Saturday, 14 February 2015

Tawny Frogmouths

The three Australian species of frogmouths (1), along with nightjars, the owlet nightjar and owls are strictly nocturnal, that is night active birds roosting by day and only becoming active after dark. The Tawny Frogmouth is possibly the most well known Australian night bird followed by the Southern Boobook and the Barn Owl.
Frogmouths and nightjars are not related to owls. On the taxonomic list of Australian birds (2) they are placed between pigeons and swifts and are probably most closely related to swifts. Owls are much further down the list coming well after raptors and after herons, ibis and spoonbills and before kingfishers. So frogmouths and nightjars evolved earlier than raptors and the more recently evolved owls.
Frogmouths derive their very apt name from their large bill and gape which when held wide open is very like the large mouth of frogs. In the past the Tawny was also called a Morepork or Mopoke, onomatopoeic names based mistakenly on the call of the Southern Boobook Owl. The Tawny Frogmouth’s common call is a “resonant, low, pulsing oom-oom-oom-oom, slow or rapid” (voice description taken from Pizzey and Knight).
The frogmouths and nightjars have evolved quite amazing camouflaged plumage, driven primarily by the need to remain undetected by predators during daylight hours when they are inactive and sleeping. In the case of the frogmouths their plumage matches the dead wood on which they mostly perch during the day. In addition to the colour match, frogmouths have developed another concealment strategy and that is to adopt an upright, bill pointing to the sky, dead limb pose. This pose is further enhanced by remaining very still, keeping the eyes closed to a slit and holding the feathers in close to the body to better resemble a tapering broken off branch. 
Note: enlarge photos with a left click of the mouse and then use the mouse wheel to scroll back and forth through the photos (can't view captions in this mode)
A male and female Tawny Frogmouth pair roosting together in a redgum woodland in mid July at the start of the breeding season.
Roosting together is a sign they are going to breed. At other times they roost alone.
The female has a brown shoulder and the male on left is striking the classic dead limb pose.
A pair perched together is a good sign that they are bonding ahead of breeding, which normally takes place between July and December – the two above were photographed on the 19th of July 2012, the start of the breeding season. Of course perching together tends to reduce the effectiveness of their dead limb disguise; I guess the need to procreate over-rules self interest, as any human parent knows.
Pair photographed at Tenterfield NSW on a very cold July morning. Their feathers are fluffed up for extra insulation. Again an adult pair roosting together at the start of the breeding season.
Very cold conditions are also a reason to over-rule the dead limb pose with feathers fluffed up for extra insulation as the birds in the photo above show. They were photographed at Tenterfield, NSW, which is high in the Great Dividing Range just south of the Queensland border. These two birds are roosting together in mid July, the start of the breeding season.

This bird was photographed just after dark at our campsite on Kilcowera Station located between the Hungerford – Thargomindah road and Currawinya National Park in remote outback Queensland. Even though it was a warm night the bird has fluffed up its feathers, as the dead limb pose is not required at night.
A pair roosting together in mid February well after the end of the July to December
breeding season.
A closer view of the pair in the photo above.
This pair were photographed in a redgum woodland near Eagle Point on the 9th of February 2015 well after the end of the breeding season when adult birds would not normally be roosting together.
Roosting pair from above photo taken from the opposite side in sunlight.
Downy feathers are visible on the right hand bird in this enlarged/cropped image.
On closer inspection of this cropped image of the two birds photographed from the opposite side, with a little sunlight on them, it became obvious that the bird in front, or on the right, still has some downy feathers showing through the plumage, indicating that this is a juvenile bird. Also the open eye is another pointer to a young inexperienced bird. An adult would look through a slit and would not open its eye and give away its disguise. So I conclude that the pair are sibling young which might explain why they are roosting together. Further evidence for this was the presence of two other birds roosting separately on nearby branches in the same tree. These are assumed to be the adult parent birds.
Adult bird roosting alone on a nearby branch in the same tree as the two young birds.
I think this is the all grey male.
The other adult bird roosting alone in same tree.
The hint of brown on side of face suggests this is the female.
Along with many other Australians who know the Tawny Frogmouth, I share a soft spot for these amazingly adapted birds of the night.
(1) The three Australian frogmouth species are: Tawny, Marbled and Papuan. The Tawny is widespread across Australia whereas the Papuan is restricted to Cape York Peninsula down to around Cairns and the Marbled has a population near the top of Cape York and another in North East NSW and South East Qld.
(2) The taxonomic list of birds (Christidas and Boles 2008) is arranged in descending order starting at the top with the Emu and Cassowary, our oldest or earliest evolved bird species and ending with finches as the most recently evolved species.

1 comment:

  1. G’day JH,
    Another informative piece, wonderfully illustrated.
    I don’t think anyone, birder or not, could not like a ‘froggie’. They are beneficial, striking and frequently accommodating birds.