More of an ‘old man’ than ‘a new man’

CONGRATULATIONS to Sinéad Shanahan of Stonehall Farm in Limerick.

Her emus, which hail from Australia, have hatched chicks for the third year in succession. Compliments also to the proud parents, particularly the daddy. He needs a bit of encouragement because emu males do all of the rearing. Mammies, as soon as they have laid the eggs, take no further interest in them, leaving incubation and baby-minding to the father. Nor do the emu daddy’s problems end there. When the brood leaves the nest, he will have to chaperone and guard his charges for another 70 days or so. It was thought that the proud father led his offspring around, but now it’s believed he traipses after them in desperation.

This bird version of the ‘New Man’ is a bit of a rara avis. In only about 6% of the world’s 9,600 bird species, does the male incubate the eggs without any help from his mate. In the case of the rhea, the reasons why the male takes over are clear. Rheas are vegetarians. Plant fibres are hard to digest and it takes time to do so effectively. Herbivores tend to be big, with large stomachs. But, if you are a bird, being big comes at a price; you won’t be able to fly. There are advantages to being grounded, of course; flightless birds don’t need to be weight-watchers and, when it comes to gorging themselves, they can afford to let it all hang out. Nor are there constraints on the size of a flightless bird’s eggs or clutches, which is why emus can lay up to 20. However, having put so much of her resources into the next generation, the poor mum-to-be is exhausted and in no condition to sit, fasting, on eggs. The male has no choice but to take over the show.

In a little over half of all bird species, both parents share incubation. In humans, a devoted husband and father is referred to, reverentially, as a ‘New Man’, but, in the case of birds, it might be more appropriate to call the caring daddy an ‘Old Man’. Species in which fathers either do all the incubating or share the task with their mate, almost always belong to the more ancient orders of birds. Seabird parents, for example, lapse into a sexless state once the eggs have been laid; each parent taking turns on the eggs. Pigeons belong to another old group and, when it comes to incubation, both sexes do their bit.

But, in the huge order of songbirds, known as the ‘passerines’, the males seldom sit on the eggs at all. This is the group which evolved most recently and the one which, it is widely held, includes the most modern sophisticated and advanced bird species. House martin and sand martin males are among the few Irish songbird males which incubate. Swallow males do so occasionally. There are a few freak records of song and mistle thrushes sitting on eggs but, for the rest of our garden birds, there is a division of labour in which the task is assigned exclusively to the mother.

Although they may not incubate, songbird males don’t spend their time amusing themselves. They must defend territories which will provide resources for their families. Most males feed their partner while she is on the eggs and almost all songbird males bring food to the chicks. For the most part, male and female birds contribute equally to raising the young. In the fierce struggle to survive and breed, no creature can afford to leave a resource untapped. A bird which puts his feet up is in for a rude awakening.

But there are species in which neither the male nor the female sits on eggs, the best known being the cuckoo. It is one of 80 criminal bird species which trick other birds into doing their parenting for them.

Birds elsewhere in the world have come up with legitimate schemes to avoid incubating. The ‘megapodes’, or ‘big feet’, are relatives of the farmyard hen and the pheasant. There are 22 species alive today but you will have to travel to Australia, or the islands of South East Asia, to see them. The heating engineers of the bird world, the megapodes, know how to exploit natural sources of energy, such as the warmth of the sun, heat from under the ground or hot decaying vegetation. Birds, which use the sun, simply dig a hole on a sandy beach, lay an egg and cover it up. The geo-thermal nesters excavate permanent burrows, close to volcanoes or hot springs, where they know that the temperature is just right. The mallee-fowl of Australia builds a mound of decaying vegetation.