Conspecific attraction in songbirds during spring migration

AO_SCPLOWBSTRACTC_SCPLOWConspecific attraction has often been hypothesized as a mechanism that could facilitate migration and territory acquisition. We studied conspecific attraction by songbirds during spring migration between 2019 and 2025 at the Dunes of Tadoussac, Quebec, Canada. This location is known to produce spectacular migration events with thousands of passerine birds flying at close range from the observers. We recorded sequences of individual birds moving just over the ground in a [~]20 m wide corridor along the edge of the St. Lawrence estuary. We also conducted hourly counts to detect conspecific clusters at a coarser temporal scale. Birds were much more likely to be following conspecifics at close range than other species, as evidenced by randomization tests, after accounting for species composition and abundance during each specific migration event. Conspecific sequences were mostly of two individuals, but much larger sequences occurred, up to 103 consecutive individuals of the same species. We found no evidence of leading species, i.e. species that were more likely to lead, rather than follow, another species. Hourly species counts were often much more variable than expected from a random (Poisson) process, at least in the case of Tennessee and Magnolia Warblers, providing evidence for conspecific attraction at a coarser temporal scale. This study provides the first detailed evidence of conspecific attraction with passerine birds during migration.