www.ukbutterflies.co.uk

Hi
I have noticed an apparent 7 year cycle with Small heath (see attached chart), 5 poor years, 2 good years, 5 poor, 2 good......
Has anyone else noticed this?
Any thoughts?

I cant find any literature about any such cycle.
What is causing it?
I presume a parasite, but what other species does it use?
How localised is this apparent cycle?
From the transect data and if I am right in thinking there is such a cycle then 2010 and 2011 should be good years for Small Heath - in the Lewes area.

Crispin

Hi,

Thats very interesting, didn't notice that myself so I don't know whats going on, I do know that this year people here in Northern Ireland are reporting seeing hundreds of small heath in various places, even I am seeing that many so this year seems like a good year for them here. I read the "Butterflies and Moths of Northern Ireland" on small heath and it reads:

"The phenology of this species in Britian and Ireland is complex. It is generally double-brooded in Southern Britian and single brooded in the north but this is complicated by variation caused by larvae developing at different rates."

Also colonies can disappear if sites are unmanaged as if they overgrown, the small heath can't survive. Also the largest populations are generally (well in Ireland anyway) found in costal areas

I first noticed this back in 2004, but thought I would give it a bit of time just to see if it followed the same pattern as the previous years - and it has at Malling Down, Lewes.

Some people have suggested the apparent cycle is coincidence and just related to weather conditions. If that is the case, I would expect a similar pattern in some other species and there isn't - so far as I can see. Obviously there are many factors to consider but the cycle is to regular to be coincidence and 2010 looks to be a good year so far.

It also is interesting you mention about the phenology of this species, the double and single broods, as this would be an additional factor to consider.
Looking at the UK BMS data it would appear Small Heath follows a 6 or 7 year cycle at SOME other sites, but not always the same 6 or 7 years which could relate to the phenology. Therefore the Collated Index of abundance for the whole country does not show the cycle.

One day I intend to look at transect data from a range of other sites to identify how regional such a trend is. Then hopefully identify what parasite is causing it and what other butterfly species may be involved.
To be honest, I shall probably never get around to it, but I may give it a try - one day.

Crispin

Hi Crispin, here is the data for the Small Heath from Hants & IOW branch 2009 Report.

This was from Martin Down, North, hope it helps.

Regards Gruditch