Blue-headed Vireo
Encyclopedia
The Blue-headed Vireo is a Neotropical migrating song bird
found in North and Central America
. There are currently two recognized sub-species that belong to the Blue-headed Vireo. It has a range that extends across Canada
and the eastern coast of the United-States, Mexico
and some of Central America. It prefers large temperate
forests with a mix of evergreen trees and deciduous
under growth.
As the name suggests, the Blue-headed Vireo is characterized by its blue-grey head and bold yellow wing bars. Both sexes are very similar in plumage
and size. Juveniles also have a similar plumage.
Populations of the Blue-headed Vireo have been steadily increasing since the 1970s and has therefore been classified as a "Least Concern
" species in 2004.
from which it gets its name. The juvenile plumage of immature Blue-headed Vireos is not distinct but very similar to the adult plumage. While this bird’s appearance is similar to the closely related Cassin's Vireo
(Vireo cassinii), the Cassin's Vireo can be differentiated by its lighter yellow patches, a smaller, thinner bill, and a brownish-grey crown. There is little to no sexual dimorphism
between males and females as both are similar in plumage colouration and size.
Like most Vireos, the Blue-headed Vireo is a relatively small bird with a length of 126-148 millimetres (4.9-5.8 in). The wingspan is usually found to be around 200-240 millimetres (7.9-9.4 in) and their weight is typically 13-19 grams (0.4-0.67 oz). There are some subtle differences between the V.s. solitarius and V.s. alticola sub-species. V.s. alticola, the larger of the two sub-species, has a darker back with a larger wing length of 76-83.5 millimetres (3-3.3 in) and a bill length of 11-12 millimetres (0.43-0.47 in). Conversely, V.s. solitarius is slightly smaller with a wing length of 69.2-77.8 millimetres (2.7-3 in), and a bill length of 8.9-11 millimetres (0.3-0.4 in).
The average lifespan of the Blue-headed Vireo in the wild has been measured to be approximately 7 years and 5 months.
Vireo
, a group of small migrating passerine birds that are characterized by their usually dull greenish colouring, and a simple, monotonous song. Members of this group are usually characterized by the presence or absence of eye-rings, eye-strips, and wing bars. There is no sexual dimorphism between sexes in this group.
Originally considered its own species, in the 1950’s, based on morphological
data, the two Blue-headed Vireo sub-species were grouped with the Plumbeous Vireo
(Vireo plumbeus) and the Cassin’s Vireo (V. Cassinii). This group of Vireos was collectively known as the “Solitary Vireo” (Vireo solitarius). This taxonomy prevailed until 1997 when new molecular data on the “Solitary Vireo” showed that the three birds were in fact distinct species. The taxonomy
was then changed back and the Blue-headed Vireo was once again its own species .
There are two recognized subspecies of Blue-headed Vireo:
, the Blue-headed Vireo enjoys a large breeding range that expands over an immense area of Canada and northern United States. The breeding range of V.s. solitarius expands from north eastern British Columbia
across Alberta
, Saskatchewan
, Manitoba
, Ontario
and Quebec
and down to southern Pennsylvania and New Jersey. V.s. alticola has a distinct breeding range that includes western Maryland
and then south, mainly in the Appalachian Mountains, to northern Georgia. At the end of the breeding season, the Blue-headed Vireo will migrate south to its overwintering area. V.s. solitarius has the longest migration of the two sub-species and inhabits an overwintering area that includes east and south Mexico to northern Central America. V.s. alticola migrates across a shorter distance to an area that expands from south-eastern Virginia
to Texas
.
During breeding, the Vireos prefer temperate forests that are found at higher elevations where it is cooler. Evergreen forests with spruce
, fir
, hemlock
and pine
with deciduous growth such as alder
shrubs, willow
shrubs, poplar
, birch
or maple
trees are the habitat of choice for the small bird . During the winter, Vireos inhabit woods of pines, hardwoods and mixed trees. They are also found in coastal and flood plain swamps as well as low shrub thickets.
Year round, even during the breeding season, population density
is somewhat low and spread out. Overwintering population densities are usually found to be lower than in the breeding season . The density of the population ultimately depends on the type of forest being inhabited.
During migration, Blue-headed vireos are often found to flock with groups of different sparrow
species but never with members of its own species.
(Adelges tsugae). These true bugs feed on the evergreen hemlock trees which leave the migrating Vireos with fewer habitats to form breeding nests until the deciduous trees begin to leaf .
