Dendroica caerulescens

Geographic Range

Black-throated blue warblers are found in northeastern North America in the summer, breeding season. They are found from the northern Great Lakes region east to the Canadian maritime provinces, throughout New England, and south through the Appalachian mountains. In winter they are found in southernmost Florida, the Antilles south to Trinidad, and the coastal Yucatan peninsula, from Mexico and Belize to Honduras.

• Biogeographic Regions
• nearctic nearctic
  • native native
• neotropical neotropical
  • native native

Habitat

Black-throated blue warblers are found in tracts of undisturbed deciduous and mixed-deciduous forests in their breeding range. Forests they occur in include those with maples ( Acer ), birches ( Betula ), beeches ( Fagus grandifolia ), eastern hemlock ( Tsuga canadensis ), spruce ( Picea ), and fir ( Abies ). The elevational range of these forests varies throughout the region. They prefer forests with a dense, shrubby understory. They migrate along woodlands and woodland fragments, including riparian forests. In winter they are found in tropical forests, including secondary forest, plantations, and disturbed forest fragments.

• Habitat Regions
• temperate temperate
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• rainforest rainforest

• Other Habitat Features
• suburban suburban
• agricultural agricultural
• riparian riparian

Physical Description

Black-throated blue warblers are about 13 cm long and from 9 to 10 g. Males and females have different plumages. Males have dark blue backs and black faces, throats, and sides. Their bellies and breasts are white. Females are olive green with buffy yellow throat, breast, and bellies. Females have a buffy eye stripe, a white semicircle below the eye, and a small white wing spot. Immature males have a greenish tinge to their dorsal feathers. They have black legs, feet, and bills, but they begin life with flesh-colored legs, feet, and bills.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes colored or patterned differently

Reproduction

Black-throated blue warblers are mainly monogamous, although rare males will maintain multiple female mates. Pairs are formed very soon after arrival at the breeding site. Mated pairs remain together for the breeding season through multiple broods or attempted broods. Males guard their mates closely and extra pair copulations are common in this warbler species. Approximately 34% of broods had nestlings that were not fathered by the territorial male.

• Mating System
• monogamous monogamous
• polygynous polygynous

Black-throated blue warblers start breeding in late May or early June and may lay second clutches in late June or early July. Females determine nest sites and build them out of strips of bark, cobwebs, and saliva. They then line them with softer materials, like moss, hair, pine needles, or shredded bark. Males may help gather nest materials. Females may build up to 5 nests in a season if she has to re-nest several times. Females lay from 2 to 5, usually 4, white, speckled eggs in a clutch. Females usually lay 1 egg each day until done and begin incubating when the last egg is laid. Most females lay multiple clutches in a year either after losing a clutch or as a second nesting attempt after a first, successfully raised brood. They have been reported laying up to 5 clutches, but 2 is more typical. Incubation takes 12 to 13 days and young begin to fly between 8 and 10 days after hatching. They leave the nest at that point, but remain nearby and are fed and protected by their parents for another 2 to 3 weeks after they have fledged. Black-throated blue warblers can breed in their first year after hatching, although males may be unsuccessful at attracting mates until their second year.

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

Females incubate the eggs and brood hatchlings. Males may feed females while on the nest. Young hatch with their eyes closed and naked. Their eyes open at about 4 days old and they leave the nest at 8 to 10 days old, when they are just beginning to learn to fly. Males and females both feed nestlings and fledglings for up to 3 weeks after they fledge. Both parents protect their young from predators with alarm calls and distraction displays.

• Parental Investment
• altricial altricial
• 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
  • protecting
    • male
    • female

Lifespan/Longevity

The oldest recorded black-throated blue warbler was at least 10 years old. There is some evidence that older individuals may have higher rates of survival, or higher site fidelity. Survival rates in the winter range were from 66 to 77% for females and males, respectively. Nestling mortality is largely from predation but nestlings also die from exposure during cold or rainy weather.

Behavior

Black-throated blue warblers flit among vegetation and can hop on the ground. They are migratory and active during the day. They spend much of their time foraging, except when females are incubating eggs or brooding young, when they spend 75% of their time incubating or brooding. They are solitary throughout the year, except for mated pairs during breeding season. Males aggressively defend territories for feeding and nesting, excluding all conspecifics from the territory.

