Sunda Frogmouth
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The Sunda frogmouth (''Batrachostomus cornutus'') is a medium-sized, old world species of bird within the order Podargiformes. It is also uncommonly referred to as the long-tailed frogmouth or the horned frogmouth. The term "Sunda" is based on the geographical range of the species to regions around the
Sunda islands The Sunda Islands (; Tetun: ''Illa Sunda'') are a group of islands in the Indonesian Archipelago. They consist of the Greater Sunda Islands and the Lesser Sunda Islands. Etymology "Sunda" denotes the continental shelves or landmasses: the Sun ...
. The genus name, '' Batrachostomus,'' is a
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
translation to ‘frogmouth’, which comes from the wide shape of the bill and slight gape. The species name ''cornutus'' is a
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
word translated to "having horns", referring to the tufts of feathers on the head.


Taxonomy

The Sunda frogmouth is found within the clade
Strisores Strisores ( ), sometimes called nightbirds, is a clade of birds that includes the living family (biology), families and order (biology), orders Caprimulgidae (nightjars, nighthawks and allies), Nyctibiidae (potoos), Steatornithidae (oilbirds), P ...
, which refers to nightbirds. It was previously grouped with order
Caprimulgiformes Nightjars are medium-sized nocturnal or crepuscular birds in the family Caprimulgidae and order Caprimulgiformes, characterised by long wings, short legs, and very short bills. They are sometimes called bugeaters, their primary source of food ...
which has a long history of classifications under different taxa. Hartert in 1892 classified
Caprimulgiformes Nightjars are medium-sized nocturnal or crepuscular birds in the family Caprimulgidae and order Caprimulgiformes, characterised by long wings, short legs, and very short bills. They are sometimes called bugeaters, their primary source of food ...
with Picariae which at the time included
hoopoe Hoopoes () are colourful birds found across Africa, Asia, and Europe, notable for their distinctive "Crest (feathers), crown" of feathers which can be raised or lowered at will. Two living and one extinct species are recognized, though for many y ...
s,
hummingbird Hummingbirds are birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With approximately 366 species and 113 genus, genera, they occur from Alaska to Tierra del Fuego, but most species are found in Cen ...
s and swifts. Frogmouths were then classified with
Coraciiformes The Coraciiformes are a group of usually colourful birds including the kingfishers, the bee-eaters, the rollers, the motmots, and the todies. They generally have syndactyly, with three forward-pointing toes (and toes 3 & 4 fused at their b ...
by Gadow in 1892 and Sharpe in 1900 which included owls, swifts, hummingbirds, trogons, and rolers. The most recent classification of Caprimulgiformes were within Strigiformes (owls) by Sibley and Ahlquist in 1990. In the early 2000s, Caprimulgiformes were separated from Strigiformes due to advancements in
DNA sequencing DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, thymine, cytosine, and guanine. The ...
. The phylogenetic analysis using N-acetyltransferase gene supported the idea that adaptations to
nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...
activity is a result of
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
. As of 2020, frogmouths are found within the order Podargiformes. This was first suggested by Gregory Mathews in 1918. The recent reasoning was that Podargidae diverged between long before other Caprimulgiformes, forming their own
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
separate from the nightjars and oilbirds. The family Podargidae contains 17 species of frogmouth under three genuses: '' Batrachostomus'', '' Podargus'' and '' Rigidipenna''. The genus ''Batrachostomus'' includes 10 species of frogmouths. It has been questioned whether it should be its own family due to mitochondrial genomics of Podargidae. There is a closer sister-taxa relationship between the Australia and New Guinea species of frogmouth from the '' Podargus'' family, than the Asian frogmouths ('' Bratrachostomus'') due to the Oligocene divergence of '' Batrachostomus'' across Wallace's Line. The Sunda frogmouth was first described by Temminck in 1822 in Recueil d’Oiseaux under '' B. javenensis''. The Sunda frogmouth was originally a subspecies of the Javan frogmouth, as were many other '' Batrachostomus''. In 1978, combined field studies of vocalizations and museum specimens were able to separate ''B. cornutus'' and label it as its own species. The two subspecies of ''Batrachostomus cornutus'', ''Batrachostomus cornutus cornutus'' and ''Batrachostomus cornutus longicaudatus'', were originally identified as such due to geographical range. ''B. c. cornutus'' was the specimen identified by Temminck in 1822, and ''B. c. longicaudatus'' was identified by Hoogerwerf in 1962. In 2021, Eaton et al. speculated that ''B.c. longicaudatus'' is more closely related to '' B. javenensis'', due to proximity in geographical location and lack of vocalization data, at the time. In June 2023, two ''B.c. longicaudatus'' were recorded on the Kangean islands finding them undifferentiated from the Sunda frogmouth, and therefore different from the Javan frogmouth.


