Testosterone increase in free-living young Blackcaps <i>Sylvia atricapilla</i> and Wood Warblers <i>Phylloscopus sibilatrix</i> during post-juvenile molt with possible implications for juvenile dispersal

Testosterone may affect many aspects of passerine maturation including the expression of plumage coloration and spring migration in adult birds. However, how the testosterone level changes during bird development is not well known. We compared the testosterone profile during juvenile development of a sexually dimorphic species, the Blackcap Sylvia atricapilla, and a monomorphic species, the Wood Warbler Phylloscopus sibilatrix. We first tested whether testosterone influences plumage coloration and increases at the onset of molt in males of the dimorphic but not the monomorphic species. We found that a testosterone level increase occurred in both sexes and species during later stages of molt, and thus was not related to male plumage coloration. We also investigated whether the increase in testosterone level coincides with juvenile dispersal. If testosterone affects dispersal behavior in these species, both sexes should show an elevated testosterone level during dispersal, but this increase should occur earlier in the Wood Warbler, which disperses earlier than the Blackcap. In juvenile Blackcaps, the increase in testosterone level occurred on the 43-68th day after hatching, while in Wood Warblers it occurred on the 32-36th day (i.e. 11-32 days earlier). The increase in testosterone level coincided with the onset of the post-juvenile dispersal in both species. This study provides the first direct evidence of a testosterone level increase during juvenile development in two free-living migratory birds. While not correlated with species plumage coloration, this increase might affect other aspects of behavior, e.g. juvenile dispersal

Testosterone increase in free-living young Blackcaps <i>Sylvia atricapilla</i> and Wood Warblers <i>Phylloscopus sibilatrix</i> during post-juvenile molt with possible implications for juvenile dispersal

Testosterone may affect many aspects of passerine maturation including the expression of plumage coloration and spring migration in adult birds. However, how the testosterone level changes during bird development is not well known. We compared the testosterone profile during juvenile development of a sexually dimorphic species, the Blackcap Sylvia atricapilla, and a monomorphic species, the Wood Warbler Phylloscopus sibilatrix. We first tested whether testosterone influences plumage coloration and increases at the onset of molt in males of the dimorphic but not the monomorphic species. We found that a testosterone level increase occurred in both sexes and species during later stages of molt, and thus was not related to male plumage coloration. We also investigated whether the increase in testosterone level coincides with juvenile dispersal. If testosterone affects dispersal behavior in these species, both sexes should show an elevated testosterone level during dispersal, but this increase should occur earlier in the Wood Warbler, which disperses earlier than the Blackcap. In juvenile Blackcaps, the increase in testosterone level occurred on the 43-68th day after hatching, while in Wood Warblers it occurred on the 32-36th day (i.e. 11-32 days earlier). The increase in testosterone level coincided with the onset of the post-juvenile dispersal in both species. This study provides the first direct evidence of a testosterone level increase during juvenile development in two free-living migratory birds. While not correlated with species plumage coloration, this increase might affect other aspects of behavior, e.g. juvenile dispersal.</p

Genes and song : genetic and social connections in fragmented habitat in a woodland bird with limited dispersal

Understanding the processes leading to population declines in fragmented landscapes is essential for successful conservation management. However, isolating the influence of disparate processes, and dispersal in particular, is challenging. The Grey Shrike-thrush, Colluricincla harmonica, is a sedentary woodland-dependent songbird, with learned vocalizations whose incidence in suitable habitat patches falls disproportionally with decline in tree cover in the landscape. Although it has been suggested that gaps in tree cover might act as barriers to its dispersal, the species remains in many remnants of native vegetation in agricultural landscapes, suggesting that it may have responded to habitat removal and fragmentation by maintaining or even increasing dispersal distances. We quantified population connectivity of the Grey Shrike-thrush in a system fragmented over more than 120 years using genetic (microsatellites) and acoustic (song types) data. First, we tested for population genetic and acoustic structure at regional and local scales in search of barriers to dispersal or gene flow and signals of local spatial structuring indicative of restricted dispersal or localized acoustic similarity. Then we tested for effects of habitat loss and fragmentation on genetic and acoustic connectivity by fitting alternative models of mobility (isolation-by-distance [the null model] and reduced and increased movement models) across treeless vs. treed areas. Birds within 5 km of each other had more similar genotypes and song types than those farther away, suggesting that dispersal and song matching are limited in the region. Despite restricted dispersal detected for females (but not males), populations appeared to be connected by gene flow and displayed some cultural (acoustic) connectivity across the region. Fragmentation did not appear to impact greatly the dispersal of the Grey Shrike-thrush: none of the mobility models fit the genetic distances of males, whereas for females, an isolation-by-distance model could not be rejected in favor of the models of reduced or increased movement through treeless gaps. However, dissimilarities of the song types were more consistent with the model of reduced cultural connectivity through treeless areas, suggesting that fragmentation impedes song type sharing in the Grey Shrike-thrush. Our paper demonstrates that habitat fragmentation hinders important population processes in an Australian woodland bird even though its dispersal is not detectably impacted.<br /

Appendix C. Details of genetic and acoustic analyses.

Details of genetic and acoustic analyses

Appendix E. Relationship between per-landscape estimates of genetic diversity (allelic richness, expected heterozygosity, effective population size), within-landscape autocorrelation coefficient, and landscape tree cover.

Relationship between per-landscape estimates of genetic diversity (allelic richness, expected heterozygosity, effective population size), within-landscape autocorrelation coefficient, and landscape tree cover

Appendix D. Results of spatial autocorrelation analyses for genetic and acoustic data on regional (study-scale) and local scale.

Results of spatial autocorrelation analyses for genetic and acoustic data on regional (study-scale) and local scale

Appendix B. Molecular methods and tests for the effect of habitat cover on genetic and acoustic diversity.

Molecular methods and tests for the effect of habitat cover on genetic and acoustic diversity

Appendix A. Sampling details and population statistics for genetic and acoustic data.

Sampling details and population statistics for genetic and acoustic data