We're nearing the end of the first week of Butterfly Conservation's fantastic Big Butterfly Count, which runs until 12 August. Like our annual Big Garden Birdwatch (which takes place in January every year), the Big Butterfly Count is easy to complete in your own garden or as part of any countryside walk. So easy, in fact, that all you need to do is record how many butterflies of each species you see in your chosen area during a 15 minute watch. What's more, you can do it several times during the three week count. As the survey is at the same time each year, it allows Butterfly Conservation's scientists to calculate population trends for many of our summer butterflies.
The Big Butterfly Count gives a snapshot of butterfly populations in mid summer, but for a more detailed comparison of population trends it's important to gather data over a longer time period, and much more regularly. To help with this, volunteers across the country will carry out weekly transect walks throughout the spring and summer, counting all of the butterflies that they see and submitting their results to Butterfly Conservation.
Here at Minsmere, two of our brilliant volunteer guides, Phil and Derek, have carried out our butterfly transect surveys for the last few years. They have several transects that they walk, covering the variety of habitats at Minsmere. During a transect walk, they count all butterflies seen within a 5 metre imaginary tunnel along their path - ie within 5 metres to either side or above, as well as on the ground.
While you might only count a few butterflies in your garden, some of the numbers recorded by Phil and Derek are quite astonishing, and really show the dedication of our volunteers. In fact, they have counted more than 1000 butterflies for both of the last two weeks, and recorded an impressive 22 species on 8 July.
Phil has sent me some of the count data from the last five weeks which help to highlight how numbers of each species can fluctuate through the season. Analysing the "browns" give some particularly interesting variation. The "brown" to emerge during June was meadow brown, and by 27 June there were 197 meadow browns counted. This had declined to just 51 yesterday. The much scarcer small heath shows a similar trend, declining from 25 on 27 June to six on 17 July, with none counted yesterday. Ringlets emerged a week so later, reaching a peak count of 303 on 3 July and declining to 95 yesterday.
Ringlet
In contrast, only three gatekeepers were counted on 3 July, but by yesterday there were an incredible 562 - more than half of the total butterflies counted! The summer generation of brown argus (which, despite its name is actually a "blue" butterfly, not a "brown") shows a similar trend, increasing from three on 3 July to 71 on 17 July.
Gatekeeper
One of our most familiar butterflies, the peacock, is also a common mid summer species. The first of the summer brood emerged in early July and 171 were counted by 17 July, although numbers have dropped off a bit since. Some of our other familiar butterflies, such as red admiral and large white, are migrants, so their numbers can be influenced by weather conditions on the continent, and especially the wind direction, but the gardeners among you will no doubt have noticed that large whites are numerous at the moment.
The regular butterfly transects have also contributed to some excellent counts of some of Minsmere's scarcer butterflies. For example, on 3 July Phil and Derek counted 13 purple hairstreaks, 26 white admirals and an incredible 27 silver-washed fritillaries. The latter is a recent colonist at Minsmere, only seen in ones and twos previously, but there have been double-figure counts through most of July.
Silver-washed fritillary by Peter Norfolk
Of course, whilst carrying out their butterfly transects, Phil and Derek also record any dragonflies that they see, as well as day-flying moths such as the six-spot burnet and silver Y. Dragonfly populations show similar changes through the flight periods of each species, with some species flying early in the summer and others emerging much later. For example, the Norfolk hawkers have almost finished flying now, while southern and migrant hawkers will continue to increase through August.
There was a new species added to Minsmere's dragonfly list this week, when a southern migrant hawker was photographed at the pond, though frustratingly it was missed by all our staff and volunteers. With luck there will be another one soon as this species is slowly colonising the UK, having been breeding in parts of Essex for several years, and there appears to be a large influx from the continent this summer.
Southern migrant hawker - a first for Minsmere - photographed by Phil Whittaker