Tuesday, July 12, 2011

Sussex Blues

Further to Brother Neil's post yesterday. I Emperored intensively in Southwater Woods during the 1970s and have returned annually since 1998, with intermittent visits in between. Not since the odious summer of 1972 (vile May & June, then a lovely July) have I struggled so badly to see iris at this stage in its season there. The mean is about 11-12 per day for this stage. Camilla was also very poor there this year (and was going over rapidly yesterday).

Brother Ken indicates unusually low occupancy of the male territories at Bookham in Surrey, though a pleasing number of males on the ground during good weather there. I haven't received any news from Kent (please!).

It looks as though numbers are particularly low in the SE this year, and in some other districts (e.g. Warwicks). I also suspect that the butterfly is right down in Savernake, Wilts, but everytime I go there it promptly clouds up ...

It's difficult to explain this patchy picture, though the situation will become clearer in time.

Certainly, the two day gale that commenced last St Swithun's Day knocked out adults in a big way, just as the females were getting into the swing of egg laying. At Savernake, they only had 2-3 days of laying before being clobbered, though in theory ladies in the SE, where the season was more advanced by 15:7:10 would have commenced laying a few days earlier. So, the 2010 egg lay should have been better in the SE.

We know precious little about the pupal stage of iris in the wild. It may well be that, as with camilla, adult emergence is best after a good June + short pupal period and worst after a poor June + long pupal period. Maybe larvae in the SE pupated there incredibly early this year (mid-late May) and the insect then got trapped for horribly long in the vulnerable pupal period, even longer than elsewhere?

Recording of males in Sussex yesterday was difficult because only one territory held more than one male, and we know that solitary males are quiet, especially during the second half of the season (now beginning). Males are far more active if they've got someone to squabble with! Also, there's a paucity of small flies in the canopy at present (following last Wednesday's mild gale): one thing I've learnt from nine days in a cherry picker is that the commonest reason for territorial males flying is small flies landing on them whilst they're basking!

But Neil and I also failed to see Herself in Sussex yesterday, and I particularly went for her...

Meanwhile, here's Brother Neil at work beside an artificially-created puddle in another Sussex wood earlier in the season. This behaviour is quite normal of course.

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