Winter Song: Why a Robin Sings When Nothing Is Breeding
On a still afternoon in the middle of winter, a robin climbs to the top of a bare hedge and sings the full, unhurried song it uses in April. Nothing is breeding. There is no nest to advertise and no female to court. The song is not a rehearsal and it is not a mistake in the calendar: it is a property notice, and this bird has been posting it, on and off, since autumn.
Two kinds of territory, one kind of song
European Robins do not hold one territory a year. They hold two kinds. In spring a male defends a breeding territory and sings from it. From autumn through winter, both sexes defend individual feeding territories — small patches of ground, and both sing from those instead.
Working on migratory robins, Hubert Schwabl compared the two situations directly. In the wintering area, males and females both defended individual territories aggressively, and both sang. In the breeding area, only males held and defended territories, and only males sang. Two very similar-looking behaviours, then, produced in two different physiological states — which is the part that turned out to matter.
A drug test that should have silenced the song
Testosterone is the standard explanation for territorial song, and for good reason: in most temperate songbirds the spring rise in day length drives a rise in testosterone, and the song follows. If winter song were simply early spring song, blocking testosterone should switch it off.
In 1991 Schwabl and Eberhard Kriner tested that with flutamide, a drug that blocks androgen receptors, in free-living and captive male robins in both autumn and spring. Spring behaved as the textbook predicts: treated males defended their breeding territories less aggressively. The singing did not fall — not in spring, and not in autumn either.
Their reading has held up: the aggressive defence of a breeding territory depends on androgens, but the year-round “keep out” signal does not. What testosterone changes is the quality of the song, the sexual signal built into it, not whether the bird sings at all. Winter song is the stripped-down version of the same message, broadcast by a bird whose hormones are, by breeding standards, flat.
Females, and where the rule breaks
The exception is instructive. Male robins holding winter territories have low luteinising hormone and low testosterone; females holding winter territories do not. In females the winter territory is defended with elevated testosterone, which is why a female robin will sing a full song in October and a male in the same hedge will not sing it as loudly. Laboratory work published in 2014 confirmed the mechanism from the other direction: give a female robin testosterone in autumn and she produces abundant song, with the song-control nucleus HVC reorganising itself the way a male’s does in spring.
So the two sexes arrived at the same behaviour from different hormonal starting points. That is a reminder of how carefully these things are wired: the song is not a by-product of a hormone level, it is a behaviour with its own control.
What February actually changes
Winter song is not uniform, and the change is not gradual. Arnaud Da Silva and colleagues recorded dawn and dusk singing across twelve woodlands — half of them street-lit — from winter through to the breeding season, following six common species. Chaffinches and Blackbirds began their morning and evening song in mid-February, on days of warm weather and when food became easier to find. Robins followed later in February. Song Thrushes came last, which fits the fact that they barely winter at that latitude at all.
Two things in that dataset are worth carrying into your own listening. Rain and low temperatures suppressed dawn and dusk song in every species examined — so a wet, cold week is not evidence that the birds have gone. And the seasonal start of song is not one event but a sequence, in a fixed order, which makes February a much more interesting month to listen in than December.
Light is a lever on the calendar
At the lit sites, dawn and dusk singing developed earlier in the year in four of the six species. That is a stronger claim than “urban birds sing earlier in the morning”: artificial light appears to shift the seasonal rhythm itself, independently of the other things cities do to a wood. The fitness consequences are still unknown, which is the honest state of the evidence — but if your local robin starts full song in the first week of January under a street lamp, you are probably not imagining it.
Great tits keep in touch
Robins are not the only winter singers, and the functions differ. In Great Tits and Blue Tits, winter song is more or less common depending on the year; pairs can form or stay together through the winter, and song is thought to keep partners in contact, while resident males may use it to announce ownership inside winter flocks. In North America the Carolina Wren sings all year round, and the function proposed for that is food, not sex: the song is a claim on a winter larder.
Which is the thread running through all of it. Winter song exists where a resource is worth defending and a neighbour is close enough to be told about it.
What to listen for
The winter version of a robin’s song is thinner and more wistful than the spring one: fewer phrases, longer pauses, a fixed perch rather than a tour of the hedge, and a strong preference for the hour around dusk. Spring song is louder, more structured and much more varied, and it comes with a bird that is prepared to fight for a nest site rather than a worm patch.
A single bird singing in December is telling you something specific: that this garden, this hedge, this compost heap is currently held. Two robins answering each other at dusk are drawing a line you could walk along. The song is a map of who owns what, redrawn every day, and it is the cheapest census of winter birds you will ever run.