protected at the federal level in both Canada and the United States.[3]

Canada warblers have been seen twice in Europe. The first record was seen in Iceland, and the second was of a first-winter female which was found in Kilbaha, County Clare, Ireland in October 2006.

In art[edit]

John James Audubon illustrates the Canada warbler in Birds of America (published, London 1827-38) as Plate 5 entitled "Bonaparte's Warbler - Muscicapa bonapartii". The single female (now properly identified as a Canada warbler) is shown perched in a Great Magnolia (Magnolia grandiflora) branch that was painted by Joseph Mason. The final, combined image was engraved and colored by Robert Havell Junior at the Havell workshops in London. The original painting was purchased by the New York History Society, where it remains to this day (January 2009).

References[edit]

  1. ^ a b BirdLife International (2009). "Wilsonia canadensis". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 3 June 2012.  Database entry includes justification for why this species is of least concern
  2. ^ Byrd. Helminth Parasites. pp. 391–410. 
  3. ^ a b c "Species Profile: Canada Warbler". http://www.registrelep-sararegistry.gc.ca. Species at Risk Public Registry, Government of Canada. 2014-05-29. Retrieved 5 Jun 2014. 
  4. ^ "Warbler, Canada". http://www.cosewic.gc.ca. Committee on the Status of Endangered Wildlife in Canada (COSEWIC), Government of Canada. 2011-11-07. Retrieved 5 Jun 2014. 
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Names and Taxonomy

Taxonomy

Comments: Formerly placed in the genus Wilsonia. Phylogenetic analyses of sequences of nuclear and mitochondrial DNA (Lovette et al. 2010) indicate that two species formerly placed in the genus Wilsonia (canadensis and pusilla)and both species formerly placed in the genus Ergaticus (rubra and versicolor) form a clade with Cardellina rubrifrons. The generic name Cardellina has priority for this clade (AOU 2011).

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