Cabal of kingfishers piques my curiosity

I SPENT the bank holiday weekend on my boat on the Grand Canal.

Drifting through the midlands at about eight kilometres an hour at the beginning of May is an extremely pleasant thing to do. You’re always close to the banks and the speed is slow enough to allow you to notice things.

I noticed several signs of the hard winter and late spring. Primroses were in full bloom at the same time as the first cowslips. I don’t remember this overlap before. Primroses are usually long gone by the time the cowslips appear. And blackthorn was still blossoming and normally it’s finished early in April.

But there were new, green shoots in the reed beds and dazzling butter-coloured clumps of that flower that’s sometimes called a marsh marigold and sometimes a king cup. Down in the murky water you could see lily pads were opening out and their stems were lengthening as they reached for the surface.

Then we arrived at a stretch of canal that was full of kingfishers. I can’t tell you how many because when a kingfisher spots a boat it usually whizzes off and disappears, and then it sometimes reappears again. This means you can end up counting the same bird twice. But there were certainly at least a dozen along a stretch of canal only a few kilometres long.

I’ve never seen this sort of density before and it puzzled me because kingfishers are supposed to be fiercely territorial. It is too early in the year for the birds to be family groups of parents and young, so why were so many adult birds tolerating the proximity of others?

The size of the territory of an animal or bird tends to be closely linked to the richness of that territory. For example, a clan of badgers living in a mature broadleaf woodland with plenty of food resources may defend a territory as small as 50 or 60 hectares while badgers living in leaner environments, such as upland or open farmland, have territories of up to 200 hectares.

Could it be that the kingfisher territories along this stretch of canal were short because they were particularly rich? Richness, for a kingfisher, is not just a question of an abundance of small fish. There must also be banks with the right soil to allow them excavate their nesting burrows and branches overhanging water of the right depth that they can use as diving platforms.

This stretch did look attractive as far as those factors are concerned and one of the birds disturbed by the boat flew straight at the bank and disappeared, making me think it was a female that had dived into her nest burrow. Others settled on overhanging branches and allowed us to watch as the boat drifted past.

One of them did something I’ve never seen before. It flew diagonally across the canal in front of the boat and then dived into the water. Many water birds dive to escape my boat but this is the first time I’ve seen evasive action like this from a kingfisher.

I noticed something else which might be relevant. It could have been a trick of the light, but all the birds seemed to have slightly darker plumage than the average kingfisher. Could these birds all be related to each other, an isolated community that carried a gene for slightly darker plumage and had been passing that gene on for several generations? Each new generation would have occupied the next available territory along the line of the canal. This could explain the unusual number of birds in a relatively short stretch as well as the dark plumage.

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