Swallow

The swallows, martins and saw-wings, or Hirundinidae, are a family of passerine birds found around the world on all continents, including occasionally in Antarctica. Highly adapted to aerial feeding, they have a distinctive appearance. The term Swallow is used colloquially in Europe as a synonym for the barn swallow. There are around 90 species of Hirundinidae,[1] divided into 19 genera, with the greatest diversity found in Africa, which is also thought to be where they evolved as hole-nesters.[2] They also occur on a number of oceanic islands. A number of European and North American species are long-distance migrants; by contrast, the West and South African swallows are non-migratory.

This family comprises two subfamilies: Pseudochelidoninae (the river martins of the genus Pseudochelidon) and Hirundininae (all other swallows, martins and saw-wings). Within the Old World, the name martin tends to be used for the squarer-tailed species, and the name swallow for the more fork-tailed species; however, there is no scientific distinction between these two groups.[3] Within the New World, "martin" is reserved for members of the genus Progne. (These two systems are responsible for the sand martin being called "bank swallow" in the New World.)

Swallow
Pied-winged swallow (Hirundo leucosoma)
Pied-winged swallow Hirundo leucosoma
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Suborder: Passeri
Family: Hirundinidae
Rafinesque, 1815
Genera

19, see text

Taxonomy and systematics

The family Hirundinidae was introduced (as Hirundia) by the French polymath Constantine Samuel Rafinesque in 1815.[4][5] The Hirundinidae are morphologically unique within the passerines, with molecular evidence placing them as a distinctive lineage within the Sylvioidea (Old World warblers and relatives).[6] They have also been linked to the white-eyes and the tits. Under the Sibley-Ahlquist taxonomy they have been placed in the infraorder Passerida.

Within the family there is a clear division between the two subfamilies, the Pseudochelidoninae which is composed of the two species of river martins,[7][8] and the Hirundininae, into which the remaining species are placed. The division of the Hirundininae has been the source of much discussion, with various taxonomists variously splitting them into as many as 24 genera and lumping them into just 12. There is some agreement that there are three core groups within the Hirundininae, the saw-wings of the genus Psalidoprocne, the core martins, and the swallows of the genus Hirundo and their allies.[9] The saw-wings are the most basal of the three, with the other two clades being sister to each other. The phylogeny of the swallows is closely related to evolution of nest construction; the more basal saw-wings use burrows as nest, the core martins have both burrowing (in the Old World members) and cavity adoption (in New World members) as strategies, and the genus Hirundo and its allies use mud nests.[10]

Description

The Hirundinidae have an evolutionarily conservative body shape which is similar across the clade but is unlike that of other passerines.[9] Swallows have adapted to hunting insects on the wing by developing a slender, streamlined body and long pointed wings, which allow great maneuverability and endurance, as well as frequent periods of gliding. Their body shape allows for very efficient flight; the metabolic rate of swallows in flight is 49–72% lower than equivalent passerines of the same size.[11]

Riparia riparia
The bill of the sand martin is typical for the family, being short and wide.

Swallows have two foveae in each eye, giving them sharp lateral and frontal vision to help track prey. They also have relatively long eyes, with their length almost equaling their width. The long eyes allow for an increase in visual acuity without competing with the brain for space inside of the head. The morphology of the eye in swallows is similar to that of a raptor.[12]

Like the unrelated swifts and nightjars, which hunt in a similar way, they have short bills, but strong jaws and a wide gape. Their body length ranges from about 10–24 cm (3.9–9.4 in) and their weight from about 10–60 g (0.35–2.12 oz). The wings are long, pointed, and have nine primary feathers. The tail has 12 feathers and may be deeply forked, somewhat indented, or square-ended.[9] A long tail increases maneuverability,[13][14] and may also function as a sexual adornment, since the tail is frequently longer in males.[14] In barn swallows the tail of the male is 18% longer than those of the female, and females will select mates on the basis of tail length.[15]

The legs are short, and their feet are adapted for perching rather than walking, as the front toes are partially joined at the base. Swallows are capable of walking and even running, but they do so with a shuffling, waddling gait.[16] The leg muscles of the river martins (Pseudochelidon) are stronger and more robust than those of other swallows.[9][16] The river martins have other characteristics that separate them from the other swallows. The structure of the syrinx is substantially different between the two subfamilies;[7] and in most swallows the bill, legs and feet are dark brown or black, but in the river martins the bill is orange-red and the legs and feet are pink.[9]

