Sex and the Birds: 10. Dunnock’s mixed bag of breeding systems

posted in: Sex | 1

Dunnocks (Punella modularis) are common garden and hedgerow birds found throughout temperate Europe and into Asia. It has a drab appearance, looking much like a sparrow, thus commonly known as Hedge Sparrow. On closer inspection it is rather attractive as it’s grey-blue head and breast become apparent. The sexes are alike although the female is less richly coloured.

What is remarkable about the Dunnock is its colourful sex life. It has evolved a unique breeding system that is extremely variable (Hatchwell, 2005):

1. Monogamy (42%) – a male and a female stay together for at least one breeding cycle.
2. Polygny (4%) – a male mates with several females during a mating season.
3. Polyandry (30%) – a female mates with several males during a breeding season.
4. Polygyandry (24%) – both the male and the female of the pair mate with more than one sexual partner during a breeding season.

In a territory with only a male and a female, the pair will cooperate to rear the chicks, thus adopting a monogamous relationship. If the territory is larger than usual, he may take in one or two more females and becomes polygynous, but this is rather uncommon. A more common scenario is where the female tries to mate with more than one male. This polyandrous breeding system is considered favourable to the female as the males she mated with will help in looking after her chicks.

In such a polyandrous situation, if the two or more males (who are not relatives) share a territory, they will compete for the female. The dominant male will naturally guard the female, not allowing any other males to copulate with her. Invariably he will fail as she will sneak off to mate with the other males. However, before copulation, the male will peck at her cloaca numerous times to stimulate her to eject the sperms from an earlier copulation (Davies, 1983), see video HERE.

As mentioned above, the advantage of a female copulating with more than one male is that she will have more than one male to care for her chicks. This will ensure an increased success of the chicks fledging, especially when food is scarce. On the other hand, a male copulating with more than one female allows him to produce more chicks, thus spreading his genes. However, the success of his chicks fledging will be reduced as they will be cared for by the usual two adults, without the help of one or more males.

Credit: YC Wee (text) & Dr Eric Tan (image of Dunnock).

Davies, N. B., 1983. Polyandry, cloaca-pecking and sperm competition in dunnocks. Nature, 302: 334-336.
2. Hatchwell, B. J., 2005. Family Prunellidae (Accentors). In: del Hoyo, J., Elliott, A. & D. A. Christie (eds.), Handbook of the birds of the world. Vol. 10. Cuckoo-shrikes to Thrushes. Lynx Editions, Barcelona. Pp. 496-513.

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