Owlet nightjars

I do not like full-flash photographs of night animals as that is not how I see them or remember my experiences with them. So here is a shot of an owlet nightjar as it emerged from its roost just as the last light was fading away. They can be found by listening for calls which they give as they prepare to leave their hollows. Then when they fly off they really take on spectral form as they slip silently through the trees.

I have been out on a few evenings/nights recently watching owlet nightjars. These are not owls, nightjars or frogmouths, but are in a family of their own. Taxonomists still debate where they fit.

Wherever they fit, they resemble owls with their large almost forward-facing eyes and their habit of nesting and roosting in tree hollows. Their bodies are similar to the slender true nightjars, but their feet and legs are stronger, enabling them to sit across branches and climb in and out of holes. And their wide bills with side-bristles also resemble nightjars, or perhaps swifts and some claim these are their closest relatives.

My interest in them comes from their main habitat - woodland, which they share with frogmouths. Both species live in the same woods and seem to forage in similar styles by pouncing on prey from a lookout perch, or rummaging around in the leaf litter. Do they successfully co-habit because they eat different prey, differentiated mainly by size? I would like to know. One advantage the owlet nightjars have over the frogmouths is that they can expand their range beyond woodland and live in man-made hollows or in rock crevices. As frogmouths rely on their camouflage for safety when roosting during the day, they need trees (see earlier postings).

Sparrowhawk in the garden


This morning, while sitting reading on the veranda, I heard a chorus of alarm calls from the garden birds. So I went over and straight away found a male collared sparrowhawk sitting in the tree above the drinking pool I have built for the birds. In the photograph below he was right in the centre of the thick green foliage.




He was quite undisturbed by me, simply continuing to scan around with those big yellow eyes, watching the small birds which were still alarm-calling from the nearby bushes.




I never see sparrowhawks in the garden during the breeding season, yet every year they turn up to hunt around the drinking pool, feeding station and the chicken shed where sparrows are always present, scavenging for split corn. The sparrowhawks come into the garden from now, mid-summer, to late winter, and I have seen adult and young birds of both sexes hunting the same area at different times, sometimes in the same day.

The bird shown here is moulting new feathers to his tail. The two outer feathers are still short - less than half the full length and appear here as short dark and grey, not protruding farther than the wing feathers. Two fully-grown new tail feathers lie in the centre of the tail, and appear here fresh and bright with distinct barring and firm bottom edges. The feathers either side of these two are old, as seen by their faded colouring, indistinct barring and frayed bottom edges.

The conventional method of distinguishing collared sparrowhawks from the closely related and similarly plumaged brown goshawk, is to class the tail as rounded or square edged at the tip. If square it is a sparrowhawk, round a goshawk. Here, while the bird is in moult it is not such an obvious plumage characteristic, although the more sharply square edges of the two ingrowing outer feathers hint at a more typical shape soon to form. The species also differ in size, goshawks being the larger - about the size of a Eurasian sparrowhawk. This male was obviously a sparrowhawk by his small size. A large female goshawk would be equally obvious as such by her large size. Most ambiguity occurs between the male goshawk and female sparrowhawk which can be similar in size.


Another feature I like about this male was the way his breast feathers were all ruffled, not neat and tidy as usually portrayed in illustrations. A real bird!

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.

www.bto.org/ringing/rmj/rmj-24-4.htm

Counts of spring passage Golden Plover Pluvialis apricaria in north Lewis
S. RAE, G. JONES, F. STEWART & R. TINGAY


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.

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.

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.