By André Desrochers and Laetitia Desbordes
Conspecific attraction refers to the tendency of an individual to move closer to other members of the same species. This phenomenon has been observed particularly in habitat selection. The idea is based on the fact that the presence of conspecifics serves as a reliable indicator of habitat quality, signaling that it is favorable for feeding, survival, and reproduction. Therefore, individuals of the same species present in a habitat act as indicators of its quality.
What about during migration?
Bird migrations often bring together multiple species at the same sites, promoting interactions and sometimes the formation of mixed-species groups. While the benefits of such gatherings for predator avoidance have long been recognized, recent research also highlights the importance of communication, especially during nocturnal migrations. Birds appear to use various cues, particularly those provided by their conspecifics, to optimize navigation, flight speed, and the choice of stopover sites.
However, the social aspects of migration remain poorly studied. It is still unclear whether conspecifics provide better information than individuals of other species, and whether this leads to voluntary groupings. While conspecific attraction is well documented in some gregarious birds such as geese, waxwings, waterfowl, waders, and parrots, it is less understood in migratory passerines. Nevertheless, it may be more common than previously thought.
Photo: Yellow-rumped Warbler (foreground) and Bay-breasted Warbler (background)
The Tadoussac Dunes: an exceptional site for a study of this scale
For several years, spectacular spring movements have been reported on the Côte-Nord. Thousands of passerines are sometimes observed migrating in reverse, from north to south, for reasons that remain unclear. On May 28, 2018, a remarkable movement of over half a million passerines, mainly warblers, was observed at the Tadoussac dunes. This unprecedented phenomenon, actively documented and covered by the media, prompted the establishment of standardized visual surveys in spring at the dunes to better understand its causes and consequences.
Since then, the site has become known for its migratory events, which are as unpredictable as they are spectacular and colorful, sometimes with thousands of passerines flying close to observers. Long-term projects of this type pave the way for more specific research, thanks to the daily presence of an ornithologist on site.
Photo: Magnolia Warbler (top) and Northern Parula (bottom)
A generally single-species flight
From 2019 to 2025, André Desrochers, full professor at Université Laval, and Laetitia Desbordes, ornithologist at the Tadoussac Bird Observatory, sought to determine whether Neotropical birds of the same species group together during spring migration. They studied conspecific attraction during migration at the Tadoussac Dunes. To better understand these events, they recorded sequences of individual birds moving just above the ground along the dunes.
From the very first observation session, it was evident that birds were much more likely to follow individuals of the same species at close range than birds of other species. This tendency was confirmed after analyzing over 87,700 sequences, taking species composition and abundance into account. Most sequences involved fewer than five consecutive individuals of the same species, but some included several dozen (up to 103). There did not appear to be “leading” species, meaning no species was more likely to lead rather than follow another.
Conspecific attraction was also observed in hourly counts, at least for the Tennessee Warbler and the Magnolia Warbler, which are more abundant species.
Photo: two Tennessee Warblers
To conclude
Conspecific attraction in migratory passerines is poorly documented, and literature on the subject is scarce. However, the reverse migrations at the Tadoussac Dunes provided an excellent opportunity to document this phenomenon on a larger scale! Based on the knowledge gained, this study provides the first detailed evidence of conspecific attraction in migratory passerines.
To read the full article: Desrochers, A., and L. Desbordes. 2025. Conspecific attraction in songbirds during spring migration. bioRxiv: 2025.2010.2020.683507. doi:10.1101/2025.10.20.683507 (download)
