Blyth's frogmouth

Blyth’s frogmouth (Batrachostomus affinis) is a species of bird in the family Podargidae. They are brownish or rufescent brown with a slightly round bill and tail, and have tufts of bristles in front of the eyes and at the base of the bill. Batrachostomus occur from India and Sri Lanka, across mainland southeast Asia and as far as Borneo, Java, and Sumatra. More specifically, the Blyth’s frogmouths are scattered between southeastern Myanmar and Indonesia. Like other frogmouth species, they are insectivorous.

Blyth’s frogmouth is a small to medium species that measures between 20 and 23 centimeters in length. B. a. continentalis weighs about 46.0 grams. The birds are brownish or rufescent brown and lack white markings on wings and tail, however, the female is usually browner and more plain than males. The underparts are generally orange-brown or yellowish-brown with some whitish spots. The feathers of the shoulder region have fewer white oval shaped spots. They have a very thin white line around their neck that looks like a small collar. Males tend to have heavier black markings on their upper and underparts, and they are said to have a cryptic plumage. Like the other frogmouth species, Blyth’s has well developed stiff facial bristles and longer black or dark-coloured ones that cover the ears called “auricular plumes”. Their function is still unknown. Juveniles have a soft-textured plumage and differ from the adult males by their coloration that has more rufous tones, and their upperparts have more dark barring and no spot. Their underparts are similar to adult females, but are duller. They also have narrow black bars on many feathers of the throat and breast. Little information exists about molts, but observations of active wing molt in Peninsular Malaysia have been made in July, September, and October. Others have observed individuals that had not replaced their feathers by January–March and in November. The molting sequence is still largely unknown even though the pattern is often asymmetrical.

Blyth’s frogmouth has a tail length of 95-111 millimeters for males and 90-107 millimeters for females. Like other Batrachostomus species, the Blyth’s frogmouth has a large tail compared to its body size, which helps for maneuverability. The trailing edges of the flight and tail feathers allow it to fly silently when hunting.

Batrachostomus frogmouths have small jaws and short, wide, and rounded bills. The size of the bill seems adapted for taking prey in flight. Slit-looking nostrils can be found at its base and are protected by an operculum, which is a lid-like structure that can open and close to protect the nares. Frogmouths have short and weak feet with unequal toes (i.e., one toe backward and the other three forward). Side toes have the ability to splay out at a 90 degrees angle, which provides the birds with a better grip. The legs and feet are either brown, pink-brown, slightly pink, or more white. The Blyth’s frogmouth has pale yellow or lemon-yellow irises.

Small frogmouths are all physically similar, which makes it hard to differentiate the Blyth’s frogmouth from other species. Its vocalizations and the geographical distribution can help identify it.

Gould’s frogmouth (B. stellatus): In some parts of Thailand, Blyth’s is the only frogmouth, but there might be some overlap between B. a. continentalis and the Gould’s frogmouth in the southern part of the country. In Peninsular Malaysia, both species overlap more extensively, but B. a. continentalis can be distinguished by its smaller bill. B. a. affinis wing feathers have less white spots than the Gould’s frogmouth and they also have very little overlap.

Hodgson’s frogmouth (B. hodgsoni): Generally larger, darker, and more spotted than B. a. continentalis.

Bornean frogmouth (B. mixtus): Less heavily spotted than B. a. affinis.

Sumatran frogmouth (B. poliolophus): Underparts are more spotted than B. a. affinis.

Sunda frogmouth (B. cornutus): Larger, darker, and more heavily marked underparts than B. a. affinis.

Blyth’s frogmouth, like other genera in the family, tends to look like owls (Strigidae), but differs from them by its lack of strong claws on the toes.

A study from 2015 also confirmed that the species Masillapodargus longpipes is a similar frogmouth in the order Podargiformes. New fossil evidence from the early Eocene German fossil site Messel confirmed its classification.