AGGESSIO AMOG OOE OIS Mlndr llt A OE IS LULU L. FITRI1,2 and HUGH A. FORD1 1Division of Zoology, University of New England, Armidale, New South Wales 2351 ² Present address : Laboratoire de Psychophysiologie et d'Ethologie, University de Paris X, 200, Avenue de la République, 92001 Nanterre Cedex, FRANCE Received: 20 August 1996 Ml dd bn Mlndr llt dpld r rn trd npf thn dd fl, nd b nvlvd n r rn th thr p. Intrpf rn nfrnt, th 2. t pr hr, prbbl b th p occurs t l dnt nd t rp hv f nhbr. Mt ntrpf rn drtd t lll lr rnd r rl frn ntvr, h thr rbn, Wntr Mr fnn nd Wll Wtl hpdr lphr. h ld hv bn d t drtd ntrpf rn, th p rbl thr l r fl dd bn, r d t ptntl pttn fr fd. Sllr rndfdn ntvr, such as thrnbll, r l th rpnt f dd bn rn. Svrl ntrtn nvlvd th ntrl rv hntr, thh bn r ftn th rr rthr thn rpnt f rn. bn t ttd ptntl nt prdtr, h hn Kbrr l nvn. l bn hd njrfnn bhvr t n ntrdn Kbrr nd ftn t ppl nr t hr nt. INTRODUCTION STUDY SITES AND METHODS The Hooded Robin Melanodryas cucullata is a The study was carried out in eucalypt woodland at three sites widespread species in Australia (Blakers et al. 1984), within 50 kilometres of Armidale (Gara, Strathaven, Torryburn, yet it appears to be common nowhere. Furthermore, described in Fitri and Ford 1997). From April 1991 to April 1992, L. L. Fitri collected time budgets of Hooded Robins by following there is evidence that it has declined markedly in individual birds and recording all activities and their duration. eucalypt woodland in southern Australia (reviewed by When aggressive acts occurred, she recorded their frequency nd the Fitri and Ford 1997). It is one of a large number of identity of the aggressor and the aggressed birds. The aggressors ground-foraging birds that occur in agricultural areas were individuals that either chased or threatened other species, and whose decline is giving rise to concern for their whereas the aggressed birds were individuals that were chased or long-term conservation (Recher and Lim 1990; Barrett threatened. An aggressor was considered to be threatening another individual when it approached within 0.5 metres of it, leading the et al. 1994). threatened bird to respond. Sometimes either threatening or threatened Although many hypotheses have been proposed birds performed agonistic displays, which included exposing for the loss of birds in fragmented and degraded wood- contrasting wing feathers and/or pointing the open beak at their opponent. land in Australia, few data are available to test these (Ford et al. in prep.). One hypothesis, which is During the breeding season (September to December 1991), supported by data and experiments, is that aggressive aggressors were considered to be threatening the Hooded Robin's nest honeyeaters, such as Noisy Miners Manorina if they went close enough to the nest to cause the parents to scold, melanocephala, exclude many insectivorous birds from fly away or display injury-feigning behaviour. degraded woodlands (Dow 1977, Grey et al. in press). Four groups of species were identified: honeyeaters, nest predators, A second hypothesis, which has some support, is that ground-feeding insectivores and others (Table 1). The third group nest predators have increased, leading to inadequate included species that glean or pounce on prey on the ground, and to breeding success and recruitment. Thirdly, simplifi- some degree capture aerial prey. Hooded Robins mostly glean or pounce on the ground throughout the year, but may spend up to 16% cation of ecosystems is believed to lead to a reduction of their time in summer in aerial pursuit of prey (Fitri 1993). in species diversity, due to competition amongst Thornbills were sometimes not identified, but as most were Yellow- ecologically similar species. This idea is best rumped and Buff-rumped, they are included in the ground-foraging developed for birds on islands (e.g. Diamond 1975), insectivore group. The final group, though heterogeneous, included but has not been applied to birds in remnant woodland a number of aerial feeding or foliage-feeding insectivores. in Australia. G tests and χ ² tt r d t pr frn f In this paper we describe aggressive behaviour by ntrpf rn nvlvn h x nd th fr n rptvl A thr- AOA d t tt vrtn n Hooded Robins. We quantify the frequency of intra- nbr f ntrtn pr hr (ntrtn rt n x f and interspecific aggression, and the extent to which dd bn t nd n fr th hl td prd t this aggression involves honeyeaters, nest predators and r l-trnfrd f th vrn r nl v pr nt ecologically similar species. lvl f nfn r d fr ll tt TABLE 1 Species that interacted aggressively with Hooded Robins. G = ground-foraging insectivore, H = honeyeater, P = predator, 0 = other. Number of cases of aggression towards Hooded Robin (>HR) and aggression from Hooded Robin (HR>). Yellow-rumped and Buff-rumped