Modern research challenges the old belief that only male birds sing. This was a relic of anthropomorphic assumptions about birds' 'family life', like the long-held belief that small birds are faithfully monogamous partners, now disproved in many species by DNA analysis. A particular problem in the field is that in many of our common songbirds, such as robin, dunnock and wren, we ourselves cannot tell male from female. But, by catching birds of known sex (in the breeding season) and marking them, for example with unique combinations of coloured leg rings, it has been found that in fact females do sing in all these species.
Both male and female robins sing in autumn, a softer, quieter song than the spring song which is mostly (but not exclusively) produced by males. Some female dunnocks sing more than others, for unknown reasons, although their song is shorter and less elaborate than that of the male. Dominant paired females may use it to manipulate their complicated menages of two or more males. Most singing wrens are indeed male, but females can sing when they choose, and have in addition a unique 'whisper-song' they use to communicate with their chicks. In fact, all female songbirds produce a wide repertoire of sounds, while feeding, as alarms and for communication with mates and young; many of these could be described as 'song'. The quieter, softer song produced by female birds is often known as 'subsong'; in many species it is produced all year round and is no less important in the birds' lives than the loud territorial song of the male.