Following the failings of 12 successive site visits over the past three weeks to get a close up sighting of a Brownie, Monday 10th September saw the 13th attempt which was also to end in failure. Many of these trips did take place in the afternoon which seems to prove the point that adults are most likely to be seen in the morning, although some sightings at the top of Ash trees have been made in the late afternoon/early evening around 5pm.
Following the latest disappointment, I resorted to egg searching at a site near Shurnock which last year produced a fantasatic result of around 300 being found. On Monday, I started at one of the Master Trees and worked along the main hedgerow for a distance of some 400 yards (I don't do metric). Surprisingly, no eggs were found near to the Master Tree but two were found on separate blackthorn suckers some 200 yards away. The remainder of that search failed to reveal any further eggs, but it is still very early.
Crossing over to the opposite hedgerow in an adjoning field which contains another Master Tree, two further eggs were found. These were on two separate and isolated blackthorn suckers, again well away from the Master Tree.
Questions that puzzle me:
- Will the female Brownie continue to egg lay in cool and cloudy conditions or will she remain buried in the hedgerow until the weather improves, assuming she does not fly back to the top of the Ash tree due to her body not being sufficiently warm enough to fly anyway?
- Does the female mate more than once and how many eggs roughly does she lay after she has mated?
3 comments:
Hi Geoff,
In response to your first question here is an entry to my diary on UK Butterflies, dated 26 August 2010.
Best Wishes, Neil
FIT TO BURST
I've always been intrigued to know how butterflies manage to deal with some of the problems associated with prolonged periods of atrocious weather, such as that experienced here in Sussex over the last few weeks. Brown Hairstreaks are usually notoriously fussy about the weather conditions under which they're prepared to go about their business - but what if they have no choice? In a 'normal' August they generally won't go egg-laying unless it's warm and sunny, and mostly between 11am and 3pm. In an average summer they will happily sit around doing nothing for a few days, until the weather dictates that every other species is on the wing, and you can hear the 'song' of grasshoppers and crickets.
At least locally, conditions have been unsuitable for oviposition since 16th August. A brief spell of milky sunshine on the 18th saw them starting to move around the canopy, but they weren't tempted to descend and lay eggs. After a further five days of rain, high winds and zero sunshine the females must have been fit to burst, and the necessity to get rid of some eggs must have become the over-riding factor in their behaviour.
On Tuesday (23rd August) I joined Colin Knight at Steyning Rifle Range, in conditions only marginally better than of late. Nothing else was flying - not even Meadow Browns, which remained cowering in the grass. However, with a brief thinning of the cloud and a modest rise in temperature, a couple of female Brown Hairstreaks were busy laying eggs - very busy! On a warm and sunny day they are usually very particular about selecting an oviposition site, constantly testing and rejecting numerous candidates before finally popping one out. This might take 15 minutes of indecision between lays, following many prolonged 'tests' on a number of blackthorn suckers. However, on Tuesday we watched a female crawl straight to the base of a sucker and squeeze out four eggs on the trot, in less than five minutes. Two were laid side-by-side and the others just above and below (one just out-of-frame in the image below). Five minutes later and a heavy shower brought the day's action to an end.
In previous years I've noticed how extended spells of particularly bad weather can influence the egg batch size in Duke of Burgundy. Whereas the 'norm' might be anything between one and three, after one particularly lengthy period of 'no fly' weather I found two batches of eight and one of ten eggs! Never a good idea to have 'all your eggs in one basket', but it seems that butterflies are quite capable of changing their behaviour when 'needs must'. Which is why of course that our butterflies are so adept at surviving our b****y awful summers!
Hi Geoff,
In response to the first part of your second question, also posed by both Gillian and Tom in their comments on 'Shurnock Success':
Unsurprisingly there seems to be very little data on repeat fertilisations in the wild. I suspect that the vast majority of female butterflies meet their maker before their last fertilised ovum has been laid, through either natural wear & tear, predation, adverse weather etc. Those who breed butterflies seriously, if not professionally, would probably have more to go on, bearing in mind that captive females should have a greater chance of surviving until their fertilised eggs are fully discharged.
However, my gut feeling is that female butterflies (including Brown Hairstreak of course) do have the potential to be mated and fertilised for a second time, although the above factors will make this a rare event. Whenever we photograph mating pairs the condition of the male varies from new to knackered, but females are invariably pristine – obviously indicating their recently surrendered virgin status. However, late last summer I photographed a pair of Small Heath in which the female was clearly being mated for the second time; both specimens had been around the block a few times. I suspect the potential for repeat mating/fertilisation is there, but rarely fulfilled due to lifespan.
Some interesting comments by Neil. I think we have seen with a number of species this year that butterflies can take advantage of even the narrowest windows of opportunity for egglaying.
One thing I would be interested to find out more about is when the majority of eggs are actually laid and it would be fascinating if Geoff is planning to continue to visit Shurnock on a regular basis to do an egg count of the same area each time he visits noting the date of additional eggs found.
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