Thrushes Sing Just as Strongly at Dusk as at Dawn
New research shows Hermit Thrush and Swainson’s Thrush are equally detectable at both ends of the day, offering greater flexibility for survey work
Dawn and dusk choruses in focus
A new study has revealed that two woodland thrushes - the Hermit Thrush Catharus guttatus and the Swainson’s Thrush Catharus ustulatus - sing just as reliably in the evening as they do at first light. The finding challenges long-standing assumptions that dawn offers the peak opportunity for detecting singing birds and suggests evening surveys could be just as effective.
The research team examined song activity at 27 sites in north-western Ontario, comparing eight short recording windows around sunrise and sunset during early, mid, and late breeding season. Both species sang consistently before sunrise, at sunrise and soon after, and again from half an hour before sunset to half an hour afterwards.
Only one period stood out: 60 minutes after sunset, when Hermit Thrushes became quieter and Swainson’s Thrushes fell completely silent. Otherwise, detections were remarkably even across the two choruses.
Late-season birds were more vocal
While both thrushes were present throughout the study, neither species sang as strongly in early June. Detection likelihood increased as the season progressed, peaking in late June and early July, when birds were well into nesting or fledging stages.
This pattern suggests that arrival on the breeding grounds may not immediately translate into high vocal activity - a consistent trait in several Catharus thrushes. Once breeding was underway, both species sang more reliably and were easier to detect.
Even so, song rate - the number of songs delivered once a bird was singing - did not show strong seasonal shifts in either species.
Hermit Thrushes sing more when neighbours join in
The study found that Hermit Thrushes increased their song rate when two or three individuals were singing at the same site, hinting at social or territorial interactions. When singing alone, they sang more modestly; when joined by others, their performance intensified.
Swainson’s Thrushes, by contrast, maintained a steady song rate regardless of how many individuals were present, suggesting different social dynamics between the two sympatric species.
Implications for bird monitoring
Because both species sang robustly at dawn and dusk, the authors conclude that surveyors can confidently monitor these thrushes at either end of the day. In some circumstances, dusk might even offer advantages, with fewer competing species singing and therefore less acoustic clutter.
To maximise detection, however, surveys should avoid extending beyond half an hour after sunset, when vocal activity declines. And with both species singing more reliably later in the season, early-June surveys may underestimate presence if based on song alone.
The research underscores the value of understanding diel and seasonal patterns in bird song - essential knowledge for optimising monitoring in rapidly changing forest landscapes.
November 2025
Read the full paper here
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