J. Zool., Lond. (2005) 267, 419–429 C  2005 The Zoological Society of London Printed in the United Kingdom doi:10.1017/S0952836905007636 Synchrony and timing of breeding influences sexual segregation in western grey and red kangaroos (Macropus fuliginosus and M. rufus) Abigail M. MacFarlane* and Graeme Coulson Department of Zoology, The University of Melbourne, Victoria, 3010, Australia (Accepted 16 March 2005) Abstract We examined whether synchrony and timing of breeding influenced magnitude and timing of sexual segregation in sympatric western grey kangaroos Macropus fuliginosus and red kangaroos M. rufus, at Hattah-Kulkyne National Park, in south-eastern Australia. These species vary in the synchrony and timing of their mating activity: western grey kangaroos mate during a relatively synchronous period, predominantly during spring, while red kangaroos mate throughout the year. Surveys were conducted during autumn and spring 2000 to examine seasonal patterns of mating activity, group composition, spatial distribution, and habitat selection of adults of both species. Habitat selection was also examined by analysing data from culls conducted from 1998 to 2002. Mating activity occurred synchronously in western grey kangaroos, thus, like in many ungulate species, there was a time of peak segregation, during autumn, when females were in lactational anoestrus, and a time of peak aggregation, during the period of peak mating activity in spring. In red kangaroos, mating activity occurred during both seasons, but showed a slight peak during autumn. Consequently, segregation was weaker than in western grey kangaroos but occurred through- out the year, with a slight peak during spring. The degree of social and spatial segregation in western grey and red kangaroos was comparable to that in ungulates, while habitat segregation was considerably lower than is typically seen in ungulates. These results indicate that breeding phenology is a major factor involved in sexual segregation, and highlight the importance of directing attention at the general conditions underlying this phenomenon. Key words: sexual segregation, sex differences, mating synchrony, Macropus fuliginosus, Macropus rufus INTRODUCTION When males and females of a species separate along a be- havioural or ecological dimension they show a behavioural pattern called sexual segregation. Sexual segregation is widespread in the Animal Kingdom, occurring in taxa as diverse as primates (e.g. Pellegrini, 2004), birds (e.g. Gonzalez-Solis, Croxall & Wood, 2000) and fishes (e.g. Croft, Botham & Krause, 2004). This phenomenon is nearly ubiquitous among sexually dimorphic and synchro- nously breeding ungulates, and is particularly prevalent amongst cervids and bovids (e.g. Clutton-Brock, Iason & Guinness, 1987; Miquelle, Peek & Van Ballenberghe, 1992; Bleich, Bowyer & Wehausen, 1997; Bowyer, 2004). Most research on sexual segregation has been focused on testing specific hypotheses about ultimate and/or proxi- mate causes (e.g. Main & Coblentz, 1996; Ruckstuhl & Neuhaus, 2002; Mooring et al., 2003; Ciuti et al., 2004), while little attention has been directed at the general conditions underlying this phenomenon. Sexual body size *All correspondence to: A. M. MacFarlane. E-mail: a.macfarlane2@zoology.unimelb.edu.au dimorphism and the periodicity of mating opportunities are recognized as key factors involved in sexual segreg- ation (Jarman, 1983; Main, Weckerly & Bleich, 1996; Isaac, 2005), but until recently, few studies had directly examined their influence on segregation (but see Mysterud, 2000; Bonenfant et al., 2004; MacFarlane & Coulson, in press). In this study, the influence of breeding phenology on sexual segregation is further explored in another group of terrestrial herbivores, the kangaroos (Marsupialia: Macropodidae). Kangaroos represent a radiation of terres- trial herbivores that has occurred in parallel to that of the ungulates, and consequently are ecologically and behaviourally comparable to them in many ways (Jarman, 1983). Like ungulates, they are characterized by life histories of synchronous breeding and sexual dimorphism in body size, and show evidence of sexual segregation (MacFarlane & Coulson, in press). Although few kan- garoos are classified as strictly synchronous breeders (Croft, 1989), mating in most species occurs within a restricted part of the year, and some populations approach the synchrony seen in the rut of ungulates. For example, in a population of eastern grey kangaroos Macropus