Brabant, R.

Degraer, S.

Lafontaine, R.-M.

Laurent, Y.

Vandendriessche, B.

Open Marine Archive

Belg. J. Zool., 146 (1): 62-65 January 2016
First offshore observation of parti-coloured bat Vespertilio murinus
in the Belgian part of the North Sea
Robin Brabant 1,*,†, Yves Laurent 2,†, René-Marie Lafontaine 2,
Bob Vandendriessche 3 & Steven Degraer 1
1 Royal Belgian Institute of Natural Sciences (RBINS), Operational Directorate Natural Environment (OD Nature), 
Aquatic and Terrestrial Ecology (ATECO), Marine Ecology and Management (MARECO), Gulledelle 100, 1200 
Brussels, Belgium.
2 Royal Belgian Institute of Natural Sciences (RBINS), Operational Directorate Natural Environment (OD Nature), 
Aquatic and Terrestrial Ecology (ATECO), Conservation Biology, Rue de Vautier 29, 1000 Brussels, Belgium.
3 Natuurpunt Studie vzw, Vleermuizenwerkgroep. Coxiestraat 11, 2800 Mechelen, Belgium.
* Corresponding author: robin.brabant@naturalsciences.be
†	 shared	first	authorship
KEy WORDS: parti-coloured bat, Vespertilio murinus, 
Belgian part of the North Sea
On September 19th, 2014 at 1:34am, a call 
sequence of a parti-coloured bat Vespertilio 
murinus	 was	 registered	 at	 approximately	 five	
kilometers off the Belgian coastline (N 51°21.40, 
E	 3°6.06).	 This	 is	 the	 first	 observation	 of	 the	
species in the Belgian part of the North Sea. The 
meteorological conditions during the time of 
the recording were good, with a temperature of 
18.6°C, a moderate easterly wind (3 Bft) and no 
precipitation.
The parti-coloured bat was detected from 
the Belgian research vessel ‘Belgica’ equipped 
with an automated acoustic SM3BAT recorder 
(wildlife acoustics Inc., Massachusetts, USA). 
The device records the echolocation calls of bats 
(between 0 and 126 kHz), from shortly before 
sunset to shortly after sunrise, hence allowing 
study of the spatio-temporal distribution patterns 
of bats in the Belgian part of the North Sea. The 
recordings were processed with the software 
programs SonoChiro (version v3.3.2; Biotope, 
France) and Batsound (version v1.3.1; Pettersson 
Elektronik, Sweden) to extract the echolocation 
calls	of	bats	and	 to	aid	 the	 identification	 to	 the	
species level. Every registration has a timestamp 
that is linked to the time and GPS registration 
of the ship, allowing determination of the exact 
time and location of observation.
The acoustic detector was operational during 
84 nights in autumn 2014 (from 11 August until 
5 December) and 76 nights in spring/summer 
2015 (from 16 March until 22 July). This record 
was the only detection of a parti-coloured bat 
during this study.
The parti-coloured bat was registered for a 
period of 20 seconds, during which the call was 
recorded 60 times. This suggests the specimen 
was not just passing by the vessel. The call 
sequence is typical for an individual crossing an 
open biotope but some foraging calls (or buzz) 
are also noticeable. The intense activity suggests 
the parti-coloured bat was attracted by the vessel 
while passing by, where it most likely foraged 
for a short period of time.
The sonogram of the registered parti-coloured 
bat call shows an average frequency of maximum 
energy at 25.4 (± 0.30 standard deviation) kHz 
and an average duration of a single call of about 
20 (± 1) ms (Fig. 1, Table 1), which is typical for 
the parti-coloured bat [1,2]. The rate of repetition 
of the calls is known to be about 5 Hz [1], which 
fits	our	recording.
The parti-coloured bat is a Palearctic species 
occurring over an extensive geographic area [1]. 
It	 is	widely	 distributed	 from	 the	Asiatic	 Pacific	
coast through Siberia to eastern, northern and 
central Europe in the west [2]. The western limit 
of its regular distribution lies in eastern France, 
63
Fig. 1. – Sonogram of the parti-coloured bat Vespertilio murinus detected in the Belgian part of the North Sea.
FI (kHz) FT (kHz) FME (kHz) Call duration (s) Intervals between two calls (s)
average 27.45 23.09 25.41 0.020 0.231
standard deviation 0.91 0.23 0.30 0.001 0.07
maximum 30.42 23.92 25.83 0.027 0.48
minimum 24.30 22.76 23.88 0.0177 0.10
TABlE 1
Average, standard deviation, maximum and minimum values of the key variables of the 21 most distinctive 
calls in the sequence of the registered parti-coloured bat specimen. FI = initial frequency; FT = end frequency; 
