Tuesday, 15 April 2008

Is spring springing yet?

When does Spring start? According to the Met Office, spring starts on 1 March, although the traditional start is the vernal equinox, on the night of 21/22 March. Here we are in mid April, so surely spring has started?

From a wildlife point of view, spring activity starts when the prevailing weather conditions permit, so in truth it's quite a variable thing, not just in terms of date, but geographically. The south of England is likely to experience signs of spring one or two weeks before they appear here in Scotland.

With some members of Lothians Bat Group, I went to Edinburgh's Blackford Pond after sunset, one evening last week. If you live in Edinburgh this is a great place to see large numbers of Daubenton's Bats (Myotis daubentonii) and Soprano Pipistrelles (Pipistrellus pygmaeus) in the summer, and the group usually run a bat walk there every year. On this occasion we wanted to see if there were the first signs of bats emerging from hibernation yet.

With an ambient temperature after sunset of just 2.5 degrees celsius, it was questionable whether we'd see any bats at all, but what was probably a lone Soprano Pipistrelle passed by a couple of times and we watched one, and later two Daubenton's Bats feeding on the pond. There was very little food for them, so they were having to range over the whole of this large pond, to find enough flying insects to eat (they looked to be small Sedge Flies). With such a low temperature, it's possible that these few bats were some of last year's juveniles, desperate for food after the long months of hibernation.

So is it spring? Well, not really from a bat point of view, as it seems like the main population are still in hibernation. The graph below shows the night-time temperatures at the Gogarmor meteorological station, to the west of Edinburgh, since the start of April. As you can see, there was a brief peak of warmer temperatures at the start of the month, but it has been quite cold at night since then.
Having said that, there are other signs of spring. As we walked around Blackford Pond, we had to tread carefully to avoid a large number of toads, commuting towards the pond, in order to mate?

Since then I have also seen some discarded eggshell from what must be a very optimistic bird and last weekend, I watched a group of Brown Hares (Lepus europaeus), boxing and chasing each other: the so-called "mad march hare" behaviour, associated with the onset of the breeding season. This behaviour actually continues through to September, but is far more noticeable just now, whilst the grass is short.

Hopefully we'll get a spell of warmer weather soon, and we'll start to see more bat activity, as the adults move out of their hibernation sites and the move towards maternity roosts commences, ready for the breeding season around June. My bat detectors are charged up and ready...

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