(Vireo olivaceus) song. The primary song is sung only by the males and usually only during the breeding season. The males become quite vocal during the breeding season, with the song frequency reaching its height prior to mating and then decreasing after copulation. Both sexes share a series of calls that are used in both defence of nests, interspecies competition, and communication between breeding pairs while foraging
.
When foraging during the breeding season, mating pairs will constantly communicate with each other using a series of high pitched chirping calls.
used for processing insect prey with a tough carapace
such as beetles. Usually, foraging will occur in the mid level of trees, a foraging Blue-headed Vireo will hop from branch to branch on the same or to an adjacent tree and will then fly towards its prey to capture it. Typical prey consist mostly of caterpillars, butterflies and moths
but may also include tree bugs, stink bugs, beetles, bees, ants, flies
, dragonflies, grasshopper
s, crickets, spiders and on some occasions, snails. Fruit feeding is seen mostly during migration and overwintering, especially when overwintering in more tropical regions where fruit is more abundant or if the insect populations are low. This large and varying diet can be attributed to a more opportunistic feeding strategy, allowing the Blue-headed Vireo to be plastic in its ability to adapt to resource availability.
Once a female has approached a suitable mate, the male will perform a series of mating rituals. Typically, these rituals involve the male building a courtship nest for the female. The courtship nest is not a full nest but is most likely an attempt by the male to display his ability to gather resources. Once the pair is established, the courtship nest is abandoned. Mating does not occur for approximately 2 weeks after pair has been established. During this time, the male and the female will cooperatively build a breeding nest which is typically formed between forking mid level branches of evergreen and deciduous trees and are composed of twigs and foliage. Breeding nests are not reused in following breeding seasons.
In one breeding season, a female will lay 3-5 eggs at a rate of 1 egg/day. Eggs are creamy white with brown or black spots and are 17-23.1 millimetres x 13.3-15.8 millimetres (0.055-0.075 in x 0.04-0.05 in). Eggs are incubated
for approximately 14 days after being laid. Once hatched, infants are highly altricial
, often having little to no downy feathers. Infants open their eyes during day 5 or 6 and will begin to fledge
after 14 days for a total chick-rearing period of 28 days. Once the young are able to leave the nest, the parents will split the juveniles and separate. Juveniles are usually dependant on the parent to provide food for approximately 1 month after leaving the nest. If the nest is destroyed or a mating pair produces a failed brood, an attempt to re-nest may occur but this ultimately depends on when the brood fails. If the brood fails early on in the season, there is a higher chance that the pair will re-nest, if later, the pair will often separate and not attempt a second brood.
Blue-headed Vireo’s have an atypical breeding strategy when compared to other closely related species. Blue-headed Vireo males will assist their mates with daytime incubation of eggs, nest construction, and feeding of the chicks (Morton et al. 1998). Also, unlike most bird species, female Blue-headed Vireos do not attempt any extra-pair copulations with other males. Likewise, males make no attempt to guard females from other males, making Blue-headed Vireos both socially and genetically monogamous birds.
and prolactin
found in the plasma
of these birds during the mating season. Testosterone, a steroid hormone
that is secreted by the testes, has been found to increase aggressive behaviour in male birds during the breeding season and that these males display less parental care if their testosterone levels are maintained. Conversely, prolactin is a peptide hormone
that is regulated by the hypothalamus
that has been found at higher levels in birds that do the majority of incubation . It was found that in the early breeding season, male Blue-headed Vireos have a low testosterone level and will maintain this low level at all stages of the season . This low level does not affect the Vireo’s ability to compete with other males for territory however, as a high testosterone level has been found to not be necessary for territory establishment . Prolactin levels of the males were found to be high very early on in the breeding season and are maintained for the duration of the season. This high level of prolactin along with a low testosterone level, explains why male Blue-headed Vireos are so involved in the construction of the nest, daytime incubation, and feeding of the nestlings.
s, Crows, and Squirrels.
Often, when a nest is attacked by a blue-jay, the male and female will execute coordinated attacks on the approaching predator. This usually involves one partner swooping towards the blue-jay while calling the mate who will then execute a second attack. Blue-headed Vireos have also been known to nest close to nesting raptorial birds that do not prey on them. It is thought that they use the raptors as protection from squirrels that are, in turn, hunted by the these bird of prey
.
