Distinctive plumage patterns enable individual recognition of the Cracticus tibicen Ishini K. Kuruppu1 and Denis A. Saunders2 1Kambah ACT 2902 Australia 2Weetangera ACT 2614 Australia [email protected] (corresponding author). Downloaded from http://meridian.allenpress.com/australian-zoologist/article-pdf/doi/10.7882/AZ.2020.046/2675957/10.7882_az.2020.046.pdf by guest on 01 October 2021 We investigated whether the plumage patterns of the Australian Magpie Cracticus tibicen, a medium- sized, black and white , common over most of mainland Australia and Tasmania, including cities and towns, were sufficiently different and distinctive to allow humans to identify individual . Eighty participants took part in our pattern matching experiment to see how many of 10 photographs of individual birds they placed correctly below a panel showing 20 individual birds, each illustrated with three different photographs. Participants were from a range of ages, although the majority were high school students. All but two successfully matched some of the birds but there were considerable differences in accuracy and speed of performance. We tested differences in accuracy and time taken by participant, gender, age, and whether testing alone or testing at the same time as four other participants. We concluded that it is possible for humans to recognise individual Australian Magpies based on the birds’ plumage. ABSTRACT

Key words: Plumage pattern matching.

DOI: https://doi.org/10.7882/AZ.2020.046 INTRODUCTION

Identification of individuals is an important research tool in many fields of behaviour and ecology. In research on birds, individual recognition has been based on marking with numbered leg bands/rings, individual combinations of coloured leg bands/rings, patagial tags, nasal nares, streamers or a combination of these. However, in order to apply these devices, the animal must be captured and handled; a process not without risks to the animal and the handler, and possibly resulting in impacts on the animal’s subsequent survival or behaviour. For example, Saunders (1988) found that Carnaby’s Cockatoos Calyptorhynchus latirostris fitted with patagial tags were subjected to significantly higher predation rates by Wedge-tailed Eagles Aquila audax than cockatoos fitted with numbered leg bands only, and Johnsen et al. (1997) found coloured leg bands affected mate guarding behaviour of male Bluethroats Luscinia svecica.

In order to avoid handling individuals, researchers have found that with experience they have been able to identify individuals of some bird species based on differences in plumage patterns: for example, male Ruff Philomachus pugnax (Hogan-Warburg 1966; Lank and Dale 2001); Bewick’s Swan Cygnus Columbianus bewickii (Bateson 1977); Osprey Pandion halyaetus (Bretagnolle et al. 1998); Andean Condor Vultur gryphus (Ríos-Uzeda and Wallace 2007); African Penguin Spheniscus demersus (Sherley et al. 2010); and Carnaby’s Cockatoo (Usher et al. 2016). Figure 1: An adult Australian Magpie on a picnic The Australian Magpie Cracticus tibicen is a medium- table, literally looking for “handouts” from picnickers sized, distinctive black and white bird (Figure 1), 37-43 (photograph D. A. Saunders). Australian 2020 Zoologist A Kuruppu & Saunders cm in length, weighing 220-350 g, living for up to 30 years, and beginning to breed in its third year or later (https://en.wikipedia.org/wiki/Australian_magpie accessed 25 August 2020). The species occurs over most of Australia and Tasmania (Pizzey and Knight 1997), with one subspecies C. t. tibicen in the Australian Capital Territory and surrounding New South Wales (Schodde and Mason 1999). The species is territorial, often living in groups consisting of a dominant pair and other subordinate members (Wilson 1946; Carrick Downloaded from http://meridian.allenpress.com/australian-zoologist/article-pdf/doi/10.7882/AZ.2020.046/2675957/10.7882_az.2020.046.pdf by guest on 01 October 2021 1963; Robinson 1956; Rowley 1974; Jones 2002). It is common in urban areas and its loud, distinctive, melodious and individual innovative vocalisations (Wilson 1946; Robinson 1956; Jones 2002) are a feature of many Australian landscapes, including towns and cities (https://en.wikipedia.org/wiki/Australian_ magpie accessed 25 August 2020).