Description


Head and body

''Batrachostomus cornutus'' is a medium-sized bird, with an average size of 25 to 28 cm. It is thought to have owl-like characteristics, due to its stocky body and stubby legs. The stocky look of this bird is because of its reduced leg length is due to small and weak tarsi. Frogmouths typically have anisodactylus feet, with the
hallux Toes are the digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plantigrade''; ...
behind and 3 toes in the front. When gripping a tree branch, the Sunda frogmouth can splay the side toes to be semizygodactylus. A characterizing feature of the Sunda frogmouth are the well-developed, stiff facial bristles. Th
semi-bristles
are dark and slender, and make tufts around the ear as ‘auricular plumes’. Rictal bristles are present around the gape. Although the function of the bristles is unknown, the best hypothesis is that they serve a tactile function for feeding, whether it be feeding young in the dark or scooping insects. The frogmouth gets its name from its wide and arched bill. The upper mandbile is dark whereas the lower mandible is more yellow. The rounded bill is thought to be used to catch prey in flight. The slit like nostrils are found at the base of the bill and are protected by an operculum surrounded by rictal bristles. The palate is covered with a hard keratinized layer of epidermis known as the rhamphotheca. Frogmouths have a desmognathous palate, meaning the maxillopalatine bones are fused. Frogmouths as well as other nocturnal birds have large eyes with poor colour recognition since the eye has more rods and less cones. The size of the eyes help capture more light, as some is still required for hunting. Frogmouths have similar visual adaptations to owls, where they have a well developed wulst, the region associated with visual and sensory processing. However, frogmouths may have better diurnal vision than owls due to oil droplets found in the cone cells that allow the eye to focus on light by adding an additional spectral filter.


Coloration

The Sunda frogmouth is a mostly brown bird. The concealing coloration blends the frogmouth with its environment and the tree branches where it roosts. There are two main colour morphs; black and white, and brown and buff. Both morphs follow the same pattern. The brown and buff morph is characterized by a more reddish/brown coloration with lighter brown and yellow speckling and streaking. The upper parts and wing coverts, as well as the underparts are mostly brown with speckles of yellow, white and black. They become paler and streaked with brown on the belly and flanks. The
scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...
rs are marked with white ovals. They have a white collar around the back of the neck and broad white
supercilium The supercilium is a plumage feature found on the heads of some bird species. It is a stripe which runs from the base of the bird's beak above its eye, finishing somewhere towards the rear of the bird's head.Dunn and Alderfer (2006), p. 10 Also k ...
. There are no white marks on the wings and tail. The reddish brown coloration of the brown and buff morph is a darker, almost black colour in the black and white morph. The yellow and lighter brown speckles and streaks are white. Individual coloration will vary based on the amount of speckling. A black and white morph could appear brown and buff due to the amount of speckling. The females are brighter and plainer than the males with a more buff coloration and smaller white spots on the scapulars. The underparts of the female are less speckled. The immature Sunda frogmouth looks similar to the adult, but has a paler, more red coloration with less streaking. The ''B. c. cornutus'' subspecies is bolder than the ''B. c. longicaudatus''. ''B. c. longicaudatus'' has less contrasting plumage with less white, and a longer tail, and narrower bill.


Plumage

The young Sunda frogmouth is covered in down. There are two successive downy plumages, which characterizes more primitive birds. The first down is much shorter than the second down. The second down occurs on the 7th day and the juvenile plumage comes in around 3 to 4 weeks. This plumage is a softer and looser texture with more pointed primary feathers. Within a few weeks of fledging, the first adult plumage comes in. The frogmouth has one
moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...
per year. The Sunda frogmouth has a round tail with a centrifugal moult, meaning it moults from the inside out. The wings are characterized by a serial descendant moult, where the
moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...
has many centers commencing at the same time proceeding in the same direction.


Similar species

The Sunda frogmouth is similar to the Javan frogmouth, the Sumatran frogmouth, the Bornean frogmouth, and the Blyth's frogmouth. * Javan frogmouth: smaller, males are less distinctly brown or black below * Sumatran frogmouth: smaller, more heavily spotted white underparts, males are more red and pale * Bornean frogmouth: smaller, males are paler, females have less white spotted underparts * Blyth's frogmouth: more white plumage


Habitat and distribution

The Sunda frogmouth is found from southwestern
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
and
Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...
through
South-East Asia Southeast Asia is the geographical southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Australian mainland, which is part of Oceania. Southeast Asia i ...
to
Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...
,
Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...
,
Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
and
Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
. B. c. ''cornutus'' is found in
Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
, the Indonesian islands Bangka and
Belitung Belitung (Belitung Malay: ''Belitong'', formerly Billiton) is an island on the east coast of Sumatra, Indonesia in the Java Sea. It covers (including offshore islands such as Mendanau Island), and had a population of 309,097 at the 2020 Cen ...
, as well as Banggi island and
Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...
. B.c. longicaudatus is restricted to the Kangean islands. Its natural
habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
s are
subtropical or tropical moist lowland forest Tropical and subtropical moist broadleaf forests (TSMF), also known as tropical moist forest, is a subtropical and tropical forest habitat type defined by the World Wide Fund for Nature (WWF). Description TSMF is generally found in large ...
, subtropical or tropical
mangrove forest Mangrove forests, also called mangrove swamps, mangrove thickets or mangals, are productive wetlands that occur in coastal intertidal zones. Mangrove forests grow mainly at tropical and subtropical latitudes because mangrove trees cannot withsta ...
, and subtropical or tropical moist
montane forest Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures lapse rate, fall as elevation increases, causing the ecosystem to stratify. This stratification is ...
. Unlike other frogmouths, ''B. cornutus'' prefers secondary growth forests, as well as the edges of lowland forests. Frogmouths are
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...
and are found in trees and sometimes bushes, as is the case of many populations in Sumatra which have been found roosting in shrubs along rivers.


