Bats about the Algarve

Bats and bat detectors

Greater Horseshoe Bat

Traditionally, bats have been a very difficult group for ecologists to study. They are commonly glimpsed in near total darkness, are often small, generally have a uniform brown colour and roost in inaccessible places. Yet in the last few decades, the study of these fascinating mammals has been revolutionised by the use of electronic bat detectors that can pick up the inaudible ultrasonic sounds that bats use to communicate and to detect insects and convert them into lower frequency signals that can be heard by the human ear. Recordings of bat calls can also be made and examined later using sound analysis software programs. As a bat species may have a particular call pattern and frequency, the skilled user of a bat detector may use this in order to identify which species are present. Visual clues such as size, shape and flight style are also useful in supplementing the audio data. A bat detector is not just helpful for making identifications; it also allows the mapping of the routes that bats take to and from their roosts.

Using a relatively simple bat detector, Chris Boyes carried out the first studies of the bats of the area around A Rocha Portugal's field studies centre at Cruzinha from May to early November 2002. The aims of Chris's study were to try to determine which species of bat feed, and perhaps roost, on the headland of Quinta da Rocha where the centre is. This study was the first systematic one of bats made by A Rocha in a region where there is little information on the distribution and abundance of these threatened mammals.

Findings

Bat detector

The results of the study showed that Quinta da Rocha supports a variety of bat species with different habitat preferences. Both rare and common, endangered and non-threatened species were found. At least seven, and possibly as many as ten, different species of bat were recorded and six species were positively identified:

Greater Horseshoe Bat Rhinolophus ferrumequinum
Common Pipistrelle Pipistrellus pipistrellus
Soprano Pipistrelle Pipistrellus pygmaeus
Kuhl's Pipistrelle Pipistrellus kuhlii
Schreiber's Bat Miniopterus schreibersii
European Free-tailed Bat Tadarida teniotis

In addition, at least one species of Noctule (genus Nyctalus) was heard and the Serotine Bat Eptesicus serotinus was probably also present. This list is by no means exhaustive and other bat species, including some with weak or hard to distinguish calls, probably also occur. Significantly, Daubenton's Bat Myotis daubentonii seemed to be absent from the western marsh where it might have been expected to occur.

Many European bats are threatened and some of these bats have a high importance for conservation because their populations in Portugal, or Europe as a whole, are small or declining. So, for example,

all Horseshoe Bat species, Rhinolophus sp., are declining and endangered.
Schreiber's Bat Miniopterus schreibersii is vulnerable and declining.
all the species of Nyctalus are rare.
the European Free-tailed Bat Tadarida teniotis is also rare in Portugal.

Significantly, the Common Pipistrelle Pipistrellus pipistrellus was found to be relatively abundant in the study area although it has not yet been officially confirmed as being present in Portugal.

Three species, the Common Pipistrelle, Soprano Pipistrelle and Kuhl's Pipistrelle were regularly observed in good light and in large enough numbers to be tracked. The observations made on these species suggest that no roosts for these species exist on the Quinta da Rocha headland but that the roosts are in the vicinity of the nearby village of Figueira.

The way ahead

Although this study with its use of a relatively simple bat detector has greatly increased the amount of information available on bats of this part of the Algarve, it is very much a preliminary study. Much more work should be done.

These results should be checked and supplemented by further work. Although of enormous value, the simple heterodyne detector has its limits. It is a relatively inefficient tool for multi-species surveys as only one frequency range can be monitored at any one time. Furthermore, there are limits to identification, as it can often be hard to distinguish the calls of different species. These problems can largely be overcome by the use of more advanced bat detectors, such as those using time expansion and frequency division technology, in combination with computer analysis.
It would be helpful to find the location of the main bat roosts. For the only species for which roosts were sought (the three Pipistrelle species), it was clearly shown that the roosts were not on the Quinta da Rocha headland. In order to locate possible roosting sites near Figueira and key feeding sites, tracking at dusk and dawn should be continued.
Some of the rare and endangered species found to be present in the study area could be focused upon as a single species study.
The presence of the Common Pipistrelle Pipistrellus pipistrellus should be confirmed.

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For more information please contact portugal@arocha.org