137 AUSTRALIAN FIELD ORNITHOLOGY 2005, 22, 137-145 Behaviour of the Little Raven Corvus mellori on Phillip Island, Victoria NORA SWINBURNE1 and ROSALIND JESSOP2 1Wesleyan University, Wesleyan Station, Middletown, Connecticut 06459, USA 2Phillip Island Nature Park, P.O. Box 97, Cowes, Victoria 3922 Summary Time-budgets of Little Ravens Corvus mellori were studied on Phillip Island, Victoria, in mid autumn (April) 2002, by scoring behaviour during observations on focal individuals (n = 199), instantaneous scans of Raven groups (n = 189), and average counts of birds at each of three sites. Ravens occurred mostly in groups; peak numbers occurred in the early mornings and evenings, with midday lows. Communal roosting occurred in early morning, midday and evening, and foraging in mid morning and mid afternoon. Much of their time was spent roosting. Focal birds also spent much time foraging, whereas birds in groups divided most of their remaining time between foraging and flying. Ravens spent most of their foraging time feeding on insects (72% ), followed by berries (17% ), seabird carrion (16%) and human food scraps (bread, 3% ). Some intra- and interspecific aggressive interactions are described. Introduction The Little Raven Corvus mellori (Corvidae) is classified as a common resident on Phillip Island (Wheeler 1981 ). In south-eastern Australia there are three species of raven: the Australian Raven C. coronoides, Forest Raven C. tasmanicus and Little Raven (Rowley 1970). The Little Raven ranges from the Northern Tablelands of New South Wales to the western coast of South Australia, and inhabits a variety of areas from alpine woodlands to coastlines and cities. The Little Raven was first described in 1967 (Rowley 1967) and only one major study has been conducted on this species, on sheep properties in inland New South Wales. That study described the Little Raven's movements and longevity, social organisation, breeding seasons, nesting and rearing of young to independence, food, separation from other Australian corvids, and predation on young lambs (Rowley 1969, 1971, 1973a,b,c,d; Rowley et al. 1973; Rowley & Vestjens 1973). During the Little Penguin Eudyptula minor breeding seasons of 2000- 01 and 2001- 02, Little Ravens were observed destroying burrows and stealing Penguin eggs and chicks (RJ pers. obs.). Previously, Little Ravens had been thought to eat only eggs ejected from the burrow by Penguins. With this evolving behaviour and its possible impacts on the Little Penguin population, a study of Little Ravens on Phillip Island commenced. The first part of the study, on the behaviour and diet during autumn, is reported here. Study area and methods Study site The study was conducted on the Summerland Peninsula, at the western end of Phillip Island Nature Park, Victoria (38°04'S, 146°22'E). Phillip Island, covering 101 km 2, is located approximately 120 km south-east of Melbourne; 90% of the island has been cleared for agriculture and urban development. The Nature Park, and in particular the Penguin Parade, is an important ecotourism and educational centre. AUSTRALIAN 138 SWINBURNE & JESSOP FIELD ORNITHOLOGY Vegetation communities on the Summerland Peninsula are Coastal Tussock Grassland, dominated by Blue Tussock-GrassPoa poiformes, and Bird Colony Succulent Herb land, dominated by Bower Spinach Tetragonia implexicoma. Some she-oakAllocasuarina woodland is present along the spine of the peninsula (Sutter & Downe 2000). Three sites, with different physical characteristics, were chosen to observe the Little Raven population: the Penguin Parade (Summerland Beach) and its surroundings, Cat Bay (sheltered north-facing beach), and a section of flat tussock grassland near the coastal cliffs facing Bass Strait (south-facing). Each site was approximately 500 m in length. Only the Cliff site resembled an open plain. During the study, weather ranged from light rain to full sun, with no strong winds. Sampling Field observations were made between 10 April and 1 May 2002, including a pilot study to 13 April that determined suitable observation sites, times and methods. The main study was conducted on 12 days fro m 14 April. Little Ravens were observed in time segments of 2 hours between 0630 h (dawn) and 1830 h (dusk). Within each 2-hour segment, birds at each of the three sites were observed for 30-35 minutes per site. Within a day, sampling was conducted in alternate 2-hour blocks, and on successive days the start time (0630 or 0830 h) was alternated, to give equal coverage. The starting order of sites was rotated to give equivalent coverage in each 2-hour time block. Three types of observations were made. 1. A 'focal bird' approach, in which all behaviours of an individual bird (n = 199) were recorded using a dictaphone for a continuous period of 3 minutes as determined by a timer (a maximum of six focal birds per site per time block, depending on the number