The most common hirundine plumage is glossy dark blue or green above and plain or streaked underparts, often white or rufous. Species which burrow or live in dry or mountainous areas are often matte brown above (e.g. sand martin and crag martin). The sexes show limited or no sexual dimorphism, with longer outer tail feathers in the adult male probably being the most common distinction.[17]

The chicks hatch naked and with closed eyes.[18] Fledged juveniles usually appear as duller versions of the adult.[3]

Distribution and habitat

The family has a worldwide cosmopolitan distribution, breeding on every continent except Antarctica. One species, the Pacific swallow, occurs as a breeding bird on a number of oceanic islands in the Pacific Ocean,[19] the Mascarene martin breeds on Reunion and Mauritius in the Indian Ocean,[20] and a number of migratory species are common vagrants to other isolated islands and even to some sub-Antarctic islands and Antarctica.[21] Many species have enormous worldwide ranges, particularly the barn swallow, which breeds over most of the Northern Hemisphere and winters over most of the Southern Hemisphere.

Hirundo abyssinica
The lesser striped swallow is a partial migrant within Africa

The family uses a wide range of habitats. They are dependent on flying insects and as these are common over waterways and lakes they will frequently feed over these, but they can be found in any open habitat including grasslands, open woodland, savanna, marshes, mangroves and scrubland, from sea level to high alpine areas.[9] Many species inhabit human-altered landscapes including agricultural land and even urban areas. Land use changes have also caused some species to expand their range, most impressively the welcome swallow which began to colonise New Zealand in the 1920s, started breeding in the 1950s and is now a common landbird there.[22]

Species breeding in temperate regions migrate during the winter when their insect prey populations collapse. Species breeding in more tropical areas are often more sedentary, although several tropical species are partial migrants or make shorter migrations. In antiquity it was thought that swallows hibernated in a state of torpor, even that they withdrew for the winter under water. Aristotle ascribed hibernation not only to swallows, but also to storks and kites. Hibernation of swallows was considered a possibility even by as acute an observer as Rev. Gilbert White, in his The Natural History and Antiquities of Selborne (1789, based on decades of observations).[23] This idea may have been supported by the habit of some species to roost in some numbers in dovecotes, nests and other forms of shelter during harsh weather, and some species even entering torpor.[9] There were several reports of suspected torpor in swallows from 1947,[24] such as a 1970 report that white-backed swallows in Australia may conserve energy this way,[25] but the first confirmed study that they or any passerine entered torpor was a 1988 study on house martins.[26]

Behaviour and ecology

Tachycineta bicolor 18319
A tree swallow attending its nest in a tree cavity

Swallows are excellent flyers, and use these skills to feed and attract a mate. Some species, like the mangrove swallow, are territorial, whereas others are not and simply defend their nesting site. In general, the males select a nest site, and then attract a female using song and flight, and (dependent on the species) guard their territory. The size of the territory varies depending on the species of swallow; in colonial-nesting species it tends to be small, but it may be much larger for solitary nesters. Outside the breeding season, some species may form large flocks, and species may also roost communally. This is thought to provide protection from predators such as sparrowhawks and hobbies.[9] These roosts can be enormous; one winter roosting site of barn swallows in Nigeria attracted 1.5 million individuals.[27] Non-social species do not form flocks, but recently fledged chicks may remain with their parents for a while after the breeding season. If a human being gets too close to their territory, swallows will attack them within the perimeter of the nest. Colonial species may mob predators and humans that are too close to the colony.[28]

Diet and feeding

For the most part swallows are insectivorous, taking flying insects on the wing.[9] Across the whole family a wide range of insects are taken from most insect groups, but the composition of any one prey type in the diet varies by species and with the time of year. Individual species may be selective; they do not scoop up every insect around them, but instead select larger prey items than would be expected by random sampling.[29] In addition the ease of capture of different insect types affects their rate of predation by swallows.[30] They also avoid certain prey types; in particular stinging insects such as bees and wasps are generally avoided. In addition to insect prey a number of species will occasionally consume fruits and other plant matter. Species in Africa have been recorded eating the seeds of Acacia trees, and these are even fed to the young of the greater striped swallow.[9][31]

