Migration #3 Summary - March
All Hard Work and No Help
Taken as a whole, March has not been a good month for migrants. The airstream over western Europe / British Isles has been consistently from the east or north-east, and only a few days where the winds dropped to light airs or local calms. Checking the records back to the start of the month, I find that there has not been one single 24-hour period where the birds would have wind at their backs for flying. And over all this, of course, the inescapable, unrelenting cold...
… it's no wonder that I haven't seen a single swallow yet, here in the North.
|Geostrophic Wind Scale for 30.3.13 (Click for larger image)|
April starts with the mixture as before. Although daytime temperatures will improve during week one, this will only be by a few degrees. The problem remains the same: “blocking” anticyclones (high pressure) over Scandinavia and central Europe will keep the usual progression of Atlantic weather systems at bay. Towards the middle of the month we should see a change towards more typical spring conditions, but average temperatures will remain on the low side of normal.
All this makes it tough work for our UK birds to reach their summer breeding sites. Even the strong fliers, like Ospreys, have to work hard for ground gained: their aviation fuel - stored fat reserves – gets used up more quickly. They suffer the same “sports injuries” as an elite Olympic athlete and face the same dilemma: stop to rest, heal and feed, or carry on and risk a bigger problem down the line.
My blog this weekend will look at the physiology of this in more detail.