Harsh winter for wrens

Garth Lowe

The winter at the end of 2010 was a particularly harsh one, starting very early with the first snow on the 26th Nov and the cold spell continuing through most of December. On nine days in this period the maximum temperature at Old Storridge never got above 0°C with some night temperatures dropping to -10°C.

These conditions put a great strain on the resident birds especially those with the least body mass such as the wren. A timely reminder from a resident of Birchwood Lane, just a ten minute walk through the woods, encouraged us to see a phenomena not observed very often. During the last winter he had observed a number of wrens going to roost in a bird box attached to one corner upright of an open barn used as a workshop, and claimed there were at least twenty entering the box. On the evening of the 19th December 2010 with the daily maximum having only reached -3°C that day, I met my sister Cherry Greenway and her husband to see how this activity actually worked.

In snowy conditions I arrived at the box at around 3 40pm with no birds to be seen and I thought it was too late and they all must be in the box as it was so cold. By 3 55 three pairs of eyes were studying the box when the first wren arrived, hung about for a bit and then went in only to reappear again as if to say I am not going to be the first! This was repeated a few times by more wrens, which had started to arrive. By 4 10pm just a few had stayed inside, but others kept on arriving and continuing with the in and out action.

By nature this bird cannot be called a social bird, setting up territories in the spring and defending them against other male wrens, so this winter gathering has to overcome that part of their make up. It is an ingenious scheme, all huddling together in a sheltered area through long cold nights, so saving on the loss of body heat. The speculation is how did this evolve?

The numbers going into the box continued to be monitored with the figure rising steadily, but dropping back still as a few birds kept coming out. The figure of 20 was soon passed and then 30, which we thought quite unbelievable in one normal sized bird box. A figure of 40 was then reached, with more wrens still arriving by the minute and queuing up around the site, so it was speculated we might even reach 50! At 4 30pm things went very quiet so the observation was terminated. It is true to say that 50 wrens were seen to go in but two came out at the end and went elsewhere, leaving still an incredible figure of 48 all tucked up warmly inside.

It is also a remarkable fact that there were still so many wrens still alive in the surrounding district with the inclement conditions. Since this number could not all be living closely around the site, some birds must have flown in quite a distance from their territory to the box. The last question of course is just how all these birds get to know that there is a wren Hilton, where they all gather for the night? Memory must work quite well as it was used last year, but how did all those youngsters from this year cotton on to this fact?

It was a magical 45 minutes watching the wrens performing their going to bed actions, which must have taken place night after night in the long period of intense cold.