Behavior


Nocturnal

The Sunda frogmouth, like other birds in the clade Strisores, are
nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...
. Frogmouths feed on insects, which are most active at night. It will hunt in the
crepuscular In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal (active during dawn), vespertine (biology), vespertine/vespertinal (active during dusk), or both. This is distinguished from diurnalit ...
hours where there is faint light to see the prey. During the day, frogmouths roost on low branches in denser forest to avoid predators.


Hunting and diet

As mentioned, frogmouths feed on insects. To hunt, it will search the area beneath the branch for prey, often using its hearing. When spotted, it will fly from perch to perch to catch insects in the air. This is also referred to as sallying or hawking. A frogmouth will catch more prey in one flight in fields, than in
woodland A woodland () is, in the broad sense, land covered with woody plants (trees and shrubs), or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunli ...
s. To hunt quietly, frogmouths have larger tails in relation to their body size. As well, the
trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 1997. ...
of the tail feathers are frayed. Different frogmouth species can cohabitate in the same ecosystem, such as the Bornean lowland forest, due to a difference in body size, and therefore prey size. Since Podargidae do not use their claws like owls, prey size depends on what they can carry in their bill.


Breeding

The Sunda frogmouth differs from species in the genus '' Podargus'' because of its small, tiny nests made from down, bark, cobwebs, moss, and lichen. The nest is only about 7 by 6 cm with a 1 cm depression to hold the egg. The adult frogmouth will hide the nest while incubating the egg. Females will incubate the nest at night, and males will incubate the nest during the day. The nest is formed on trees, saplings and shrubs, with a tendency to favour rotting wood with peeling bark. There is usually only one whitish, elliptical egg per nest. There is usually a single
clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...
and brood every year, however if the
clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...
is lost early on, the frogmouth will lay a replacement one. The suspected breeding seasons vary with different populations of Sunda frogmouths with the constant remaining that spring and summer re for growth as that is when insects are largest. The
Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
populations are suspected to breed in May–July, the
Belitung Belitung (Belitung Malay: ''Belitong'', formerly Billiton) is an island on the east coast of Sumatra, Indonesia in the Java Sea. It covers (including offshore islands such as Mendanau Island), and had a population of 309,097 at the 2020 Cen ...
populations in April–June and the
Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...
populations in January–April. To protect the chicks, adults may pick up the young and fly away with them between their legs. As well, they will assume an alarm posture: closed eyes, neck and head stretched upwards, feathers compressed into body, motionless. If this fails, frogmouths will perform a defence display by spreading its wings and tail, fluffing its
plumage Plumage () is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, there can b ...
whilst making a circular motion with its head and hissing. In rare cases, the frogmouth will perform a distraction display by flapping a stretched out wing to mimic an injury.


Other behaviors


Vocalizations

The analysis of sonograms is the best way to identify frogmouth species. The calls make a "gwaa" noise. The females will make the main territorial call. The other main vocalization from frogmouths is hissing during defence behavior.


Heat regulation

The main method of heat regulation from frogmouths is panting, rather than gular fluttering. The mouth is opened, the throat area is lowered, the wings are slightly spread, and the body feathers are compressed. This has been most studied in the
tawny frogmouth The tawny frogmouth (''Podargus strigoides'') is a species of frogmouth native to the Australian mainland and Tasmania and found throughout. It is a big-headed, stocky bird often mistaken for an owl due to its nocturnal habits and similar colouri ...
, but is thought to occur in all frogmouth species.


Waterproofing

Frogmouths will take fat from powderdowns and distribute it amongst feathers to increase their waterproofing ability. The Sunda frogmouth has two large powderdowns on each side of its rump with 50 short plumose feathers that continuously exude fat.


Conservation

The Sunda frogmouth population does not appear to be declining. A study on the birds of Kangean Island in 2024 noted the presence of ''B.c. longicaudatus'' in a selectively logged site in 2023, where the habitat is characterized by a dense understory and minimal large trees. As well, the mangroves that cover the perimeter of the Kangean islands are resistant to human exploitation and seem to host a significant amount of ''B.c. longicaudatus''. The Sunda frogmouth is listed as least concern as per the IUCN red list.


External links


IUCN redlist

Cornell Lab

Xeno canto recordings


References

{{Taxonbar, from=Q1264388 Batrachostomus Birds of Sumatra Birds of Borneo Birds described in 1822 Taxonomy articles created by Polbot