09-Mar-2008, 00:00
A kestrel hunting behind my house
No, not the latest album by The Fall; I’ve just started reading The Eye: a Natural History by Simon Ings. On page 28, I came across the following fascinating snippet:
Even with their superb visual acuity and excellent colour sense, extending well into the ultraviolet, kestrels find it hard to spot the drab voles which are their favourite food. Happily for the kestrels, however, voles communicate by leaving trails of urine—indeed, they pee almost continuously—and mole urine reflects ultraviolet light. For kestrels, hunting voles is simply a matter of following the arrows.
Amazing.
I must admit, I was initially irked by Ing’s use of the word happily to describe what appeared clearly to be a marvellous hunting adaptation evolved by the kestrel. But not so: all birds can see into ultraviolet wavelengths, apparently; so kestrels can’t have evolved their ultraviolet vision specifically to hunt voles. The apparent adaptation turns out to be a lucky coincidence, which the kestrel has put to good use—possibly refining it over time.
Ultraviolet mole piss detection isn’t so much an adaptation as an exaptation, it would seem.
16-Sep-2006, 00:00
A crane fly on my window last week
It’s crane fly season here in West Yorkshire. Last week, we were suddenly inundated with them. One week there wasn’t any sign of them, the next they were all over the place—particularly in the evenings.
I didn’t know, until I looked it up, that crane flies spend most of their lives underground in their larval forms, which are known a leatherjackets. I knew that leatherjackets were very common round here, and are a favourite food of the local crows (particularly the rooks), but I did not know that leatherjackets transform into crane flies. You learn something every day.
I naturally supposed that crane flies emerge en masse to increase their chances of encountering a mate—which I still guess is right. But then I had another thought: emerging en masse will also give the individual crane flies a better chance of avoiding being eaten by predators: plenty more fish in the sea, so to speak. And then it occurred to me that they emerge in early September, which is about the time that swallows traditionally start heading south for the winter. Could the timing of the crane flies’ emergence in September be an adaptation to avoid being eaten by swallows?
If so, it isn’t a 100% reliable strategy. One evening last week, a family of swallows spent a good half-hour hunting around the west-facing eaves of my house. I initially mistook them for local bats—I had not seen swallows that close to the house before. I wonder if they were hunting crane flies, which appear to be attracted to the residual warmth of the building after sunset.
See also: Swallows preparing for migration
Postscript: Telegraph: Hot weather breeding boom brings invasion of the daddy long-legs
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