FME = frequency of maximum energy.
Switzerland and southern Scandinavia (Fig. 2) [1]. 
The species is rare or absent in western and southern 
Europe, however vagrants have been recorded 
far outside its normal range, e.g. Tuscany [3], 
Spanish Pyrenees [4], Isle of Arran [5], Shetland 
Islands [5] and even oil rigs in the North Sea [6]. 
The species is known to migrate long distances 
of up to 2000 kilometers from Scandinavia and 
Central Europe to more temperate regions of 
Western Europe, and back [7,8,9]. Observations 
at the western limit of its distribution are linked to 
autumn dispersion and probably also hibernation 
[10]. For more information about the ecology 
of Vespertilio murinus, we refer to Rydell & 
Baagøe (1994) [1].
In Belgium, the parti-coloured bat has until 
now been recorded 41 times, including eight 
in 2014. The majority of those records were 
made in September and October, but there are 
also records in Belgium from February, March, 
April	and	June.	The	first	observation	was	made	
in 1989 in the coastal community Blankenberge. 
A second record was made in the year 2000, 
and from 2006 onwards there is an increase in 
the number of records. Nine records were made 
with an acoustic detector, other records concern 
found (dead or injured individuals) or captured 
specimens or were sightings at a roosting 
location. Only three of the eight observations in 
2014 were recorded by a detector. Most of the 
First offshore observation of Vespertilio murinus in the Belgian part of the North Sea
64 Robin Brabant, yves laurent, René-Marie lafontaine, Bob Vandendriessche & Steven Degraer
Belgian observations were made onshore along 
the coast and along large riverbeds [11]. Similar 
to the Belgian records, 11 of the 24 observations 
of this species in the Netherlands between 1977 
and 1995 were obtained from coastal localities 
[12]. Forty specimens were detected near the 
Swedish coast in 2005, 2006 and 2008 [13,14]. 
The parti-coloured bat has previously been 
detected offshore in the North and Baltic Seas. 
Three specimens were found on oil rigs in the 
Dutch part of the North Sea, once in 2004 and 
twice in 2006, at 69, 48 and 124 km from the coast 
[6]. Our observation hence contributes to this 
data series with increasing numbers of offshore 
observations. The species was, however, not 
recorded during an extensive study in the Dutch 
part of the North Sea [15], stressing the rarity of 
offshore observations as yet.
Our record of the parti-coloured bat at sea 
and other recent observations in Belgium 
may be considered indicative of an increased 
number of specimens in our region. Together 
with the reported records of specimens in e.g. 
the Spanish Pyrenees [4] and Italy [3], this 
suggests the species is extending its range of 
distribution to the West. The IUCN red list [16] 
also reports expanding populations in some part 
of the species’ distribution range, for example 
in Denmark and the Netherlands. On the other 
hand, the contribution of improved methods 
of detection (e.g. acoustic techniques) and an 
increased search effort (both in time and space) 
also very likely contributed to the increased 
number of detections of the parti-coloured 
bat. For the Belgian records, this is, however, 
unlikely as only nine of the in total 41 records 
were done with an acoustic recorder. Of the eight 
records from 2014, only three were made with 
an acoustic detector. More extensive studies are 
indispensable to any unambiguous conclusion on 
the real status of the parti-coloured bat in south-
western Europe.
Fig. 2. – Distribution range of the parti-coloured bat Vespertilio murinus with indication of its breeding area 
(light grey) and its migration area (dark grey). The dotted line indicates the area where migrating individuals 
have been observed (adapted from aRthuR & lemaiRe 2015 [10] and www.eurobats.org [2]).
65First offshore observation of Vespertilio murinus in the Belgian part of the North Sea
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Received: July 24th, 2015
Accepted: January 12th, 2016
Branch editor: Johan Michaux


First offshore observation of parti-coloured bat <i>Vespertilio murinus</i> in the Belgian part of the North Sea

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