Corella, 1993, 17(4): 107---:110

INTERSPECIFIC AGGRESSIVE BEHAVIOUR BETWEEN ROBINS AND OTHER IN EUCAL YPT FOREST

DOUG ROBINSON

Department of Ecology and Evolutionary Biology, Monash University, Clayton, 3168 Present address: 28 Bath Street, Mornington, Victoria 3931

Received 16 November 1992

Records were kept for 328 interactions between Scarlet/Flame Robins and other landbirds at a site in south-eastern . Fifty-seven per cent of interactions were between robins and other ground-foragers, particularly with (41 % ). Bark-foragers, foliage-foragers and honey­ eaters were rarely, if ever, attacked, except when they came near of robins. were responsible for 57 per cent of the attacks directed at robins.

INTRODUCTION STUDY SITE AND METHODS Many species of Australian aggres­ The study was carried out at a site of approximately 300 ha near Nimmitabel, on the Southern Tablelands of New South sively defend food resources and space from ° ° intruders; not only from conspecifics but also Wales (36 46'S, 149 22'E). The site consists of open viminalis, E. pauciflora forest and some grassland, and is from a wide range of interspecificintruders (Dow described in more detail elsewhere (Robinson 1992). 1977; Paton 1980; Loyn et al. 1983; Woinarski 1984). Their aggressive behaviour has been Between March 1984 and March 1986, individually colour­ banded Scarlet and Flame Robins were followed for periods described as 'remarkably indiscriminate' (Dow of 5-45 minutes. during which time the frequency and duration 1977) and extends to species as ecologically dis­ of all interspecific disputes, the identity of the aggressor and similar as fairy-wrens, finches and grebes (Dow identity of the being attacked (hereafter termed 'recipient') 1977; Paton 1980). were recorded. Possible causes of the aggressive behaviour were noted whenever possible. Records of interspecific aggression among other Australian are few. Interspecific RESULTS territoriality, -site defence or dominance behaviour have been recorded for some species Twenty-eight species of bird were involved in a of robin, whistler, treecreeper, and total of 328 interspecific interactions with Scarlet/ corvid (Rowley 1973; Erickson 1974; Noske 1979; Flame Robins at Nimmitabel - 16 species with Loyn 1980; Debus 1982; Woinarski and Rounsevell and 23 species with 1983; Robinson 1989a). Other studies of sympatric (Table 1). For those interactions in which Scarlet/ species of fantail, whistler, fairy-wren and Flame Robins were the aggressor (n = 159), 80 pardalote conversely have reported little or no per cent were with ground-foraging species, notably interspecific aggression (Rowley 1963; Woinarski with Jacky Winter (70%) and occasionally with and Rounsevell 1983; Cameron 1985; Woinarski Hooded Robin, Eastern Yellow Robin and Buff­ 1987). Here I present information on aggressive rumped Thornhill. Only six per cent of attacks by interactions recorded between either Scarlet robins were directed at honeyeaters (Table 1). Robins multicolor or Flame Robins Species that were never, or rarely, involved in P. phoenicea and other species of bird in a forest aggressive interactions with Scarlet/Flame Robins environment in south-eastern . I also despite being common in the study area included: discuss the possible causes of the observed Superb Fairy-wren, White-browed Scrubwren aggressive behaviour. Sericornis frontalis, Striated Thornhill, Golden

107 108 0. Robinson: lnterspecific aggression between robins Corella 17(4)

TABLE L Records of aggressive interactions between Scarlet/Flame Robins and other species of birds. Records are arranged by frequency within the subsets of honcycatcr interactions. ground-forager interactions and interactions with other species. An asterisk indicates that birds were displaced from close to nests.

Scarlet/flame Robin as Aggressor Recipient Sc Fl Sc fl Total

I IONEYEA lloRS Whitc-napcd l loncycatcr Meli1hrep111s /1111a111.,· 12 37 51 White-cared Honcyeater Lichawsron111s le11c01is 27 9 38 Yellow-faced Honcyeater Lic/1enos1on111s chrysops 8 9 13rown-hcadcd Honcycatcr Meli1hrep1us breviros1ri.1· 2 2 -I New Holland I loncycatcr Phylidonyris 11ovaelwll1111ili11e I , 2 3 Eastern Spincbill Aca11rhorhy11c/111.1· /e,,uirosrris I (;ROUND-FORi\(;ERS Jacky Winter 1Hicroeca leucoplwea 59 52 (, 17 134 Eastern Yellow Robin F,opsaliri11 a11srralis I 19 20 Hooded Robin Mi!lanodrl'lls c11c11l/a1a 2· 3 8 13 !:luff-rumpedThorn bill A�·11lllhiza reg11/oides 7 I 8 Grey Shrike-thrush Col/11rici11cla /11m11011irn I* 2 -I Willie Wagtail Rhipid11m le11cophrys 2 3 Superb Fairy-wren Ma/urnscy1111e11s I 2 Yellow-rumped Thornhill/\ca111hiza chry.rnrrlwa Richard's Pipit A111hus 11m•acsccla11diae

