The Dunnock – the Most Extraordinary of Ordinary Birds
From Tits and Magpies to Bee-eaters and Dunnocks – a story in collaboration
Introduction:
Before I launch into the intriguing tale of the Dunnock, I would like to take a step back to the spring 2020 when we watched a pair of Long-tailed Tits nest building high in an oak tree. The nest was a beautiful creation of moss, spiders web, feathers and lichen. But sadly it soon failed, wrecked by one of the likely suspects – Jays, Greater Spotted Woodpeckers, or squirrels.
The nest construction was a fascinating process to watch, as we saw the pair go off together and return each with a feather, always working as pair, manoeuvring these into the nest, and then off again for more. We were sad to see its demise, but in fact it was a very likely outcome. In Lack and Lack’s classic study during the 1950s in Wytham Wood in Oxfordshire, they recorded an 80% failure rate of Long-tailed Tit nests – see: https://woodcockwood.com/nesting-and-the-long-tailed-tit/
What happened to the pair we don’t know, but the chances were that male went off to join a pair that were having more success, to help them raise their brood. But this wouldn’t be just any pair, it would likely be one of his siblings.
Other Collaborative nesters
This sounds like an extraordinary response, and indeed it is a rare occurrence in the animal kingdom. It is estimated that about 200 of the 9000 species of birds have additional adults collaborating in some way in the rearing of young. In our sphere this includes the Dunnock, the European Bee-eater: https://woodcockwood.com/the-european-bee-eater/, and the Azure Winged Magpie https://woodcockwood.com/eurasian-jays-and-azure-winged-magpies/.
It was the observations last spring that got us thinking about our own humble Dunnock – the subject of this article.
The Dunnock
Appearance of the Dunnock – a seemingly ordinary bird
The Dunnock has a passing resemblance to a female House Sparrow, except for the long fine bill of an insectivorous bird, that sets it in the family Accentor. It is common in the UK and is widespread across Europe, inhabiting parks and gardens, hedgerows and the edge of woodland.
Although common and widespread, it may not be well known as it tends to skulk in undergrowth, except during the breeding season, when the male will appear above its small territory and sing heartily, with a song somewhat reminiscent of a Robin.
The female Dunnock builds the nest and incubates the eggs. When the young hatch the male participates fully in their care.
A bird of excellent principals, or so it would seem … that is until N.B. Davies* began to publish the findings of his long term study of the Dunnock, conducted in the Cambridge Botanical Gardens during the course of the 1980s. What was revealed would be fitting for publication in any of the Sunday tabloids.
Davies’s detailed study reveals so much more
In early spring the female will select her nesting territory low down in the dense vegetation. She will protect the boundaries from other females.
A male will be attracted and take on the defence of her territory from other males. He will stay close to the female, except when he emerges to proclaim his territory – which is when we will most often see him and hear him singing vigorously. This may be the final point in the story – and the pair of Dunnocks will nest and rear their young.
However, it doesn’t often happen like this. While the male is at his singing post, the female will do her best to attract other males, perhaps from neighbouring territories, perhaps lone males looking for a mate. In the latter case, another male may join the pair, one male becoming dominant and the other submissive. The pair of males will jointly defend the female’s territory against other males. The dominant male will mate with the female, and when he can find the opportunity, so will the submissive male. If the submissive male succeeds, he will join the dominant male to help rear the young, but only if he succeeds in mating.
Once the young are on the scene, competition between the males stops, and their combined effort will go into raising the young.
But there is more of course. The situation can arise where one male takes on the defence of two or three female territories. He may become the sole male to mate with these females. His work is then cut out when it comes to the time for supporting the females to rear their collective broods.
Over the decade of his study, Davies recorded the following combinations within one territory and calculated the probability of these combinations: 3 males to 1 female, 2 males to 1 female, 3 males to 3 females, 2 males to 3 females, 2 males to 2 females, 1 males to 2 females, and last but not least 1 male to 1 female. And so nests of young could be fathered by one, two or three males, and of course, the more males that helped to rear the young, the more successful the outcome.
Sentiment aside, breeding is about survival of the genes
The story doesn’t end there. Much of this behaviour had been observed before B. N. Davis’s study, but what this diligent researcher discovered was the meaning behind a unique behaviour of the Dunnock, that of cloacal pecking, something that had puzzled ornithologists for years.
But whose genes?
The Female Dunnock has a particularly distended cloacal sack, where the sperm of the male is stored prior to the fertilisation of the eggs. Males had often been observed spending up to a minute pecking at the female’s cloaca before mating takes place.
Davies discovered that this pecking often ended in the female ejecting a small amount of stored sperm. Clearly the benefit of this to the male was that she might be ejecting the sperm of a rival male, before he introduced his …. well, the dull plumage of the Dunnock is surely compensated for by the most colourful of sex lives.
Davies’s Research:
Based on years of detailed observations, DNA testing etc Davies has built a comprehensive picture of mating patterns, brood survival, and a theoretical basis for the type of competitive, collaborative and cooperative set of behaviours. And I’m sure the few paragraphs above do not do justice to a decade of study by Davies and his team, but I hope I’ve provided sufficient detail for you to look afresh when you spot a humble Dunnock!
A fascinating read: Davies B.N. “Dunnock Behaviour and Social Evolution”, 1992, Oxford University Press