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Diet of an Eastern Grass Owl Tyto Longimembris in Northern New South Wales

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Diet of an Eastern Grass Owl Tyto Longimembris in Northern New South Wales Australian Field Ornithology 2021, 38, 44–48 http://dx.doi.org/10.20938/afo38044048 Diet of an Eastern Grass Owl Tyto longimembris in northern New South Wales Stephen G. Kearney School of Earth and Environmental Sciences, University of Queensland, Brisbane QLD 4072, Australia. Email: [email protected] Abstract. A single Eastern Grass Owl Tyto longimembris was observed in Bundjalung National Park, New South Wales, in September 2019. Pellets (n = 17) collected from its roost contained the remains of House Mouse Mus musculus, Grassland Melomys Melomys burtoni, Black Rat Rattus rattus, Swamp Rat R. lutreolus, Fawn-footed Melomys Melomys cervinipes, Common Planigale Planigale maculata, Eastern Blossom Bat Syconycteris australis and honeyeater Phylidonyris sp. The most interesting findings were the Eastern Blossom Bat (the first published record of a bat in the diet of an Eastern Grass Owl in Australia) and that one of the Grassland Melomys specimens had pink bones. Introduction a predator mainly of small terrestrial mammals, especially rodents (Fitzgerald & Thorstensen 1994; Maciejewski The Eastern Grass Owl Tyto longimembris is considered 1997; Britton & Rose 1999; Higgins 1999; Carlson 2004; rare across the Australian continent, although northern New Schulz & Magarey 2010; Clulow et al. 2011). South Wales is considered one of its strongholds (Debus In September 2019, an Eastern Grass Owl was observed et al. 1998). It is listed as Vulnerable under the Biodiversity leaving its day roost not far from a track in Bundjalung Conservation Act 2016 in New South Wales, where it is National Park, New South Wales. The area from which threatened by a variety of processes, including habitat it flew was searched and 17 regurgitated pellets were loss, fire and the impact of pesticides (on it and its prey: found and collected. Since these pellets were collected, OEH 2018a). Although listed as Least Concern globally, an extensive fire burned the region (Figure 1), potentially its population is declining (BirdLife International 2016). It is impacting the Grass Owl population in the area and its Figure 1. The location of the Eastern Grass Owl sighting and pellet collection (white cross) within Bundjalung National Park, New South Wales. On the left side of the figure, protected areas are shown by green hatching. Protected area data from the 2018 Collaborative Australian Protected Area Database (DAWE 2018). On the right side of the figure, the extent and severity of the fires that burned much of Bundjalung National Park in late November–early December 2019 are shown. Maps of burnt area from the New South Wales Government’s Google Earth Engine Burnt Area Mapping (DPIE 2020). Eastern Grass Owl diet, northern New South Wales 45 food and habitat resources. In this article, I report on the narrow the species search (e.g. Archer 1981; Van Dyck contents of these pellets so as to provide some information et al. 2013) and then specific literature was used to confirm on the Eastern Grass Owl and its prey species before the identification (e.g. Archer 1976; Ziegler 1982). fire. Results Study area and methods Rodent species comprised >95% of the biomass (89% The area where the pellets were collected (–29.353, by number) of the identifiable contents of the pellets 153.306: Figure 1) is a wet heathland vegetation community from this Eastern Grass Owl in Bundjalung National Park composed of Fern-leaved Banksia Banksia oblongifolia, (Table 1). The most numerous prey item was the House Olive Tea-Tree Leptospermum liversidgei, Wallum Grass Mouse Mus musculus, with a total of 22 individuals recorded Tree Xanthorrhoea fulva, Sporadanthus interruptus and and occurring in 47% of pellets (Table 1). Despite the Sprengelia sprengelioides (OEH 2011). Although the House Mouse being the most numerous prey species, the 2 National Park is large (>200 km ), the Eastern Grass Owl Black Rat Rattus rattus comprised the greatest biomass, was in the far south of the protected area and within 2 km accounting for an estimated 46% of pellet biomass of low-density urban development and 3 km of sugarcane (Table 1). Introduced rodent species therefore accounted farming (Figure 1). Eucalypt forests were within 500 m of the for 67% of biomass and 69% of prey individuals of this roost, Broad-leaved Paperbark Melaleuca quinquenervia Owl’s pellets. within 1 km and Riberry Syzygium leuhmannii forests within 6 km. The Grassland Melomys Melomys burtoni was the second most common prey item, with five individuals recorded and Age of pellets varied from hours or days (intact with high- occurring in 29% of pellets (Table 1). Interestingly, one gloss outer layer) to weeks