Austral Ecology (2006) 31, 58–67 doi:10.1111/j.1442-9993.2006.01543.x © 2006 Ecological Society of Australia *Corresponding author. Accepted for publication July 2005. Does rock disturbance by superb lyrebirds (Menura novaehollandiae) influence habitat selection by juvenile snakes? JONATHAN K. WEBB 1 * AND MARTIN J. WHITING 2 1 School of Biological Sciences, The University of Sydney, Sydney, NSW 2006 Australia (Email: jwebb@bio.usyd.edu.au); and 2 School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Private Bag 3,Wits 2050, South Africa Abstract: Vertebrates that destroy or disturb habitats used by other animals may influence habitat selection by sympatric taxa. In south-east Australian forests, superb lyrebirds (Menura novaehollandiae) displace soil, leaf litter and rocks during their daily foraging activities. We investigated whether superb lyrebirds disturb small sandstone rocks that endangered broad-headed snakes Hoplocephalus bungaroides and common small-eyed snakes Cryptophis nigrescens use as diurnal thermoregulatory sites. To estimate the frequency of lyrebird rock disturbance, and to assess whether lyrebirds also attack small snakes, we placed 900 plasticine snake replicas under stones on rock and soil substrates along transects on three sandstone plateaux. Because juvenile snakes must select retreat sites that simultaneously allow them to thermoregulate and minimize predation risk, we quantified the thermal environments underneath stones on rock and soil substrates. During the 6-week experiment, animals disturbed rocks on soil substrates twice as often (16.9%) as rocks lying on rock substrates (8.2%). Disturbed rocks were significantly smaller and lighter than undisturbed rocks on both substrates. Lyrebirds were the major agents of disturbance, and attacked 40% of snake models under disturbed rocks. Rocks on soil substrates conferred the greatest thermal benefits to snakes, but both species of snake avoided these microhabitats in the field. Instead, juvenile snakes selected rocks on rock substrates, and sheltered under stones that were too heavy for superb lyrebirds to disturb. By disturbing rocks over millennia, superb lyrebirds not only have shaped the physical landscape, but also may have exerted strong selection on habitat selection by sympatric snakes. Key words: biopedturbation, disturbance, predation risk, thermoregulation, trade-off. INTRODUCTION Disturbance is a fundamental force that influences the structure and function of ecosystems (Wootton 1998). Although it is well known that large-scale abiotic disturbances (fires, floods, hurricanes) strongly affect biological diversity (Huston 1994), smaller-scale biotic disturbances caused by vertebrate digging and burrow- ing (biopedturbation) can also influence the spatial heterogeneity and diversity of many landscapes (Meadows & Meadows 1991; Jones et al. 1994; Whitford & Kay 1999). By creating holes or depres- sions that trap nutrients, seeds and water, burrowing vertebrates profoundly influence the physical and chemical properties of soils, and the germination and survival of plant seedlings. For example, in Australia, burrows created by Gould’s sand goanna influence water infiltration rates and the distribution of mulga (Acacia aneura) woodlands (Whitford 1998), while pits excavated by kangaroos influence soil chemistry and the spatial heterogeneity of nutrient-rich sites in arid and semi-arid woodlands (Eldridge & Rath 2002). To date, most Australian studies on vertebrate bio- pedturbators have focused on their effects on soil biol- ogy (Garkaklis et al. 1998, 2003; Whitford 1998; Eldridge & Rath 2002) or seedling germination and survival (Ashton & Bassett 1997; Theimer & Gehring 1999). By contrast, the effect of vertebrate biopedtur- bation on the behaviour of sympatric native animals has not been studied in detail. Many species respond to animals that create disturbance (especially humans) as potential predators (Frid & Dill 2002), and modify their behaviour to minimize the risk of predation (Lima 1998; Gill et al. 2001). For example, timber rattlesnakes Crotalus horridus abandon their preferred habitats (rocks) after capture or after the rocks are disturbed by humans (Brown 1993). Other studies on mammals and birds have found that human distur- bance can cause habitat shifts (Boyle & Samson 1985), disruption of foraging activities (Gander & Ingold 1997), home range displacement (McLellan & Shackleton 1988) or reduced reproductive success (Giese 1996). Although the effects of human distur-