DOI: 10.5061/dryad.z08kprr9n
title: How butterflies keep their cool: physical and ecological traits influence thermoregulatory ability and population trends.

description: Understanding which factors influence the ability of individuals to
 respond to changing temperatures is fundamental to species conservation
 under climate change. We investigated how a community of butterflies
 responded to fine-scale changes in air temperature, and whether
 species-specific responses were predicted by ecological or morphological
 traits. Using data collected across a UK reserve network, we investigated
 the ability of 29 butterfly species to buffer thoracic temperature against
 changes in air temperature. First, we tested whether differences were
 attributable to taxonomic family, morphology or habitat association. We
 then investigated the relative importance of two buffering mechanisms:
 behavioural thermoregulation versus fine-scale microclimate selection.
 Finally, we tested whether species’ responses to changing temperatures
 predicted their population trends from a UK-wide dataset. We found
 significant interspecific variation in buffering ability, which varied
 between families and increased with wing length. We also found
 interspecific differences in the relative importance of the two buffering
 mechanisms, with species relying on microclimate selection suffering
 larger population declines over the last 40 years than those that could
 alter their temperature behaviourally. Our results highlight the
 importance of understanding how different species respond to fine-scale
 temperature variation, and the value of taking microclimate into account
 in conservation management to ensure favourable conditions are maintained
 for temperature-sensitive species.
description: Data were collected in the UK, on four calcareous grassland
 reserves in Bedfordshire owned and managed by The Wildlife Trust for
 Bedfordshire, Cambridgeshire & Northamptonshire (Totternhoe Quarry
 [-0.56836, 51.89199], Totternhoe Knolls [-0.58039, 51.88989], Pegsdon
 Hills [-0.37020, 51.95354] and Blows Downs [-0.49580, 51.88321]); at two
 sites in Cumbria (Irton Fell [-3.34000, 54.40672] and Haweswater
 [-2.84598, 54.50756]); at one site in Scotland owned and managed by the
 National Trust for Scotland (Ben Lawers [-4.27326, 56.53287]); and at a
 calcareous grassland reserve in Wiltshire owned and managed by the Royal
 Society for the Protection of Birds (Winterbourne Downs [-1.68500,
 51.14963]). Between April and September 2009 in
 Bedfordshire, and between May and September 2018 at all sites, adult
 butterflies were surveyed at each site. After recording the behaviour of
 each butterfly when first encountered, we caught as many individuals as
 possible using a butterfly net. We did not chase individuals, to ensure
 that the temperature recorded reflected the activity of the butterfly
 prior to capture. Immediately after capture, we used a fine (0.25 mm)
 mineral-insulated type K thermocouple and hand-held indicator (Tecpel
 Thermometer 305B) to record external thoracic temperatures
 (T<sub>body</sub>). Only three individual devices were used
 for data collection, and were calibrated to the same readings prior to
 use. The thermocouple was pressed gently onto an exposed area of each
 butterfly’s thorax, while the butterfly was held securely in the net, away
 from the hands of the recorder to avoid artificially elevating the
 recording or causing any damage to the butterfly. Butterflies were then
 released. A second temperature recording was then taken at the same
 location in free air, in the shade, at waist height
 (T<sub>air</sub>). In 2018, for butterflies perching on
 vegetation at the time of capture, a third temperature reading was taken
 by holding the thermocouple a centimetre above the perch location
 (T<sub>perch</sub>). Information on habitat
 specialisation was added from Asher <em>et al.</em> (2001),
 mean wingspan was taken from Eeles (2020), and colour category was
 determined by assigning each species a score from 1 (white) to 6 (black)
 on the basis of how pale/dark wing colours appeared by eye (see Bladon
 <em>et al.</em> 2020 for details). References Asher J, Warren MS, Fox R, Harding P, Jeffcoate G & Jeffcoate S (2001) <i>The Millennium Atlas of Butterflies in Britain and Ireland</i>. Oxford: Oxford University Press. Bladon AJ, Lewis M, Bladon EK, Buckton S, Corbett S, Ewing SR, Hayes MP, Hitchcock GE, Knock RI, Lucas CBH, McVeigh A, Menéndez R, Walker J, Fayle T & Turner EC (2020) How butterflies keep their cool: physical and ecological traits influence thermoregulatory ability and population trends. <i>Journal of Animal Ecology</i>. Eeles P (2020) UK Butterflies. Retrieved from UK Butterflies website: https://ukbutterflies.co.uk/index.php
description: Perch temperatures are all missing for 2009, as they were only
 collected in 2018.