VOL.18 (3) SEPTEMBER 1999 Noisy Flight of Rufous 121

Noisy Flight and Other Observations of the Rufous Owl rufa in the Northern Territory

The Rufous Owl Ninox rufa is a large owl, occurring in northern and north-eastern and through the lowlands of (Schodde & Mason 1980). The flight of is generally described as silent (Welty 1975, Schodde & Mason 1980). Noisy flight in owls has not been described previously, and little is known about the behaviour of the Rufous Owl other than some calls and postures used to advertise or display (Higgins 1999). While surveying owls in the Northern Territory for sound-recording purposes, I have noticed Rufous Owls engaged in aggressive and noisy flight when agitated. Owls of the genus Ninox tend to be territorially aggressive and I have often mimicked their calls, usually for several minutes, to see if any owls responded, thus indicating that a territory was occupied in the area. Most observations were of an opportunistic nature and only once did I visit the same area on two successive nights, to collect additional sounds. Noisy flight of the Rufous Owl was first heard on 15 July 1984 at Acacia Gap, when I mimicked the Owl's call. Subsequently, this behaviour was also recorded on 22 and 28 July 1984 at the Reynolds River, on 6 August 1984 at UDP (Gunlom) Falls, May 1985 at Umbrawarra Gorge, and April 1987 at the Alligator River crossing. In discussions with colleagues of noisy flight of the Rufous Owl, it was suggested that the noise might have been fruit-bats in flight. On 18 April1987 at the Alligator River crossing on the old Jim Jim road, in company with T. Hertog, I called up a pair of Rufous Owls and recorded beyond doubt that the noisy flight was made by an agitated Rufous Owl. Both observers heard the Owl's noisy flight as both flew overhead about 30 seconds apart, but it was not recorded which made the noisy flight. In August 1992, in company with L. Moad, I called up a pair of Rufous Owls at a patch of monsoon forest near the Daly River. The Owls responded within a minute of hearing the mimicked calls. One individual, particularly, was highly agitated and very aggressive, landing heavily on branches with its wings drooping in similar fashion to a diurnal raptor mantling a kill, as described by Hollands (1991) and Higgins (1999) for various owls. The bird was calling and constantly looking around for the intruder. Initially the calls were a soft deep growl, almost inaudible, after which it began to hoot, softly at first but gradually increasing in volume. The call, although soft, could be heard some distance away (refer Buckingham & Jackson 1990 and Higgins 1999). The bird was presumed to be male by its large size and call, which was a double note. Female calls are either single or double notes (Hollands 1991) and are higher in pitch (Schodde & Mason 1980). At no time did the smaller bird participate in the aggressive display, but it was observed taking a small bat in flight before leaving the area. On several occasions when the birds disappeared, mimicked calls resulted in a noisy flight response. The noisy fight was reminiscent of a fruit-bat or the swooshing flight of a duck. At the time few fruit-bats were present, thus allowing positive identification of the wing-noise. Hollands (1991) described the flight-feathers of the Rufous Owl as stiffer and lacking the velvety surface of those of other owls, thus implying that in flight some wing-noise may be produced. The Rufous Owl's flight is normally silent, and noisy flight was not observed during any other activity by the Owls. This type of AUS1RAUAN 122 VAN GESSEL BIRD WATCHER aggressive flight behaviour might be a deterrent to other conspecifics. Aggressive response to playback of tape-recorded calls of Rufous Owls was also reported by Hollands (1991) and Schodde & Mason (1980), but these authors did not mention noisy flight. I found that playback of tape-recorded calls was of limited use, as usually only one or two different calls have been pre-recorded on tape, with the Owls responding to each in a different way. Noisy flight may not have been documented previ"usly because the higher nocturnal noise level in North precludes hearing this flight response. Aggressive flight of the Barking Owl N. connivens and N. strenua seems mostly silent. However, the latter also responds with crash-landings to playback of calls (G. Campers. comm. ), and wing-noise was heard when Powerful Owls were attracted to playback sites where they crash-landed aggressively with drooping wings (S. Debus pers. comm. ). Barking Owls also behave aggressively towards playback or mimicry in their territory, and personal observations suggest that females are the first to respond, sometimes with drooping wings (see also Debus 1997). Calls of female Powerful and Barking Owls are also consistently higher in pitch than those of males (Schodde & Mason 1980, Hollands 1991, Higgins 1999). For instance, in August 1992 at Fogg Dam, I and several observers called up a pair of Barking Owls in daylight; the female appeared the more aggressive, and called at a higher pitch. All these large Ninox owls, including the Rufous, vigorously defend their nests (Hollands 1991, Higgins 1999). In the Northern Territory Rufous Owls occupy small patches of monsoon and riverine forest, mostly near watercourses. Personal observations, supported by other observers (T. Hertog pers. comm. ), suggest that they are probably more abundant than published data indicate. Rufous Owls have been observed regularly in the Botanical Gardens and Holmes Jungle Swamp around Darwin. Nielsen (1995) and Kanowski (1998) also suggested that the species is probably more abundant in north-eastern Queensland than previously considered. Likewise, the Powerful Owl is now known to be more common than previously believed (Higgins 1999 and references therein). Rufous and Powerful Owls tend to roost low in trees, often only 3-4 m high (pers. obs. ). In the Northern Territory, the Rufous Owl often prefers to roost over water (pers. obs.; T. Hertog pers. comm. ). In north-eastern Queensland it prefers to roost high in trees (Schodde & Mason 1980), but also uses low roosts (Hollands 1991). Wherever Rufous Owls were found roosting in the Northern Territory, there were large numbers of Little Red Pteropus scapulatus and Black Flying-foxes P. alecto, which were taken as prey by the Owls (pers. obs.; T. Hertog pers. comm.). Estbergs & Braithwaite (1985) concluded that flying-foxes make up a small proportion of the important prey species, but their data only covered one area from May to September. They suggested that flying-foxes were probably more important during the latter part of the dry season. In Queensland flying-foxes are common in the Rufous Owls' diet (Schodde & Mason 1980, Nielsen 1995), as is the case for the Powerful Owl (Higgins 1999). When disturbed while roosting, Rufous Owls flew to the top of the tree canopy. Often, the first indications of their presence were the alarm calls of Sulphur-crested Cockatoos Cacatua galerita, Spangled Drongos Dicrurus bracteatus or Silver­ crowned FriarbirdsPhi/emon argenticeps (also Schodde & Mason 1980, Hollands 1991). VOL. 18 (3) Nocturnal Feeding SEPTEMBER 1999 by White-faced Heron 123