The largest contributor to the low nesting success rate of the Blue-headed Vireo is most likely the parasitic Brown-headed Cowbird
(Molothrus ater). These birds will often lay their large eggs overtop the existing brood, causing the parents to feed the cowbird which will ultimately starve the infant Vireos.
Song Bird
Song Bird is a 1977 album by Deniece Williams. The album went to number 23 and number 66 on the Black and Pop album Charts respectively. The single Baby, Baby My Love's All For You reached number 13 and number 32 on the Black and UK singles....
found in North and Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
. There are currently two recognized sub-species that belong to the Blue-headed Vireo. It has a range that extends 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...
and the eastern coast of the United-States, 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 some of Central America. It prefers large temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
forests with a mix of evergreen trees and 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...
under growth.
As the name suggests, the Blue-headed Vireo is characterized by its blue-grey head and bold yellow wing bars. Both sexes are very similar in plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...
and size. Juveniles also have a similar plumage.
Populations of the Blue-headed Vireo have been steadily increasing since the 1970s and has therefore been classified as a "Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
" species in 2004.
Description
The Blue–headed Vireo has similar plumage year round and does not drastically change its appearance during the breeding season. It can be characterized by its olive green upper body, two bold yellow wing bars down the edge of its wing, and a deep blue-grey crownCrown (anatomy)
A crown is the top of the head.The following birds and other animals are said to have a crown on their head:* Cranes** Grey-crowned Crane** Red-crowned Crane** Black-crowned Crane* Crowned eagle* Gray-crowned Rosy Finch* Yellow-crowned Gonolek...
from which it gets its name. The juvenile plumage of immature Blue-headed Vireos is not distinct but very similar to the adult plumage. While this bird’s appearance is similar to the closely related Cassin's Vireo
Cassin's Vireo
Cassin's Vireo is a small North American songbird, ranging from southern British Columbia in Canada through the western coastal states of the United States. This bird migrates, spending the winter from southern Arizona to southern Mexico.The vireo is 11–14 cm in length, with a gray head, back,...
(Vireo cassinii), the Cassin's Vireo can be differentiated by its lighter yellow patches, a smaller, thinner bill, and a brownish-grey crown. There is little to no sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
between males and females as both are similar in plumage colouration and size.
Like most Vireos, the Blue-headed Vireo is a relatively small bird with a length of 126-148 millimetres (4.9-5.8 in). The wingspan is usually found to be around 200-240 millimetres (7.9-9.4 in) and their weight is typically 13-19 grams (0.4-0.67 oz). There are some subtle differences between the V.s. solitarius and V.s. alticola sub-species. V.s. alticola, the larger of the two sub-species, has a darker back with a larger wing length of 76-83.5 millimetres (3-3.3 in) and a bill length of 11-12 millimetres (0.43-0.47 in). Conversely, V.s. solitarius is slightly smaller with a wing length of 69.2-77.8 millimetres (2.7-3 in), and a bill length of 8.9-11 millimetres (0.3-0.4 in).
The average lifespan of the Blue-headed Vireo in the wild has been measured to be approximately 7 years and 5 months.
Taxonomy
The Blue-headed Vireo is placed in the genusGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Vireo
Vireo
The vireos are a group of small to medium-sized passerine birds restricted to the New World. They are typically dull-plumaged and greenish in color, the smaller species resembling wood warblers apart from their heavier bills...
, a group of small migrating passerine birds that are characterized by their usually dull greenish colouring, and a simple, monotonous song. Members of this group are usually characterized by the presence or absence of eye-rings, eye-strips, and wing bars. There is no sexual dimorphism between sexes in this group.
Originally considered its own species, in the 1950’s, based on morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
data, the two Blue-headed Vireo sub-species were grouped with the Plumbeous Vireo
Plumbeous Vireo
The Plumbeous Vireo is a small North American songbird, ranging from far southeastern Montana and western South Dakota south to the Pacific coast of Mexico, including the extreme southern regions of Baja California Sur...
(Vireo plumbeus) and the Cassin’s Vireo (V. Cassinii). This group of Vireos was collectively known as the “Solitary Vireo” (Vireo solitarius). This taxonomy prevailed until 1997 when new molecular data on the “Solitary Vireo” showed that the three birds were in fact distinct species. The taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
was then changed back and the Blue-headed Vireo was once again its own species .
