Butterfly monitoring on Quinta da Rocha

Old farmland habitat on Quinta da Rocha

A Rocha’s oldest site is at Quinta da Rocha in the Algarve, where biological surveys go back 20 years. In August 2004 Jane Hayden and Ben Carpenter repeated a survey of butterfly species diversity and abundance on the various habitats of the Quinta da Rocha estate that had previously been carried out in 1991. The rationale for this repeat study was that many of the traditional farming practices which were still widespread in 1991 have all but disappeared on the Quinta, and that such changes are likely to be reflected in the butterfly assemblages.

Nine transects of 300 m in length were walked once a week between 0800h and 1400h from the week ending 11 May until the week ending 17 August, and each butterfly seen was noted. Every effort was made to keep the 1991 and 2004 results comparable.

A total of 1020 butterflies of 24 different species were recorded across the transects in 2004. While this may seem encouraging, over two-thirds of the individuals recorded belonged to just four species. If these species are discounted, just 276 individuals of the remaining 20 species were recorded whilst walking a total of 27 km of transect!

Comparing the results separated by 13 years shows that there were both more individuals and more species recorded in 1991 than in 2004. The difference in number of individuals was shown to be statistically significant. This decline in butterfly numbers and probably diversity could be explained either by the nature of the life cycle of some butterfly species (which tend to have natural peaks and troughs) or by the unusually hot and dry weather conditions of summer 2004. However, the difference could also be the result of habitat impoverishment due to land-use changes on the Quinta. As the butterflies in decline were mainly those that share a preference for diverse, dry, flowery habitats, this suggests that such habitats may be scarcer. Analysis of a vegetation study also repeated in 2004 may confirm that these habitats have indeed changed.

Long-tailed Blue

Two main recommendations are made as a result of this study:

Whenever possible annual butterfly transects should be continued. This will enable any effects due to weather or natural butterfly cycles to be seen and would clarify whether 2004 was an anomalous year.
The 1991 and 2004 butterfly data should be analysed alongside the vegetation data to see whether a linkage can be established between vegetation and butterfly abundance.

Project leader: Jane Hayden. For further information contact A Rocha Portugal.