ANIMAL BEHAVIOUR, 2004, 68, 751e758 doi:10.1016/j.anbehav.2003.12.006 Neighbouring male spotted bowerbirds are not related, but do maraud each other JOAH R. MADDEN*,TAMSINJ.LOWE*,HANNAHV.FULLER*, REBECCA L. COE†, KANCHON K. DASMAHAPATRA*, WILLIAM AMOS* &FRANCINEJURY‡ *Department of Zoology, University of Cambridge yInstitute of Cell, Animal and Population Biology, Ashworth Laboratory, University of Edinburgh zCentre for Integrated Genomic and Medical Research, University of Manchester Medical School (Received 29 July 2003; initial acceptance 24 October 2003; final acceptance 15 December 2003; published online 8 September 2004; MS. number: 7804) Males with elaborate secondary sexual traits can enhance their mating success both by choosing to display at a site that increases the efficacy of their signal and by displaying at a site where the population is structured to provide inclusive fitness benefits via kin selection. Theoretical models and field studies reveal that, across a range of species and especially those with nonresource-based mating systems, males do display with kin. Bowerbirds use a nonresource-based mating system where males show spatial site fidelity and females visit the sites for the purpose of mate choice. However, neighbours can interfere with bower display by marauding (destroying and decoration stealing). Models suggest that local nonaggression pacts provide the best conditional strategy for males, a situation that may be facilitated by kin-mediated inclusive fitness benefits if males displayed together. We used a novel method of calculating relatedness, based on amplified fragment length polymorphism (AFLP), in a population of spotted bowerbirds, Chlamydera maculata, and found no evidence of fine-scale genetic structuring of display sites. Furthermore, males did not display next to kin, but instead an owner’s neighbours were those most likely to maraud his bower. Marauders did not discriminate between kin and nonkin as their victims. Such theft and destruction may affect the mating success of the targeted bower owner. Ó 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Males of several species display close to relatives (Ho¨glund Vehrencamp 1995; Saether et al. 1999; Webster & Robinson et al. 1999; Petrie et al. 1999; Shorey et al. 2000). 1999). It may also influence sexual success indirectly, for Theoretical models predict that relatives should display example by causing females to mate away from unusually together to acquire inclusive fitness benefits (Kokko & violent display sites (Lanctot et al. 1998), or by determining Lindstro¨m 1996). Females prefer to make their choice the size and structure of aggregations that males form from larger aggregations of males, so including even low- (Westcott 1997). Thus, although theory predicts that kin quality males in an aggregation increases its attractive- should display close together, in certain circumstances ness, with direct benefits for the most successful males costs of interference may negate potential benefits. and, consequently, indirect benefits to lower-quality kin. Male bowerbirds of 17 of the 20 species of the family However, males displaying together may hinder as well Ptilonorhynchidae construct and decorate bowers, which as help each other. Intrasexual interference may take the act as targets for female choice. Bowers are also targets of immediate form of disruptions of copulations (The´ry & intrasexual competition, with males destroying structures and stealing decorations from others in the population Correspondence: J. R. Madden, Department of Zoology, University of (Borgia 1985; Borgia & Mueller 1992; Lenz 1994; Madden Cambridge, Downing Street, Cambridge CB2 3EJ, U.K. (email: 2002). For satin bowerbirds, Ptilonorhynchus violaceus, [email protected]). R. L. Coe is at the Institute of Cell, Animal and Population Biology, Ashworth Laboratory, University of Edinburgh, geographically close neighbours are those most likely to King’s Buildings, West Mains Road, Edinburgh EH9 3JT, U.K. F. Jury is maraud each other (Borgia 1985). For other species, at the Centre for Integrated Genomic and Medical Research, University including the spotted bowerbird, Chlamydera maculata, of Manchester Medical School, The Stopford Building, Oxford Road, and Macgregor’s bowerbird, Amblyornis macgregoriae, Manchester M13 9PT, U.K. such a pattern of exclusively local conflict is less clear 751 0003e3472/03/$30.00/0 Ó 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. 