163 AUSTRALIAN FIELD 2004, 21, 163-165 Why Do Rainbow iris Place Wallaby Dung at the Entrance to Their Nests?

UDO M. ZIMMERMANN1•2 and RICHARD A NOSKE 1 1Key Centre for Tropical Wildlife Management, School of Science, Charles Darwin University, Darwin, Northern Territory 0909 2Present address: Weidenstrasse 42, 8645 Jona, Switzerland

Summary Thirty-four percent of Rainbow Pitta Pitta iris nests examined at Fogg Dam near Darwin, Northern Territory, had wallaby faecal pellets at their entrances. This may have an anti-predator function by providing an odour 'camouflage' that prevents predators from smelling eggs, nestlings or incubating adults.

Introduction Several of pittas (Passeriformes: Pittidae) are known to build a 'doormat' of fine twigs at the entrance to their dome-shaped nests (Erritzoe & Erritzoe 1998), but only two species, both Australian, are known to add mammal dung to this doormat. Favalaro (1931) was first to note that the Pitta versicolor used wallaby faeces to pave the approach to, and interior floor of, its nest. Both he and Mervin Goddard (in Erritzoe & Erritzoe 1998) noted that this material stained the eggs, after it had been carried in upon the feet of the parents. To our knowledge, no explanation has been proposed for this use of mammal faeces. Indeed Erritzoe & Erritzoe (1998) inferred that the unsanitary nest conditions resulting from the habit may have contributed to the high ectoparasite loads reported for the species.

Method Nests of Rainbow Pittas P. iris were located by following or by systematic nest searches, and monitored, during three breeding seasons from October 1992 to February 1995 at Fogg Dam, near Darwin, Northern Territory (12o33'S, 131°18'E). Objects found at the entrance to nests were qualified and quantified.

Results At Fogg Dam, Rainbow Pittas built their large domed nests at varying heights (0-20 m) from the ground, and lined the inside with fronds of ferns or rootlets (Zimmermann & Noske 2003). Of the 64 accessible nests at this site, 22 (34%) possessed up to ten faecal pellets of Agile Wallabies Macropus agilis at the base of the entrance. An additional five nests had a single feather at the entrance, while another four had other 'decorations', including hair and a scat of a Canis lupus. Nests with wallaby scats were found more often in mixed eucalypt-Pandanus forest than in monsoon rainforest (71 % vs 16% of accessible nests in each habitat; X2 with Yate's correction factor = 16.7, df = 1, n = 64, P< 0.001) (Table 1). Predation of Pitta eggs was significantly higher in the monsoon rainforest than in the mixed forest (Zimmermann 1996). However, nests with wallaby scats were depredated at a similar rate to those without scats (53 % cf. 55 %, X2 = 0.37, df = 1, n =50, P >0.05) (Table 1). AUSTRALIAN 164 ZIMMERMAN & NOSKE FIELD ORNITHOLOGY

Table 1: Occurrence of wallaby scats at the entrance to nests of Rainbow Pittas at Fogg Dam, near Darwin, N.T., in difl'erent habitat types, and predation at the nests.

With wallaby Without scats scats Total Eucalypt-Pandanus 15 6 21 Monsoon rainforest • 7 36 43 Total 22 42 64

Depredated 9 18 27 Successful 8 15 23 Fate uncertain 5 9 14

Discussion We hypothesise that the placing of mammal faeces at nest entrances by Rainbow Pittas (and possibly also Noisy Pittas) has an anti-predator function, by providing an odour 'camouflage' that may prevent predators from smelling eggs or nestlings, or even the incubating adults. Evidence from the condition of depredated nests, the fate of artificial eggs with radio-transmitters, and the tooth marks left on plasticine dummy eggs (Zimmermann 1996) suggest that the major predators of eggs of Rainbow Pittas at the study site were snakes and rats, both of which are predominantly nocturnal and use olfactory, rather than visual, cues. Wallaby faeces were common at the study site, and therefore did not allow predators to associate wallaby scats with Rainbow Pitta nests. The similarity of nest-predation rates between nests with wallaby scats and those without scats may have been because of the small sample size of the former or possibly to a high abundance of nest­ predators at the site. Alternatively, the behaviour may have evolved to protect the incubating adults, rather than their eggs and young, since enclosed (domed) nests offer less scope than open cup-shaped nests for escape from entering predators. Coates (1990) observed that incubating adult Red-bellied Pittas P erythrogaster in New Guinea were easily caught on the nests. Nest protection by odours has been reported in nuthatches. White-breasted Nuthatches Sitta carolinensis (Passeriformes: Sittidae) in North America sweep the bark surrounding their nest-holes while holding beetles which excrete oily fluids that may repel hole competitors like squirrels Sciunts (Kilham 1971). Such behaviour constitutes a seldom-recognised form of nest-defence, apparently aimed at confusing or deceiving nest-predators or competitors (Type 'B' in the classification of Collias & Collias 1984). The role of wallaby scats in protecting eggs and nestlings could be tested experimentally by removing scats from some nests and adding them (or new scats) to other nests, preferably at a different site from that used in the present study. However, the possible role of scats in protecting parents would be difficult to demonstrate, given the apparent low mortality rate of adults (Zimmermann 1996). Could other objects at the entrance to pitta nests have a simil ar function to wallaby scats? It seems unlikely that feathers, the most frequent object other than wallaby scats, offer the same odour camouflage as faecal pellets. We speculate that such decorations may serve to communicate the status of pitta territories, or of the birds themselves, to partners and/or other pairs. VOL. 21 (4) DECEMBER 2004 Wallaby Dung at Rainbow Pitta Nests 165

Acknowledgements This manuscript was improved by the comments of two anonymous referees. The study was funded by the Department of Employment Education & Training, the Northern Territory University, the M.A. Ingram Trust, the Australian Nature Conservation Agency and the Parks & Wildlife Commission of the Northern Territory.

References Coates, B.J. (1990), The Birds of Papua New Guinea, vol. 2, Dove Publications, Brisbane. Collias, N.E. & Collias, E.C. (1984), Nest Building and Behaviour, Princeton University Press, Princeton, New Jersey, U.S.A. Erritzoe, J. & Erritzoe, H.B. (1998), Pittas of the World, Lutterworth Press, Cambridge, U.K. Favaloro, N.J. (1931), 'Notes of a trip to the Macpherson Range, south-eastern Queensland', Emu 31, 48- 59. Kilham, L. (1971), ' Use of blister beetle in bill-sweeping by White-breasted Nuthatch', Auk 88, 175-176. Zimmermann, U.M. (1996). Ecology of the Monsoon-rainforest E ndemic Rainbow Pitta Pitta iri~~ PhD thesis, Northern Territory University, Da1win. Zimmermann, U.M. & Noske, R.A. (2003), 'Breeding biology of the Rainbow Pitta Pitta iris, a species endemic to Australian monsoon-tropical rainforests', Emu 103, 245-254. Received 7 Janu(lly 2004 •