Notes on Vocal Behaviour and Breeding of the Plumed Frogmouth Podargus Ocellatus Plumiferus by G.R
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AUSTRALIAN 192 BIRD WATCHER AUSTRALIAN BIRD WATCHER 1997, 17, 192-197 Notes on Vocal Behaviour and Breeding of the Plumed Frogmouth Podargus ocellatus plumiferus by G.R. BERULDSEN, 47 Broadmoor Street, Kenmore Hills, Queensland 4069 Summary Nocturnal field observations were conducted on the Plumed Frogmouth Podargus ace/latus plumiferus over September-December 1996 in subtropical rainforest of the D' Aguilar Range near Brisbane, Queensland, at times with the aid of playback of tape-recorded calls. The Frogmouth sometimes responded silently to playback, by approaching the source of broadcast calls. Plumed Frogmouths appeared to start calling later in the evening than did some other nocturnal birds. The Tawny Frogmouth P. strigoides sometimes occurred in rainforest and appeared to react aggressively towards the Plumed Frogmouth. An occupied nest of the Plumed Frogmouth was located on 28 October, in the fork of a rainforest sapling, and regularly observed until the single nestling fledged at the end of November or the beginning of December. The parent brooding by day was apparently the male, both sexes visited the nest at night during the nestling phase, and the nestling period lasted at least 31 days. Introduction Little has been recorded on the breeding of the Marbled Frogmouth Podargus ocellatus, and then mostly on the northern subspecies P.o. marmoratus of Cape York Peninsula (Schodde & Mason 1980, Hollands 1991). Data are limited to a few records of nest site and construction, laying season, clutch size, brood size and description of downy young. Furthermore, from data on sexual dimorphism, parental roles and rufous morphs in females of the Marbled and other frogmouths (Schodde & Mason 1980), it is apparent that Hollands (1991) incorrectly assigned gender to the adult frogmouths he was observing at nests (all species) and hence his information on sex roles is questionable (see Debus 1992). The supposed breeding record of Welsh (1933) for the southern subspecies, Plumed Frogmouth P.o. plumiferus, has been referred to the Tawny Frogmouth P. strigoides (Schodde & Mason 1980). Therefore, the only information on breeding of the Plumed Frogmouth concerns a nestling found in a creek late in the year (Fleay 1981), indicating laying in spring and a creekside nest site within subtropical rainforest. Britton (1990) listed a report by I. Tarrant of a pair of Plumed Frogmouths 'nesting' in July, but no further details or observations of that event have been published. The Marbled Frogmouth has three principal and well-known calls: the koo-loo, the gobble or 'laugh/bill-clap', and the rapid drumming or 'Cane Toad' call (e.g. Schodde & Mason 1980, Hollands 1991, Corben & Roberts 1993). Response of the Marbled Frogmouth to playback of tape-recorded calls has been described by Hollands (1991), who found that in the breeding season the birds always replied. Similarly, Corben & Roberts (1993) found that playback elicits a response. Their list of negative locations, where no response was detected, was taken as implying the bird's absence from those survey sites. Meggs (1993) described calling behaviour and response to playback, noted that the birds call at any time of the night, and found that some false negatives proved positive on a second survey at those sites. The Tawny Frogmouth sometimes occurs in rainforest (Corben & Roberts 1993), particularly along roads and tracks (Debus 1992), although the latter may partly reflect observer bias. As well as misidentifications and consequent false records of Marbled Frogmouths, occurrences of the Tawny Frogmouth in rainforest could result in interactions between the two species. VOL. 17 (4) DECEMBER 1997 Vocal Behaviour and Breeding of Plumed Frogmouth 193 This paper describes a breeding record of the Plumed Frogmouth, its calling behaviour and response to playback, and interactions with the Tawny Frogmouth. Study area and methods Observations were conducted in the subtropical rainforest of the D 'Aguilar Range near Brisbane, Queensland, from September to December 1996 with the aid of tape-recordings made of both subspecies of Marbled Frogmouth. The present study was preceded by familiarity with the northern subspecies on Cape York Peninsula, including nocturnal observations, tape-recording and playback of its calls (e.g. Beruldsen 1993). When an active nest of the Plumed Frogmouth was discovered in late October 1996, regular day and night observations were conducted, sometimes with Erina Beruldsen (hereafter EB), until early December when the fledgling could no longer be located. Night observations generally terminated around 2100-2130 h. Plumed Frogmouth territories were located by listening and using playback from ridges and gullies, and plotting the calling centres of simultaneously calling neighbouring pairs by triangulating from different points, taking account of sexual differences in the kooloo and gobble calls. For instance, close and distant calling birds at the junction of three gullies, in different directions, were