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We determined whether nest-site characteristics influence reproductive success and whether experience influences nest-site selection in a population of cooperatively breeding Long-tailed Tits (Aegithalos caudatus). Nest predation was high; only 17% of breeding attempts resulted in fledged young. The height of nests was an important determinant of success; low nests were significantly more successful than high nests. A breeder's age, natal nest site, and breeding experience had no significant effect on nest-site selection. However, failed breeders who helped at the successful nests of conspecifics built subsequent nests lower than nests built prior to their helping experience. Failed breeders who did not help showed no reduction in tlse height of subsequent nests. Moreover, the subsequent reproductive success of failed breeders who helped was significantly higher than that of failed breeders who did not help. We conclude that helpers gain information on nest-site quality through their helping experience and thus gain a direct fitness benefit from their cooperative behavior. We suggest that experience as a helper offers a more reliable cue to nest-site quality than breeding experience because helpers are associated with nests only during the nestling phase when few nests are depredated. In contrast, although successful breeders may experience success with a low nest, they are even more likely to have experienced the failure of low nests because of the high rate of nest predation.A MAJOR DETERMINANT of reproductive success for many organisms is the ability of breeders to protect their offspring from predation. This is particularly true of many open-nesting passerines where the rate of nest predation may be extremely high (Lack 1954, Ricklefs 1969, Martin 1995). A variety of antipredator strategies has evolved among birds to reduce nest predation, including colonial or dispersed breeding, use of cavities, nest concealment or camouflage, elaborate nest design, and protective nesting associations (see Collias and Collias 1984). Numerous studies have shown an intraspecific relationship between nesting success and various characteristics of nests or nest sites, e.g. nest structure (Baeyens 1981), nest density (Andersson and Wiklund 1978, Potts et al. 1980, Hatchwell 1991, Chamberlain et al. 1995, Meilvang et al. 1997), and nest conspicuousness (Picman et al. 1993, Hatchwell et al. such effect (e.g. Holway 1991, Colwell 1992, Filliater et al. 1994, Cresswell 1997a). If predation risk is random with respect to nest-site char-E-mail: b.hatchwell@sheffield.ac.uk acteristics, then no consistent selection may exist for choice of particular nest sites. However, if breeding success is consistently related to certain nest traits, then high rates of nest predation will exert strong directional selection against the choice of low-quality sites by breeders, resulting in low variance in the critical characteristics. Alternatively, in the absence of consistent selection for particular nest sites, site choice may be a variable trait, w...

Long-tailed tits Aegithalos caudatus are cooperative breeders in which helpers exhibit a kin preference in their cooperative behaviour. We investigated the mechanism through which this preference is achieved by ¢rst conducting an experiment for testing whether breeders could recognize the calls of their relatives while controlling for spatial e¡ects. We found that there were signi¢cant di¡erences in the responses of breeders to the vocalizations of kin and non-kin, suggesting that vocal cues may be used for kin recognition. We conducted a second experiment in order to investigate whether recognition is achieved on the basis of relatedness per se or through association. Nestlings were cross-fostered between unrelated broods in order to create broods composed of true and foster siblings. In subsequent years, survivors from experimental broods did not discriminate between true and fostered siblings when making helping decisions, indicating that recognition is learned and not genetically determined. We discuss the e¡ectiveness of learning through association as an indirect cue to kinship.

Summary1. Long-tailed tits Aegithalos caudatus L. are cooperative breeders in which breeders that have failed in their own breeding attempt become helpers at the nest of relatives. We investigated the effects of kinship on the spatial dynamics of non-breeding flocks of long-tailed tits in order to determine the information available on the kinship of other members of the population from their use of home ranges. 2. A novel method of home range analysis was devised based on 'convex hull peeling'. This method takes into account the dispersion of all fixes within a home range and permits the quantitative analysis of home range use. In addition, the method allows the extent of overlap between adjacent home ranges to be determined and the use of those areas to be investigated. 3. Non-breeding flocks of long-tailed tits were composed mainly of relatives, but also included unrelated immigrants. Flock ranges were large and there was extensive overlap between adjacent flocks. 4. The degree of range overlap was significantly affected by the relatedness of flocks. If two flocks contained close relatives they were more likely to overlap than two flocks containing non-relatives. Moreover, the amount of overlap was significantly greater for two adjacent related flocks than for two adjacent unrelated flocks. 5. The use of overlapping areas of non-breeding ranges of long-tailed tit flocks was also influenced significantly by relatedness. Overlapping flocks that were unrelated to each other usually avoided areas of overlap, while related flocks did not generally show such avoidance behaviour. 6. Kinship has significant effects on the spatial dynamics of non-breeding flocks of long-tailed tits and therefore flock behaviour can provide information on the relatedness of other members of the population that might be important for helping decisions in this cooperatively breeding species.

The decision of whether to divorce a breeding partner between reproductive attempts can signi¢cantly a¡ect individual ¢tness. In this paper, we report that 63% of surviving pairs of long-tailed tits Aegithalos caudatus divorced between years. We examine three likely explanations for the high divorce rate in this cooperative breeder. The`better option' hypothesis predicts that divorce and re-pairing increases an individual's reproductive success. However, divorcees did not secure better partners or more helpers and there was no improvement in their reproductive success following divorce. The`inbreeding avoidance' hypothesis predicts that females should disperse from their family group to avoid breeding with philopatric sons. The observed pattern of divorce was consistent with this hypothesis because, in contrast to the usual avian pattern, divorce was typical for successful pairs (81%) and less frequent in unsuccessful pairs (36^43%). The`forced divorce' hypothesis predicts that divorce increases as the number of competitors increases. The pattern of divorce among failed breeders was consistent with this hypothesis, but it fails to explain the overall occurrence of divorce because divorcees rarely re-paired with their partners' closest competitors. We discuss long-tailed tits' unique association between divorce and reproductive success in the context of dispersal strategies for inbreeding avoidance.