Pipistrelle bat tracking in the Algarve

Bats are one of the natural world's better kept secrets. Due to their nocturnal existence and preference for secluded dwellings, they remain, for the most part, separated from the public eye and are liable to many misconceptions. There are 45 different species of bats within Europe, of which 23 are present within Portugal and 13 species can be found in the Algarve. In 2002, at the A Rocha Portugal study site of Quinta da Rocha, surveys were undertaken which established that at least seven and up to ten species of bat were using the area as a feeding ground, including the endangered Greater Horseshoe Bat and the vulnerable Schreiber’s Bat.

Pipistrelle in the hand, France 2003

The 2002 survey also involved some preliminary investigations into the roosting sites of the pipistrelles feeding in the locality. In August 2006 A Rocha continued this work and carried out surveys to identify the location(s) of roosting sites for the Pipistrelles feeding on Quinta da Rocha. The Pipistrelle family is a commonly found and widespread group within Europe and they were the most frequently recorded family within the 2002 study, when three species were identified: Common Pipistrelle Pipistrellus pipistrellus, Soprano Pipistrelle, Pipistrellus pygmaeus and Kuhl's Pipistrelle Pipistrellus kuhlii. Bats tend to roost in different locations during the summer (when they form maternity colonies) and in the winter (when they hibernate). July and August are an optimum time of year to locate their summer roosts, as at this time the roost will be at its peak numbers, so there are more individuals to follow back to the site.

Roost hunts are conducted by watching the direction that bats come from as they arrive at their feeding grounds during the 30 minutes after sunset and then tracking them as they return to their roosts, from 90 minutes before dawn until 30 minutes after dawn. Through repeating this process over a series of nights, the surveyor gradually follows the bats along their flight-path until the roost is reached. Bats tend to use linear landscape features such as hedgerows, rivers, roads and railways as navigation tools to find their feeding grounds. The identification of such features helps the surveyor to determine the exact flight-path that the bats are taking and to follow them, particularly through areas of limited access. The roost itself is identified by the witnessing of swarming behaviour and the recording of low frequency roost noises by a heterodyne bat detector. Subsequent surveys can then be undertaken to discover the exact entry and exit holes of the roost and to count the number of bats within the roost.

Soprano Pipistrelle roost site

The 2006 study tracked a colony of Soprano Pipistrelles across Quinta da Rocha back to their roost site in a mature Cork Oak tree on the fringe of a Cork Oakland meadow near the village of Figueria. The 2.9km flightpath followed tracks, hedgerows and the Riberia do Farelo across the Quinta da Rocha, turning onto the Lagos – Faro railway line passing the village of Figueria and finally following a track to the roost site.

The structure of the Cork Oak where the colony is located makes recording the numbers of bats difficult. The tree contains many different entry and exit holes and further study is needed but the initial counts suggest that the colony is quite small, up to 36 individuals.

An interesting observation was the presence of the bats within the roost in November. It is generally recognised that bats move to a separate roost site in the winter. Their continuing presence at this roost may be due to the warm climate, allowing them to stay in one location for a longer period of time and perhaps all year round. Further research needs to be undertaken to ascertain whether and when the colony moves to a winter roost.

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Project Leader: Will Simonson. For further information please contact portugal@arocha.org