Food Piracy by Dusky Woodswallows 143
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VOL. 15 (3) SEPTEMBER 1993 ROBINSON: Food Piracy by Dusky Woodswallows 143 Food Piracy by Dusky Woodswallows Whilst bird-watching in Grey Box Eucalyptus microcarpa woodland near Benalla, Victoria, on 24 January 1992, I observed a Dusky Woodswallow Artamus cyanopterus successfully stealing prey from several smaller birds. Between 1900 and 1923 h, the woodswallow launched four attacks on foraging Yellow-rumped Thornbills Acanthiza chrysorrhoa and one attack on a Striated Pardalote Pardalotus striatus. During the same time period, it only made two foraging manoeuvres of its own accord. The woodswallow alternated perches between two 5 m high dead trees in a large grassy clearing and a low stump. From these perches, it appeared to monitor the activities of thornbills foraging on the ground nearby. On two occasions when thornbills obtained a prey item, the woodswallow flew directly at the successful bird and chased it a short way; both thornbills then dropped their prey, the woodswallow caught the prey item mid-flight and flew to a perch beyond the clearing to consume it. On the third occasion the woodswallow again flew at a thornbill, but the thornbill instead ate the prey. On the fourth occasion, a thornbill displaced a prey item which the woodswallow swooped on first, the thornbill flying a short distance away. The foraging action of the Striated Pardalote was not recorded, but the woodswallow was seen to swoop on the pardalote (which was perched on a low stump) and catch the released prey. The woodswallow flew off, with the pardalote in pursuit, and subsequently consumed the prey. In every instance, the prey appeared to be a small moth (c. 15 mm long). Since these observations, Dusky Woodswallows have twice been seen flying at Jacky Winters Microeca leucophaea and once at a Southern Whiteface Aphelocephala leucopsis to make these individuals release their prey. On every occasion, the woodswallow was successful and flew off with the re-captured prey. Food piracy has been well documented for birds such as skuas, gulls and some birds of prey (Brockmann & Barnard 1979; Campbell & Lack 1985). It has not been recorded for many passerine species (Brockmann & Barnard 1979), and does not appear to have been recorded previously for any species ofwoodswallow (Blakers et al. 1984; Barker & Vestjens 1990; H. Ford, H. Recher, S. Debus pers. comms). Although interspecific aggression has been recorded among a range of birds in Australia, it has usually been interpreted in the sense of competing species, or honeyeaters defending a localised food source (Dow 1977; Paton 1980; Loyn et al. 1983; Robinson in press). These few observations of aggression by the woodswallow suggest that some interspecific acts of aggression may also represent acts of piracy. But, after all, the seizure of nectar sources or psyllid infestations by aggressive honeyeaters (e.g. Dow 1977; Ford 1981; Loyn et al. 1983) might simply be considered as piracy on a grander scale. My thanks to Hugh Ford, Harry Recher and Stephen Debus for comments on the manuscript. References Barker, R.D. & Vestjens, W.J.M. (1990), The Food ofAustrolian Birds, 2. Passerines, CSIRO, Melbourne. Blakers, M. , Davies, S.J.J.F. & Reilly, P.N. (1984), The Atlas ofAustralian Birds, Melbourne University Press, Melbourne. Brockmann, H.J. & Barnard, C.J. (1979), 'Kieptoparasitism in birds', Anim. Behav. 27, 487-514. Campbell, B. & Lack, E. (Eds) (1985), A Dictionary of Birds, T. & A.D. Poyser, Calton. Dow, D. D. (1977), 'Indiscriminate interspecific aggression leading to almost sole occupancy of space by a single species of bird', Emu 77, 115-121. AUSTRALIAN 144 GRIFFITHS & HOLYOAK BIRD WATCHER Ford, H.A. (1981), 'Territorial behaviour in an Australian nectar-feeding bird', Aust. J. Ecol. 6, 131-134. Loyn, R.H., Runnalls, R.G., Forward, G.Y. & Tyers, J. (1983), 'Territorial Bell Miners and other birds affecting populations of insect prey', Science 221, 14II-1413. Paton, D.C. (1980) , 'The importance of manna, honeydew and lerp in the diets of honeyeaters', Emu 80, 213-226. Robinson, D. (in press), 'Interspecific aggressive behaviour between robins and other insectivorous birds in eucalypt forest', Corella 17. By DOUG ROBINSON, 28 Bath Street, Mornington, Victoria 3931 Received 5 March 1992 • .