investigated by forays up and down the gullies, noting from various points whether calling birds were upstream or down. However, no attempt was made to plot territory boundaries. Field identification The Marbled Frogmouth has a reputation for being difficult, if not impossible, to distinguish from the Tawny Frogmouth by morphological criteria in the field. This reputation rests largely on inexperienced observers relying on plumage characters, and consequently mistaking immature or rufous morph Tawny for Marbled. However, the difficulty is overstated as the two species differ substantially in build: Tawny is bulky, with massive head and bill and rather short, ragged tail; Marbled is slender, with finer head and bill and long, sometimes forked tail (e.g. Fleay 1981 , Hollands 1991). Consequently, their silhouettes differ (visibly so even at night). Furthermore, the underparts of the Tawny Frogmouth are streaked whereas those of the Marbled Frogmouth are marbled, distinguishably so in good views by day or when illuminated at night. The Marbled Frogmouth occasionally utters a soft oom-oom... call somewhat like that of the Tawny Frogmouth (Beruldsen 1993). With experience, they are distinguishable on quality: the normal droning oom-oom... call of the Tawny Frogmouth differs from the equivalent Marbled Frogmouth call by being louder and more resonant, whereas that of the Marbled is inaudible beyond 10-20 m. These morphological and vocal differences were used to identify the respective species in the following account of interactions between Plumed and Tawny Frogmouths. Ultimately, the most important criteria for distinguishing the two species were the kooloo and gobble calls of the Plumed Frogmouth. Vocal behaviour Response to conspecific calls My experience of the response by this species to playback is that although a response can be obtained throughout the year, a vocal response in a known area cannot always be expected. There were occasions when I played the tape in a known territory without eliciting any vocal response, only then to find, with the aid of a spotlight, a Marbled Frogmouth sitting quietly on a branch overhead, apparently having been attracted by the playing of the taped call. Even when a call was played with the bird under observation by spotlight, the only response was a movement of the head toward the source of the call. On other occasions, including on Cape York Peninsula but especially with the Plumed subspecies in south-eastern Queensland, I have found that calling did not commence until 1.5- 2 hours after sunset, often an hour or more after Southern Boobooks Ninox novaeseelandiae or Sooty Owls Tyto tenebricosa started calling. Likewise, I found a corresponding reluctance by the Plumed Frogmouth to answer playback until that hour. I frequently found that I could not elicit any vocal response to playback, of any of the three principal calls of the bird, for instance in October, until 1930-2000 h. AUSTRALIAN 194 BERULDSEN BIRD WATCHER Interactions with Tawny Frogmouth Through September and October 1996 I spent about 80 night hours in the forest of the D' Aguilar Range, listening to the calls of the Plumed Frogmouth and locating territories. Tawny Frogmouths occasionally appeared in some of the territories, despite the habitat being closed-canopy rainforest up to 0.5 km from the nearest roadways or eucalypt forest. Plumed Frogmouths sometimes responded, as described below, to the presence of a Tawny Frogmouth within a territory. On the afternoon of 28 September, I located a Tawny Frogmouth (with heavily streaked underparts, no marbling) perched in the forest within a known territory of a pair of Plumed Frogmouths. After dark that evening the droning oom-oom ... calls of a Tawny Frogmouth could be heard in the gully close to where the perched bird had been seen that afternoon. No Plumed Frogmouths were heard to call that evening, at least until I left around 2100 h. The Tawny Frogmouth was then still calling. Despite playing a tape that night of three of the Plumed Frogmouth's calls (kooloo, gobble and 'toad' call), no vocal response from any Plumed Frogmouth was detected, notwithstanding frequent calling by the birds in the same area on the previous night. The weather was similar on both evenings, clear and still with the moon almost full. Between 30 September and 24 October Plumed Frogmouths called each night that I visited (about 10 nights, every second or third night), but no further Tawny Frogmouth calls were heard. On the night of 26 October Plumed Frogmouths commenced calling (kooloo and gobble), but only occasionally, shortly after 1930 h. By 2000 h the birds were calling frequently from five different locations, all clearly audible from where I was listening. At about 2010 hI played a taped Plumed Frogmouth call (gobble) and immediately a frogmouth approached and landed, the silhouette being clearly visible against the sky. It then called from directly overhead, with the typical gobble of the Plumed Frogmouth. Some minutes later a Tawny Frogmouth gave a droning oom-oom... call nearby, whereupon all the Plumed Frogmouths became silent (possibly as a response to the Tawny Frogmouth).