Tawny Frogmouth study - 11

A scientific paper based on my studies of Tawny Frogmouths has been published in: Emu, 2009, 109, 327–330

www.publish.csiro.au/journals/emu

Comparisons between nesting densities of Tawny Frogmouths (Podargus strigoides) in open- and closed-canopy woodlands

Stuart Rae

I mapped and measured the distances between the nests of contiguous breeding pairs of frogmouths in woods in the Australian Capital Territory. There were three types of woodland: partly cleared grassy woodland, open-canopy grassy woodland and closed-canopy dry sclerophyll forest. Although the nests were regularly spaced in all three sites, they were at different densities. The highest density of nesting birds was 0.05 nests ha–1 in partly cleared woodland; there were 0.02 nests ha–1 in the open-canopy woodland and 0.006 nests ha–1 in closed-canopy forest. This is the first survey of this type of these birds, and it is planned that a long term study will monitor the breeding birds over the years to test for any effects of habitat or climate changes on their densities and productivity.

Close-canopy dry sclerophyll forest, with tall grasses and small shrubs as ground cover on poor, thin gravelly soils.




Open-canopy grassy woodland, with richer soils and short grass ground cover - grazed by grey kangaroos.



Part-cleared grassy woodland with numerous wide glades between the trees, and similar richer soils and grazed grasses as in the open canopy grassy-woodland. This habitat seems to offer richer food sources, and perhaps the frogmouths' prey is more easily found and caught there as the birds tend to hunt over open ground from perches.

Tawny Frogmouth study - 10

This nest site on the end of a broken branch is a bit cramped for an adult and two large chicks. However, the birds still succeed in maintaining their inconspicuousness.

These chicks are almost old enough to fledge, although they have not yet spontaneously adopted the concealment pose - like their father - upon the approach of a possible predator.

This fledgling has adopted the full concealment pose, mimicking its parent to form a branch-like profile as they sit motionless while observed. Once they sense that there is no longer any danger they will slowly shift around to perch across the branch and relax into a more conventional perched-bird pose.

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These chicks show their 'frogmouths' very well as they stretch and fidget about on their nest. Their very precarious nest. These are simple platforms of twigs laid across a fork in a horizontal branch, with a sprinkling of gum leaves for a lining to hold the eggs safely. By this stage, the platforms are falling apart. Time to leave.


Little bandits - at this age the chicks have a dark band of feathers across their eyes. This works well in breaking up the outline of their light grey fluffy down, although not so well with their big yellow eyes wide open.

Bird-banding at the Weddin Mtns, NSW.



Over the weekend I was at the Weddin Mountains assisting with a long-term study of birds in the area. John Rawsthorne was organising the trip this time and Richard Allen who has been running the study for many years now was also there.

Several of us camped for the weekend and caught birds in mist nets set in the woodland at the base of the hills. Once caught we banded them so that they can be individually identified when caught in later years.

Here a dusky woodswallow is being fitted with a band.


Once banded, the birds were all measured and if possible their sex and age established from such features as their plumage colouring or size. Here the length of a woodswallow's head and bill are being measured very precisely.


One of the more abundant birds at the site were rufous whistlers, especially adult females like the one shown below.

Much of the land is still dry following the recent drought. Although the vegetation had grown well this spring after the rains, many birds were still not breeding. The bird on the left below is an adult brown-headed honey-eater, that on the right is a juvenile. Note the colour differences and the young bird's yellow gape. These birds are co-operative breeders - they live in extended family groups where they all help to rear the chicks. As can be seen, these are small birds, yet some of those which we caught had been banded several years ago. One bird was more than ten years old and another more than 14. Many Australian bird species seem to have adopted a strategy of long life and not necessarily breeding every year - unlike, for example, many northern European species which have short lives and breed every year. The former life-plan has perhaps evolved as an efficient method for maintaining a population through periods of drought.


Often, when a male bird cannot find a mate, he will sing all day long trying to attract one to his territory. This hooded robin was doing this, his whistle sounding to me much like that of a green woodpecker.


One of our party was Bill Mannan, visiting from Arizona where he studies Coopers Hawks. Here he is with a male collared sparrowhawk which we caught.

Tawny Frogmouth study - 8

The frogmouth chicks are quite large now, although they are slow-growing. Most are about four weeks old and ready to leave the nest.

These chicks are typically lying quietly in the nest while the adult male keeps watch from farther along the branch.

The chicks are still partly downy and can only fly short distances. This chick has flown to the next branch from its nest, where its sibling was still with the male. The female meanwhile stands guard over this fledgling.

Two days after leaving the nest this chick was about seventy metres from the nest. Although they can be regarded as fledglings at this stage because they have left the nest. They are still much smaller than the adult birds and weak fliers. They are more aptly described as branchers.

Their tails are still short and wing feathers rather stumpy. The bristle feathers on their forehead have developed well though, and these help to conceal them when they instinctively adopt their head-erect concealment pose.