As Australian Magpies occur in groups, are territorial, and actively defend their territories (Wilson 1946; Robinson 1956; Carrick 1963; Jones 2002), they must recognise other individuals, both members of their group and individuals other than group members. In fact, not only do they recognise different Australian Magpies, they also recognise different humans and react differently based on that recognition (DAS pers. obs.) particularly during the breeding season in late Austral winter/spring when they are defending their nest sites. Figure 2. Lateral views of nine individual Australian In this paper, we investigate whether Australian Magpies Magpie specimens from the Australian National Wildlife have individually distinctive plumage patterns. If so, is Collection (photographs Chris Wilson). it possible for humans to use their plumage patterns to identify individual birds reliably? (35026’36S; 149048’06E), Batemans Bay (35042’49S; 150011’05E), Sutton Forest (34034’07S; 150015’25E) and Newcastle (35057’58S; 151039’01E) (Figure 3); an average METHODS of six photographs/individual. Photographs of individuals Museum specimens Ideally, to examine a range of were taken during a single encounter and were taken with plumage patterns displayed by Australian Magpies, either an Apple Iphone model 6s or 10s. visiting a museum and examining their collection of specimens would have been the logical starting point. Twenty individual birds were selected from the However, as we conducted this experiment during the available sample for our pattern matching experiment. “lockdown” as a result of the 2020 Covid-19 pandemic, Photographs of four different lateral views of each we could not visit CSIRO’s Australian National Wildlife of these individuals were selected. To ensure that no Collection (ANWC) in Canberra, nor could we borrow identifying features (e.g., foregrounds or backgrounds) their specimens. Instead, staff at the ANWC took three were available as clues to participants, each photograph photographs of 24 individual specimens of Australian was edited so only the bird was displayed. The Magpies from the Australian Capital Territory and its photographs were edited further to make sure the surrounds. For each specimen they provided dorsal, birds faced in the same direction in all 80 photographs dorso-lateral, and lateral views (Figure 2). Examination of and they occupied the same space in the photographs these photographs indicated that plumage patterns were (Figure 4). The final edited photographs were printed different between these individuals. This confirmed the on 102 by 152 mm photographic paper. rationale for our research and helped form the basis of our experimental pattern matching procedure. Pattern matching experiment Three of the photographs of each of the 20 individuals were laid out on a bench so Photographs of wild Australian Magpies Between there were 20 columns of three photographs. The fourth 3 May and 27 June 2020, we took 295 photographs photographs of the 20 individuals were shuffled and 10 of 51 individual Australian Magpies (subspecies G. t. of these given to the participants. We chose to use only tibicen) from North (35015’02S; 149002’58E) and 10 photographs for pattern matching in order to reduce South (35023’31S; 149004’04E) Canberra, Braidwood the chances of an early incorrect placing leading to Australian B Zoologist 2020 Distinctive plumage patterns in Australian Magpies Downloaded from http://meridian.allenpress.com/australian-zoologist/article-pdf/doi/10.7882/AZ.2020.046/2675957/10.7882_az.2020.046.pdf by guest on 01 October 2021

Figure 4. Photographs of the same nine individual Figure 3. Photographs of nine individual Australian Australian Magpies depicted in Figure 3 set out in the Magpies (photographs the authors). same order, edited with all identifying features removed so the only clues available to participants in the pattern subsequent incorrect placings. Participants were briefed matching experiment were the birds’ plumage patterns on the experiment with the following notes. (photographs the authors).

