Using Song Dialects to Assess the Migration Strategy of the Golden-crowned Sparrow

Most techniques used to study migration of wild birds require capture for banding or for attachment and/or recovery of tags or transmitters. We took advantage of the fact that the Golden-crowned Sparrow (Zonotrichia atricapilla) sings in winter, combined with published data on the distribution of its distinct song dialects in the breeding range, to assess its migration strategy and migratory connectivity by means of these dialects. Using recordings of the Golden-crowned Sparrow’s song across much of its winter range, we categorized these birds by song type to identify their likely origin in some subset of the breeding range. This method allows examination of migration without the need to capture birds. Our results fit best with a pattern of chain migration, with the northernmost breeders wintering in the northernmost part of the winter range, and the southerly breeders wintering farther south. The results suggest strong migratory connectivity between segments of the breeding and winter ranges, though our small sample size makes it difficult to draw firm conclusions on connectivity.

Machine learning reveals cryptic dialects that guide mate choice in a songbird

Culturally transmitted communication signals – such as human language or bird song – can change over time through a process of cultural drift, and may consequently enhance the separation of populations, potentially leading to reproductive isolation1–4. Local song dialects have been identified in bird species with relatively simple songs where individuals show high cultural conformity5–10. In contrast, the emergence of cultural dialects has been regarded as unlikely11–13 for species with more variable song, such as the zebra finch (Taeniopygia guttata). Instead, it has been proposed that selection for individual recognition and distinctiveness may lead to a complete spread across the space of acoustic and syntactical possibilities11–15. However, another possibility is that analytical limitations have meant that subtle but possibly salient group differences have not yet been discovered in such species. Here we show that machine learning can distinguish the songs from multiple captive zebra finch populations with remarkable precision, and that these ‘cryptic song dialects’ drive strong assortative mating in this species. We studied mating patterns across three consecutive generations using captive populations that have evolved in isolation for about 100 generations. Cross-fostering eggs within and between these populations and quantifying social interactions of the resulting offspring later in life revealed that mate choice primarily targets cultural traits that are transmitted during a short developmental time window. Detailed social networks showed that females preferentially approached males whose song resembled that of their adolescent peers. Our study shows that birds can be surprisingly sensitive to cultural traits for mating that have hitherto remained cryptic, even in this well-studied species that is used as a model for song-learning13,14,16–28.

Inter-dialect dispersal is common in the Puget Sound white-crowned sparrow

Dispersal in birds can have an important influence on the genetic structure of populations by affecting gene flow. In birds that learn their songs, dispersal can affect the ability of male birds to share songs in song dialects and may influence mate attraction. We used Inductively Coupled Plasma Mass Spectrometry (ICP-MS) trace element analysis on the body feathers of birds to assess dispersal among four song dialects. We found that (1) most males had a feather element profile typical of only one dialect location; (2) males singing non-local (‘foreign’) dialects in a focal population often learned their foreign songs outside the dialect; and (3) females often dispersed among dialects. We estimated 5% dispersal per year by yearling males between the site of moulting and breeding. Our estimate is consistent with genetic estimates of widespread gene flow between dialects in this subspecies of the white-crowned sparrow.