The first surprise of the day was a Swallow, sitting as bold as brass on a telegraph wire, in the middle of an arable field. It was a juvenile, apparently completely unmoved by the fact that it now goes down into the history books as my latest ever Swallow in the UK! Cocky little blighter....
With work completed for the day, and back in civvies, I moved on to a nearby (inland) nature reserve. It was ok for birds, with a couple of Black-necked grebes, some Pochard and a few Tufted duck, but it was much more interesting for invertebrates, and I was pleased to find a Clouded Yellow butterfly on a patch of short grassland. Clouded Yellows are a migrant species in Britain, and this individual has presumably been blown here on the recent southerly winds. It's only my 8th ever record of the species in the UK, with the last being as long ago as 2003. It's generally a late summer / early autumn migrant, most numerous on the coast, though I did see one on Reed's Moss near the Bottle and Glass in St Helens a few years back. Todays individual seems to me to be a very late record, especially for an inland site. I find it slightly ironic that having left the migration hotspot of Gibraltar Point behind and moved inland, I should then find two of the best migrants of the week! Other butterflies today included a Comma and several Peacocks.
Around the pools, there were plenty of dragonflies, mainly all Common Darters, and it was pleasing to see several pairs ovipositing. Also today, a few Migrant Hawkers.
I said that Clouded Yellow is a migrant species, but it's not a migrant like we would call a bird a migrant. Birds migrate between their breeding and wintering grounds several times during their lifetime. When a Little stint leaves Africa to fly to the Arctic to breed, it migrates through the UK, and the same individual is programmed to return before the Arctic winter. It's also programmed to take the same route to and from the Arctic every year. In contrast, this Clouded Yellow will never return to its birth place in southern Europe, for one thing it won't live long enough, and even if it lays eggs here, the species cannot currently survive the winter in the UK in any stage of its life cycle. So it would appear to be a pointless and wasted journey. Furthermore, when it set out on its journey, it was programmed to disperse, to leave its home, but not necessarily to end up in Britain, so clearly what ever is going on, it's not the same as the stints migration.
Well then, call it a vagrant you might say. But no, it's not a vagrant either. A vagrant is a Grey-cheeked thrush on Shetland. When the thrush set off on its journey, it was programmed to migrate south in North America, but something went wrong, most likely it got caught up in a weather system and it ended up somewhere it didn't want to be, on the wrong side of the Atlantic. From a species point of view, that individual might as well be dead, because it will never breed and offers nothing more to the Grey-cheeked thrush gene pool. Superficially that might seem to be the same outcome as my Clouded Yellow, but it's not, it's very different.
Yes the Clouded Yellow I saw today is going to die soon, but from the species point of view, the butterfly didn't get here accidentally like the thrush, rather it was a species programmed dispersal. This type of dispersal serves an important function. If the species keeps dispersing in this way, eventually the climate will change, and the species will be able to breed in new areas and expand its range, making this species more robust to climate change than other more static species. So it's not a migrant or a vagrant as we know it in bird terms. Perhaps I should have called it an opportunistic dispersing butterfly.....
Ovipositing (egg laying) Common darters. Contrary to what you might think, these dragonflies are not mating, and nor are they about to mate. In fact they've already mated. This is called flying in tandem or guarded oviposition. The male grasps the back of the females head, while she dips her ovipositor into the water to lay the eggs. Even though she already has his sperm, the eggs aren't fertilised until the female starts to lay the eggs. If another male mates with her before oviposition, it will be his sperm which fertilises the eggs. Therefore in these photos the male is guarding the female, or more specifically he's guarding his sperm.
Hang on a minute, I thought it was nearly winter.........
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