Nature Notes

By Denis O’Connor

Wharfedale Naturalists Society

A THUD on the glass of our patio door drew my attention to a small bird which fell to the ground to be immediately pounced on by a second small bird. The victim escaped briefly but only managed to fly five yards before both again formed a struggling heap on the flagstones, one pinned beneath the other. Normally I abide by the rule that nature is red in tooth and claw and do not interfere but this was too much so I went out to separate them. The aggressor made off over the hedge into the woods while the victim flew to the stone wall of the house where it clung for over ten minutes, apparently secure in the knowledge that the assailant would not return while a human stood a few feet below it.

At first I assumed that the fighting birds were robins which, belying their benign Christmas card image, are in fact aggressively territorial and extremely pugnacious in defence of their territory’s boundaries with fights to the death accounting for a yearly mortality rate of up to 10 per cent.

I was surprised to find that the bird on the wall was in fact a wren (pictured) for, although wrens sing loudly for most months of the year and do defend winter territories based around their preferred feeding areas, most of their disputes are resolved by singing and posturing. However, they do fight at times, especially in the spring when they are setting up breeding territories.

In severe winter weather, males are even known to temporarily abandon their aggressive habits and attract other wrens to a communal roost by calling and making short flights. Dozens of wrens have been found huddled together in nest boxes, arranged in layers with tails pointing outwards as they share their body heat overnight before dispersing again at dawn. The greatest number documented for a nest box stands at an incredible 61, during a freezing spell in 1969, with quite a few records of 30 to 40.

Another possibility is that the attacking bird was in fact a robin for there are recorded instances of them attacking other small birds. Although they have many prey items such as insects and spiders in common the hunting strategies of robins and wrens are different with the wren, living up to its Latin name of Troglodytes, the cave dweller, a bird of tangled undergrowth, nooks and crannies. However, both species love the vegetation at the edges of our ponds and perhaps neither wishes to share such a rich hunting ground with a rival, either from its own or a different species.