The Dunnock: Sex in the Shrubbery
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ABOUT BIRDS The Dunnock: sex in the shrubbery he Dunnock is one of those birds that rather unusual groupings seem to occur because can easily go unnoticed within the male and female Dunnocks maintain their Tgarden. About the size of a Robin, own, largely independent, territories during but slimmer in build, this small, rather plain the breeding season. Since male territories are looking bird, tends to forage on the ground larger than those of the females, you might beneath bushes and shrubs. Yet its unobtrusive expect a single male to have access to more nature and drab plumage hide an extremely than one female, giving rise to polygyny. charismatic and engaging bird, whose social However, what makes the social complexities behaviour and living habits are nothing, if not all the more interesting is that some male rather unusual. territories are shared by two males. One of By Mike Toms Perhaps the most striking aspect of the two males (termed the ‘alpha’ male) will GBW Organiser Dunnock behaviour is its complex social system. be dominant over the other (the ‘beta’ male). While many Dunnocks adopt a monogamous The beta male manages to secure his position relationship with a would-be partner, others within the territory of the alpha male through engage in more complicated arrangements. It sheer persistence, something which provides is quite common for one female to engage in him with a degree of access to any females. a relationship with two males (something that However, access is not guaranteed, since the is given the rather grand title of ‘polyandry’). alpha male spends a great deal of time guarding Somewhat less commonly, a single male may his female, especially as she approaches the establish bonds with two or more females egg-laying period. (known as ‘polygyny’) and there are even cases A series of pre-copulation displays have of groups of two or three males consorting with evolved alongside this bizarre social system three or four females (‘polygynandry’)! These and these displays are geared towards attempts John Harding – BTO Collection | Summer 2007 Bird Table DUNNOCK on the part of the male to guarantee his of her given sufficient opportunity. However, parentage of any offspring resulting from the the female is also seeking to maximise her FACT BOX union. Immediately prior to copulation, a advantages from this social system and she female Dunnock will crouch low in front of her does this by actively soliciting mating attempts Common name: Dunnock prospective mate, fluff up her body feathers, from the beta male. Sometimes the female will raise her tail and quiver. The male, positioned shake off her alpha male so that she can elope Scientific name: Prunella modularis behind the female, will then hop from side to with the beta male for a brief liaison. She does side before pecking at the female’s vent (also this because a male will only help to rear her Family: known as the cloaca). The male’s pecking of chicks if he has been able to secure several Accentors the cloaca may continue for several minutes matings with her. By encouraging both males UK population and, over this period, it may become pink and to mate with her, the female should secure 2.2 million pairs (summer) swollen. As it swells, it makes strong pumping both of their services when the eggs hatch. Conservation status: movements and these result in the ejection Amber listed of sperm from previous mating attempts. In he Dunnock is also interesting because it Migratory status: is one of the main hosts for the Cuckoo, this way, a male can increase his chances of T Resident fathering any young resulting from the union. a species renowned for laying its eggs in the Another frequently observed display nests of other species – a behaviour known as Breeding: Clutch size: 4–5 eggs occurs where two or more males come together brood parasitism. A female Cuckoo, visiting to dispute a territory. Such interactions involve the nest of a Dunnock, will remove one of Incubates: 14–15 days bouts of wing-flicking and chasing, and it is the Dunnock’s eggs before laying one of her Young in nest: 12–15 days interesting to note that beta males work with own directly into the nest. Individual female Number of broods: 2 (3) their alpha male to defend the ‘shared’ territory Cuckoos specialise on one particular host, Breeding season: Mar–Aug from would-be intruders. Both males will also usually Dunnock, Robin, Meadow Pipit, Age at first breeding: 1 indulge in song to advertise their ownership of Reed Warbler or Pied Wagtail. The eggs of the territory. This might suggest that there is a the different host species vary in colour and Typical lifespan: benefit for an alpha male in having a