There are two recognized subspecies of Blue-headed Vireo:
- Vireo solitarius solitarius is the nominate species. It is slightly smaller and breeds across Canada to south PennsylvaniaPennsylvaniaThe Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
and New JerseyNew JerseyNew Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
. It overwinters in north-central and southern Mexico. - Vireo solitarius alticola is slightly larger than the nominate species. It breeds mainly in the Appalachian MountainsAppalachian MountainsThe Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...
to northern GeorgiaGeorgia (U.S. state)Georgia is a state located in the southeastern United States. It was established in 1732, the last of the original Thirteen Colonies. The state is named after King George II of Great Britain. Georgia was the fourth state to ratify the United States Constitution, on January 2, 1788...
. It overwinters in the Gulf States after a short migrationBird migrationBird 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...
.
Habitat and Distribution
Native to North AmericaNorth 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...
, the Blue-headed Vireo enjoys a large breeding range that expands over an immense area of Canada and northern United States. The breeding range of V.s. solitarius expands from north eastern British Columbia
British 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...
across Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
, Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
, Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...
, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
and Quebec
Quebec
Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....
and down to southern Pennsylvania and New Jersey. V.s. alticola has a distinct breeding range that includes western Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...
and then south, mainly in the Appalachian Mountains, to northern Georgia. At the end of the breeding season, the Blue-headed Vireo will migrate south to its overwintering area. V.s. solitarius has the longest migration of the two sub-species and inhabits an overwintering area that includes east and south Mexico to northern Central America. V.s. alticola migrates across a shorter distance to an area that expands from south-eastern Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
to Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
.
During breeding, the Vireos prefer temperate forests that are found at higher elevations where it is cooler. Evergreen forests with spruce
Spruce
A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...
, fir
Fir
Firs are a genus of 48–55 species of evergreen conifers in the family Pinaceae. They are found through much of North and Central America, Europe, Asia, and North Africa, occurring in mountains over most of the range...
, hemlock
Tsuga
Tsuga is a genus of conifers in the family Pinaceae. The common name hemlock is derived from a perceived similarity in the smell of its crushed foliage to that of the unrelated plant poison hemlock....
and pine
Pine
Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...
with deciduous growth such as alder
Alder
Alder is the common name of a genus of flowering plants belonging to the birch family . The genus comprises about 30 species of monoecious trees and shrubs, few reaching large size, distributed throughout the North Temperate Zone and in the Americas along the Andes southwards to...
shrubs, willow
Willow
Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...
shrubs, poplar
Poplar
Populus is a genus of 25–35 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar , aspen, and cottonwood....
, birch
Birch
Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...
or maple
Maple
Acer is a genus of trees or shrubs commonly known as maple.Maples are variously classified in a family of their own, the Aceraceae, or together with the Hippocastanaceae included in the family Sapindaceae. Modern classifications, including the Angiosperm Phylogeny Group system, favour inclusion in...
trees are the habitat of choice for the small bird . During the winter, Vireos inhabit woods of pines, hardwoods and mixed trees. They are also found in coastal and flood plain swamps as well as low shrub thickets.
Year round, even during the breeding season, population density
Population density
Population density is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, and particularly to humans...
is somewhat low and spread out. Overwintering population densities are usually found to be lower than in the breeding season . The density of the population ultimately depends on the type of forest being inhabited.
During migration, Blue-headed vireos are often found to flock with groups of different sparrow
Sparrow
The sparrows are a family of small passerine birds, Passeridae. They are also known as true sparrows, or Old World sparrows, names also used for a genus of the family, Passer...
species but never with members of its own species.
Habitat loss
When arriving to the breeding grounds in mid-April, many deciduous trees have not begun to leaf out, prompting the migrating Blue-headed Vireos to nest in the evergreen hemlock tree. Recently, however, some of the native habitat of the Blue-headed Vireo has been deteriorated by an invasive Asian insect, the Hemlock woolly adelgidHemlock Woolly Adelgid
Hemlock woolly adelgid , commonly abbreviated as HWA, is a true bug native to East Asia that feeds by sucking sap from hemlock trees . In eastern North America, it is a destructive pest that poses a major threat to the eastern hemlock and the Carolina hemlock...
(Adelges tsugae). These true bugs feed on the evergreen hemlock trees which leave the migrating Vireos with fewer habitats to form breeding nests until the deciduous trees begin to leaf .
