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Posted by Jes

Butterfly Season Report

What a year 2013 was! Scorching summer temperatures, reasonable sunshine levels and dry settled conditions prevailed much of the time from June to September. Surely all the right conditions existed for a butterfly population explosion? Indeed, numbers of many species reached spectacular levels.

How good was our summer?

If we count May as a summer month then conditions were poor for butterflies; “cold and wet everywhere, dull and wet in places” is a good synopsis of May 2013. June was mixed. There were good sunshine and high temperatures from the middle of the third week until about June 9th. Good weather returned mainly during the final ten days of June but June outside the dates mentioned saw plenty of wind and rain.

July 5th to 22nd saw dry settled sunny weather, ideal for butterfly activity. A blocking high pressure from the Azores settled over Ireland, keeping Atlantic rain belts away from Ireland. On July 19th a temperature of 30.3 degrees Celsius was recorded at Ardfert, County Kerry. Heat wave conditions (defined as five days or more with the highest temperature of over 25 degrees Celsius) were recorded at nine weather stations between 7th and the 13th of July. The sunshine levels were above average. Rainfall occured, especially early and late in July but rain is especially important because prolonged dry spells often result in desiccation of larval food plants and low nectar release.

August was “dry and warm nearly everywhere; dull overall” but there were some exceptional days such as August 17th when the temperature reached 24.3 Celsius at Oak Park, Carlow. Cloud cover was the limiting factor for butterflies during August; butterflies are active in cloudy conditions if air temperatures are high but their activity levels are lower.

September followed a similar pattern but some beautiful weather later in the month (September 21st was especially hot and sunny) saw plenty of late season butterfly activity, and October brought some good sunshine to extend the butterfly season.

Which species did well in 2013?

Early season butterflies suffered as conditions were dull and cold. The Orange-tip, a single-brooded butterfly that mainly flies in April and May showed low numbers, a clear indication of the bitter weather that clung on until May’s end. Some species emerged later than expected because of the prolonged cold early in the season; the Wood White and Pearl-bordered Fritillary were unseen in any numbers until June. Numbers were high for Cryptic Wood White, Large and Small White, Green-veined White, Small Tortoiseshell, Peacock, Ringlet, Meadow Brown and Speckled Wood; these are mostly generalist species flying mainly during June to September; these widespread, mobile butterflies will visit “wildlife friendly” gardens.

The Common Blue and Holly Blue (the Holly Blue’s numbers were especially low, with most sightings being singletons) fared much less well, although the Common Blue was numerous enough in its coastal haunts.

Silver-washed Fritillary: range expanding.©J.Harding.

Many habitat specialists performed well; the Silver-washed Fritillary continues to expand its distribution in Ireland to take advantage of new woods generating on cutaway bogs. The Dark Green Fritillary, a semi-natural grassland inhabitant also appeared in good numbers. A personal highlight was the sight of over 200 Dark Green Fritillaries settling to spend the night in a communal roost in a Burren wetland. It was simply a magical vista, with dozens visible at each step, wings glowing orange in the setting sun. The exquisite Marsh Fritillary, which suffered massive drops in its inland populations in 2011 and 2012 due to prolonged cold during its flight period, showed a partial recovery. This endangered butterfly produces one generation of adult butterflies a year so its continued recovery requires benign weather next June. The Brown Hairstreak, an elusive butterfly mainly confined to the Burren and the last species to emerge (mainly in August) showed increases on the two previous seasons. The Hedge Brown failed to reach high numbers in any count I know about and was not found when searched for in Old Bawn, near Cahore, Wexford where I have seen it over a number of years. The butterfly’s larva appears to need warm springs for its development and the bitter weather up to June may explain its really low numbers. The Wall Brown, a once common butterfly now much reduced in distribution showed no signs of increase, although the sight of eight individuals at Portrane on 08/06 was a positive experience. Another notable feature of 2013 is the low numbers of regular migrants. There were few Red Admirals, Painted Ladies and Clouded Yellows. The Red Admiral population build up, lower than expected, occurred later than usual with good numbers only in some coastal areas in September/October. Perhaps the continent had all these migrant butterflies needed so the travel impulse was lessened.