752 ANIMAL BEHAVIOUR, 68, 4 (Pruett-Jones & Pruett-Jones 1982; Borgia & Mueller 1992). METHODS Marauding reduces the subjectively measured quality of the bower, an attribute that relates to the mating success Study Site and Species of its owner in a range of bowerbird species (Borgia 1985; Birds at Taunton National Park, Queensland, Australia Borgia & Mueller 1992; Lenz 1994; Uy & Borgia 2000). (site details in Miles & Madden 2002), were caught in mist Females do not appear to gain benefits by mating at nets from August to November, during the male display a particular location, other than those provided directly by and breeding seasons, in 1998, 1999 and 2000. Birds were the male (Borgia 1993; Pruett-Jones & Pruett-Jones 1994). ringed with unique combinations of coloured bands as Therefore, bowerbirds of a range of species have been well as a metal Australian Bird and Bat Banding Scheme described as having a lek (Borgia 1997), exploded lek (Frith (ABBBS) band. This allowed us to identify individual birds & Frith 1995; Ho¨glund & Alatalo 1995) or nonresource- from direct observation at bowers or by motion-activated based mating system (Borgia 1993; Pruett-Jones & Pruett- video cameras set at bowers (Madden 2003). Video Jones 1994). Behavioural studies of female sampling meth- equipment allowed us to record marauding events at ods also suggest similarities to lek like mating systems, bowers remotely. These events were typified by violent with females sampling males by visiting and inspecting tugging on parts of the wall until it collapsed. One or two bowers that are spatially aggregated, using experience to microhaematocrit tubes of blood were collected from most limit their search tactics (Uy et al. 2000, 2001). birds (exceptions occurred when birds escaped from the Without the demands of resource defence, male bower- hand) and stored in ethanol in refrigerators or freezers. birds have, at least in theory, many sites where they could Bower owners were defined as those birds who regularly potentially display. Despite this apparent freedom, bowers frequented, maintained and displayed at a particular are spatially fixed and the same sites are frequently reused bower and who were in attendance at a bower for more over several years; there is a rigid network of even spacing than 75% of the time for which we recorded at least one between members of a population (Frith & Frith 1995, bird present. Molecular sexing indicated that all these 2000a). birds were males. Bower locations and interbower dis- One explanation for this pattern is that suitable tances were calculated as in Miles & Madden (2002), with environments for maximizing display efficacy are limited. the addition of data collected in the same way in 2000. For For example, spotted bowerbirds select bushes of partic- analysis of natural marauding and experimental stealing ular species with a narrow range of canopy thickness, events, bowers were classified as those of either neigh- apparently to increase the efficacy of their signal (Miles & bours or nonneighbours. Bowers were separated by a Madden 2002). This finding is analogous to those studies mean G SD nearest-neighbour distance of 1059G516 m suggesting that males maximize their signal efficacy by (Miles & Madden 2002). Therefore, those bowers within choosing or competing for suitable light environments 2 km of the focal bower were classified as neighbours, and (e.g. Endler & The´ry 1996; Andersson et al. 1998; Barry & those beyond were classified as nonneighbours. Hawryshyn 1999; Fleishman & Persons 2001; Heindl & Winkler 2003). However, such explanations fail to account for the regularity of interbower spacing, nor do Marking Decorations and Retrieval they prescribe where a male should set up his bower in relation to other males in the population. Human artefacts used as decorations on bowers (in- In this study, we investigated a complementary expla- cluding glass, plastic and metal) were marked with the nation for site selection, by considering social factors that bower identity number using a permanent pen (see also affect the location of bowers by male spotted bowerbirds. Borgia & Gore 1986) during our three seasonal measure- Specifically, we evaluated the trade-off between the in- ment visits to bowers in 1998 and 1999 (Madden 2003). clusive fitness benefits that displaying near relatives could Such decorations were also marked during a single bower bring to a male and the possibility of reduced fitness based measurement visit in 2000. During these visits and a sub- on the observation that other (neighbouring) males may sequent bower inspection in August 2001, we recorded all maraud the bower. marked human artefacts found on bowers. If they were not Pruett-Jones & Pruett-Jones (1994) constructed models originally from the bower, as indicated by their identity that showed that the best individual strategy that a male number, we added the new number of the thief’s bower. could perform to maximize mating success was to maraud neighbours’ bowers. However, neighbouring males who guarded their bowers and did not disrupt each other Stealing Experiment always did better than those who marauded each other. Such a conditional strategy could be enhanced, or its Between 28 May and 28 June 2002, five pieces of broken evolution facilitated, if males who display next to kin also green glass were placed 1 m in front of the avenue of accrue inclusive fitness benefits. Spotted bowerbirds show newly located bowers, primarily to assess whether the unusually low levels of marauding (Borgia & Mueller bower was in use. These were marked as before with the 1992), so this species may provide a case where such bower identity number.