Vocalizations
The primary song of the Blue-headed Vireo is a simple, slow, monotonous tune that is often confused with the faster Red-eyed VireoRed-eyed Vireo
The Red-eyed Vireo, Vireo olivaceus, is a small American songbird, 13–14 cm in length. It is somewhat warbler-like but not closely related to the New World warblers...
(Vireo olivaceus) song. The primary song is sung only by the males and usually only during the breeding season. The males become quite vocal during the breeding season, with the song frequency reaching its height prior to mating and then decreasing after copulation. Both sexes share a series of calls that are used in both defence of nests, interspecies competition, and communication between breeding pairs while foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
.
When foraging during the breeding season, mating pairs will constantly communicate with each other using a series of high pitched chirping calls.
Diet
Blue-headed Vireos are mainly insectivorous birds but are also known to eat fleshy berries and fruit. They are equipped with short, strong billsBills
The Bills were a youth subculture that thrived in Léopoldville in the late 1950s, basing much of their image and outlook on the cowboys of American Western movies...
used for processing insect prey with a tough carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
such as beetles. Usually, foraging will occur in the mid level of trees, a foraging Blue-headed Vireo will hop from branch to branch on the same or to an adjacent tree and will then fly towards its prey to capture it. Typical prey consist mostly of caterpillars, butterflies and moths
Moths
Moths may refer to:* Gustav Moths , German rower* The Moths!, an English indie rock band* MOTHS, members of the Memorable Order of Tin Hats...
but may also include tree bugs, stink bugs, beetles, bees, ants, flies
Fließ
Fließ is a municipality in the Landeck district and is located5 km south of Landeck on the upper course of the Inn River. It has 9 hamlets and was already populated at the roman age; the village itself was founded around the 6th century. After a conflagration in 1933 Fließ was restored more...
, dragonflies, grasshopper
Grasshopper
The grasshopper is an insect of the suborder Caelifera in the order Orthoptera. To distinguish it from bush crickets or katydids, it is sometimes referred to as the short-horned grasshopper...
s, crickets, spiders and on some occasions, snails. Fruit feeding is seen mostly during migration and overwintering, especially when overwintering in more tropical regions where fruit is more abundant or if the insect populations are low. This large and varying diet can be attributed to a more opportunistic feeding strategy, allowing the Blue-headed Vireo to be plastic in its ability to adapt to resource availability.
Reproduction
When arriving to the breeding ground in mid-April, male Vireos will hold large, individual territories that can range from 1.5-6.6 hectares. Females will choose a male to mate with depending on the male’s ability to defend and control a large territory. While defending their territory from other males, the male Vireos will sing a primary song to attract females. Undecided females can usually be seen flying along the edges of competing male territories; usually this will force the two males into direct conflict for the right to copulate with the female.Once a female has approached a suitable mate, the male will perform a series of mating rituals. Typically, these rituals involve the male building a courtship nest for the female. The courtship nest is not a full nest but is most likely an attempt by the male to display his ability to gather resources. Once the pair is established, the courtship nest is abandoned. Mating does not occur for approximately 2 weeks after pair has been established. During this time, the male and the female will cooperatively build a breeding nest which is typically formed between forking mid level branches of evergreen and deciduous trees and are composed of twigs and foliage. Breeding nests are not reused in following breeding seasons.
In one breeding season, a female will lay 3-5 eggs at a rate of 1 egg/day. Eggs are creamy white with brown or black spots and are 17-23.1 millimetres x 13.3-15.8 millimetres (0.055-0.075 in x 0.04-0.05 in). Eggs are incubated
Avian incubation
Incubation refers to the process by which certain oviparous animals hatch their eggs, and to the development of the embryo within the egg. The most vital factor of incubation is the constant temperature required for its development over a specific period. Especially in domestic fowl, the act of...
for approximately 14 days after being laid. Once hatched, infants are highly altricial
Altricial
Altricial, meaning "requiring nourishment", refers to a pattern of growth and development in organisms which are incapable of moving around on their own soon after hatching or being born...
, often having little to no downy feathers. Infants open their eyes during day 5 or 6 and will begin to fledge
Fledge
Fledge is the stage in a young bird's life when the feathers and wing muscles are sufficiently developed for flight. It also describes the act of a chick's parents raising it to a fully grown state...
after 14 days for a total chick-rearing period of 28 days. Once the young are able to leave the nest, the parents will split the juveniles and separate. Juveniles are usually dependant on the parent to provide food for approximately 1 month after leaving the nest. If the nest is destroyed or a mating pair produces a failed brood, an attempt to re-nest may occur but this ultimately depends on when the brood fails. If the brood fails early on in the season, there is a higher chance that the pair will re-nest, if later, the pair will often separate and not attempt a second brood.
