A Rocha Portugal Observatory Report 2009-2010

36 A Rocha Portugal Observatory Report 2009-2010
Brown) was ending its flight period at the beginning of the survey period, thus one would expect the
numbers of this species to be low, however it might also have been more common in previous years. Some
of the Pieridae had also just ended their expected flight period (Euchloe belemia, Euchloe crameri) as well
as Medanargia ines (Spanish Marbled White) and Euphydryas aurinia (Marsh Fritillary). The low number of
Pieris brassicae (Large White) recorded was assumed to be caused by the scarcity of available food plants.
This species clearly takes advantage of Cruciferae growing abundantly in cultivated fields on Quinta da
Rocha, a rare situation in Abicada due to the current lack of agricultural activity. In addition, the conditions
in 1991 might have been unusually favourable for Pieris brassicae. Regarding the absence of Lasiommata
megera (Wall Brown) in 2009, it should be noted that it never appeared in very high numbers and it used to
be most numerous on the limestone scrubland and coastal scrubland (transect 3, 5 in 1991), these habitat
associations were not represented in the current survey and are no longer accessible on Quinta da Rocha.
During the period of this survey the lowlands of Abicada were rather poor both in flowering plants and host
plants. The most common butterfly species along Transect A1 was Pararge aegeria (Speckled Wood) which
appeared to be taking advantage of the shade provided by the high reeds. Pyronia cecilia (Southern
Gatekeeper) was present, but in low numbers. The rest of the butterflies recorded along this transect
(Pieris rapae, Pieris brassicae and Papilio machaon), were mainly fast flying, attempting to reach a more
sheltered area in the usually windy conditions. The observation of Celastrina argiolus (Holly Blue) was
interesting because although widespread and common, this species is most commonly seen in woodland
margins rather than in open marshland habitats. However, the individuals observed were seen crossing the
open areas and seeking shelter around the reedbed, perhaps indicating that this species is more mobile
than many other Lycaenidae.
Although the butterfly species diversity in transects A2, A3 and M1 were dominated by grassland species,
they clearly differed from each other in terms of composition. Transect A2 was the most sheltered site and
included the greatest number of wood/scrubland specialists 4 . In comparison the vegetation around
transects A3 and M1 was more open and, as might be expected, a higher number of grassland specialists 5
was recorded at these locations. Muschampia proto (Sage Skipper) and Carcharodus tripolina (False Mallow
Skipper), species observed mostly at the Mexilhoeira Grande site, M1, are known to show a strong
correlation with their food plants.
Conclusions and recommendations
The diversity of butterfly species in the wider Alvor Estuary area was similar to that observed in previous
studies in Quinta da Rocha. One notable difference in 2009 was the great abundance of Pyronia cecilia
(Southern Gatekeeper), representing 48.5% of the total number of recorded individuals. A potential
explanation for this difference includes the fact that the Abicada peninsula had less habitat diversity than
Quinta da Rocha and the predominant habitat type (grassland) is very favourable for this species.
While recognising the fact that populations fluctuate every year, the infrequent occurrence of Pieris
brassicae (Large White) and Pontia daplidice (Bath White) was notable. Again the difference in habitat type,
in this case the lack of cultivated fields on the Abicada peninsula, may have been a major contributing
factor. These two species are not currently endangered but it would be interesting to continue to monitor
their population dynamics.
4 Iphiclides podalirius, Satyrium spini, Celastrina argiolus, Pararge aegeria
5 Lycaena phlaeas, Aricia cramera, Polyommatus icarus, Maniola jurtina, Pyronia cecilia, Coenonympha pamphilus,
Muschampia proto, Carcharodus tripolina, Thymelicus acteon