Australian Field Ornithology 2014, 31, 107–112

Spotted Harrier hunting lizards on foot

Ralph Buij

Animal Ecology, Alterra Wageningen University and Research Centre, P.O. Box 47, 6700 AA Wageningen, The Netherlands. Email: [email protected]

Summary. A Spotted Harrier Circus assimilis was observed and photographed in mid July 2013 in northern Queensland, as it foraged on foot for lizards, by walking long transects, flushing and chasing skinks on foot, and intermittingly flying short distances low over the ground. Capture success was 14.3% (n = 21 attempts). The Harrier appeared to locate the lizards at least partly by auditory cues, in behaviour previously undescribed for this species.

Introduction The diet of the Spotted Harrier Circus assimilis is composed largely of mammals, birds, reptiles (especially lizards) and various insects (Marchant & Higgins 1993), with birds and reptiles, or mammals and birds, dominating dietary biomass during the breeding season (Baker-Gabb 1984; Aumann 2001). The documented foraging strategy is typical for most harriers, with a rather slow, low-level quartering flight over open areas followed by sudden dives at terrestrial prey or occasionally flushed birds (Ferguson-Lees & Christie 2001). Various other foraging strategies of congeners have been described, illustrating the group’s behavioural and ecological flexibility. For example, the foraging behaviour of the Eurasian Marsh Harrier C. aeruginosus, Cinereous Harrier C. cinereus, and Hen Harrier C. cyaneus includes still-hunts from a perch or on the ground (Ferguson-Lees & Christie 2001). Bird-hunting Hen and Pallid Harriers C. macrourus fly faster, using vegetation, ditches or dikes to conceal their approach (Schipper et al. 1975; Buij 2012), the latter also mounting surprise attacks from a concealed position on the ground. Eurasian Marsh and Swamp Harriers C. approximans often exhaust waterfowl on the water surface by hovering over them (Schipper et al. 1975; Baker-Gabb 1983). Other opportunistic strategies include following Red Foxes Vulpes vulpes to capture flushed birds (Montagu’s HarriersC. pygargus: Kitowski 2003), tracking military activities for flushed rodents (Northern Harriers C. hudsonius: Jackson et al. 1977) or fires and livestock for fleeing grasshoppers (Montagu’s and Pallid Harriers: pers. obs.), pirating food from other raptors, or scavenging (various species: Ferguson-Lees & Christie 2001), increasingly when carcasses become more readily available (Swamp Harrier: Baker-Gabb 1986). Here, I present an account of a previously undescribed foraging strategy by a Spotted Harrier in Queensland, northern Australia.

Observations On 13 July 2013, at 1328 h local time, I detected an adult Spotted Harrier on the side of the Wallaman Falls Road (18°36′S, 145°55′E), west of Ingham in north- 108 Australian Field Ornithology R. Buij

Figure 1a–f. Spotted Harrier foraging behaviour, 13 July 2013: (a) steady gaze and (b) slightly raised facial ruff and nape feathers while locating skinks in dense grass; (c) 1-m jump at moving lizard; (d) chasing prey on foot; (e) flushing a skink; and (f) swallowing skink. Photos: Ralph Buij eastern Queensland. The area is characterised by low-lying forest at the foot of forested hills, with 100-m wide grassland margins bordering the road on each side, dotted by trees, and larger open areas including sugarcane plantations and cattle farms. The weather was almost calm with partly clouded skies and some wind, after strong winds and heavy downpours the previous day. Observations were made from a vehicle. The Harrier walked at a slow but steady pace through and over the tall grass sward, stopping at intervals of a few metres or less to Spotted Harrier hunting lizards on foot 109