beta male pattern and, since an unusual looking egg is Two years within his territory. However, any benefits likely to be rejected by the host, there is a Max. recorded lifespan: that come from having another male to help selection pressure on the female Cuckoo to 11 years and three months with territorial defence are balanced by the produce eggs that closely resemble those of the www.bto.org/birdfacts disadvantages of having a male sharing your host. This is why individual female Cuckoos territory who is looking for any opportunity to tend to specialise on one particular host. mate with your partner. This is why the alpha Cuckoos that parasitise species like Reed males invest so much time in guarding their Warbler and Meadow Pipit produce eggs that females (as much as 40 minutes an hour). closely match those of their host. However, in Now, all this may seem a bit harsh on the case of the Dunnock, the Cuckoo eggs look the poor female, constantly followed by one very different from the blue eggs produced by male, with another looking to take advantage the Dunnock and you might expect them to Jill Pakenham – BTO Collection Bird Table 50 Summer 2007 | ABOUT BIRDS be rejected by the parent birds. Interestingly, will lead a largely solitary existence, only Dunnocks rarely reject Cuckoo eggs and coming together to feed in small groups if a this suggests that they are not particularly feeding opportunity is particularly rich or food discerning parents. Since it is in the Dunnock’s is hard to come by elsewhere. As with other interest to spot the Cuckoo egg, it seems small birds, overwinter mortality can be high likely that the Dunnock is a relatively recent if conditions are unfavourable, either because host and has not yet shown an evolutionary of starvation or because individuals take more response to this act of nest parasitism. Because risks to get at food and so leave themselves Dunnock nest - Christopher Rowe the level of nest parasitism is low within the open to predation by cats or Sparrowhawks. BTO Collection Dunnock population as a whole, it may be There may be competition for food and as you some time before an evolutionary response might expect it is the dominant individuals, becomes apparent. like adult males, which are able to gain first Once the young Cuckoo has hatched from access to food. its egg it will set about removing any other eggs During periods of cold weather, therefore, or young Dunnocks that remain in the nest. In it is often worth putting out food for Dunnocks, this way the Cuckoo chick is able to secure all placing small seeds, grated cheese and bread the attention of its adopted parents, quickly crumbs under the shelter of bushes and other growing in size on the food provided. It may garden plants. The fine bill is ideally suited seem surprising that adult Dunnocks continue for dealing with smaller items of food and it to feed the Cuckoo chick even though it is also a useful feature to look for if you are will eventually come to dwarf them in size. unsure about separating your Dunnocks from However, the urge to feed any begging mouth your sparrows. While Dunnocks use their fine may be so strong that the parents will feed the bills to tackle small seeds, sparrows will use interloper even though it looks very different their heavier bills to deal with grain and other from a chick of their own species. Experiments, large seeds. carried out by researchers studying animal Over the last few years we have received behaviour, have discovered that Dunnocks increasing numbers of reports of Dunnocks (and virtually all other Cuckoo hosts) won’t feeding from tables and hanging seed feeders. discriminate between Cuckoo chicks and their This suggests a general change in feeding own chicks, even if the two are paired together behaviour, perhaps following the introduction in the same nest. Ending up with a Cuckoo of more diverse seed mixes. Even so, Dunnocks in your nest may seem disastrous but, since a appear rather timid around feeding stations, pair of Dunnocks can rear two or even three preferring to make brief sorties rather than broods in a season, they could still have the linger for longer bouts of feeding. Watch opportunity to rear chicks of their own later your visiting Dunnocks and you are likely in the year. to discover that they are a long way down BELOW: As well as the pecking order, unable to hold their own parasitising Dunnocks, Cuckoos also regularly utside of the breeding season, Dunnock against most other species. Robins seem to give parasitise Reed Warbler Osocial behaviour is rather less complicated. Dunnocks a particularly hard time. As regular (left), Meadow Pipit During the winter months, many Dunnocks readers will know, Robins are surprisingly (right), Pied Wagtail and even Robin.