EDP Foz Tua: Bat Habitats - Complementary Studies [2010]

Study Extent

The data were collected within a 5-km radius buffer around the lower valley of River Tua (Northeast Portugal), up to 45 km from the mouth, in the municipalities of Alijó, Carrazeda de Ansiães, Mirandela and Murça.

Sampling

Sampling was designed to cover all suitable foraging habitats for bats in the study area. A stratified sampling procedure was used, with the number of samples allocated to each habitat in proportion to the area occupied and/or its significance for bats. A total of 48 sampling points were set in natural woodlands (7), river margins (15), shrublands (7), orchards/olive groves (5), vineyards (8) and urbanized areas (6). Each point was visited once between 8 and 22 April 2010, within ± 3 hours of sunset, and acoustic sampling was carried out for 20 (consecutive) minutes. The detection of the specimens in flight was made with a bat detector (Pettersson Elektronik, D240X model), with a frequency range of 10-120 kHz. The detector was connected to an automatic digital recorder (model Nomad Jukebox 3, from Creative Technology Ltd.) which saved the recordings in a “Wave” format, at a frequence of 44.1 kHz and at an expanded mode of 10x, making them audible to the human ears while, at the same time, preserving the original acoustic characteristics. The analysis of the sound records was made in the lab, with the software “Batsound Pro – Sound Analysis”, from Pettersson Elektronik. This software generates graphics (oscillograms, sonograms and power spectrums) that allow the identification of the detected species by comparing them with those available in reference bat sound libraries. The acoustic variables used to identify the sounds are (1) the structure of the pulse, (2) the frequency of maximum energy (kHz), (3) the range of frequencies (kHz), (4) the pulse duration (ms), (5) the interval between pulses (ms), and (6) the pulse repetition rate (Hz). The exact identification of the bat species by sound analysis is not always possible, due to problems in detectability and/or identifiability. In the context of this work, all records that could not be unequivocally attributed to a given species were assigned to the “species complex” that best fitted their frequency characteristics. Thus, 3 multi-specific groups sharing the same acoustic characteristics were considered: Myotis spp. (in turn subdivided in “large” Myotis – M. myotis and M. blythii – and “small” Myotis – the remaining 7 species), Pipistrellus ssp. (several complexes of different combinations of species, including Miniopterus schreibersii, whose vocalization is undistinguishable from that of Pipistrellus pygmaeus), and Nyctalus spp. (N. lasipoterus and N. noctula).

Quality Control

All individual identifications were performed by qualified technicians

Method steps

The taxonomic coverage of this dataset spans 1 phylum, 1 class, 1 order, 4 families, 9 genus and 11 species positively identified. Additionally, a set of 9 potential species may be present in the 7 “species complexes” identified.

1. Chordata
   rank: phylum
2. Mammalia
   rank: class
3. Chiroptera
   rank: order
4. Vespertilionidae
   rank: family
5. Miniopteridae
   rank: family
6. Rhinolophidae
   rank: family
7. Molossidae
   rank: family

The data were collected within a 5-km radius buffer around the lower valley of River Tua (Northeast Portugal), up to 45 km from the mouth, in the municipalities of Alijó, Carrazeda de Ansiães, Alijó, Mirandela and Murça.