I am engaged in research in the ACT Science Mentors the same time. Accordingly, the 80 photographs were Program. I am trying to establish if the local subspecies reproduced to make five testing sets and, to make of Magpies have unique plumage patterns so that the experiment easier to set up, the photographs of they may be individually identified by their plumage. the 20 individuals on display were glued to a backing I am grateful to you for your participation in my sheet. Each testing set consisted of 10 sheets, each experiment. Please wear these gloves when conducting of which displayed two individuals with their three the experiment. On the bench are the photographs of 20 different photographs. Each testing session involved Magpie individuals with three different photographs of five participants at once, spaced such that they were each individual. I have cleaned the original photographs not able to influence the choice of other participants. of their background and made sure each individual faces Each participant had the 10 display panels laid out in a the same direction. I have done this to remove anything different sequence. Participants were provided with 10 that may help identify the individual other than the photographs from the shuffled pack of 20 photographs. plumage pattern; that is, the shape of the various white The group testing sessions were conducted between 10 markings on the birds. I will give you a selection of 10 and 12 August 2020. photographs; there is one different photograph of 10 of the individuals displayed on the panel. I would like Each participant was given a number, so they were not you to carefully examine each of these 10 photographs, personally identified. Their age and gender were recorded, compare them with the 20 individuals displayed on the as were the time and date they undertook the pattern panel, and then place each photograph at the bottom matching experiment, their correct score (out of 10), of the three photographs you think is the individual and the time (minutes) taken for them to complete their featured in the photograph. Please take your time. task. Once they had completed the experiment, their If after you have laid out the photographs you think completed layout was photographed with their identifying you have wrongly identified any, feel free to move the number (Figure 5). photographs to where you think they should be. When you are happy with your selection, please call me. Statistical analyses Results were tested with linear correlations and differences between groups by t-tests. Between 14 July and 10 August 2020, the first 20 participants were tested alone. After each test, the order the 20 individual birds were presented was shuffled as RESULTS were the 10 cards given to each participant. However, Eighty participants were tested; 48 females (aged 12-44) we realised that in order to obtain a large sample of and 32 males (12-73); 90% of participants were school participants, more participants needed to be tested at students aged 18 or younger. Australian 2020 Zoologist C Kuruppu & Saunders Downloaded from http://meridian.allenpress.com/australian-zoologist/article-pdf/doi/10.7882/AZ.2020.046/2675957/10.7882_az.2020.046.pdf by guest on 01 October 2021

Figure 5. Layout of a completed pattern matching panel. Three different photographs of each of 20 individual Australian Magpies were pasted on cardboard sheet with two individuals/sheet. A fourth photograph of 10 of the 20 individuals on display was given to the participant to place below the individual they believe it depicted (orange dot on photograph). This photograph is of the completed layout of Participant 25 (photograph I. K. Kuruppu).

There were no significant differences between the mean DISCUSSION correct scores of females and males, nor the mean In their ecological and behavioural studies over much time taken by females and males (Table 1). Over all of the range of Australian Magpies, Wilson (1946), participants, mean correct score was 4.9 ± 2.5 (standard Robinson (1956), Carrick (1963), Hughes et al. (1983, deviation) and mean time 4.2 ± 2.4 minutes. 1996), and Jones (2002) described various categories of social groups that included: permanent groups of a There was a positive linear trend between participant dominant pair and other members holding permanent age and their correct score (Figure 6); at age 15 the breeding territories over many years; marginal groups predicted score was 4.6 and at 55 was 7.4. There was of adult birds occupying poor quality territories also a positive linear trend between participant age and in which they attempt to breed, but were rarely the time taken to complete the pattern matching task successful; mobile groups occupying a territory only (Figure 7); at age 15 predicted time was 3.6 minutes in the breeding season, commuting to foraging areas and at 55 was 8.7 minutes. There was a significant (p = outside the territory, and never breeding successfully; 0.01) positive linear correlation between the time taken open groups of non-breeding adults existing in areas to complete the experiment and correct score (Figure of permanent food; and flock groups of non-breeding 8); at 2 minutes the predicted correct score was 4.2 and birds of all ages and sexes, numbering a few birds to at 10 minutes was 6.7. Those tested individually (ages several hundred. All members of these groups need to 14-73) took significantly (p = 0.004) longer to complete identify individuals and know their place in their social the task than those tested in groups (ages 12-16) (6.13 hierarchy. It is reasonable to assume they do this on compared with 3.53 minutes) and obtained significantly physiognomy, especially plumage, as well as behaviour (p = 0.017) higher scores (5.9 compared with 4.5). and vocalisations (Wilson 1946; Kaplan 2018).

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Table 1. Results of pattern matching of photographs of 10 individual Australian Magpies by female and male participants; mean score is the correct score out of 10, and mean time is the time taken for the test in minutes. Upper and lower CI are 95% confidence intervals.

Upper CI Mean Lower CI N Range p value Score (out of 10)

Female participants 5.3 4.6 3.8 48 0-10 0.21 Male participants 6.2 5.3 4.4 32 1-10 Downloaded from http://meridian.allenpress.com/australian-zoologist/article-pdf/doi/10.7882/AZ.2020.046/2675957/10.7882_az.2020.046.pdf by guest on 01 October 2021 All Participants 7.4 4.9 2.3 80 0-10 Time (mins)

Female participants 4.3 3.8 3.3 48 1.5-10.4 0.07 Male participants 5.8 4.8 3.7 32 1.9-17.3 All Participants 6.5 4.2 2.4 80 1.5-17.3

