Mystery of the missing blue tit mate

You can watch the antics of two blue tit families by logging on to the Mooney page on RTÉ’s website.

The birds are at slightly different stages in the breeding process and face rather different challenges.

One nest is at the Mary Aikenhead daycare centre in Donnybrook, where nine chicks have hatched. Such large broods are the norm for blue tits. Most songbirds produce two or three clutches in a season but blue tits, here and in Britain, have only one. The caterpillars on which they feed their babies, are available for a few weeks only.

Tits must make hay while the sun shines, so they lay as many eggs in their one clutch as other birds do in several. The rain of recent weeks has not helped the Mary Aikenhead family but, with improvements in the weather, their prospects are brighter.

The same can’t be said for the second web-cam nest. At the invitation of President Mary McAleese, nest boxes were installed in the gardens of Áras an Uachtaráin and a blue tit nested in one of them. Incubation began 11 days later than at the Mary Aikenhead centre.

The nest is particularly interesting, not because of its prestigious location, but for the absence of the male bird. He will have fed his mate during courtship, helping her to form the eggs.

When the female began incubating, he should have continued bringing food but he didn’t. Newly hatched chicks can’t control their body temperatures and the mother must remain on the nest to keep them warm. Her mate should supply enough food for the family but the Áras female gets no support at all. She has to go hunting caterpillars, then hasten back to warm her chicks, a difficult juggling act.

So where is the mate? “In the midst of life we are in death” as the saying goes – life for small birds is precarious. Was he taken by a sparrowhawk or a cat? Did a car hit him? We don’t know. There is, however, another possibility. A study in Belgium found that at least 3.4%, and perhaps up to 10.8%, of blue tit males were bigamous.

Some tits even had three wives. There were similar cases in Germany. Is our bird an adulterer and why would any sensible male take on an extra family?

Turlough O’Donnell, a 16th century descendant of Niall of the Nine Hostages, had about 80 sons and grandsons. He had an unusual form of the Y chromosome and this is found today in about one-fifth of the men living in north-west Connacht.

Like Turlough, a male bird wants to have as many descendants as possible. When the resources of his territory allow it, recruiting a second wife makes good sense.

But is the Áras bird a “secondary female”? There’s another reason to think she might be. She laid a paltry six eggs, instead of the usual 10 or 12.

Females must reach a particular weight in order to ovulate. Late-nesting females, like this one, often have difficulty reaching the required weight. Not a great “catch”, she may be a concubine rather than a wife. In the Belgian studies, however, bigamous males usually brought food to both wives so, if this is a case of two-timing, why is the male not doing so here?

Perhaps he spends all his resources on the other brood, assuming he has one.

If so, it’s just about possible that he will reappear to make amends for past neglect as soon as the young from the first nest are off his hands.

This is all wild speculation on my part, but what are to prospects for the Áras nest? Young have been raised successfully by blue tit single parents, so failure is not inevitable.

Normally, however, both parents must work from dawn until dusk to keep a brood supplied, making up to 900 food deliveries a day.

With a single parent, the number of deliveries will be halved but, in the Áras case, the brood is only half the normal size and she might just manage it.

It has to be said, though, that the prospects for the family of a deserted wife or a widow are not great. By the time you read this, the issue may have been decided.

* To find out more log on to www.rte.ie/mooney.

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