Butterfly Atlas 2021

Dr. Liam Lysaght provides an update on the Butterfly Atlas 2021 and reports on the large amount of information that is being generated through this citizen science project on the impacts of climate and landscape change on butterfly populations.


Why a Butterfly Atlas 2021?

Studying butterflies provides valuable insights into the impact of factors such as climate and landscape change on Ireland’s biodiversity. In response to climate change adult butterflies are emerging earlier each year and others are expanding their ranges. In a changing and increasingly intensively managed landscape some species are finding less and less suitable habitat for their survival. Tracking and understanding these changes provides valuable insights into pressures on Ireland’s biodiversity and it allows for the development of appropriate actions to mitigate these impacts. To provide these detailed, high quality insights into Ireland’s butterflies is why the Butterfly Atlas 2021 has been developed.

The Butterfly Atlas 2021 is a comprehensive programme of recording that comprised two main elements, namely:
1. Mapping species’ sites and ranges.
2. Population monitoring


Mapping species’ sites and ranges

The Butterfly Atlas 2021 is generating detailed information on the spatial distribution of all butterfly species across the island of Ireland and its offshore islands.  This allows us to identify what sites are most important for the conservation of butterflies and to track the range contraction or expansion in butterfly populations in order to prioritise conservation action. The Butterfly Atlas is a partnership project with Butterfly Conservation Ireland and Butterfly Conservation UK so that we can get a picture of what is happening across the entire island of Ireland.  The information on the distribution of butterflies in the Republic of Ireland is submitted to the National Biodiversity Data Centre through Ireland’s Citizen Science Portal. Since the launch of the Butterfly Atlas 2021 project in 2016 there has been a very significant increase, year on year, in the amount of data generated. In 2019, 1,253 people submitted 20,922 records from more than 8,000 different locations (see Table 1).

Table 1: Overview of progress with casual butterfly recording

In 2019, more than 2,000 records were submitted of the four most commonly reported species, speckled wood (2,048), small tortoiseshell (2,402), painted lady (2,281) and peacock (2,097). More than 1,000 records were received of a further five species, red admiral (1,936), green-veined white (1,479), meadow brown (1,349), orange-tip (1,266) and common blue (1,109). It was a particularly good year for painted lady and clouded yellow, two of our migrant species. There were 2,281 records of painted lady, reporting on 10,279 individuals seen. It was also the best year for clouded yellow since 2014 with 102 sightings submitted, the majority from along the south coast.

2019 was the best year for Clouded Yellow sightings since 2014

There was a huge influx of Painted Lady butterflies in 2019


Figure 1: Map showing the number of butterfly species recorded for each 10km square between 2015 and 2019

The current map of coverage for the Butterfly Atlas 2021 looks very impressive (Figure 1). Taking the entire island of Ireland and its offshore islands, land extends into 1,022 different 10km squares of the Irish Grid. With two years surveying for the Atlas remaining, already 15 or more species have been recorded in 308 of the 10km squares, and there are only 100 squares, or partial squares, for which no butterfly species have been recorded. This coverage will increase significantly when the 2019 Northern Ireland data, which is managed by Butterfly Conservation UK, is added to the Atlas database. The challenge remains to increase recording activity in the north midlands, central Munster and large parts of counties Galway and Mayo.

This butterfly dataset will be important to enable changes in the distribution of species to be detected and these data will be available to enable a new Butterfly Red List to be compiled in due course. Already, the mapping has detected the dramatic spread of the Comma from the Raven Nature Reserve where it was first recorded in 2000 to now commonly reported from across the east of the country. The Essex Skipper was also recorded in Wexford town for the first time in 2006, and while its range expansion has not been quite as dramatic as that of the Comma, it too is spreading and can now be found at many sites across County Wexford.


Overall, this is a huge level of recording activity and having such a large dataset means that factors such as observer and recording bias becomes less of a dominant factor. Indeed, 2019 saw the total number of butterfly records across all the programmes and datasets exceed more than 250,000 records so there is now also good temporal spread of records. The result is that we will be able to produce very detailed maps of the distribution of all Ireland’s butterflies at the end of 2021, and this can then be used as a benchmark for detecting future changes in butterfly distribution in Ireland.


Comma has seen a dramatic expansion in its range in recent years

Essex Skipper has also expanded its range in Co. Wexford since 2006


Population monitoring
Thanks to a large network of volunteers, butterfly populations are monitored from year to year. This is an essential component of the Butterfly Atlas 2021 project to detect how butterfly populations are changing from year to year. Volunteers walk a fixed route (transect) either on a weekly basis between 1st April and 30th September as part of the Irish Butterfly Monitoring Scheme, or five times during the main butterfly season as part of the Five Visit Monitoring Scheme. Both schemes provide data that allow us to detect changes in butterfly populations from year to year, however, the more extensive Irish Butterfly Monitoring Scheme data allows us also to detect fine level changes that might be occurring in the timing of butterfly flight periods. The Irish Butterfly Monitoring Scheme network is delivered by a very dedicated team of volunteers who walk their transect on 26 weeks during the summer. This scheme generates really important data where the counts of species can be linked to know section lengths along transects, thereby allowing robust population estimates to be derived.

