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Dispersal is expected to enhance individual fitness, and individuals should thus disperse from areas with poor conditions to areas with more favourable conditions. Few studies have compared conditions before and after dispersal of the same individuals, and in birds little is known about the effects of sex ratio and female density on male dispersal decisions. In this study we examined various fitness-related parameters that adult male ortolan buntings, Emberiza hortulana, might use as cues in their decisions to disperse and settle. The study population has a strongly male-biased sex ratio. Using pairwise comparisons of pre- and post-dispersal conditions, we found that males moved from areas with low female density and a severely male-biased sex ratio to areas with higher female density and a less male-biased sex ratio. Male density and male age structure did not affect male dispersal and settlement. The sex ratio of the pre-dispersal sites was below the population average, but post-dispersal sites were not significantly better than the population average. This suggests that dispersal was triggered by poor conditions, whereas settlement may have been unrelated to the conditions at the new site. In the year of dispersal, males that undertook dispersal were less successful at acquiring a female than males that remained faithful to the site, but in subsequent years there was no difference. We suggest that dispersal might be adaptive under more natural conditions with a more balanced sex ratio. These results show that male ortolan buntings abandon areas with low female density and a severely male-biased sex ratio, and thereby end up in better places, although probably not better than the population average.

Songbirds learn to sing by imitating their conspecific songs through social learning. It is commonly thought that in species with small repertoires, so‐called crystallization of the song repertoire takes place before the first breeding attempt and afterwards their repertoires remain unchanged. However, the number of studies in which individual song repertoires have been tracked longitudinally under natural conditions is still small. The ortolan bunting (Emberiza hortulana) is a small Eurasian passerine species. Studies on this species have shown that males have small song repertoires (usually 2–3), share the same final phrase within a local dialect area, and their repertoires remain unchanged during their lifetimes. We studied the whole, isolated Norwegian population of this species with 100–150 individually marked males. We compared repertoire sizes and contents using cross‐sectional and longitudinal approaches. We focused on marked males aged 2–10 years and recorded in up to five breeding seasons between 2001 and 2006. There was no local dialect because songs with different final phrases occurred both within and between males. Repertoire size varied between 1 and 24 (4.7 ± 3.4) song types per male. Longitudinal analysis showed an increase in repertoire size in 29% and a decrease in 21% of males. Males whose repertoires remained the same in size between years often substantially changed in contents. New song types appeared in almost 70% of males, and over 30% of males started singing new syllable types after the second calendar year. In almost 50% of males, new song types appeared that were built as new combinations of syllables shown in previous years. In 30% of males, the song complexity increased with age. Simultaneously, over 60% of males selectively ceased singing some song types. We suggest that these repertoire alterations are linked to the isolation and fragmentation of this population, which may affect song learning patterns through increased breeding dispersal and a strongly male‐biased sex ratio. Similar studies from abundant and continuous populations of the species are needed to test this idea. [ABSTRACT FROM AUTHOR]