Ninox Novaeseelandiae in Suburban Canberra
Total Page：16
File Type：pdf, Size：1020Kb
VOL. 19 (4) DECEMBER 2001 109 AUSTRALIAN BIRD WATCHER 2001, 19, 109-114 Winter Home Range of an Adult Female Southern Boobook Ninox novaeseelandiae in Suburban Canberra JERRY OLSEN1 and STEVE TAYLOR2 1Applied Ecology Research Group, Division of Communications and Education, University of Canberra, A.C.T. 2601 2Environment Australia, G.P.O. Box 787, Canberra, A.C.T. 2601 Summary A radio-tagged female Southern Boobook Ninox novaeseelandiae was followed for 12 tracking nights over a 54-day period in the non-breeding season. She moved 10 km from her breeding home range in a Canberra woodland to establish a non-breeding home range in a suburban residential zone. She ranged over an estimated 122 ha calculated for 100% minimum convex polygon (MCP) and 91 ha for 95% MCP. She returned once to her breeding territory, and mate, before losing the radio-tag at her urban winter roost. The results suggest that home. ranges for Southern Boobooks near Canberra are at least three times larger than published estimates of 37 ha. Introduction The Southern Boobook Ninox novaeseelandiae can be found in most wooded habitats from arid to tropical and temperate climates across Australia (Higgins 1999). In the Australian Capital Territory it is found in urban areas, adjacent woodland, open forest, and in wetter forest of the ranges. Despite this broad distribution, the critical habitat requirement is the availability of tree-hollows for nesting (Tuylor & COG 1992). This adaptability to a broad range of habitats means that Southern Boobooks have a large variation in home range, defined as the area in which all of a bird's activities take place (Newton 1979). In a recent review of the species, del Hoyo et al. (1999) said that the area of its home range was reported to be between 8 ha and 37 ha, based on studies by Schodde & Mason (1980) and Olsen & Bartos (1997). Higgins (1999) reported home ranges of approximately 100 ha for one radio tagged male, and at least 50 ha for a colour-banded male, based on the study by Olsen & rrost (1997). Because there are no published studies for winter home ranges for the species in Australia, it is unknown whether adults remain in the breeding territory or migrate elsewhere (Olsen & Trost 1997). Our aims in this study were to observe the Southern Boobook during the non-breeding season, and to provide the first estimate of a winter home range for the species. The study is a temporal extension of data on a female Southern Boobook which had been the subject of a previous study in a Canberra nature reserve (Olsen et al. 2001). Study area and methods The female Southern Boobook was captured at its nest (Olsen et al. 2001) using a wire bal chatri trap baited with a House Mouse Mus domesticus (Olsen & Woollard 1975). The owl was leg-banded with a metal band (Australian Bird and Bat Banding Scheme) and a colour band, measured, and fitted with a backpack-style Sirtrack single-stage transmitter with a string harness aild a weak link designed to break if entangled (Karl & Clout 1987). The total mass of the transmitter and harness (6.4 g) was about 2% of the owl's body mass at capture (mass = 305 g). AUSTRALIAN 110 OLSEN & TAYLOR BIRD WATCHER The female had nested in open Scribbly Gum Eucalyptus rossii!Red Stringybark E. macrorhyncha forest in Canberra Nature Park from at least 1993 (colour-banded) to the time of this study. However, during some of the non-breeding months of 1999 and 2000, she had moved 10 km south-east of the breeding home range to a suburban street near Parliament House (Olsen et al. 2001; G. Hayes unpubl. data). We used a hand-held Sirtrack three-element yagi antenna and a Tulonics TR-4 receiver to follow the owl. Radio-tracking and observation sessions were conducted on 12 nights, from 7 June to 31 July 2000. Ilacking sessions began when the owl left the roost-tree at times varying from 1730 to al"ound 2000 h, and lasted for 1-3 hours. We arrived at the roost-tree at dusk and, from the time the owl left, followed her on foot to record each perch location on a street map (scale 1:20,000) and noted any prey-capture methods that she used. Tulemetry locations and observations were imported into a geographic information system (ArcView 3.0a) for estimation of home range (minimum convex polygon, MCP) usin,g the Animal Movement Extension (Hooge & Eichenlaub 1997). The MCP method is consistent with the Newton (1979) definition of home range if there are sufficient observations spread across the polygon. The 100% and 95% isopleths of