present). After the 3 minutes, a new bird was watched. Only those birds not flying at the start of the 3 minutes were watched, and the observation was aborted if the bird fl ew out of sight before the 3 minutes expired. Durations of each activity were later determined by analysis of recordings. Activities noted were flying, roosting, preening, feeding, walking, standing, socialising, vocalisation, and vigilance. Flying was defined as any movement through the air; roosting as time spent at rest in a non-erect, non­ moving position; preening as time spent grooming with the beak; feeding as time spent pecking; walking as time spent moving on the ground or a structure; standing as time spent not moving; socialising as a physical interaction with another bird; vocalisation as the occurrence of calling (i.e. foca l bird called during the 3 minutes); and vigilance as the time spent rotating the head to peer at the surroundings. The focal-bird approach provides information on everything a bird does. 2. An 'instantaneous scan' approach, in which groups of Little Ravens in the area (n = 189) were scanned and the behaviour of each individual within the group recorded at that moment (up to nine replicates per site per time block). These scans gave frequencies of behaviour for individuals in the group. Activities by individuals within groups were flying, roosting, preening, feeding, walking, standing and socialising, as defined above. 3. A mean count of all individuals at each site in each time block (five counts per site per session, except for the 1630-1830 h block which had four counts because dusk was closer to 1800 h). Observations were made using Gerber Montego 10 x 30 LE binoculars and a 25x Kowa TSN-1 telescope. In the field observations were recorded using a Sony M-540V microcassette recorder and timed using a stopwatch. Results of microcassette recordings were later analysed for time-budgets of focal birds and frequencies of behaviour for individuals in group scans, and the information transferred to a database. Results Temporal pattern of abundance The largest number of Little Ravens was observed in the early morning, between 0630 and 0830 h; numbers then declined until the middle of the day before increasing toward evening (Figure 1). VOL. 22 (3) SEPTEMBER 2005 Behaviour of Little Raven 139 50 DCat Bay 45 •cliffs 40 c: llll Penguin "'Q) > 35 Parade 0::"' Q) 30 :J 25 .....= ....0 Q) 20 .0 E :I 15 z 10 5 0 0630 0830 1030 1230 1430 1630 Time (h) Figure 1. Location of Little Raven throughout the day at the three study sites (y axis shows mean ± standard deviation). Area preferences The three sites showed different daily patterns of Little Raven presence (Figure 1). At the Penguin Parade the Little Ravens were most numerous during the early morning from 0630 to 0830 h and in the evening from 1430 to 1630 h. The Cat Bay site showed a similar pattern, with the most birds being fo und in the first and last intervals. At the Cliffs most birds were observed between 0830 and 1030 h, followed by 1430 to 1630 h (Figure 1). During daylight hours the average number of birds seen at the Penguin Parade was 12, Cat Bay 16 and the Cliffs five. Gregariousness The Little Ravens were observed mostly in groups. Sixty-six percent of the 199 focal birds were found to be within a group of two or more, and 34% were solitary. These groups ranged from two to 53 although only 7% of the groups observed were larger than 20 individuals. The incidence of solitary and grouped birds among sites was similar. There was little apparent temporal change in the incidence of solitary birds versus groups, as both classes showed a similar trend through the day. However, the incidence of groups was low in late morning, and for solitary birds there was a slight mid-morning peak and a slight decline towards the evening. Behaviour The data from both the group scans (37% of 189 groups) and the focal­ individual observations (44% of 199 individuals) showed that Little Ravens spent the largest amount of their time roosting (Figure 2). For group birds, flying (31%) was the next most likely activity, whereas for individuals standing (19% ), feeding (13%) and walking (12%) occupied similar amounts of time (Figure 2). However, this difference may be partly related to the method used, as observations of focal birds were biased towards non-flying individuals and the 'instantaneous scan' AUSTRALIAN 140 SWINBURNE & JESSOP FIELD ORNITHOLOGY Individual Activity Socialising <1% Walking 12% Roosting 44% Standing 19% Feeding 13% Preening 4% Group Activity Flying 31% Roosting 37% Socialising 0% Walking 7% Standing 13% Figure 2. Group and individual time spent on various activities by Little Ravens (all sites combined). approach, although providing information on activities that are carried out for long periods of time such as roosting, may underestimate activities that occur for short periods of time such as bouts of feeding.