Country and Coast: Mystery of the baby blackbirds with two dads

Blackbirds have built a nest in our ivy and have produced youngsters. The female is particularly tame, even tapping on a neighbour's window to request titbits but as I pen these notes she is working hard to feed her chicks. Foraging among the leafy debris of our borders, she is always brisk and noisy but knows where and when to search, even when humans are nearby.
By The Newsroom
Published 30th Apr 2010, 17:06 BST
Updated 30th Apr 2010, 17:06 BST

The male finds his food elsewhere but therein lies the puzzle. Two males are feeding the same brood. At first I was unsure about this but close observations over a period confirmed my belief. As one male leaves the ivy, having done his duty, the other turns up with a beak-full of delights, feeds the chicks and goes off to seek fresh supplies.

Recently there has been a great deal of blackbird activity in our garden with a pair of males endlessly chasing one another with much chattering and lots of alarm calls. But watching the two cocks feed the same brood makes me wonder whether they have settled their differences to produce a menage-a-trois.

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The question is whether such things occur regularly in wild bird society. Laying eggs in the nests of others is not uncommon with perhaps the best-known being the cuckoo, now with us for the summer. The female will lay one egg in perhaps a dozen nests of other unsuspecting species and thereafter neither parent will take any further interest in their offspring.

Partridges are also prolific layers of eggs with a female producing up to 20 eggs or more in one season. The red-legged partridge, sometime known as the French partridge, will make use of two nests, with her beau incubating one nest while she cares for the other. That's breeding on a massive scale.

Two females of our own native partridge will lay up to 20 eggs each in the same nest, thus producing a clutch of up to 40 but I'm not sure whether both females share the task of incubation or whether some hapless male finds himself with a bigger family than he anticipated. Feeding baby partridges is not of major concern to the parents because, like most ground-nesting birds, they quickly leave the nest to forage for themselves.

Feeding baby blackbirds is much more demanding. They remain in the nest for a couple of weeks or so, and continue to depend upon their parents for food over the next three weeks or more, hiding in the bushes while mum and dad go hunting. It means that pair of daddy blackbirds are going to be busy for a while.

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This does raise the question as to whether all wild birds will feed and protect the young of others. It is done by the foster parents of baby cuckoos but birds that live in flocks seem far more protective than those living solitary lives. Whether this extends to the feeding of others' nestlings is quite separate from the instinct to survive against predators, something at which flocks are particularly skilled.

CW 1/5/10