Figure 1g–j. Spotted Harrier foraging behaviour, 14 July 2013: (g) searching for prey on foot; (h) note small size of prey, as in Figure 1f, and depth of grass layer; (i) head tilted from side to side (0.1 sec. between images); and (j) raised feathers on throat to aid location of prey. Photos: Ralph Buij intently stare at the grass, occasionally with raised facial ruff and nape feathers (Figures 1a, b). After several minutes, the Harrier lunged forward ~60 cm into the grass from a standing position, trying to capture an agile terrestrial prey item (prey later identified as skinks Scincidae). It stayed in the same position for ~20 seconds with flapping wings and grasping legs outstretched, rapidly scanning the grass around its legs. The prey, the Harrier’s tarsi (length: 8.5–10.7 cm: Ferguson-Lees & Christie 2001) and part of its tibiae were invisible in the dense grass. The Harrier subsequently took off, flew 10–15 m at 50–70 cm above the ground, with tail spread against the wind and head pointed vertically down or angled slightly forwards. Another strike at prey failed, and the Harrier started walking again in the same direction as before. After 3 minutes and a 12-m walking transect, the Harrier unsuccessfully struck five times within 21 seconds at a fleeing lizard in a 1.5-m2 circle, hopping around with wings and tail held in a raised position and legs outstretched before each strike (Figure 1c), twice attempting to capture the lizard after a brief chase on foot (Figure 1d). Thereafter, it flew off, and another failed attempt was followed by interesting behaviour: while balancing on top of grass tussocks with both wings outstretched, the Harrier made several rapid, rhythmic forward thrusting movements with both legs, simultaneously 110 Australian Field Ornithology R. Buij scanning the immediate surroundings, and apparently flushed a lizard which was missed after a short chase; it appeared that the Harrier was intentionally flushing the lizard rather than trying to seize it. The same behaviour was again seen later and photographed (Figure 1e). The Harrier subsequently flew off 300 m in the direction opposite from where it had been moving, to resume foraging on the same side of the road and in the same direction as previously. A fifth attempt was successful and a small brown skink was caught and swallowed whole in 12 seconds (Figure 1f). Thereafter, the Harrier disappeared from sight in a ditch, probably to drink, made a sixth attempt (while flying) to capture a lizard, and then dozed off for 16 minutes on the spot. It resumed hunting on foot again from 1419 to 1433 h, walked ~15 m in a single straight transect, periodically staring at the grass with its head tilted for as long as 15 seconds in one spot, but no attempts were made to capture prey. From 1433 h, the Harrier settled to roost in the grass, with eyelids closed or half-closed, until at least 1600 h, when observations ceased. This period coincided with greater cloudiness and light drizzle, possibly lowering the activity of the skinks. On 14 July, the Spotted Harrier was relocated at 0814 h no more than 50 m from the previous day’s roost-site. The sky was clear and the Harrier was foraging. Like the previous day, the Harrier walked in a single direction for 80–100 m (Figure 1g), with occasional short flights of 5–10 m, remaining in the same 400-m stretch of rough road-edge vegetation. It made three attempts to capture prey on foot in 16 minutes and caught one skink (Figure 1h). From 0839 h, the walking strategy was interrupted by more frequent, longer glides with few shallow wing- beats and feet hanging near the top of the grass stalks, the Harrier often briefly banking or hovering. The feathers on its nape, throat, and collar were often slightly raised and the head tilted in flight (Figures 1i, j). Of twelve capture attempts with known outcome between 0839 and 1024 h, from flight and on foot (twice), one was successful and again a small lizard was caught. This included a period of rain from 0950 h, after which the Harrier walked longer distances without flying, once ~45 m, and made only one unsuccessful attack. Around 1024 h, it was completely overcast and the Harrier settled to roost in the grass.

Discussion This observation demonstrates that Spotted Harriers use a foraging strategy previously unrecorded in the literature, by walking long transects, flushing and chasing skinks on foot, intermittingly flying short distances low above the ground. Although the behaviour was seen on 2 days, the capture success at 14.3% (n = 21 attempts) and small size of the skinks (Figures 1f, h) suggest that profitability was probably low. The position of the skinks deep in the grass layer, which covered close to 100% of the ground and was at least 10–20 cm tall in most parts, suggests that the Harrier located them at least partly by auditory cues. Indeed, the well-developed facial ruff in this species seems an adaptation to the detection of terrestrial prey concealed by a dense grass layer, as in closely-related vole specialists (e.g. Hen, Northern, and Pallid Harriers: Simmons 2000). Rice (1982) found that Northern Harriers can determine the direction of sounds with slightly less accuracy than owls, which possess morphologically similar feathers Spotted Harrier hunting lizards on foot 111 in a parabolic cowl around the eyes (Clark & Stanley 1976). The observed raised facial ruff possibly further improves hearing ability (Simmons 2000). The low- level flight of the Spotted Harrier, lower than usual in harriers (usually 1–6 m, but up to 10–20 m above the ground: Ferguson-Lees & Christie 2001), is likely to further aid sound detection of ground-dwelling prey (Rice 1982, 1983), and the relatively short attack distances witnessed here point to prey location using acoustic cues (Bye et al. 1992). In comparison, sympatric Swamp Harriers often fly several metres higher above the ground (Baker-Gabb 1984), which makes a significant difference in the relative use of auditory versus visual cues (Rice 1983). Correspondingly, Swamp Harriers have been reported to have a relatively mild degree of acoustic specialisation, with a small facial ruff and a lack of stiff backing for the facial disc (Calford et al. 1985; Baker-Gabb 1993). Unlike harriers, owls of the genera Aegolius and Tyto have clearly asymmetrical ear openings to determine prey location in vertical and horizontal planes (Payne 1971; Norberg 1978). Still, Spotted Harriers could determine horizontal and vertical directions with a tilting of the head, as observed, similar to some owls with symmetrical ear openings (Norberg 1987). The observations described here thus support the idea that Spotted Harriers are reliant on auditory cues when foraging, and that their hearing might well be acute enough to locate small lizards underneath a dense grass layer at close range (<1 m).