The swallows generally forage for prey that is on the wing, but they will on occasion snap prey off branches or on the ground. The flight may be fast and involve a rapid succession of turns and banks when actively chasing fast moving prey; less agile prey may be caught with a slower more leisurely flight that includes flying in circles and bursts of flapping mixed with gliding. Where several species of swallow feed together they will be separated into different niches based on height off the ground, some species feeding closer to the ground and others feeding at higher levels.[32] Similar separation occurs where feeding overlaps with swifts. Niche separation may also occur with the size of prey chosen.[32]

Breeding

Swallow chicks nesting at the Skomer Marine Conservation Zone; 2017. Video by Natural Resources Wales
Cliff Swallow-27527-2
Two American cliff swallows constructing mud nests

The more primitive species nest in existing cavities, for example in an old woodpecker nest, while other species excavate burrows in soft substrate such as sand banks.[9] Swallows in the genera Hirundo, Ptyonoproggne, Cecropis, Petrochelidon and Delichon build mud nests close to overhead shelter in locations that are protected from both the weather and predators. The mud-nesters are most common in the Old World, particularly Africa, whereas cavity-nesters are the rule in the New World. Mud nesting species in particular are limited in areas of high humidity, which causes the mud nests to crumble. Many cave, bank and cliff dwelling species of swallow nest in large colonies. Mud nests are constructed by both males and females, and amongst the tunnel diggers the excavation duties are shared as well. In historical times, the introduction of man-made stone structures such as barns and bridges, together with forest clearance, has led to an abundance of colony sites around the globe, significantly increasing the breeding ranges of some species. Birds living in large colonies typically have to contend with both ectoparasites and conspecific nest parasitism.[33][34] In barn swallows, old mated males and young unmated males benefit from colonial behaviour, whereas it is likely that females and mated young males benefit more from nesting by themselves.[35]

Pairs of mated swallows are monogamous,[36] and pairs of non-migratory species often stay near their breeding area all year, though the nest site is defended most vigorously during the breeding season. Migratory species often return to the same breeding area each year, and may select the same nest site if they were previously successful in that location. First-year breeders generally select a nesting site close to where they were born and raised.[37] The breeding of temperate species is seasonal, whereas that of subtropical or tropical species can either be continuous throughout the year or seasonal. Seasonal species in the subtropics or tropics are usually timed to coincide with the peaks in insect activity, which is usually the wet season, but some species like the white-bibbed swallow nest in the dry season to avoid flooding in their riverbank nesting habitat.[9] All swallows will defend their nests from egg predators, although solitary species are more aggressive towards predators than colonial species.[38] Overall the contribution of male swallows towards parental care is the highest of any passerine bird.[9]

A wire-tailed swallow feeding a recently fledged chick

Wire tailed swallow2 @kannur
Wire tailed swallow @kannur

The eggs of swallows tend to be white, although those of some mud-nesters are speckled. The average clutch size is around four to five eggs in temperate areas and two to three eggs in the tropics. The incubation duties are shared in some species, in others the eggs are incubated solely by the females. Amongst the species where the male helps with incubation the contribution varies amongst species, with some species like the cliff swallow sharing the duties equally and the female doing most of the work in others. Amongst the barn swallows the male of the American subspecies helps (to a small extent) whereas the European subspecies does not. Even in species where the male does not incubate the eggs the male may sit on them when the female is away to reduce heat loss (this is different from incubation as that involves warming the eggs, not just stopping heat loss). Incubation stints last for 5–15 minutes and are followed by bursts of feeding activity. From laying, swallow eggs take between 10–21 days to hatch, with 14–18 days being more typical.[9]

The chicks of swallows hatch naked, generally with only a few tufts of down. The eyes are closed and do not fully open for up to 10 days. The feathers take a few days to begin to sprout, and the chicks are brooded by the parents until they are able to thermoregulate. On the whole they develop slowly compared to other passerine birds. The parents do not usually feed the chicks individual insects but instead a bolus of food comprising ten to a hundred insects. Regardless of whether the species has males that incubate or brood the chicks, the males of all hirundines will help feed the chicks. It is difficult to judge when the young fledge, as they will be enticed out of the nest after three weeks by parents but frequently return to the nest afterwards in order to roost.[9]

Calls

Song of the purple martin.

