Common Blue - female imago MIA

[jonhd]

(Appreciate that this could've gone in the Species-Specific forum for Polyommatus Icarus...)
Site: North end of Southampton Common, a patch of wildflower meadow, approx. 70m. x 70m. Copious Bird's Foot Trefoil. The area is peppered with small anthills
Over the past decade or so, there has been a reasonably stable, if small, population of Common Blue. (Along with Small Copper - very small numbers; Cinnabar moth - there's plenty of Common Ragwort; Small Skipper.)
It's probably what would be described as a meta-population. I rarely see more than 4 or 5 Males at the same instant.

This year, Males first appeared around 1st June. I have yet to see a female, having looked very carefully - in bright sunlight; in cloud cover; early & late [when I can find males roosting]). The males are now looking rather tatty, and numbers are down to a few. So, I'm assuming this brood is nearing the end of it's flight period.
It's too early for Small Skipper, I appreciate; Cinnabar also a bit early - I saw one today, but not seen the large numbers of cats I would expect. Small Copper very low numbers - an occasional singleton.

So my question is whether there could be any possible reason for the extreme disparity in male:female numbers of Common Blue? I did find this paper, but I don't think it would explain the complete dearth of females... https://www.jstor.org/stable/4220098
The only other factor I can think of is that we're seeing many more rooks in this area of the Common, than in past times. They are ever-present in the meadow, methodically pecking at the entire area, hoovering-up anything edible. But, can't see why that would affect females specifically.

I guess the veracity of what I've observed will be evident in the (lack of) 2nd brood. Maybe I'm just becoming even more myopic that I thought I was

BR, Jon
P.S. Females at this site have always been very brown - rarely seen a 'blue' female. Confident that I'm not mistaking males for females.

[David M]

Hi Jon, could it not just be down to the females being naturally far less seldom seen than the males?

I would estimate that for every female icarus I see there are 20+ males; in fact, so far this year I reckon I've seen no more than 7 or 8 females whereas I've clocked up at least 200 males (although females DO make up a greater proportion towards the end of the flight period).

Female butterflies are usually far more infrequently observed than males, especially those species (like Common Blue) where males use a 'patrolling' strategy to hunt for mates.

In addition, males of this species are visually far more conspicuous than females, being bright blue rather than predominantly brown.

Once mated, females will also lie low to avoid further harassment, and when out on ovipositing missions, will frequently fly short distances, very close to the ground and will spend much time grounded whilst they inspect potential LHPs.

Like you, I don't find it plausible that birds would have significantly greater success in predating the females rather than the males (that would be disastrous from an evolutionary perspective).

[jonhd]

Thanks for those thoughts, David. I am aware of the more 'clandestine' nature of the female's life. Which is why I have been looking very closely & exhaustively around & about the Birds-Foot Trefoil, and surrounding flowers, mostly at ground level. (And also checking grass stems for roosting.) I have seen females, over the years, at this site.

Unfortunately, my eyesight (combined with knackered knees) is not really up to looking for ova...

In order to eliminate allegations of incompetence(!), I should really wait until the 2nd flight period is underway, I guess

Thanks again, Jon