Species studied
Birds and butterflies are recognized biodiversity indicators both in
natural and human-modified landscapes. Their use as bioindicators comes
from the variability within species and their ability to respond fast to
environmental changes; including agricultural intensification and land
abandonment (12 ,13 ,14 ,51 ). We
obtained butterfly data from the Catalan Butterfly Monitoring Scheme
(CBMS;http://www.catalanbms.org/)
running for the last 25 years (thus accounting for variable data
length). The survey consists of a network of sites where visual counts
of adult butterflies along transects are undertaken by volunteers. In
each transect butterflies’ surveys are done weekly during the flight
period of imagos (March-September) along lineal transects of ca.
700-2500m length (mean and median length = 1715 and 2010m respectively,
wide 5m). Each transect is divided in smaller sections per dominant
habitat type, leading to 6 to 14 sections per transect. Number of
individuals (i.e. observations) are then recorded per species in each
section, and then summarized per transect. We used 91 transects for the
BMR (2009). In the case of birds, we obtained data from the Catalan
monitoring scheme of common birds (SOCC;www.giraffa.co/ico-catalan-ornithological-institute/).
Transects consist on a 3-km track with six sections of 600m. Along
these, the observers record bird observations and auditions, and then
summarize data per transect. Two yearly censuses are performed for
breeding species (April-May and May-June), and two for wintering species
(December and January). We used 23 transects for the BMR (2009).