Swallows are able to produce many different calls or songs, which are used to express excitement, to communicate with others of the same species, during courtship, or as an alarm when a predator is in the area. The songs of males are related to the body condition of the bird and are presumably used by females to judge the physical condition and suitability for mating of males.[39] Begging calls are used by the young when soliciting food from their parents. The typical song of swallows is a simple, sometimes musical twittering.

Status and conservation

Species of hirundine that are threatened with extinction are generally endangered due to habitat loss. This is presumed to be the reason behind the decline of the critically endangered white-eyed river martin, a species that is only known from a few specimens collected in Thailand. The species presumably breeds in riverbanks, a much diminished habitat in SE Asia. As the species hasn't been reliably seen since 1980 it may already be extinct.[40] Two insular species, the Bahama swallow and golden swallow, have declined due to forest loss and also competition with introduced species such as starlings and sparrows, which compete with these swallows for nesting sites. The golden swallow formerly bred on the island of Jamaica, but was last seen there in 1989 and is now restricted to the island of Hispaniola.[41]

Relationship with humans

Purple martin colony
An artificial purple martin nesting colony

Swallows are tolerated by humans because of their beneficial role as insect-eaters, and some species have readily adapted to nesting in and around human habitation. The barn swallow and house martin now rarely use natural sites. The purple martin is also actively encouraged by people to nest around humans and elaborate nest boxes are erected. Enough artificial nesting sites have been created that the purple martin now seldom nests in natural cavities in the eastern part of its range.[42]

Because of the long human experience with these conspicuous species, many myths and legends have arisen as a consequence, particularly relating to the barn swallow.[9] The Roman historian Pliny the Elder described a use of painted swallows to deliver a report of the winning horses at a race.[43] During the nineteenth century, Jean Desbouvrie attempted to tame swallows and train them for use as messenger birds, as an alternative to war pigeons. He succeeded in curbing the migratory instinct in young birds and persuaded the government of France to conduct initial testing, but further experimentation stalled.[43][44] Subsequent attempts to train homing behaviour into swallows and other passerines had difficulty establishing a statistically significant success rate, although the birds have been known to trap themselves repeatedly in order to obtain bait from traps.[43]

According to a sailing superstition, swallows are a good omen to those at sea. This probably arose from the fact that swallows are land-based birds, so their appearance informs a sailor that he is close to shore.[45] An old term of venery for swallows is a "flight" or "sweep".[46]

Species list

Video clip of European barn swallow in Lindisfarne, England
Wire-tailed Swallow (Hirundo smithii) W IMG 0540
Wire-tailed swallow, Hirundo smithii
Vogels door Jan van Oort (07)
Sand martin, Common house martin, Barn swallow
Barn Swallow (Randunica)
European Barn Swallow, seen in Romania

Family: Hirundinidae

References

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External links

American cliff swallow

The American cliff swallow (Petrochelidon pyrrhonota) is a member of the passerine bird family Hirundinidae, the swallows and martins. The scientific name is derived from Ancient Greek; Petrochelidon originates from the petros meaning "rock" and khelidon "swallow", pyrrhonota comes from purrhos meaning "flame-coloured" and -notos "-backed".American cliff swallows are extremely social song birds that can be found in large nesting colonies reaching over 2,000 nests. They are frequently seen flying overhead in large flocks during migration, gracefully foraging over fields for flying insects or perching tightly together on a wire preening under the sun.Cliff swallows build gourd-shaped nests made from mud with small entrance holes. They build their nests tightly together, on top of one another, under bridges or alongside mountain cliffs. Living in large populations, these aerial insectivores use extensive vocalizations to communicate warnings or food availability to the other individuals.

Andrew Swallow

Andrew Swallow (born 2 June 1987) is a former professional Australian rules footballer who played for the North Melbourne Football Club in the Australian Football League (AFL). He was the captain of North Melbourne from 2012 to 2016.

Barn swallow

The barn swallow (Hirundo rustica) is the most widespread species of swallow in the world. It is a distinctive passerine bird with blue upperparts and a long, deeply forked tail. It is found in Europe, Asia, Africa and the Americas. In Anglophone Europe it is just called the swallow; in Northern Europe it is the only common species called a "swallow" rather than a "martin".There are six subspecies of barn swallow, which breed across the Northern Hemisphere. Four are strongly migratory, and their wintering grounds cover much of the Southern Hemisphere as far south as central Argentina, the Cape Province of South Africa, and northern Australia. Its huge range means that the barn swallow is not endangered, although there may be local population declines due to specific threats.