Blue-headed Vireo’s have an atypical breeding strategy when compared to other closely related species. Blue-headed Vireo males will assist their mates with daytime incubation of eggs, nest construction, and feeding of the chicks (Morton et al. 1998). Also, unlike most bird species, female Blue-headed Vireos do not attempt any extra-pair copulations with other males. Likewise, males make no attempt to guard females from other males, making Blue-headed Vireos both socially and genetically monogamous birds.
Hormonal Effects on Parental Care
The increase in male Blue-headed Vireo parental care is thought to be attributed to the levels of testosteroneTestosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
and prolactin
Prolactin
Prolactin also known as luteotropic hormone is a protein that in humans is encoded by the PRL gene.Prolactin is a peptide hormone discovered by Henry Friesen...
found in the plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
of these birds during the mating season. Testosterone, a steroid hormone
Steroid hormone
A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into five groups by the receptors to which they bind: glucocorticoids, mineralocorticoids, androgens, estrogens, and progestogens...
that is secreted by the testes, has been found to increase aggressive behaviour in male birds during the breeding season and that these males display less parental care if their testosterone levels are maintained. Conversely, prolactin is a peptide hormone
Peptide hormone
Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.Like other proteins, peptide hormones are synthesized in cells from amino acids according to an mRNA template, which is itself synthesized from a DNA template inside the...
that is regulated by the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
that has been found at higher levels in birds that do the majority of incubation . It was found that in the early breeding season, male Blue-headed Vireos have a low testosterone level and will maintain this low level at all stages of the season . This low level does not affect the Vireo’s ability to compete with other males for territory however, as a high testosterone level has been found to not be necessary for territory establishment . Prolactin levels of the males were found to be high very early on in the breeding season and are maintained for the duration of the season. This high level of prolactin along with a low testosterone level, explains why male Blue-headed Vireos are so involved in the construction of the nest, daytime incubation, and feeding of the nestlings.
Predation
Blue-headed Vireos have a low nesting success rate, with about 10-30 percent of hatchlings surviving. Common predators of the Blue-headed Vireo eggs and chicks include Blue jayBlue Jay
The Blue Jay is a passerine bird in the family Corvidae, native to North America. It is resident through most of eastern and central United States and southern Canada, although western populations may be migratory. It breeds in both deciduous and coniferous forests, and is common near and in...
s, Crows, and Squirrels.
Often, when a nest is attacked by a blue-jay, the male and female will execute coordinated attacks on the approaching predator. This usually involves one partner swooping towards the blue-jay while calling the mate who will then execute a second attack. Blue-headed Vireos have also been known to nest close to nesting raptorial birds that do not prey on them. It is thought that they use the raptors as protection from squirrels that are, in turn, hunted by the these bird of prey
Bird of prey
Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....
.
The largest contributor to the low nesting success rate of the Blue-headed Vireo is most likely the parasitic Brown-headed Cowbird
Brown-headed Cowbird
The Brown-headed Cowbird is a small brood parasitic icterid of temperate to subtropical North America. They are permanent residents in the southern parts of their range; northern birds migrate to the southern United States and Mexico in winter, returning to their summer habitat around March or...
(Molothrus ater). These birds will often lay their large eggs overtop the existing brood, causing the parents to feed the cowbird which will ultimately starve the infant Vireos.
External links
- Blue-headed Vireo - Vireo solitarius - USGS Patuxent Bird Identification InfoCenter
- Blue-headed Vireo Information - South Dakota Birds and Birding
- Blue-headed Vireo Species Information - Cornell Lab of Ornithology
- Blue-headed Vireo photo gallery VIREO-(with pictures of bulky cup nest)
- http://nationalzoo.si.edu/scbi/migratorybirds/featured_birds/default.cfm?bird=Blue-headed_Vireo - Smithsonian National Zoological Park
- http://www.birdzilla.com/birds/Blue-headed-Vireo/bent_life_history.html - Blue-headed Vireo life history
- http://www.iucnredlist.org/apps/redlist/details/146468/0 - IUCN Redlist