• Key Behaviors
• arboreal arboreal
• scansorial
• flies
• diurnal diurnal
• motile motile
• migratory migratory
• solitary solitary
• territorial territorial

Home Range

Foraging and nesting territories are from 1 to 4 hectares in size during the breeding season. In winter, foraging territories are from 0.2 to 0.3 hectares for males and slightly smaller for females. Although black-throated blue warblers don't seem to return to their natal site in their first year, adults seem to return to the same breeding and wintering sites each year.

Communication and Perception

Black-throated blue warblers use a series of calls and songs to communicate. Females vocalize sometimes, but males perform the majority of songs. Male songs vary with individual, but there are two main song types: 1) a song of 3 to 7 buzzing notes that trills upward at the end, sounding like "zee-zee-zee-zreeee," and 2) a song of 2 to 5 notes that descends at the end, sounding like "zee-zee-zhurrr." The first song type is the most commonly heard and varies substantially among males. Males use other kinds of songs as well, although their purposes and contexts are not well understood. Most songs are used during the breeding season, but there is some singing during migration and in winter. Males sing from perches in their home range.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Black-throated blue warblers are mainly insectivorous during the breeding season and supplement their insect diet with fruits during the winter. In the breeding range, these warblers eat mainly beetles , caterpillars , butterflies and moths , flies , bugs , and spiders . In the winter they eat as much as 95% insects, but supplement their diet with berries, other fruits, flower nectar, and honeydew excretions from scale insects . Black-throated blue warblers forage by themselves from 22 to 70% of daylight hours, depending on the season and their energy requirements. Females forage more during nest-building and the weeks leading up to egg laying, up to 70% of daylight hours. Males generally forage for 30-32% of daylight hours, but forage for an additional 20% when they are singing to defend nesting territories. They forage in undergrowth shrubs and forest canopy layers, taking most of their prey from leaves and bark.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• body fluids
• insects
• terrestrial non-insect arthropods

• Plant Foods
• fruit
• nectar

Predation

Black-throated blue warbler adults are preyed on by birds of prey, such as Cooper's hawks ( Accipiter cooperi ). Eggs and nestlings are taken by a wide variety of nest predators, including sharp-shinned hawks ( Accipiter striatus ), blue jays ( Cyanocitta cristata ), red squirrels ( Tamiasciurus hudsonicus ), eastern chipmunks ( Tamias striatus ), martens ( Martes americana ), fishers ( Martes pennanti ), flying squirrels ( Glaucomys ), raccoons ( Procyon lotor ), black bears ( Ursus americanus ), and garter snakes ( Thamnophis sirtalis ). Black-throated blue warblers will mob predators and perform broken-wing displays to distract them. Parents give a high-pitched warning call when they see raptors and will respond to the warning calls of other birds.

Ecosystem Roles

Black-throated blue warblers are important predators of insects in their forest habitats. They may also help to disperse seeds of the fruits they eat. There are few reported parasites in black-throated blue warblers. Only 2 nesting records indicate parasitism: bot flies ( Oestridae ) in one and parasitic fly larvae ( Calliphoridae ) in another. Brown-headed cowbirds will parasitize the nests of black-throated blue warblers, especially in areas of disturbed forest. If parasitized, they can successfully raise a cowbird young about 60% of the time.

Economic Importance for Humans: Positive

There is no direct positive impact of black-throated blue warblers on humans. However, they are lovely and interesting members of native faunas and may attract bird watching interest.

Economic Importance for Humans: Negative

There are no known adverse effects of black-throated blue warblers on humans. However, along with many other bird species, they carry West Nile virus.

• Negative Impacts
• injures humans
  • carries human disease

Conservation Status

Black-throated blue warblers have a large range and large populations without evidence of significant population declines. They are considered "least concern" by the IUCN. They are considered sensitive to forest fragmentation, preferring areas of forest over 100 hectares in size, but they are found in disturbed forests and secondary growth, provided there is a lush understory. Similarly, in their winter range, black-throated blue warblers are found in a variety of forests, including disturbed forests, orchards, and plantations, but populations may be negatively impacted by habitat destruction. They are also found dead as a result of collisions with man-made objects, such as television towers, during migration.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Tanya Dewey (author), Animal Diversity Web.

References

Holmes, R., N. Rodenhouse, T. Sillett. 2005. Black-throated Blue Warbler (Dendroica caerulescens). The Birds of North America Online , 87: 1-20. Accessed April 18, 2009 at http://bna.birds.cornell.edu.proxy.lib.umich.edu/bna/species/087 .