Thornbills were combined as they were not always identified to species. Species >HR HR> Sacred Kingfisher (G) Todiramphus sancta 0 1 Brown Treecreeper (G) Climacteris leucophaea 3 7 Buff-rumped Thornbill (G) Acanthiza reguloides 4 33 Yellow-rumped Thornbill (G) Acanthiza chrysorrhoa Jacky Winter (G) Microeca fascinans 14 35 Scarlet Robin (G) Petroica multicolor 1 15 Yellow Robin (G) Eopsaltria australis 0 2 Grey Shrike-thrush (G) Colluricincla harmonica 4 1 Restless Flycatcher (G) Myiagra inquieta 1 2 Willie Wagtail (G) Rhipidura leucophrys 26 22 White-eared Honeyeater (H) Lichenostomus leucotis 2 2 Fuscous Honeyeater (H) L fuscus 6 6 White-plumed Honeyeater (H) L penicillatus 8 11 White-naped Honeyeater (H) Melithreptus lunatus 1 0 Eastern Spinebill (H) Acanthorhynchus tenuirostris 0 1 Laughing Kookaburra (P) Dacelo novaeguineae 2 4 Pied Butcherbird (P) Cracticus nigrogularis 1 0 Australian Magpie (P) Gymnorhina tibicen 6 0 Pied Currawong (P) Strepera graculina 2 0 Australian Raven (P) Corvus coronoides 7 0 Scaly-breasted Lorikeet (O) Trichoglossus chlorolepidotus 1 0 Eastern Rosella (O) Platycercus eximius 1 0 Rainbow Bee-eater (O) Merops ornatus 0 2 Crested Shrike-tit (O) Falcunculus frontatus 1 0 Golden Whistler (O) Pachycephala pectoralis 1 1 Rufous Whistler (O) P rufiventris 3 1 Grey Fantail (O) Rhipidura fuliginosa 1 2 White-winged Triller (O) Lalage sueurii 1 1 Dusky Woodswallow (O) Artamus cyanopterus 16 2 Diamond Firetail (O) Emblem guttata 0 3 Total 113 154 RESULTS that the roles of individuals were hard to follow. After stopping for a few seconds at a perch, they Description of Aggressive Behaviour sometimes continued chasing until lost from sight. In general, the aggressive displays of Hooded Robins Chasing was frequent between males and females, were not spectacular. The following intraspecific and among males. Some of this chasing could have interactions were noted: been courtship. When males chased each other, sometimes females took part, by following their a) Threat display: dominant birds landed on a perch partners in chasing the other male. This behaviour and either held their body low with wings close to was similar to the aggression shown in border the body or fluffed their feathers, flicked their disputes, but occurred between members of a group. wings, and pointed their bill at their opponent. Sometimes the threatened bird gave a `squee' sound, d) Pecking: where one bird pecked another. On two followed by either displacement to another perch or occasions, a male pecked a female at Torryburn in flying away. Displacement comprised the dislodging order to take prey from his partner's bill. Once, at of a threatened bird from its perch with the Gara, an adult male was seen to peck an immature approaching bird then occupying the same perch. male which was still in grey plumage. Dominant females more frequently threatened submissive females rather than supplanting, chasing, Intraspecific Interactions or pecking them. Hooded Robins may live as pairs or in groups, including one or more non-breeding helpers (Fitri and b) Supplanting: where the dominant bird landed near Ford 1997). Interactions between groups were seen less another bird, causing the latter to leave its perch. frequently than those within groups. Interactions Supplanting was rarely followed by any threat display. Females were usually supplanted by males. between neighbouring groups were usually seen during border disputes. Most disputes were between males c) Chasing: where the birds chased one another, with rather than between males and females or between agitated piping sounds. They chased irregularly, females. Border disputes commonly involved two sometimes high through the trees and so rapidly males from neighbouring territories, which had come within 10 metres of each other. Trespassing birds were interactions differed significantly between seasons, usually chased from perch to perch by the territory being most frequent in autumn and least frequent in owner. This was accompanied by agitated piping and spring (Table 4). There was no significant difference scolding. Birds never made physical contact in the air in interaction rate between sites and none of the (i.e. one had already left a perch before the other statistical interactions among sex, site or season was arrived at the same or different perch). Disputes lasted significant (Table 4). up to 4 minutes and traversed up to about 40 metres, From 9-21 per cent of aggressive encounters with chasing occurring among the canopy of trees involved honeyeaters at each site (Tables 1 and 3). rather than near the ground. Hooded Robins were as likely to be aggressive towards Members of a group maintained close proximity for honeyeaters (20 observations) as they were to be the most of the time.