137 AUSTRALIAN FIELD ORNITHOLOGY 2005, 22, 137-145 Behaviour of the Little Raven 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 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 () is classified as a common resident on Phillip Island (Wheeler 1981 ). In south-eastern there are three species of raven: the C. coronoides, 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 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. Preening was noted mainly during periods of rest, and occurred at all sites throughout the day. Birds were often perched on a telephone pole or tree, and preened there for several bouts before roosting or flying off. VOL. 22 (3) SEPTEMBER 2005 Behaviour of Little Raven 141

Socialising was noted occasionally, including allopreening between the members of presumed mated pairs, and beak-biting and vigorous wing-flapping by interacting individuals apparently in a squabble. The latter activity may have been to establish social dominance. Some aggressive behaviour was observed. Once, a Little Raven that was feeding on a Short-tailed Shearwater Puffinus tenuirostris carcass aggressively pushed away another that attempted to join in. Also, competitive interactions with juvenile Pacific Gulls Larus pacificus occurred over shearwater carrion; the larger gulls returned the aggression and almost always won possession of the carcass. Data for focal individuals indicate that site influenced the time spent undertaking various activities. At Cat Bay and the Penguin Parade roosting behaviour was the most common activity (56% and 43%, respectively), whereas at the Cliffs birds spent only 11% of their time roosting (Figure 3). Birds spent significantly longer feeding at the Cliffs than at the Penguin Parade (t-test: t = 4.01, df = 64; P <0.01) or Cat Bay (t-test: t = 6.55, df = 57; P <0.01). Foraging behaviour (feeding, walking and standing) comprised 80% of the time of birds observed at the Cliffs, but only 31% and 48% at Cat Bay and the Penguin Parade, respectively (Figure 3). There were some temporal differences in activity throughout the day (see below).

Roosting Observations of individuals showed that birds were most likely to be roosting in the early morning (0630 h) and late afternoon (from 1630 h), with a lesser peak in the middle of the day (1230-1430 h) (Figure 4). Suitable roost-sites such as power poles and trees were located near the Penguin Parade and Cat Bay sites. Night-time roosts appeared to be in trees located close to these two sites (NS & RJ pers. obs). No suitable roosting sites were located near the Cliff site.

Feeding When Little Ravens were not roosting they were feeding. Peak feeding times were 1030 hand 1430 h (Figure 4). Activities classified as standing and walking were mostly associated with feeding. For example, many of the birds feeding on the beach walked for 10 seconds, fed for 15 seconds, stood for 5 seconds, and repeated a similar pattern with various time intervals.

Vocalisation Vocalisation was recorded significantly more often at Cat Bay ( 41 % of 91 birds) than the Cliffs (25% of 28 birds) (t-test: t = 2.86, df = 22; P = 0.01). Vocalisation appeared to be more common at Cat Bay than at the Penguin Parade (25% of 80 birds), but this difference was not significant (t-test: t = 1.70, df = 22; P = 0.10). Birds called most often in the early morning (49% of birds calling at 0630 h); vocalisations then decreased almost linearly through the morning to 32% calling at 1230 h, then dropped sharply to zero at 1430 h, before rising to 16% of birds just before sunset (1630 h). Peak numbers of birds vocalising coincided with peak numbers of birds roosting; however, the number of birds vocalising did not rise in the middle of the day as did those roosting. The number of birds calling was lowest in the early afternoon (1430 h) when more birds were feeding. AUSTRALIAN 142 SWINBURNE & JESSOP FIELD ORNITHOLOGY

Cat Bay Walking Socialising 9% 0%

Feeding 7%

Cliffs

Feeding 22%

Penguin Parade Socialising Walking 0% 17%

Standing 13% Roosting 43%

Figure 3. Time spent by individual Little Ravens undertaking various activities at the three study sites. VOL. 22 (3) SEPTEMBER 2005 Behaviour of Little Raven 143

70.------~

-- Roosting ~> 60 +---""'c------1 tl --+-Feeding t'll \ g 50

-[ 40 +---~--=--f------,---~Lr--1 rn \ I Q) E 30 +------y---.f------1

Q) g> 20 -+------~c__-'\,------1 -r::: ...~ 10 -+--~~------~-1 Q) a.. 0 +---,--,---,---,--,--~ 0630 0830 1030 1230 1430 1630 Time (h)

Figure 4. Percentage of time spent by Little Ravens (199 observations) roosting and feeding (all sites combined). Forty percent of single focal individuals vocalised, for 3-50 seconds per calling period (mean call length 17.0 ± 2.5 seconds). Little Ravens in groups called less often (28% of birds), for a shorter period of time (mean 6.4 ± 4.8, range 1-17 seconds).

Diet The diet of the Little Raven is represented as the proportion of foraging time spent feeding on different food resources (Figure 5). The majority of the time in

Ol c: 80 "0 70 C1l ~ 60 C1l 50 .§ 40 5 30 .....s 20 0 C1l 10 Ol ta 0 "E C1l Short-tailed Berries Insects Human food ...0 C1l Shearwater (bread) Q. carrion Food source

Figure 5. Percentage of time that Little Ravens spent feeding on various food sources (all sites combined). AUSTRALIAN 144 SWINBURNE & JESSOP FIELD ORNITHOLOGY this study in autumn (72%) was spent feeding on insects taken from the ground, beach debris, sand, pavement, and wood. Feeding on berries from Ruby Saltbush Enchylaena tomentosa and Seaberry Saltbush Rhagodia baccata occupied 17% of the Little Ravens' feeding time. Short-tailed Shearwater carrion occupied 16% of the birds' feeding time and was seen only at the Penguin Parade and the Cliffs. Although Shearwaters nest at Cat Bay, perhaps no carcasses were present during the study period. The remaining 3% of feeding time was on bread supplied by a resident.