The barn swallow is a bird of open country that normally uses man-made structures to breed and consequently has spread with human expansion. It builds a cup nest from mud pellets in barns or similar structures and feeds on insects caught in flight. This species lives in close association with humans, and its insect-eating habits mean that it is tolerated by humans; this acceptance was reinforced in the past by superstitions regarding the bird and its nest. There are frequent cultural references to the barn swallow in literary and religious works due to both its living in close proximity to humans and its annual migration. The barn swallow is the national bird of Estonia.

Common house martin

The common house martin (Delichon urbicum), sometimes called the northern house martin or, particularly in Europe, just house martin, is a migratory passerine bird of the swallow family which breeds in Europe, north Africa and temperate Asia; and winters in sub-Saharan Africa and tropical Asia. It feeds on insects which are caught in flight, and it migrates to climates where flying insects are plentiful. It has a blue head and upperparts, white rump and pure white underparts, and is found in both open country and near human habitation. It is similar in appearance to the two other martin species of the genus Delichon, which are both endemic to eastern and southern Asia. It has two accepted subspecies.

Both the scientific and colloquial name of the bird are related to its use of human-made structures. It builds a closed cup nest from mud pellets under eaves or similar locations on buildings usually in colonies.

It is hunted by the Eurasian hobby (Falco subbuteo), and like other birds is affected by internal parasites and external fleas and mites, although its large range and population mean that it is not threatened globally.

David Swallow

David Swallow (born 19 November 1992) is an Australian rules footballer playing for the Gold Coast Suns in the Australian Football League (AFL). Swallow won the Gold Coast Suns Club Champion award in 2014, becoming the second player to win the award after Gary Ablett Jr. won the award in the club's first three seasons. He received a nomination for the 2011 AFL Rising Star award in round 14 of the 2011 season. Swallow will serve as Gold Coast co-captain from the 2019 season.

Dysphagia

Dysphagia is difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, in some contexts it is classified as a condition in its own right. People with dysphagia are sometimes unaware of having it.It may be a sensation that suggests difficulty in the passage of solids or liquids from the mouth to the stomach, a lack of pharyngeal sensation or various other inadequacies of the swallowing mechanism. Dysphagia is distinguished from other symptoms including odynophagia, which is defined as painful swallowing, and globus, which is the sensation of a lump in the throat. A person can have dysphagia without odynophagia (dysfunction without pain), odynophagia without dysphagia (pain without dysfunction) or both together. A psychogenic dysphagia is known as phagophobia.

Ellen Swallow Richards

Ellen Henrietta Swallow Richards (December 3, 1842 – March 30, 1911) was an industrial and safety engineer, environmental chemist, and university faculty member in the United States during the 19th century. Her pioneering work in sanitary engineering, and experimental research in domestic science, laid a foundation for the new science of home economics. She was the founder of the home economics movement characterized by the application of science to the home, and the first to apply chemistry to the study of nutrition.Richards graduated from Westford Academy (second oldest secondary school in Massachusetts) in 1862. She was the first woman admitted to the Massachusetts Institute of Technology. She graduated in 1873 and later became its first female instructor. Mrs. Richards was the first woman in America accepted to any school of science and technology, and the first American woman to obtain a degree in chemistry, which she earned from Vassar College in 1870.Richards was a pragmatic feminist, as well as a founding ecofeminist, who believed that women's work within the home was a vital aspect of the economy.

Fellatio

Fellatio (also known as fellation, and in slang as blowjob, BJ, giving head, or sucking off) is an oral sex act involving the use of the mouth or throat, usually performed by a person on the penis of another person. If performed on oneself, the act is called autofellatio. Oral stimulation of the scrotum may also be termed fellatio, or colloquially as teabagging.Fellatio can be sexually arousing for both participants, and may lead to orgasm for the receiving partner. It may be performed by a sexual partner as foreplay before other sexual activities such as vaginal or anal intercourse, or as an erotic and physically intimate act of its own. Like most forms of sexual activity, oral sex creates a risk of contracting sexually transmitted infections (STIs/STDs); however, the risk is significantly lower than that of vaginal or anal sex, especially for HIV transmission.Most countries do not have laws banning the practice of oral sex, though some cultures may consider it taboo. People may also refuse to give or receive it due to negative feelings or sexual inhibitions. Commonly, people do not regard forms of oral sex as affecting the virginity of either partner, though opinions on the matter vary.