or months (falling apart and of the Grassland Melomys specimens had pink bones no obvious remnants of the glossy outer layer), potentially (Figure 2); the pellet containing this individual had no indicating intermittent use of the roost. Identification of prey evidence of pink on its surface and no other material in the was undertaken using a variety of diagnostic literature. pellet was pink. For rodent species, Taylor & Horner (1973) and Watts & Aslin (1981) served as the primary reference material. The other rodents recorded in the pellets were one Fawn- For other species, a variety of literature was consulted to footed Melomys Melomys cervinipes and one Swamp Table 1. Prey species recorded in 17 Eastern Grass Owl pellets, Bundjalung National Park, New South Wales, September 2019: number of individuals (n) and percentage of total number of prey items; biomass (g) (number of individuals x the weight of the prey item) and percentage of total biomass of the prey species; and frequency of pellets containing the prey items (number and percentage of pellets where the prey species was recorded). Weights of mammals are averages taken from Van Dyck et al. (2013). Weight for the Phylidonyris honeyeaters is an average of New Holland Honeyeater P. novaehollandiae (20 g) and White-cheeked Honeyeater P. niger (18 g) (Dunning 2008). Prey species Weight (g) Number Biomass Frequency n % g % n % House Mouse 17 22 61.1 374 20.5 8 47 Mus musculus Grassland Melomys 68 5 13.9 340 18.7 5 29 Melomys burtoni Fawn-footed Melomys 76 1 2.8 76 4.2 1 6 Melomys cervinipes Black Rat 280 3 8.3 840 46.1 3 18 Rattus rattus Swamp Rat 125 1 2.8 125 6.9 1 6 Rattus lutreolus Total introduced rodents 25 69.4 1214 66.7 9 52.9 Total all rodents 32 88.9 1755 96.4 16 94 Common Planigale 9 1 2.8 9 0.5 1 6 Planigale maculata Eastern Blossom Bat 19 1 2.8 19 1.0 1 6 Syconycteris australis Honeyeater Phylidonyris sp. 19 2 5.6 38 2.1 1 6 Total 36 100.0 1821 100.0 46 Australian Field Ornithology S.G. Kearney Figure 2. The remains of a Grassland Melomys with pink bones from an Eastern Grass Owl pellet collected in Bundjalung National Park, New South Wales. The top right and bottom right images show the same skull and right mandible, showing the dorsal/ventral and facial/lingual views. The left image shows other skeletal remains from the pellet. Rat Rattus lutreolus. Also recorded was one Common strenua in Brisbane, Queensland: Pavey 1995; Barn Planigale Planigale maculata, one Eastern Blossom Bat Owl Tyto alba in arid Australia: Morton & Martin 1979; Syconycteris australis and two honeyeaters Phylidonyris McDowell & Medlin 2009). To my knowledge, this is the sp. (Table 1). first published record of a bat in the diet of an Eastern Grass Owl in Australia. Discussion Predation on bats raises two questions: (1) Why is my record the first published of a bat in the diet of an Eastern The information from this study is consistent with Fleay’s Grass Owl and (2) How did the Owl catch the Eastern observation that “the Grass Owl is a hunter of fairly catholic Blossom Bat? On the first question, my record could be taste, all being grist that comes to the mill” (Fleay 1968, the first published because of the paucity of diet analyses p. 128). Despite being species-rich (eight species recorded published, or predation on bats may just be a particularly in 17 pellets), the diet of this Eastern Grass Owl had a rare occurrence. Although reports of the diet of Eastern very high proportion of rodent prey, which is consistent with Grass Owls in Australia are sparse, collectively thousands dietary data previously presented for the species in the of Grass Owl pellets have been analysed from Asia same region (Fitzgerald & Thorstensen 1994; Maciejewski (e.g. Lin et al. 2007; Kunsorn et al. 2015) and Africa (of 1997). In her 1997 study, Maciejewski highlighted the the African Grass Owl Tyto capensis: e.g. Vernon 1972; predominance of introduced rodents in the diet in and Riegert et al. 2008) and only one study from South Africa around disturbed areas in northern New South Wales recorded bats (Pocock 1963). Hence, it seems plausible (78% of prey items in that study). Conversely, Fitzgerald & that this is a record of a particularly rare event. However, Thorstensen (1994) reported that native rodents comprised as the Eastern Blossom Bat (head + body length 60 mm, 75% of prey items and 93% of biomass in pellets collected mean weight 19 g: Van Dyck et al. 2013) is similar in size from more natural habitat. Although introduced rodent to other Eastern Grass Owl prey and these bats forage species dominated the diet of the Eastern Grass Owl in in Banksia heathland near Iluka, <8 km from this Grass Bundjalung in the present study, the mixture of introduced Owl roost (Law 1993), this is not a completely unexpected and native prey species in its diet potentially indicates a finding.
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