OTHER Sl'cCIFS Grey Fantail Rhipid11mjiilifii110.rn 5 -l. 5 15 Striated ThornhillArn111hiza li11ea1a 4* I 5 Dusky Wuodswallow A r1a11111s cya11op1en1s I* 3 -l Rufous Whistler l'ad1yceph11/a r11fivc111ris I* 2 3 Laughing Kookaburra fJacelonuvaeguineae I* Sacred Kin�fisher /lalcvo- 11 .\"/IIICta I• Satin Flycatcher Myiag·mcy11110/e11rn I' Varied Sittclla D11phoe11osi11a chrysop1cm Striated Pardalo1c 1'11rda!0111s s1ria111.1· Hursficld's 13ronze-rnckooChrysornccy.r /Jasalis Shining Bronze- C/1rysococcyx /11cidus Fan-tailed Cuckoo C11c11/us p_vrrhoph1111us Pallid Cuckoo C11rn/11sp11/lid11s

l'OTAI.S 85 7-l 58 111 .\28

Whistler Pachycepha/a pecwm/is, Rufous Whistler, 57 per cent were initiated by honeyeatcrs. Red-hrowcd Trcecrecpcr Climacteris erythrops, especially by White-eared Honeycatcr and Whitc­ White-throated Treecreeper C. feucophaea, naped Honeyeater (Table I). A further 35 per Spotted Pardalotc Parda/0111s punctatus and cent were initiated by ground-foragers, including Striated Pardalotc. 14 per cent begun by .Jacky Winters (Table I). Some species were only/mainly displaced by Scarlet/Flame Robins if they came within c. JO m lnterspecific interactions occurred throughout of nests (Table I). The robins also displaced or the year (Table 2) but some seasonal patterns scolded Pallid . Fan-tailed Cuckoos, appeared to differ between the two species of Shining Bronze-cuckoos and Horsficld's Bronze­ robin. Thus. Flame Robins interacted most often cuckoos that came too close to nests. with Jacky Winters in winter and spring, while For those interactions in which Scarlet/Flame Scarlet Robins interacted most often with Jacky Robins were the recipients of the attack (n = 169). Winters in autumn. September, 1993 D. Robinson: lnterspecific aggression between robins 109

DISCUSSION TABLE 2 As found by some other studies of interspecific Seasonal distribution of aggressive encounters between robins aggression between insectivorous birds(Slagsvold and other species of birds expressed as number of encounters/ hour. The smaller sample sizes for Flame Robins in autumn 1978; Woinarski and Rounsevell 1983), nest-site and winter are due to the birds' absence from the study site defence was one cause of aggression between from late April to August. robins and other bird species. Interspecific aggression by robins towards cuckoos also Autumn Winter Spring Summer presumably represented· nest-site defence or SCARLET ROBIN defence of young: one pair of Flame Robins Observation time (h) 37.8 34.4 21.7 29.1 played host to a Fan-tailed Cuckoo and cuckoldry Interactions with: of Scarlet Robins by Horsfield's Bronze-cuckoo All honeyeaters (n/h) 0.38 0.29 0.41 0.34 has been observed elsewhere (Howe 1932). How­ All non-honeyeaters 167 0.26 0 88 0.3] ever, interspecific interactions between robins • Ground-foragers 1.46 0.23 0.73 0.10 and other insectivores occurred throughout the • Jacky Winter l.26 0.06 0.65 0.03 year, not just in the breeding season (Table 2), FLAME ROBlN and additional causes are needed to explain the Observation time (h) 16.3 8.8 22.5 22.9 remaining aggressive behaviour. Interactions with: Mistaken identity has been proposed as one All honeyeaters (n/h) 0.12 1.02 1.24 1.04 All non-honeyeaters 1.17 3.52 2. l8 1.00 possible cause of interspecific aggressionbetween • Ground-foragers 110 3.52 1.73 0.70 similarly plumaged birds (Murray 1971; Savard • Jacky Winter 0.31 2.73 l.38 0.39 and Smith 1987). It was an unlikely cause of the aggression directed towards male robins by honeyeaters and other species, given the bright­ Buff-rumped Thornbill. The latter three species red breasts of adult males. However, it may all forage on the ground (Recher and Holmes explain why robins sometimes attacked Jacky 1985; Ford et al. 1986, pers. obs), and overlapped Winters, as Jacky Winters somewhat resemble at least partly with Scarlet and Flame Robins in female robins in appearance and behaviour. Field their use of habitat and space(Robinson 1989b). observations, though, showed that robins Accordingly, the larger Hooded and Eastern responded to nearby Jacky Winters much less Yellow Robins may have benefittedfrom displacing often than they responded to nearby robins, Scarlet/Flame Robins whenever they entered the implying that the robins were able to identify larger birds' foraging space; Scarlet/Flame Robins Jacky Winters and behaved accordingly. may have benefitted from displacing the smaller Instead, competition for food appeared to be Buff-rumped Thornbills from mutual foraging the most likely cause of interspecific aggression sites. Although interspecific aggression between between Scarlet/Flame Robins and Jacky Winters. these species was recorded only rarely, it has been The Jacky Winter was one of the few other proposed that such occasional disputes may signify insectivores at the study site that pounced for prey interference competition between dominant and in the open forest. Its foraging behaviour and use subordinate species (Beaver and Baldwin 1975; of foraging space in winter and spring was similar Sherry 1979; Maurer 1984) and may lead to to that of the robins; each species tending to avoidance of the dominant's foraging space by the forage in open forest and pouncing or snatching subordinate bird (Morse 1974; Beaver and for prey on or close to the ground. Both species Baldwin 1975). of robin consequently may have benefittedby dis­ placing Jacky Winters from shared feeding sites Aggressive interactions between robins and in order to increase their potential food supply; honeyeaters comprised a tiny percentage of the particularly as the time cost of the aggressive robins' behavioural time budgets ( c. 0.1% , behaviour was low(< 0.2%, Robinson 1989b). Robinson 1989b). Honeyeaters nonetheless were the most frequent aggressors towards robins Potential increases in food availability similarly (Table 1) and sometimes chased them for distances may explain the interspecific aggression observed of up to 40 m. These observations support results occasionally between Scarlet/Flame Robins and suggesting that honeyeaters exclude many birds Hooded Robin, Eastern Yellow Robin and which enter their foraging space in order to 110 D. Robinson: lnterspecific aggression between robins Corella 17(4)