As described by Wilson (1946), immature Australian account of his study of Australian Magpies in Kings Park Magpies change plumage patterns as they become adult. (Perth, Western Australia), during which he recognised Wilson was able to identify immature birds over time more than 80 individuals of both sexes as well as adults through successive moults. Australian Magpie plumage and immatures on their distinctive plumage patterns. patterns are under genetic control (Dobson et al. 2019) He wrote, “One of my strongest impressions was of the and distinctive plumage patterns should remain the individual characters of the Magpies, which appeared as same over successive moults throughout the life of distinct as those of a number of men and women.” the individual. As a result, Wilson was able to identify individuals over several breeding seasons. Similarly, While our experiment demonstrated the potential for Usher et al. (2015) noted that Carnaby’s Cockatoo with identification of Australian Magpies on their plumage, distinctive markings retained them over several years. it revealed more about human observation and variation in pattern matching skills than it revealed As instructed before they started our pattern matching about the birds. As mentioned in the Results Section, experiment, participants used the different patterns of 90% of participants were high school students, aged 18 white displayed on the birds to discriminate between years younger. As this project was conducted during them. With no prior training, our 80 participants scored the Covid-19 “lockdown” in Canberra, engaging with 4.9 correct photograph placings out of 10, indicating students at the same school as the senior author was that plumage patterns of Australian Magpies may be the only practical method of organising a large sample used by humans to recognise individuals. After we had size in the time available to conduct the project under completed our experiment, we read Wilson’s (1946) the social distancing constraints.

Figure 6. Positive linear trend between participant age Figure 7. Positive linear trend between participant age and correct score. Data from the 72 student participants and the time taken to complete the pattern matching aged between 12 and 18 have been pooled and their task. Data from the 72 student participants aged average age and correct score used in the analysis. between 12 and 18 have been pooled and their average age and time taken for the task used in the analysis.

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Interestingly, participants not tested in groups took longer to complete their task and achieved higher scores than those tested in groups. These participants may have scored higher due to them feeling less pressured to complete the task, compared to those testing in a group, during which they may have felt the need to complete the task so they were not the last of the group to finish, and thus taken less care in their decisions.

Our pattern matching experiment involved participants Downloaded from http://meridian.allenpress.com/australian-zoologist/article-pdf/doi/10.7882/AZ.2020.046/2675957/10.7882_az.2020.046.pdf by guest on 01 October 2021 in one, unrepeated task. It is likely that with practice, as Wilson (1946) established, most participants would have increased their scores in subsequent tests. Unfortunately, Figure 8. Significant linear correlation between time due to constraints imposed by the Covid-19 pandemic, taken for pattern matching task and correct score. it was not possible to replicate the experiment with the There was no difference between human females and same 80 participants. However, what is readily apparent males in their ability to pattern match plumage, nor in from our results is that plumage patterns of Australian the time they devoted to the task. However, there was Magpies are idiosyncratic and may be used reliably to a difference in ability based on age, with older people identify individual birds. This is a useful result for those more likely to achieve higher scores. In addition, the wishing to study behaviour and ecology of Australian longer the time taken devoted to the task, the more Magpies, but not wishing to subject them to handling in likely a higher score would result. order to fit leg bands/rings to aid individual recognition as demonstrated by Wilson (1946).

ACKNOWLEDGEMENTS

This project was conducted as part of IKK’s research in specimens of Australian Magpies; IKK’s Year 10 science Year 10 at Namadgi School in the 2020 Science Mentors- teachers, Dr Roisin Boadle and Ms Laura Shevlin, for Australian Capital Territory (SM-ACT) program. It helping her conduct this experiment on the students at was conducted with appropriate approvals from the Namadgi School, and for assistance with her SM-ACT Australian Capital Territory Education Directorate. We report; Darrell Hancox and Dhanashree Vedanti for are grateful to: the 80 individuals who participated in helping create the additional four panel testing sets; our pattern matching experiment; Geoff McNamara Professor John Craig ONZM, Dr Ross Cunningham, Dr AM, Convenor of SM-ACT for his encouragement; Dr Penny Olsen AM, Dr Eleanor Russell, and an anonymous Leo Joseph and Chris Wilson of the CSIRO Australian reviewer for critical reviews on earlier drafts of our paper; National Wildlife Collection for photographs of museum and Dr Martin Predavec for his editorial support.

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