Weather No apparent difference in Little Raven numbers or behaviour was noted under the various weather conditions. However, no strongly adverse weather was encountered.

Discussion The Little Ravens at Phillip Island roosted communally in the early morning and evening at Cat Bay and the Penguin Parade; fed (sometimes solitarily) in mid morning and mid afternoon, mostly at the Cliffs; and also roosted around midday although some birds were undetected at this time, either unseen in trees or away from the three study sites. Vocalisation was most intense in the early morning, particularly at the major roost-site (Cat Bay), with a minor resurgence again towards evening. By contrast, there was little vocalisation in mid afternoon at peak foraging time. Communal roosts may function as 'information centres' at which birds learn the foraging trajectories and feeding sites of successful foragers (Ward & Zahavi 1973). Our observations generally agree with previous information on the social organisation and behaviour of non-breeding Little Ravens, which are nomadic, forage in loose flocks, and roost during the middle of the day (Rowley 1967, 1970, 1973a). Little Ravens on Phillip Island spent most of their time within a cohesive group. However, for a supposedly communal species there was also a high incidence of solitary individuals. The largest group observed was 53 birds and. most groups were less than 20, unlike the large flocks of 100 to 300 birds reported in New South Wales by Rowley (1973c ). Perhaps the larger flocks represent nomadic birds, whereas smaller flocks are composed of 'local' birds, individuals of which may also forage alone at times. The diet of Little Ravens at Phillip Island, as measured by time spent feeding on the various food classes, was similar to the proportions recorded by Rowley & Vestjens (1973) from stomach contents, suggesting that relative foraging effort approximates relative volumetric contribution to the diet. The main foraging site on the island (the Cliffs grassland) most closely resembled the Little Raven's preferred foraging habitat of open plains elsewhere (Rowley 1967). At Phillip Island Little Ravens appeared to have a roaming approach to their foraging, which is consistent with the observation that foraging by ravens is mainly restricted to the ground while walking (Rowley 1973a). Diet may vary seasonally, with a peak of carrion-feeding in winter (Rowley & Vestjens 1973). The present study was timed to coincide with available shearwater carrion. However, and contrary to expectation, the Little Ravens spent little foraging time on this resource. Because of the lack of wind in the weeks of the study, there were no large exoduses of juvenile shearwaters and hence few carcasses VOL. 22 (3) SEPTEMBER 2005 Behaviour of Little Raven 145 available. Furthermore, Pacific Gulls may have provided a level of competition for carrion similar to that from large raven species elsewhere in the Little Raven's range. This study was a preliminary behavioural study of the Little Raven population on Phillip Island, as a baseline for further studies during other seasons of the year. Of particular interest will be spring when the Little Penguins are breeding. A study at this time could show how the Little Raven's utilisation of resources changes when Penguin eggs and chicks are available. It would also shed light on whether their levels and times of activity change with this shift in the Little Ravens' environment.

Acknowledgements This study was an undergraduate project by NS through the School for International Training, Cairns (Queensland). NS thanks Phillip Island Nature Park for permission to conduct the study and for providing office accommodation, advice, supervision and housing during her stay; researchers and staff at the Park for their generosity; and Andre Chiaradia for computing and statistical advice. Thanks to the two referees whose comments improved this manuscript.

References Rowley, I. (1967), 'A fourth species of Australian corvid', Emu 66, 191-210. Rowley, I. (1969) 'An evaluation of predation by "crows" on young lambs', CSIRO Wildlife Research 14, 153- 179. Rowley, I. (1970), 'The genus C01vus (Aves: Corvidae) in Australia', CSIRO Wildlife Research 15, 27- 71. Rowley, I. (1971), 'Movements and longevity of ravens in south-eastern Australia', CSIRO Wildlife Research 16, 49-72. Rowley, I. (1973a), 'The comparative ecology of Australian corvids. I. Introduction, study areas and methods of study', CSIRO Wildlife Research 18, 1-23. Rowley, I. (1973b), 'The comparative ecology of Australian corvids. II. Social organization and behaviour', CSIRO Wildlife Research 18, 25-65. Rowley, I. (1973c), 'The comparative ecology of Australian corvids. IV. Nesting and the rearing of young to independence', CSIRO Wildlife Research 18, 91- 129. Rowley, I. (1973d), 'The comparative ecology of Australian corvids. VI. Why five species?', CSIRO Wildlife Research 18, 157- 169. Rowley, 1., Braithwaite, L.W. & Chapman, G.S. (1973), 'The comparative ecology of Australian corvids. III. Breeding seasons', CSIRO Wildlife Research 18, 67-90. Rowley, I & Vestjens, W.J.M. (1973), 'The comparative ecology of Australian c01vids. V. Food', CSIRO Wildlife Research 18, 131- 155. Sutter, G. & Downe, J. (2000), ~getation Community Swvey and Mapping of the Phillip Island Nature Park, Arthur Rylah Institute for Environmental Research, Melbourne. Ward, P. & Zahavi, A. (1973), 'The importance of certain assemblages of birds as "information centres" for food finding', Ibis 115, 517-534. Wheeler, W.E. (1981), The Birds ofPhill ip Island, Western Port Bird Obse1vers Club, Victoria.

Received 10 July 2004 •