145 AUSTRALIAN FIELD ORNITHOLOGY 2008, 25 , 145–148 Diet of an Eastern Barn javanica on the Patho Plains, Northern Victoria

JAMES A. FITZSIMONS 1,2, DEANNA MARSHALL 3 and A.B. ROSE4 1School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125 (Email: [email protected]) 2The Nature Conservancy, Suite 3.04, 60 Leicester Street, Carlton, Victoria 3053 3Department of Sustainability and Environment, Box 3100, Bendigo, Victoria 3554 4Associate, Australian Museum, 6 College Street, Sydney, New South Wales 2010 (Present address: 61 Boundary Street, Forster, New South Wales 2428)

Summary A small sample of Eastern Tyto javanica pellets, from native on the Patho Plains in northern Victoria in February 2007, contained the remains of 48 prey individuals: 38 Australian Plague Locusts Chortoicetes terminifera , nine House Mice Mus domesticus and one Fat-tailed Dunnart Sminthopsis crassicaudata. Such a high proportion of locusts in the Eastern Barn Owl’s diet is noteworthy, and is discussed in the context of recent locust-spraying operations in the region.

Introduction The Eastern Barn Owl Tyto javanica is an opportunistic predator, although it preys mostly on small mammals (Higgins 1999). It is considered the best-studied owl in in terms of its diet (Debus et al . 2004). In Victoria, previous studies of its diet have been undertaken at Werribee (Morton 1975; Baker-Gabb 1984, 1985) and Snake Island (McNabb et al . 2005). No dietary studies have been undertaken for this species in northern Victoria, although Hutton & Brickhill (1985) analysed the Owl’s diet in the New South Wales Riverina. Bennett et al . (1998) considered the Eastern Barn Owl widespread but uncommon on the Victorian Northern Plains; however, it is regularly recorded around the Patho Plains (M. Antos pers. comm.; D. Marshall pers. obs.).

Study area and methods Four pellets characteristic of the Eastern Barn Owl (by their size and ‘glazed’ coating) were collected late in February 2007 at the hollow base of a single large old Grey Box Eucalyptus microcarpa within a previously cropped paddock of Northern Plains (36°05 aS, 144°18 aE), directly to the north of the grassland section of the Terrick Terrick National Park. An Eastern Barn Owl feather was also located at the base of this tree. The age of the pellets was unknown. Pellets were analysed by ABR, and the minimum numbers of individual prey items determined, by counting skeletal parts, specifically lower jaws for mammals and mandibles for , and by comparison with reference material.

Results The four pellets contained the remains of 48 prey individuals, comprising 38 Australian Plague Locusts Chortoicetes terminifera , nine House Mice Mus domesticus and one Fat-tailed Dunnart Sminthopsis crassicaudata (Table 1). Most AUSTRALIAN 146 FITZSIMONS, MARSHALL & ROSE FIELD ORNITHOLOGY

Table 1 Prey individuals in Eastern Barn Owl pellets at Terrick Terrick, northern Victoria.

Pellet no. Size (mm) No. prey individuals House Mouse Australian Plague Locust Fat-tailed Dunnart

1 40 × 32 6 0 0 2 45 × 25 1 12 0 3 55 × 26 1 22 0 4 36 × 26 1 4 1 Total 9 38 1 of the House Mice were not adult. Locust eggs were also found in all but one of the pellets, but were not included in the number of prey individuals as they were from gravid female locusts. As a proportion of biomass, House Mice represented 81.8%, Australian Plague Locusts 10.2% and Fat-tailed Dunnart 8.0% (assuming mean prey weights of 17 g for House Mouse, 15 g for Fat-tailed Dunnart and 0.5 g for Australian Plague Locust: Edge & Casimir 1975; Strahan 1995).

Discussion Previous studies of the Eastern Barn Owl’s diet in Australia, and of the wider Barn Owl complex (formerly Tyto alba ) internationally, have found that this superspecies preys mostly on small mammals (del Hoyo et al . 1999; Higgins 1999). Many studies in Australia have found the House Mouse to be the predominant (and sometimes exclusive) prey item of the Eastern Barn Owl, by number and by biomass (e.g. Morton 1975; Baker-Gabb 1984; Rose 1996; Palmer 2001; Debus & Rose 2004; Debus et al . 2004). Fat-tailed Dunnarts have been found in many analyses of Eastern Barn Owl diet (Morton 1975; Morton et al . 1977; Baker-Gabb 1984, 1985; Rose 1996; Debus et al . 2004, 2008). These dunnarts are considered ‘near threatened’ in Victoria (DSE 2007), but are relatively common in the grasslands of the Terrick Terrick National Park and other Northern Plains grasslands (Hadden 2002; Michael et al . 2003). Although the sample size was small, the proportion of locusts in the diet of Eastern Barn in this instance (79% of prey individuals) was higher than for other studies in Australia. Most studies have recorded only the presence of insects in low numbers or not at all. Although Morton et al . (1977) found 67 Australian Plague Locusts in 137 pellets at Sandringham Station in south-western Queensland in 1970 and ‘some orthopteran remains’ in 156 pellets from the same site in 1969, these represented only a small proportion of total prey individuals. Dickman et al . (1991) found ‘large tettigoniid orthopterans’ (katydids) in eight of 13 pellets containing material (out of a total of 151 pellets) in Western Australia. In Victoria, Morton (1975) recorded only a few insects and no orthopterans in the diet of Eastern Barn Owls at Werribee, whereas Baker-Gabb (1984, 1985) found orthopterans (species not specified) to represent 7% of the diet by prey individuals (11 in autumn, one in winter) in the same location. In the New South Wales Riverina, large irruptions of Eastern Barn Owls have been recorded, but these Owls were preying primarily on House Mice (Hutton & Brickhill 1985). VOL. 25 (3) SEPTEMBER 2008 Diet of Barn Owl in Northern Victoria 147

Szabo et al . (2003) noted that Eastern Barn Owls do occasionally capitalise on swarms of locusts, but despite the extensive literature on the Owl in Australia and internationally, very few studies have documented this habit (although see Symens 1990). A notable exception is two recent studies by Debus et al . (2007, 2008), who found 64 locusts in Eastern Barn Owl pellets from Diamantina National Park in western Queensland in 2006 and a further 89 locusts at the same location in 2007, representing 69% and 48% of the total prey individuals for those years, respectively. The finding from the present study on the Patho Plains supports the contention by Debus et al . (2007, 2008) of dietary flexibility, but suggests that this propensity may not be limited to the arid zone in Australia. The presence of large numbers of locusts in the diet of Eastern Barn Owls on the Northern Plains also has potential implications for management. Barn Owl deaths have been attributed to secondary poisoning from the spraying of organophosphorus insecticides for locust control in other parts of the world (e.g. Mendelssohn & Paz 1977; Hill & Mendenhall 1980). The locust swarm in the Patho Plains region in late 2005 resulted in the spraying of parts of the region, including the native grasslands within the Terrick Terrick National Park and nearby nature conservation reserves, with the bio- (native fungus) Metarhizium (Cameron 2005). This pesticide is specific to locusts/grasshoppers and is likely to have a more benign impact on vertebrate fauna than previous control techniques in Australia (Story et al . 2005, 2007; Szabo 2005). However, the impact of reduced food sources should also be considered for those species for which locusts may be an important, if temporary, dietary component.

Acknowledgements Thanks to Stephen Debus and an anonymous referee for comments on a draft.

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Received 19 March 2008 n