Monty Python and the Holy Grail

Monty Python and the Holy Grail is a 1975 British comedy film concerning the Arthurian legend, written and performed by the Monty Python comedy group of Graham Chapman, John Cleese, Terry Gilliam, Eric Idle, Terry Jones and Michael Palin, and directed by Gilliam and Jones. It was conceived during the hiatus between the third and fourth series of their BBC television series Monty Python's Flying Circus.

In contrast to the group's first film, And Now for Something Completely Different, a compilation of sketches from the first two television series, Holy Grail draws on new material, parodying the legend of King Arthur's quest for the Holy Grail. Thirty years later, Idle used the film as the basis for the musical Spamalot.

Monty Python and the Holy Grail grossed more than any British film exhibited in the US in 1975. In the US, it was selected as the second-best comedy of all time in the ABC special Best in Film: The Greatest Movies of Our Time. In the UK, readers of Total Film magazine ranked it the fifth-greatest comedy film of all time; a similar poll of Channel 4 viewers placed it sixth (2000).

Northern rough-winged swallow

The northern rough-winged swallow (Stelgidopteryx serripennis) is a small, migratory swallow. It is very similar to the southern rough-winged swallow, Stelgidopteryx ruficollis.

Outline of birds

The following outline is provided as an overview of and topical guide to birds:

Birds (class Aves) – winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich.

Purple martin

The purple martin (Progne subis) is the largest North American swallow. They are known for their speed and agility in flight, and when approaching their housing, will dive from the sky at great speeds with their wings tucked.

Red-rumped swallow

The red-rumped swallow (Cecropis daurica) is a small passerine bird in the swallow family. It breeds in open hilly country of temperate southern Europe and Asia from Portugal and Spain to Japan, India, Sri Lanka and tropical Africa. The Indian and African birds are resident, but European and other Asian birds are migratory. They winter in Africa or India and are vagrants to Christmas Island and northern Australia.

Red-rumped swallows are somewhat similar in habits and appearance to the other aerial insectivores, such as the related swallows and the unrelated swifts (order Apodiformes). They have blue upperparts and dusky underparts.

They resemble barn swallows, but are darker below and have pale or reddish rumps, face and neck collar. They lack a breast band, but have black undertails. They are fast fliers and they swoop on insects while airborne. They have broad but pointed wings.

Red-rumped swallows build quarter-sphere nests with a tunnel entrance lined with mud collected in their beaks, and lay 3 to 6 eggs. They normally nest under cliff overhangs in their mountain homes, but will readily adapt to buildings such as mosques and bridges.

They do not normally form large breeding colonies, but are gregarious outside the breeding season. Many hundreds can be seen at a time on the plains of India.

Sand martin

The sand martin (Riparia riparia) or European sand martin, bank swallow in the Americas, and collared sand martin in the Indian Subcontinent, is a migratory passerine bird in the swallow family. It has a wide range in summer, embracing practically the whole of Europe and the Mediterranean countries, part of northern Asia and also North America. It winters in eastern and southern Africa, South America and the Indian Subcontinent.

Sinkhole

A sinkhole, also known as a cenote, sink, sink-hole, swallet, swallow hole, or doline (the different terms for sinkholes are often used interchangeably), is a depression or hole in the ground caused by some form of collapse of the surface layer. Most are caused by karst processes – the chemical dissolution of carbonate rocks or suffosion processes. Sinkholes vary in size from 1 to 600 m (3.3 to 2,000 ft) both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may form gradually or suddenly, and are found worldwide.

Steve Swallow

Steve Swallow (born October 4, 1940) is a jazz bassist and composer noted for his collaborations with Jimmy Giuffre, Gary Burton, and Carla Bley. He was one of the first jazz double bassists to switch entirely to electric bass guitar.

Tailcoat

A tailcoat is a knee-length coat with the front of the skirt cut away, so as to leave only the rear section of the skirt, known as the tails.

The tailcoat shares its historical origins in clothes cut for convenient horse riding in the Early Modern era. Ever since the 18th century, however, tailcoats evolved into general forms of day and evening formal wear, in parallel to how the lounge suit succeeded the frock coat (19th century) and the justacorps (18th century).