Acknowledgements I thank two anonymous referees for their comments that improved an earlier draft.

References Aumann, T. (2001). An intraspecific and interspecific comparison of raptor diets inthe south-west of the Northern Territory, Australia. Wildlife Research 28, 379–393. Baker-Gabb, D.J. (1983). Comparative ecology and behaviour of Swamp Harriers Circus approximans, Spotted Harriers Circus assimilis and other raptors in Australia and New Zealand [thesis abstract]. Raptor Research 17, 123–124. Baker-Gabb, D.J. (1984). The breeding ecology of twelve species of diurnal raptor in north- western Victoria. Australian Wildlife Research 11, 145–160. Baker-Gabb, D.J. (1986). Ecological release and behavioral and ecological flexibility in Marsh Harriers on islands. Emu 86, 71–81. Baker-Gabb, D.J. (1993). Auditory location of prey by three Australian raptors. In: Olsen, P. (Ed.). Australasian Raptor Studies: Proceedings 10th Anniversary Conference Australasian Raptor Association, pp. 295–298. Australasian Raptor Association, Melbourne. Buij, R. (2012). Pallid Harrier bird hunting behaviour and capture success in northern Cameroon. Ostrich 83, 27–32. Bye, F.N., Jacobsen, B.V. & Sonerud, G.A. (1992). Auditory prey location in a pause-travel predator: Search height, search time, and attack range of Tengmalm’s Owls (Aegolius funereus). Behavioral Ecology 3, 266–276. Calford, M.B., Wise, L.Z. & Pettigrew, J.D. (1985). Coding of sound location and frequency in the auditory midbrain of diurnal birds of prey, families Accipitridae and Falconidae. Journal of Comparative Physiology 157, 149–160. Clark, R.J. & Stanley, B.L. (1976). Facial feathers of the Harrier (Circus cyaneus hudsonius), Long-eared Owl (Asio otus) and Short-eared Owl (Asio flammeus) compared. Proceedings of the Philadelphia Academy of Science 50, 86–88. 112 Australian Field Ornithology R. Buij

Ferguson-Lees, J. & Christie, D.A. (2001). Raptors of the World. Helm, London. Jackson, J.A., Schardien, B.J. & Daniel, M.C. (1977). Opportunistic hunting of a Marsh Hawk on a bombing range. Raptor Research 11, 86. Kitowski, I. (2003). Age related differences in foraging behaviour of Montagu’s Harrier Circus pygargus males in south-east Poland. Acta Ethologica 6, 35–38. Marchant, S. & Higgins, P.J. (Eds) (1993). Handbook of Australian, New Zealand & Antarctic Birds, Volume 2: Raptors to Lapwings. Oxford University Press, Melbourne. Norberg, R.A. (1978). Skull asymmetry, ear structure and function, and auditory localization in Tengmalm’s Owl, Aegolius funereus (Linné). Philosophical Transactions of the Royal Society of London, B: Biological Sciences 282, 325–410. Norberg, R.A. (1987). Evolution, structure, and ecology of northern forest owls. In: Nero, R.W., Clark, R.J., Knapton, R.J. & Hamre, R.H. (Eds). Biology and Conservation of Northern Forest Owls: Symposium Proceedings, February 3-7, 1987, Winnipeg, Manitoba, Canada, pp. 9–43. General Technical Report RM-142. USDA Forest Service, Fort Collins, Colorado, USA. Payne, R.S. (1971). Acoustic location of prey by Barn Owls (Tyto alba). Journal of Experimental Biology 54, 535–573. Rice, W.R. (1982). Acoustical location of prey by the Marsh Hawk: Adaptation to concealed prey. Auk 99, 403–413. Rice, W.R. (1983). Sensory modality: An example of its effect on optimal foraging behavior. Ecology 64, 403–406. Schipper, W.J.A., Buurma, L.S. & Bossenbroek, P. (1975). Comparative study of hunting behaviour of wintering Hen Harriers Circus cyaneus and Marsh Harriers Circus aeruginosus. Ardea 63, 1–29. Simmons, R. (2000). Harriers of the World. Oxford University Press, Oxford, UK.

Received 22 August 2013