Meadow yellow

Meadow yellow
Bulbous Buttercup (Ranunculus bulbosus) in a Devon meadow

Thursday, 4 March 2010

Don’t knock Dunnocks

I’ve been watching a group of Dunnocks (Prunella modularis) over the last few days feeding near our birdtable and noticed how frequently there are three individuals. This bird, also known as the Hedge Sparrow, is rather shy and retiring and so often over looked. But as they say, you need to keep an eye on the quiet ones! It is closely related to the Alpine Accentor (Prunella collaris) which inhabits the French Pyrenees and other accentor species which live primarily in mountain habitats. Indeed the Dunnock is a montane bird over much of its European distribution. So what is doing in our gardens?

Now I also recall from my childhood reading about this bird being an unusual bigamist – each female courts two male escorts. My bird books indicate that it is a bit more complicated than this with various ratios of male to female when it comes to the mating game. However research has found that a female has more reproductive success if she has more than one male (polyandry), usually two, helping her with the brood. There is usually one dominant male (the ‘alpha’) and a subordinate. But to the casual observer it is usually impossible to know that all this gamesmanship is being played out, particularly as the sexes are near identical in appearance. It does lead the question of whether other birds show similar behaviour, and interestingly there is evidence to support this, such as with the Alpine Accentor.

Other research (*Langmore et al.) has shown that when female Dunnocks are under competitive pressure for breeding with other females they increase their testosterone levels and this prompts more singing to compete for males. Again a bit of a physiological/behavioural sex reversal.

....And then to complicate matters further, the Dunnock is also prey to the crafty Cuckoo (Cuculus canorus), laying its similar speckled egg in the host nest for the Dunnocks to raise as an obese protégé.

Perhaps not such a dull life for this little brown bird, having descended from the mountains with its strange sexual behaviour.

* Langmore, N.E., Cockrem, J.F. and Candy, E.J. (2002) Competition for Male Reproductive Investment Elevates Testosterone Levels in Female Dunnocks, Prunella modularis. Proceedings: Biological Sciences, 269 (1508):2473-2478

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