Thus, in 21st-century Western dress codes for men, mainly two types of tailcoats have survived:

Dress coat, an evening wear with a squarely cut away front, worn for formal white tie

Morning coat (or cutaway in American English), a day wear with a gradually tapered front cut away, worn for formal morning dressIn colloquial language without further specification, "tailcoat" typically designates the former, that is the evening (1) dress coat for white tie.

Tree swallow

The tree swallow (Tachycineta bicolor) is a migratory bird of the family Hirundinidae. Found in the Americas, the tree swallow was first described in 1807 by French ornithologist Louis Vieillot as Hirundo bicolor. It has since been moved to its current genus, Tachycineta, within which its phylogenetic placement is debated. The tree swallow has glossy blue-green upperparts, with the exception of the blackish wings and tail, and white underparts. The bill is black, the eyes are dark brown, and the legs and feet are pale brown. The female is generally duller than the male, and the first-year female has mostly brown upperparts, with some blue feathers. Juveniles have brown upperparts, and a grey-brown-washed breast. The tree swallow breeds in the US and Canada. It winters along southern US coasts south, along the Gulf Coast, to Panama and the northwestern coast of South America, and in the West Indies.

The tree swallow nests either in isolated pairs or loose groups, in both natural and artificial cavities. Breeding can start as soon as early May, although this date is occurring earlier because of climate change, and it can end as late as July. This bird is generally socially monogamous (although about 8% of males are polygynous), with high levels of extra-pair paternity. This can benefit the male, but since the female controls copulation, the lack of resolution on how this behaviour benefits females makes the high level of extra-pair paternity puzzling. The female incubates the clutch of two to eight (but usually four to seven) pure white eggs, usually for 14 to 15 days. The chicks hatch slightly asynchronously, allowing for the female to prioritize which chicks to feed in times of food shortage. The chicks generally fledge about 18 to 22 days after hatching. The tree swallow is sometimes considered a model organism, due to the large amount of research done on it.

An aerial insectivore, the tree swallow forages both alone and in groups, eating mostly insects. Molluscs, spiders, and fruit are also found in the diet. The nestlings, like the adult, primarily eat insects, fed to it by both the male and the female. This swallow is vulnerable to parasites, but, when on nestlings, these do little damage. The effect of disease can become stronger as a tree swallow gets older, as some parts of the immune system decline with age. Acquired T cell-mediated immunity, for example, decreases with age, whereas both innate and acquired humoral immunity do not. Because of its large range and stable population, the tree swallow is considered to be least concern by the International Union for Conservation of Nature. In the US, it is protected by the Migratory Bird Treaty Act of 1918, and in Canada by the Migratory Birds Convention Act. This swallow is negatively affected by human activities, such as the clearing of forests; acidified lakes can force a breeding tree swallow to go long distances to find calcium-rich food items to feed to its chicks.

Upper gastrointestinal series

An upper gastrointestinal series, also called an upper gastrointestinal study or contrast radiography of the upper gastrointestinal tract, and often known as a barium meal, is a series of radiographs used to examine the gastrointestinal tract for abnormalities. A contrast medium, usually a radiocontrast agent such as barium sulfate mixed with water, is ingested or instilled into the gastrointestinal tract, and X-rays are used to create radiographs of the regions of interest. The barium enhances the visibility of the relevant parts of the gastrointestinal tract by coating the inside wall of the tract and appearing white on the film. This in combination with other plain radiographs allows for the imaging of parts of the upper gastrointestinal tract such as the pharynx, larynx, esophagus, stomach, and small intestine such that the inside wall lining, size, shape, contour, and patency are visible to the examiner. With fluoroscopy, it is also possible to visualize the functional movement of examined organs such as swallowing, peristalsis, or sphincter closure. Depending on the organs to be examined, barium radiographs can be classified into barium swallow, barium meal, barium follow-through, and enteroclysis (small bowel enema). To further enhance the quality of images, air or gas is sometimes introduced into the gastrointestinal tract in addition to barium, and this procedure is called double-contrast imaging. In this case the gas is referred to as the negative contrast medium. Traditionally the images produced with barium contrast are made with plain-film radiography, but computed tomography is also used in combination with barium contrast, in which case the procedure is called CT enterography.

Swallows (family: Hirundinidae)

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