Tawny Frogmouth

Appearance

Tawny frogmouths are large, big-headed birds that can measure from 34 to 53 cm long. Weights have been recorded up to 680 g in the wild, but these are exceptionally high. In the nominate race, 55 males were found to weigh a mean of 354 g, while 39 females weighed a mean of 297 g, with a range between both of 157 to 555 g. Among the subspecies "P. s. brachypterus", 20 unsexed birds were found to average 278 g with a range of 185 to 416 g. In "P. s. phalaenoides", a weight range of 205 to 364 g was reported. Thus, in terms of average if not maximal body mass, the tawny is a bit smaller than its relative, the Papuan frogmouth. Tawny frogmouths are stocky and compact with rounded wings and short legs. They have wide, heavy, olive-grey to blackish bills that are hooked at the tip and topped with distinctive tufts of bristles. Their eyes are large, yellow, and frontally placed, a trait shared by owls.

Tawny frogmouths have three distinct colour morphs, grey being the most common in both sexes. Males of this morph have silver-grey upperparts with black streaks and slightly paler underparts with white barring and brown to rufous mottling. Females of this morph are often darker with more rufous mottling. Females of the subspecies "P. s. strigoides" have a chestnut morph and females of the subspecies "P. s. phalaenoides" have a rufous morph. Leucistic or albinistic all-white aberrant plumage for this species has been documented.

Distribution

Tawny frogmouths are found throughout most of the Australian mainland except in far western Queensland, the central Northern Territory, and most of the Nullabor Plain. In Tasmania, they are common throughout the northern and eastern parts of the state.

They can be found in almost any habitat type, including forests and woodlands, scrub and heathland vegetation, and savannahs. However, they are rarely seen in heavy rainforests and treeless deserts. They are seen in large numbers in areas populated with many river gums and casuarinas, and can be found along river courses if these areas are timbered. Tawny frogmouths are common in suburbs, having adapted to human presence. They have been reported nesting in parks and gardens with trees.

Status

The conservation status of tawny frogmouths is "least concern" due to their widespread distribution. However, a number of ongoing threats to the health of the population are known. Many bird and mammalian carnivores are known to prey upon the tawny frogmouth. Native birds, including ravens, butcherbirds, and currawongs, may attempt or steal the protein-rich eggs to feed their own young. Birds of prey such as hobbies and falcons, as well as rodents and tree-climbing snakes also cause major damage to the clutches by taking eggs and nestlings. In subtropical areas where food is available throughout the year, tawny frogmouths sometimes start brooding earlier in winter to avoid the awakening of snakes after hibernation. Since 1998, a cluster of cases of neurological disease has occurred in tawny frogmouths in the Sydney area, caused by the parasite "Angiostrongylus cantonensis", a rat lungworm.

Habitat

Tawny frogmouths are found throughout most of the Australian mainland except in far western Queensland, the central Northern Territory, and most of the Nullabor Plain. In Tasmania, they are common throughout the northern and eastern parts of the state.

They can be found in almost any habitat type, including forests and woodlands, scrub and heathland vegetation, and savannahs. However, they are rarely seen in heavy rainforests and treeless deserts. They are seen in large numbers in areas populated with many river gums and casuarinas, and can be found along river courses if these areas are timbered. Tawny frogmouths are common in suburbs, having adapted to human presence. They have been reported nesting in parks and gardens with trees.

Reproduction

Tawny frogmouths form partnerships for life, and once established, pairs usually stay in the same territory for a decade or more. Establishing and maintaining physical contact is an integral part of their lifelong bond. During breeding season, pairs roost closely together on the same branch, often with their bodies touching. The male carries out grooming by gently stroking through the plumage of the female with his beak in sessions that can last for 10 minutes or more.

The breeding season of tawny frogmouths is from August to December, but individuals in arid areas are known to breed in response to heavy rains. Males and females both share in the building of nests by collecting twigs and mouthfuls of leaves and dropping them into position. Nests are usually placed on horizontal, forked tree branches and can reach up to 30 cm in diameter. Loose sticks are piled together, and leaf litter and grass stems are placed to soften the centre. The nests are very fragile and can disintegrate easily.

The clutch size of the tawny frogmouth is one to three eggs. Both sexes share incubation of the eggs during the night, whilst during the day, males incubate the eggs. For the duration of the incubation period, the nest is rarely left unattended. One partner roosts on a nearby branch and provides food for the brooding partner. Once hatched, both parents cooperate in the supply of food to the young. The fledging period of the tawny frogmouth is 25 – 35 days, during which they develop half their adult mass.

Food

Tawny frogmouths are carnivorous and are considered to be among Australia's most effective pest-control birds, as their diet consists largely of species regarded as vermin or pests in houses, farms, and gardens. The bulk of their diet is composed of large nocturnal insects, such as moths, as well as spiders, worms, slugs, and snails but also includes a variety of bugs, beetles, wasps, ants, centipedes, millipedes, and scorpions. Large numbers of invertebrates are consumed to make up sufficient biomass. Small mammals, reptiles, frogs and birds are also eaten.

During daylight hours, healthy tawny frogmouths generally do not actively look for food, though they may sit with their mouths open, snapping them shut when an insect enters. As dusk approaches, they begin actively searching for food. Tawny frogmouths feed mainly by pouncing from a tree or other elevated perch to take large insects or small vertebrates from the ground using their beaks with great precision. Some smaller prey, such as moths, can be caught in flight. Foraging flights consist of short, snatching flights to foliage, branches, or into the air.

Tawny frogmouths do not consume prey collected on the ground or in flight on the spot unless it is very small. The captured prey is held in the tip of the beak and taken to a nearby branch, where it is then processed. Insects are generally pulped at the rim of the beak before being swallowed, and larger prey such as lizards or mice are generally killed before consumption by being bashed against a branch with great force.

Predators

The conservation status of tawny frogmouths is "least concern" due to their widespread distribution. However, a number of ongoing threats to the health of the population are known. Many bird and mammalian carnivores are known to prey upon the tawny frogmouth. Native birds, including ravens, butcherbirds, and currawongs, may attempt or steal the protein-rich eggs to feed their own young. Birds of prey such as hobbies and falcons, as well as rodents and tree-climbing snakes also cause major damage to the clutches by taking eggs and nestlings. In subtropical areas where food is available throughout the year, tawny frogmouths sometimes start brooding earlier in winter to avoid the awakening of snakes after hibernation. Since 1998, a cluster of cases of neurological disease has occurred in tawny frogmouths in the Sydney area, caused by the parasite "Angiostrongylus cantonensis", a rat lungworm.