Friday, 29 March 2013

What's going on in the shrubbery?

The dunnocks are much in evidence in the garden at the moment, with plenty of song and display. Known to some readers as the hedge sparrow, the dunnock isn’t a sparrow at all but it does like the cover afforded by hedges and other shrubbery so this sometimes-used name is not completely wrong. The dunnock is an often-overlooked bird, perhaps because of its skulking habits or maybe because of its rather drab appearance and superficial similarity to the more familiar house sparrow. Despite this, the dunnock is a particularly engaging bird with a fascinating private life.

As with many other familiar garden birds, the dunnock maintains a breeding territory that is advertised through song. The song itself is rather melodic and is comprised of a series of sweet-sounding phrases, well worth listening out for. Although most dunnock pairs are monogamous, with one male and one female paired together, some indulge in rather more complicated living arrangements. Instances of polyandry (one female with two males) are rather common, as is polygyny (one male with two or more females) and there are even occasions where two or three males may form a relationship with three or four females. It is thought that such complex relationships develop because male and female dunnocks maintain their own, largely independent, territories during the breeding season. Male territories tend to be larger, so each male territory may overlap with several females.

Instances where two males appear to share a territory are also fairly common, with one male (the alpha male) dominant over the other (the beta male). Although both males may mate with the resident female, the alpha male gets the greater share of the matings. The two males will work together to defend the territory against other males, with both birds singing and displaying when faced with potential rivals.

Such complex relationships have also given rise to some interesting courtship behaviour. Prior to mating the female dunnock will crouch before her partner, quivering her body and lifting her tail. This prompts the male to peck at the female’s cloaca (which is associated with her sexual organs). The repeated pecking causes the cloaca to enlarge and this is then followed by a series of pumping movements by the female which serve to eject some of the sperm from any previous mating. It is thought that this ejection of sperm increases the chances that the current male will sire a greater proportion of the offspring. Such behaviour surprises many people and may even be enough to make them blush, especially if they have asked the question as to why dunnocks may sometimes peck each others’ behinds! It is surprising what goes on in our gardens!

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