111crcase the honeycaters' potential food supply, Loyn . R. H., Runnalls. R. G., Forward. G. Y. and Tycrs. J. even when overlap in foraging niche is relatively (1983). Territorial Bell Miners and other birds affe cting _ small (Ford 1981; Ford and Paton 1982; Loyn et populations of prey. Sc ience 221: 1411-1413. Maurer, B. A. ( 1984). Interference and exploitation in bird al. 1983; Wykes 1985). Results from this study further suggest that some insectivorous birds in com111uni1ies. Wilson Bull. 96: 380--395. ustralia likewise use brief acts of aggression to Morse, D. H. (1974). Niche breadth as a function of social � _ dominance. Amer. Nat. l08: 818-830. displace lmds that forage in similar ways or utilize Murray, 13. G., Jr. (1971). The ecological consequences of the same feeding area. It remains to be seen inlerspecilic territorial behaviour in birds. Ecology 52: whether such aggressive acts lead to increases in 414--423. the robins' available food supply. Noske, R. A. (1979). Co-existence of three species of tree­ creepers in north-eastern New South Wales. £11111 79: 120-128 Paton, D. C. (1980). The importance of manna. honeydew and lerp in the diet of honeyealers. Emu 80: 213-226. ACKNOWLEDGMENTS Recher, 1-1. r-. and Holmes, R. T. (1985). Foraging ecology and seasonal patternsof abundance in a forest avifauna. In: My thanks to the landholders who kindly 'Birds of Eucalypt Forests and Woodlands: Ecology. Con­ allowed me to work on their properties. Com­ servation, Manage ment' (Eds: A. Keast. H. F. Recher. H. ments by Mike Cullen, Hugh Ford, John Ford and D. Saunders) pp. 79-96. (RAOU and Surrey McLaughlin, Moira Robinson and John Really and Sons: Chipping Norton.) Woinarski greatly Robinson, D. ( I989a). lnterspecific aggr ession and territorial improved earlier drafts. Mike behaviour between Scarlet Robin Petroica 11111/ticolor and Cullen also assisted considerably with data Flame Robin P. phoe11ice11. t=:1 1111 89: 93-101 . analysis. The study was partly funded by a Robinson, D. (1989b}. Ecology and behaviour of the Scarlet Monash University Post-Graduate Scholarship. Robin Pe1roica 111,dticolor and Fla111c Robin P. phoe11icea in southeastern Australia. l'h.D thesis. Monash University. Robinson. D. ( 1992). 1-labital use and foraging behaviour of the Scarlet Robin and Flame Robin at a site of breeding­ 19: REFERENCES season sympatry. Wil d/. Res. 377-395. Rowley, I. (1%3). The reaction of the Superb 131ue Wren. Malurus cyaneus, lo models of the same and closely related rlcaver. D. L. and Ualdwin. P. H. ( 1975). Ecological overlap species. Fmu 63: 207-21-l. and the problem of comp.:tition and sympatry in the West­ Rowley. I. ( 1973). The comparative ecology of Australian ern and Hammond"s f-lyc atchcrs. Condor 77: 1-13. corvids. II. Social organization and behaviour. CS/RO Cameron. E. ( 1985). Habitat usage anti foraging behaviour of Wild/. 18: 25--65. three fantails (Rhipidura: Pachycephalidae). In: •Birds of !