The data from 2019 are currently being analysed and the trends will be updated shortly. The analysis that has been completed up to 2018 tracked changes in the butterfly population index from the base year of 2008, the first year of the monitoring scheme. The population index which aggregates trends from the 15 most widespread species found that 2018 was a bumper year for butterflies, and there was an overall increase of 29% in butterfly populations since 2008. The populations of two species, peacock and silver-washed fritillary have fared particularly well, whereas those of small heath and small copper have declined most. It will be interesting to see if this pattern has continued in 2019.

Table 2: Overview of the Irish Butterfly Monitoring Scheme

Each year this scheme alone generates more than 13,000 records of more than 33,000 individual butterflies (Table 2). There is no doubt but that the 26 week Irish Butterfly Monitoring Scheme is an onerous commitment and we are extremely grateful to those volunteers who give of their time to do this monitoring. Not everyone has the time to be available to do a walk every week. It also requires that weather conditions are suitable to enable a walk to be done on any given week, which often is not the case, particularly early in the seasons. Consequently 2019 saw a significant drop in the number of transects that were monitoring, dropping to 87. This still generates sufficient data to enable us to derive a population index, but obviously the more sites we have, the better quality the results.

Table 3: Overview of the Five Visit Monitoring Scheme

To complement the full Irish Butterfly Monitoring Scheme, a reduced five visits monitoring scheme was introduced in 2016. This scheme involves establishing a monitoring transect but walking the route only five times during the season – two visits from mid-April to mid-June and three visits in from beginning of July to end of August.  This scheme has proven to be popular with the network of volunteers and 2019 saw more than a doubling of the number of transects walked, raising from 36 in 2018 to 88 in 2019. Last year this generated 7,534 records of 22,903 individual butterflies.

At the outset of the Butterfly Atlas 2021 project we knew it was not feasible to get comprehensive coverage of butterfly counts in all 10km squares. To mitigate this, we established a ‘checkerboard’ system with a combination of high-priority and low-priority squares. This system allows us to target high-priority squares for monitoring, thereby reducing by half the number squares that ideally need to be monitored to get a very detailed picture of butterfly populations across the Republic of Ireland.

At the end of 2019 there were 238 10 km squares where some form of monitoring was undertaken over the last few years. A full download of the squares showing the overall progress can be downloaded here [10 km squares download (Excel 119 KB )] . This is a remarkably extensive monitoring network, and it generates really high quality data, all of which will be useful in deriving estimates of butterfly relative abundance for the entire country.


Butterfly recording in 2020 and the Coronavirus (Covid-19)

This season will be greatly disrupted by the Coronavirus (Covid-19) emergency and staying safe has to be the top priority. All recorders must abide by the official restrictions put in place to deal with the pandemic by staying with 2km of their home and practicing social distancing. In practical terms, this means that anyone whose butterfly transect is more than 2km for their home will have to abandon monitoring for the immediate future. However, the opportunity still remains for casual recording of butterflies with 2km of your home, so please continue to submit sighting through Ireland’s Citizen Science Portal. For anyone who is still very interested in monitoring butterflies and has a suitable site close to home, its is possible to establish a new five visit monitoring scheme transect within a 2km radius of your home. Details can be found here of how to establish a new transect from this link Establishing a Monitoring Transect.

It is intended also to pilot a new Garden Butterfly Monitoring Scheme to be launched for the beginning of May. The purpose of this scheme is to identify how important gardens are for butterflies, and to generate some meaningful population data without having to leave your garden. More details of this will be released over the coming weeks.


Thank you

Dr. Tomás Murray, who was the driving force behind the Butterfly Atlas 2021 project, has left the National Biodiversity Data Centre to follow a new career path. Not having his scientific input and drive will be a loss to the initiative, but on a personal note, I wish him every best success in his new post and thank him sincerely for the great work he did with the Butterfly Atlas 2021 to date.

A special thank you also to everyone who has submitted butterfly records to the Butterfly Atlas 2021 project and especially to those who have participated in the monitoring schemes over the years. This really is a hugely impressive, and important, citizen science initiative generating a very important scientific data.  We hope that the results outlined above show the benefits of the great work that is being done. We are still planning to host the Annual Recorders Field Meeting in  Donegal 14th-16th August, based in Glenties. Please pencil in that date, however everything is uncertain at the moment, so final details will be posted closer to the time.

This project is a collaboration between the National Biodiversity Data Centre, Butterfly Conservation Ireland and Butterfly Conservation UK.


Dr. Liam Lysaght is Centre Director at the National Biodiversity Data Centre and has taken over responsibility for the Butterfly Atlas 2021 initiative.

2 April 2020