the MCP were calculated for comparison with other Southern Boobook home-range studies. Results The owl roosted in a cluster of three Mediterranean Cypresses Cupressus sempeTVirens all within 10 m of each other, along a cul-de-sac (Sydney Avenue near Parliament House). The three trees were approximately 7 m tall and had very dense foliage, so she was invisible to passers by. We estimated the 100% and 95% MCP home ranges to be 122 ha and 91 ha respectively (Figure 1; the 100% MCP includes the one outlying observation to the south-east). The home range included a mix of native and exotic trees and shrubs arrayed across parks, gardens, houses, flats, offices, a· school, shops, quiet streets, and some main roads. On a typical evening the owl first moved from deep within the roost-tree to the outer branches and peered out. During this time she occasionally preened and sometimes disappeared back into the roost-tree, to reappear a short time later. She flew up to 30 m, and perched, before commencing foraging flights. On two occasions the owl did not leave the roost during 3 hours of observations. The owl often hunted in open areas containing large eucalypt trees, e.g. Tulopea Park and the grounds of Telopea Park High School, or in the narrow, bushy corridors between flats and townhouses. The middle portion of the home range contained houses with established gardens where the owl flew over during tracking times but did not stop, as evidenced in Figure 1 by the absence of perch locations. For perches the owl used native and exotic trees, tall shrubs ( > 2 m high), and artificial structures such as light-poles, fences and rooftops (Table 1 ). While perched the owl looked around, stared, or preened. We did not see her catch any prey, but saw her use three hunting methods: direct flying from a perch, pouncing on the ground from a perch, and looking into a shrub while hovering around it. The owl had returned (10 km north-west) to her breeding territory in Canberra Nature Park on 4 August and was seen that night with her (colour-banded) mate; she moved back to the Sydney Avenue roost on or before 11 August. Sometime around 11 August the weak link on the harness broke; we found the transmitter lodged in the roost-tree on 14 September. At dusk on 14 September we flushed the owl (identified by her colour-band) from a nest-hollow, in Canberra Nature Park, that she had used in 1998 and 1999 (Tuble 2). Figure 1. Winter home range of female Southern ~d Boobook tracked for @t""' Kings Avenue 12 nights from N 7 June to 31 July 9~ 2000. Triangles :;;:i~ denote owl locations, heavy line denotes g A 95% minimum convex ...... polygon (MCP). D 95%MCP A Telemetry locations g,~ Telopea Park czi s· o c 0 g-;t .... 0 :::I 3 i:i::io 0 :;;:i Wentworth Avenue g. l>O o~ ~o Canberra Avenue 0 1 kilometre c::= --- ::i ...... ...... AUSTRALIAN 112 OLSEN & TAYLOR BIRD WATCHER Table 1 Perches used by a female Southern Boobook over 12 observation nights in her winter home range, Canberra, A.C.T. Perch type No. observations % Eucalyptus spp. tree 14 33 Other native tree/tall shrub 2 5 Deciduous exotic tree 11 26 Other exotic tree/tall shrub 8 19 Artificial structures 7 17 Total 42 100 On 12 May 2001, 7 years and 4 months after she was banded as a breeding adult, this female was killed on her wintering home range by a domestic Cat Felis catus. Discussion The estimated home range, 122 ha calculated for 100% isopleth MCP and 91 ha for 95% isopleth MCP, is a minimum, because the owl was tracked for only 1-3 hours after leaving the roost, and for a limited number of nights during a two month period. After these times, and on other nights, the owl may have moved to areas outside this polygon. The 100% isopleth MCP gave a 34% larger home range than the 95% isopleth MCP estimate, a function mainly of one observation in the south-east of the area in Figure 1. Further study over longer periods with more radio-tagged owls is needed to determine which type of measure gives the most accurate estimate. The home range in this study (122 ha calculated for 100% isopleth MCP) is similar to the 100 ha estimated for a breeding male by Olsen & Trost (1997), but larger than the estimate for a non-breeding male (37 ha for 100% MCP), given by Olsen & Bartos (1997). This last estimate is about one-third the area given in the other two studies, even though all three studies were conducted in or near Canberra. The different estimates could reflect individual differences, but direct comparisons are obviously confounded by gender, breeding status, breeding season, and study duration (Thble 3).