I thank T. Hertog, J. Hardy and two referees for comments on a draft, helpful suggestions, and additional references.

References Buckingham, R. & Jackson, L. (1990), A Field Guide to Australian Bird Song, cassette 5, Bird Observers Club of Aust., Melbourne. Debus, S.J.S. (1997), 'Vocal behaviour of the Southern Boobook Ninox novaeseelandiae and other nocturnal birds', in Czechura, G. & Debus, S. (Eds), Australian Raptor Studies II, 71-85, Birds Australia Monograph 3, Birds Australia, Melbourne. Estbergs, J .A. & Braithwaite, R. W. ( 1985), 'The diet of the Rufous Owl Ninox mfa near Cooinda in the Northern Territory', Emu 85, 202-205. Higgins, P. (Ed.) (1999), Handbook ofAustralian, New Zealand and Antarctic Birds, val. 4, Oxford University Press, Melbourne. Hollands, D. (1991), Birds of the Night, Reed, Sydney. Kanowski, J. (1998), 'The abundance of the Rufous Owl Ninox mfa in upland and highland of north-east Queensland', Emu 98, 58-61. Nielsen, L. (1995), 'Notes on the Rufous Owl in North Queensland', Sunbird 25, 71-72. Schodde, R. & Mason, I.J. (1980), Nocturnal Birds ofAustralia, Lansdowne, Melbourne. Welty, J.C. (1975), The Life of Birds, Saunders, Philadelphia. By F.WC. van GESSEL 64 Dorothy Avenue, Woy Woy, NS. W 2257 Received 28 January 1999 •

Nocturnal feeding by a White-faced Heron

On 11 July 1992, we observed a single White-faced HeronEgretta novaehollandiae feeding at night on the edge of the Murray River at Morgan, South Australia. Plumes on its upperparts, which were obvious against its folded wings, indicated that the bird was an adult (Marchant & Higgins 1990). The area in which the bird was foraging was lit by a floodlight, and the Heron and its behaviour were easily observed. We watched the Heron for 45 minutes, from 2245 to 2330 h. It was foraging in shallow water along a sandy stretch of the riverbank, with a gently sloping grassed bank behind it. The bottom could be seen to a depth of about 30cm. The Heron stood in the water for the entire period of our observation, within 3-4m of a cluster of pylons in the water, and about 100m from the Morgan Ferry, which was in operation and made several crossings during our observation. Other than following a successful strike, the Heron faced the centre of the river, with the floodlight behind it. Its shadow was cast into the river. For most of the time, about 40 minutes, the Heron stood 1-1.5 m from shore, in water that covered the belly, tail, wing-tips and the lower edge of the folded wings, remaining stationary and alert, with its neck fully extended, or nearly so, and moving its head from side to side. For a few minutes, it retracted its neck, though it was still alert and moving its head to and fro.