Butterflies in agricultural environments
Summary
The populations of butterflies in agricultural environments have, on average, declined somewhat during the 2000s. The most significant declines have been observed in species that fly in early summer and whose larvae feed on grasses. In contrast, many butterflies that fly later in the summer or whose larvae feed on herbs or trees have remained stable or even increased. The annual population fluctuations of butterflies are considerable and are heavily influenced by the weather conditions during the summer seasons.
Status
The status for butterfly in agricultural environments has not been determined. This is because finding an appropriate reference point for the current situation is challenging, as the monitoring data only begins in 1999. Since the trend is assessed over the period from 2000 to 2023, the indicator’s status and recent development would be closely linked. However, based on the trend assessment, it can be said that the populations are smaller today than at the start of the monitoring.
Of the 45 species included in the indicator, five have significantly declined, and thirteen have slightly declined compared to the beginning of the monitoring period. Significant increases have been observed in two species, while five species have shown slight increases (Heliölä et al. 2022).
Trend
The trend for the indicator in the 2000s is declining. Butterfly populations in agricultural environments have, with 90 percent probability, decreased by just under one percent per year. The annual changes in butterfly populations are substantial, influenced particularly by summer weather conditions and fluctuations in the number of parasitoids affecting butterfly larvae. Despite this significant variation, a gradual long-term decline is apparent.
Significance
The indicator reflects the abundance and diversity of butterfly species in agricultural environments. Long-term changes in butterfly abundance and species richness are particularly linked to changes in land use in agriculture and forestry, as well as climate warming.
Over the decades, species associated with meadows and field margins have particularly declined due to the intensification of agriculture (Heliölä et al. 2021). The area of natural pastures, as well as field margins and other traditional habitats important for butterflies, has decreased. However, new habitats, such as roadsides and power line corridors, have somewhat compensated for these losses.
The temperature and rainfall of summer seasons strongly influence butterfly populations. On average, butterflies benefit from warm and dry summers. However, prolonged drought periods increase larval mortality, reducing butterfly numbers in the following summer. Climate warming has particularly benefited species like the map butterfly and the silver-washed fritillary, which have seen significant population increases since the 2000s (Heliölä et al. 2022).
References
Data used
The indicator is based on monitoring counts coordinated by the Finnish Environment Institute, conducted by volunteers with professional-level butterfly knowledge. The monitoring is carried out through line transect counts, repeated at least seven times each summer. The length of each transect is usually between one and two kilometers. In recent years, the monitoring has covered approximately 50 observation sites annually. The network is comprehensive in southern and southwestern Finland but is less extensive in central and northern parts of the country.
The species included in the indicator, listed in order of prevalence, are:
1. Ringlet – Aphantopus hyperantus
2. Green-veined White – Pieris napi
3. Essex Skipper – Thymelicus lineola
4. Small Tortoiseshell – Aglais urticae
5. Brimstone – Gonepteryx rhamni
6. Lesser Marbled Fritillary – Brenthis ino
7. Peacock – Aglais io
8. Small Pearl-bordered Fritillary – Boloria selene
9. Green Hairstreak – Callophrys rubi
10. Scarce Copper – Lycaena virgaureae
11. Arran Brown – Erebia ligea
12. Large Skipper – Ochlodes sylvanus
13. Amanda’s Blue – Polyommatus amandus
14. Dark Green Fritillary – Speyeria aglaja
15. Chestnut Heath – Coenonympha glycerion
16. High Brown Fritillary – Fabriciana adippe
17. Mazarine Blue – Cyaniris semiargus
18. Wall Brown – Lasiommata maera
19. Comma – Polygonia c-album
20. Wood White – Leptidea sinapis
21. Silver-studded Blue – Plebejus argus
22. Map Butterfly – Araschnia levana
23. Orange Tip – Anthocharis cardamines
24. Painted Lady – Vanessa cardui
25. Pearl-bordered Fritillary – Boloria euphrosyne
26. Idas Blue – Plebejus idas
27. Common Blue – Polyommatus icarus
28. Black-veined White – Aporia crataegi
29. Silver-washed Fritillary – Argynnis paphia
30. Heath Fritillary – Melitaea athalia
31. Northern Chequered Skipper – Carterocephalus silvicola
32. Holly Blue – Celastrina argiolus
33. Clouded Apollo – Parnassius mnemosyne
34. Red Admiral – Vanessa atalanta
35. Purple-edged Copper – Lycaena hippothoe
36. Mourning Cloak – Nymphalis antiopa
37. Geranium Argus – Eumedonia eumedon
38. Cranberry Blue – Agriades optilete
39. Small Copper – Lycaena phlaeas
40. Small White – Pieris rapae
41. Northern Brown Argus – Aricia artaxerxes
42. Large White – Pieris brassicae
43. Moorland Clouded Yellow – Colias palaeno
44. Cryptic Wood White – Leptidea juvernica
45. Small Heath – Coenonympha pamphilus
More information on the data:
Indicator calculation
The indicator for butterflies in agricultural environments is produced by the Finnish Environment Institute (Syke) in collaboration with the Finnish Biodiversity Information Facility of the Finnish Museum of Natural History. This indicator combines estimates of the population trends of individual species into a single index value. The multi-species indicator updates automatically, and its index value reflects the relationship to a reference year (2000). The indicator is calculated as the geometric mean of the indices for the 45 most abundant butterfly species that are permanently resident in Finland. Each of these species is given equal weight in the index.
The calculation of the multi-species indicator begins with assessing the abundance trends of individual species. These trends are evaluated based on the number of butterflies observed during counts, using generalized linear statistical models that account for differences between counting locations and dependencies between consecutive years.
Species-specific estimates based on sampling-dependent statistical models always contain some uncertainty. This uncertainty is addressed and incorporated into the multi-species indicator using Monte Carlo simulations.
For this site, annual population trend estimates for different time periods have been calculated from the indicator produced by the Finnish Biodiversity Information Facility.
Indicator as a table:
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Janne Heliölä
Researcher (Syke), Monitoring of butterflies in agricultural landscapes
Kimmo Saarinen
Conservation expert (Ely-centre), National butterfly monitoring