Marsh Fritillary, 2013 success.©J.Harding.

A season snapshot is provided by counts at Butterfly Conservation Ireland’s reserve in Lullybeg, County Kildare, where 2,331 butterflies comprising 20 species were counted from April to October in the course of 26 visits, up from 1,240 butterflies counted there during 2012. On July 10th, when the temperature during the count was 25 degrees Celsius, 288 butterflies were counted.

The most successful of the widespread butterflies in 2013 in terms of abundance were the Small Tortoiseshell (it managed a third brood in some areas), Peacock (19 seen in my garden on 20/08 far exceeds the previous high for my garden), Ringlet and Meadow Brown (these latter two were often uncountable on good habitats during July). Regarding the more localised species, the Small Blue, Silver-washed Fritillary, Dark Green Fritillary, Marsh Fritillary and Small Heath enjoyed high abundance. One habitat specialist was profoundly influenced by the weather in 2013. In the Burren the emergence of the bulk of the Wood White population was delayed by the cold that persisted into early June and thereafter good numbers were seen in July, later than is typical for the butterfly. Only one second brood individual, a female, was recorded on 02/08. It appears that the lateness of the emergence militated against the second brood which is often seen in the Burren in late July to mid-August. There is also the possibility that the hot July weather stressed the larval food plants (Tufted Vetch, Bird’s-foot-trefoil) growing on the thin soils making swift larval development impossible.

Although warm, sunny weather helps our butterflies, weather conditions here vary greatly and cannot be changed or controlled. While butterflies respond markedly to changes in weather and climate, it is habitat that has the greatest effect on butterfly survival. The continued existence of the specialist species especially requires high quality, often extensive and connected areas of semi-natural habitats. Indeed some butterflies that were formerly common are now considered habitat specialists because Ireland’s countryside has changed drastically since the 1970’s. To secure the future for the jewels of our countryside we must focus our efforts on ensuring extensive, well managed habitats continue to exist.

I thank everyone who recorded butterflies during 2013 and to the Dublin Naturalists’ Field Club which runs the “butterflyireland” website.
Jesmond Harding 2014.

Species First Date Last Date Highest count
Dingy Skipper 16-May 06-Jul 33
Small Skipper 08-Jul 13-Aug 50 plus
Essex Skipper 12-Jul 28-Jul 30
Wood White 17-May 02-Aug 13
Cryptic Wood White 21-May 20-Jul 12
Clouded Yellow 21-Aug 23-Oct 7
Brimstone 03-Apr 05-Oct 14
Large White 29-Apr 29-Sep 50
Small White 19-Apr 05-Oct 50 plus
Green-veined White 27-Apr 13-Oct 56
Orange-tip 01-May 06-Jul 20
Green Hairstreak 10-May 08-Jul 70
Brown Hairstreak 25-Jul 25-Aug 16
Purple Hairstreak 21-Jul 12-Aug 27
Small Copper 19-May 04-Oct 20 plus
Small Blue 01-Jun 05-Jul 137
Common Blue 22-May 22-Sep 100 plus
Holly Blue 06-Apr 22-Sep 2
Red Admiral 04-Jan 06-Nov 40
Painted Lady 19-Aug 19-Oct 6
Small Tortoiseshell 29-Mar 29-Nov 287
Peacock 02-Apr 12-Oct 65
Comma 05-Apr 23-Oct 3
Pearl-bordered Fritillary 21-May 13-Jun 12
Dark Green Fritillary 10-Jun 02-Sep 200 plus
Silver-washed Fritillary 29-Jun 06-Sep 40
Marsh Fritillary 25-May 29-Jun 100
Speckled Wood 19-Apr 29-Oct 15
Wall 07-May 25-Aug 8
Grayling 06-Jul 31-Aug 20
Hedge Brown 17-Jul 31-Aug 7
Meadow Brown 11-Jun 24-Sep 92
Ringlet 18-Jun 16-Aug 106
Small Heath 19-May 31-Aug 67
Large Heath 5-Jun 08-Jul 35