A Rocha Portugal Observatory Report 2009-2010

Introduction
A Rocha Portugal Observatory Report 2009-2010 29
BUTTERFLY MONITORING AROUND THE ALVOR ESTUARY, JUNE – OCTOBER 2009
Bert Van der Auwermeulen
This project is a follow-up to the 2004 butterfly monitoring project on Quinta da Rocha by the Alvor
estuary (Hayden & Carpenter, 2005), which compared results with a study undertaken in 1991 (Gardiner,
1992). Due to a change of landownership, none of the transects used in the previous studies were still
accessible, therefore it was necessary to create a series of new transects. Three transects were created
near the Roman ruins in Abicada and one on the north side of the N125 in Mexilhoeira Grande.
Casual observations in Quinta da Rocha during the weekly bird surveys in 2009, and an additional survey
conducted in the Cruzinha garden (Van der Auwermeulen, unpublished), provided more information
regarding the presence or absence of species in the locality throughout the year.
Aims and objectives
The aim of this study was to acquire an understanding of butterfly abundance and species diversity across a
variety of habitats around the Alvor Estuary during the summer of 2009, and to make a comparison with
previous surveys undertaken in Quinta da Rocha.
Methods
The methods followed in this study were based on those described in the Butterfly Monitoring Scheme
(Pollard & Yates, 1993) that was used for the studies in 1991 and 2004.
Using transect lines passing through different habitat types in a given area, provides a representative index
of butterfly species diversity and abundance. Whilst walking a set transect, records were made of each
butterfly seen in the defined area: three metres either side of the transect line, and five metres in front of
the recorder. This did not lead to an estimate of population size, but allowed a comparison to be made with
previous studies.
The transects were chosen in order to sample a variety of habitats found in Abicada and Mexilhoeira
Grande around the Alvor estuary. An obvious location-marker was used (and photographed) as the starting
point for each transect to help future relocation. The surveys took place between 09:00 and 13.30 hrs in
sunny conditions or, if cloudy, when the temperature exceeded 20 °C.
Four transects, each 300m in length, were walked once a week from the beginning of June until the end of
August, and once in both September and October. On 2 nd June records were limited to transects 1, 2 and 3.
The time taken to walk each transect was longer than in the previous studies and the vegetation was
disturbed in order to flush resting individuals. The time to complete one transect was often 30 minutes,
especially at the beginning when there were more identification difficulties. Some transects were
necessarily crossed again on the way back. In such cases counts were also made of any species which were
not recorded the first time.
A location map is presented in Appendix 1 and brief habitat descriptions of each transect follows.