Thursday, 17 December 2009

Golden plover paper

A scientific paper, based on my work on golden plover in the Outer Hebrides in Scotland, has been published in Ringing & Migration 2009, 24, 253-258.

Counts of spring passage Golden Plover Pluvialis apricaria in north Lewis

The rich lowland grasslands of Lewis in the Outer Hebrides are used as foraging grounds by many thousands of golden plover in spring. The more boldly marked birds within these flocks are believed to be of the northern altifrons form which breeds in Iceland, and the Lewis grasslands are possibly very important for theses birds which stop there to feed before flying across the Atlantic Ocean.

A flock of golden plover of the altifrons type, feed in Lewis grassland. Some of the birds have very bold black and white plumage, probably males, while the less well marked birds are probably females.

A male Golden Plover of the southern apricaria form, which was breeding on the nearby moorland in Lewis. He is typically less boldly marked than the males seen on passage in the grasslands, as above.

Tuesday, 15 December 2009

Goshawks fledging

The brown goshawks which nest in the same woods as the tawny frogmouths are busy feeding fledglings now. They have had mixed fortune in their success, with one pair rearing three chicks, one with two, another with one and one pair failed to rear any. Prey remains below the nests included several young rabbits, two magpie fledglings and a galah.

An adult male brown goshawk calls in alarm as I approached his nest with young.

A female brown goshawk flies past me screaming in alarm. She is larger than the male and can be seen to be moulting tail and primary feathers.

Two fledglings stand on branches next to their nest while another has stayed in the nest.
The nest is typically set in a clump of mistletoe high in a tall yellow box tree.

Monday, 14 December 2009

Tawny Frogmouth study - 11

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

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.

Monday, 16 November 2009

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.

Thursday, 12 November 2009

Tawny Frogmouth study - 9

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.

Monday, 9 November 2009

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.

Sunday, 1 November 2009

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.

Sunday, 18 October 2009

Tawny frogmouth study - 7

The first tawny frogmouth chicks hatched about two weeks ago and it is only now that they can be seen as they have become too large for the bird to cover completely all the time as they wriggle around in the nest. The male bird broods them all day, drooping his wings over them. This hides their white down from the roving eyes of predators, such as currawongs, and protects them from excessive heat from the sun, or the cool wind and rain - which there has been much of in Canberra since they hatched.

Tawny frogmouth study - 6

Tawny frogmouths occasionally nest in the old nests of other species. Here a pair have used an old clay nest built by white-winged choughs. The nest is set about half way along a branch 12m up in a yellow box tree overhanging a gully.

Saturday, 26 September 2009

Tawny Frogmouth study - 5

While the male birds sit on the nests during the day, the females roost on a nearby perch. Whenever a predator or person approaches they stretch into their cryptic pose. This bird is only half in this pose as she was familiar with me and the photograph was taken with a 400m lens from a distance far enough for her to consider me as only a possible threat.
Tawny frogmouths are so well adapted to concealment in the trees. Here, the bird sits on a dead limb, which they almost invariably do, and the dashes on the grey feathers of her belly match the pattern of the dead wood. The feathers on her back, the coverts on her wings and her scapulars all resemble the flecks of peeling bark on the trunk of the tree which she is sitting close up against. Her eyebrows droop like strips of bark and all the time she keeps her eyelids closed, yet still watching from behind them, through tiny gaps in the not quite straight fitting closure.We might not see them but they are always watching us as we pass by unaware of their presence.

Tawny Frogmouth study - 4

Most nests are set in a horizontal fork of a tree branch, however some are craftily set on the end of broken limbs, such as this one. As he sits relaxed, the bird is difficult to discern from the branch, but when the bird sits in its concealment pose, with head erect and the bristles above his bill spread, he so resembles the broken end of the branch.

Tawny Frogmouth study - 3

Twenty of the pairs I am monitoring now have eggs and the males are incubating all day every day for approximately a month until the first eggs hatch. They mostly lay two eggs, but can lay one or three. The eggs are pure white, about ping-pong ball size, and as they are white they need to be covered all day to prevent magpies, ravens or currawongs taking them. The birds usually sit in a relaxed pose, but when a potential predator – like me with a camera – approaches they slip into their broken branch pose and blend into the form and colour of the tree.

Wednesday, 23 September 2009

Tawny Frogmouth study - 2

These birds are incredibly difficult to find.

They are nocturnal birds and roost all day relying on their cryptic plumage and motionless posture for defence from predators. Here a pair roost inconspicuously, the female who is slightly smaller and has a touch of red/brown in her feathers, sits nearer to the main stem of the tree.

Tawny Frogmouth study

It is Spring in Canberra and the birds are nesting. For the past few years I have been studying tawny frogmouths; plotting their distribution and following their breeding success.

This pair have begun a nest high on a branch about fifty metres away. Once an egg is laid the male will incubate it and keep it covered all day, while the female roosts on this or another nearby perch.