1. Butterfly Monitoring:
analysis and scientific use of data
Chris van Swaay,
De Vlinderstichting / Dutch Butterfly Conservation
Butterfly Conservation Europe (BCE)
Statistics Netherlands (CBS)
Thousands of volunteers
Adapted by Martin Wiemers (UFZ, BCE)
2. What is butterfly monitoring?
“Collect information on the changes in butterfly abundance”
We have to follow a protocol to detect real trends
Fieldwork
• Basis: samples
• Regular counts
• Fixed method
In the Netherlands 400 transects generate 200000
records per year
4. Criteria for indicators
• Scientific sound method
• Sensitive
• Affordable monitoring, available and routinely collected
data
• Spatial and temporal coverage of data
• Measure progress towards target
• Policy relevance
• Broad acceptance
6. • 1976: start of the first Butterfly Monitoring
Scheme in the UK
• Well founded by many scientific papers
• Now at least 2500 transects in 14 countries
• Every year our European volunteers
count once around the world (40.000 km)!
Butterfly Monitoring
available and routinely collected
9. From transects to
European indicator
• Location of the transects
• Quality of the observer
• Quality of the observations
• Validation of the observations
• Calculating trends
• Building indicators
10. From transects to
European indicator
• Location of the transects
• Quality of the observer
• Quality of the observations
• Validation of the observations
• Calculating trends
• Building indicators
11. Choice of locations
• Free choice of transects (e.g. in the UK, Netherlands,
Germany)
– Pro: appealing to volunteers, easy to keep them motivated, rare
species included
– Con: data is biased (but can be corrected by weighting)
• (Partly) random (e.g. France)
– Pro: less bias
– Con: sometimes transects on unattractive sites, no trends of rare
species (often the ones with high conservation value)
• Regular grid (e.g. Switzerland)
– Pro: almost no bias
– Con: hard to achieve (only on professional basis); no trends of
rare species (often the ones with high conservation value)
12.
13.
14. From transects to
European indicator
• Location of the transects
• Quality of the observer
• Quality of the observations
• Validation of the observations
• Calculating trends
• Building indicators
15. Basic idea
• We realise we can’t count all butterflies
• But by taking samples we can estimate trends
• As a consequence we don’t know the population size
• But we can calculate changes in the population size
efficiently
• With random or grid sampling transects are properly
distributed over the country
• But in many countries recorders have a free choice
• Solution: weighting
16. Why weighting?
• Not all species are equally distributed over the country
• Not all transects are equally distributed over the country.
In the Netherlands especially the dunes are
‘oversampled’, agricultural areas in the clay and peat
regions are ‘undersampled’.
17. Weighting by Dutch physical
geographic region and main
habitat type
Habitat types:
• Woodland
• Heathland
• Agriculture
• Open dunes
• Urban
• Moorland
18. Distribution of the population
over the strata
The distribution of each species per
stratum is calculated. For example:
Hipparchia semele
Dunes - mainland
Dunes - Waddensea
Heathland - north
Heathland - centre
Heathland - south
19. Distribution of the transects
over the strata
Dunes- mainland
Dunes- Waddensea
Heathland- north
Heathland- centre
Heathland- south
distribution
20. Big difference between weighted
and unweighted indexes
1
10
100
1992 1994 1996 1998 2000 2002 2004 2006
Weighted
Unweighted
21. The trend in the dunes is different
from the trend on the heathlands
distribution
transects
1
10
100
1000
1990 1993 1996 1999 2002 2005
Heathland
Coastal dunes
22. From transects to
European indicator
• Location of the transects
• Quality of the observer
• Quality of the observations
• Validation of the observations
• Calculating trends
• Building indicators
23. Grassland Butterfly Indicator:
main habitat for European butterflies
• For 57% of the species, grasslands are their main
habitat.
Grassland; 280
Woodland and
scrub; 153
Heath, bog
and fen; 25
others; 31
25. From national trends to a
European trend
0
25
50
75
100
125
150
175
1990 1994 1998 2002 2006 2010
Index(firstyear=100)
France
The Netherlands
Spain - Catalonia
United Kingdom
0
20
40
60
80
100
120
1990 1994 1998 2002 2006 2010
Index(1990=100)
+ 9 other countries
33. Relationships between butterflies
and environmental indicators
• Plants: Ellenberg values
• Like plants some species have a preference for rich or
wet situations, others for poor or dry places
• Butterfly monitoring gave us info on the presence of
butterflies
• We made vegetation surveys at transects and calculated
the average Ellenberg value for Nutrient, acidity and
moisture.
37. 0
10
20
30
40
50
60
0 1 2 3 4 5 6 7 8 9
Probabilityofoccurrence(%)
Acidity-value (Ellenberg scale)
Pmax=37%
Tolerance=2.3
Optimum=5.0
Response curve of
Araschnia levana for
Ellenberg’s acidity-
value, showing the
Optimum (U), the
maximum probability
of occurrence (Pmax)
and the Tolerance (T).
38. 0
20
40
60
80
0 2 4 6 8 10
Prob/Freqofoccurrence(%)
Nutrient-value (Ellenberg scale)
(a) observed
expected
0
20
40
60
80
0 2 4 6 8 10Prob/Freqofoccurrence(%)
Nutrient-value (Ellenberg scale)
(b) observed
expected
Two examples of response curves of butterflies on Ellenberg’s nutrient value, showing the calculated
logistic regression model (expected) and the observed frequency of the species in the relevés falling in
nutrient value classes with a width of 0.25: (a) the unimodal (Gaussian) response of Thymelicus lineola
and (b) the sigmoidal response of Ochlodes sylvanus.
42. Use butterfly monitoring results
for site information
0
1
2
3
4
5
6
7
8
1990 1995 2000 2005 2010
Moisture/Nitrogenvalue
Moisture index
Nitrogen index
Luttenbergerven
43. Multiple relationships
• Give the relationship between the three indicators
• When more than one is significant, we get a multi-
dimensional plane or surface
• For a site it can give an insight in the effects of a
changing environment on butterflies
