Ortmann's funnel trap - Universität Bielefeld

Herpetology Notes, volume 3: 13-21 (2010) (published online on 20 January 2010)
Ortmann’s funnel trap –
a highly efficient tool for monitoring amphibian species
Introduction
Axel Drechsler 1 , Daniel Bock 2 , Daniel Ortmann 3 and Sebastian Steinfartz 1*
Abstract. In the face of the worldwide amphibian decline, efficient sampling and monitoring of amphibian species becomes
increasingly important. We report on the detailed construction and application of a new kind of amphibian funnel trap, the Ortmann
funnel trap, which can be applied in aquatic environments for sampling and monitoring amphibian species both at the larval and
adult stage. It can be quite easily constructed with everyday items for low overall costs. The repeated application of 140 traps
(150 inspections from March to July in 2004, 2005 and 2006) in ponds and ditches of a former flooding area of the Rhine River
near Krefeld (Germany) carried out by a single person resulted in 111,338 larval and adult trapped amphibians of all five species
inhabiting this area. As compared with commonly used collapsible nylon traps (fish traps), the catching efficiency for crested
newts (Triturus cristatus) in a study site near Hamburg was considerably higher for Ortmann’s funnel trap in two different setups,
while the escape rate of trapped newts during a 24-h monitoring period was significantly higher for the collapsible nylon traps.
The possibility to completely construct this trap out of plastic items with smooth plastic surfaces allows for an efficient and reliable
disinfection of pathogens in the field. Therefore, the potential spread of pathogens such as Batrachochytrium dendrobatidis (Bd),
which causes Chytridiomycosis through monitoring efforts is limited.
Keywords. Amphibians, monitoring, funnel traps, Triturus cristatus, Batrachochytrium dendrobatidis.
Worldwide, amphibians today are experiencing the
greatest decline among all vertebrate classes (Stuart et
al., 2004; Collins and Crump, 2009). The drivers for
this decline are various and are linked to one another,
spanning from habitat fragmentation over infectious
diseases to climate change (Nystrom et al., 2007; Lips et
al., 2008; Sodhi et al., 2008). Chytridiomycosis, a disease
caused by the pathogenic fungus Batrachochytrium
dendrobatidis (Bd), is considered to be one of the
main specific drivers worldwide of the rapid decline of
amphibian populations (Lips et al., 2008).
1 University of Bielefeld, Department of Animal Behavior, Unit
of Molecular Ecology and Behavior
2 University of Hamburg, Dept. of Biology, Research Group of
Animal Ecology and Conservation
3 Zoologisches Forschungsmuseum Alexander Koenig, Bonn
e-mail: cruzecontrol@gmail.com
*Author for correspondence: Sebastian Steinfartz, University
of Bielefeld, Dept. Animal Behavior, Morgenbreede 45, D-
33615 Bielefeld, Germany; Phone: (+49) 5211062653; Fax:
(+49) 5211062998
Email addresses:
AD: drechsler@uni-bielefeld.de
DB: Daniel.Bock2@gmx.de
DO: ortmannda@hotmail.com
SS: sebastian.steinfartz@uni-bielefeld.de
For amphibians, an effective sampling of individuals
is crucial to detect declines, monitor the general
demography of focus populations and document
emergence as well as monitor the pertinence of infectious
diseases in populations. Moreover, national and
international habitat directives, e.g., the FFH guidelines
according to Council Directive 92/43/EEC in Europe,
are mainly based on monitoring amphibian focus
species in selected populations to derive assumptions
on the conservation status of such species.
The majority of monitoring efforts and methods for
amphibians make use of the fact that frogs, toads, newts
and salamanders are, to a varying degree, dependent on
water for their reproduction and spend different amounts
of time in or near respective aquatic reproduction
habitats. Males of many frog and toad species use vocal
signals to attract females during courtship and can
therefore be more easily located or counted (Dorcas
et al., 2009) than the “silent” and more cryptic newt
species. For them, monitoring approaches normally
include trapping individuals with dip nets, drift fences
around the reproduction habitat (in most cases, ponds),
or different kinds of funnel traps (see Willson and
Gibbons, 2009 for an overview). Although drift fences
should catch almost all amphibians on the move to a
specific pond, their efficiency has been questioned over
the last few years (Arntzen et al., 1995; Jehle et al., 1997;
Schmidt, 2003; Weddeling et al., 2004). In a recent study,

14
Axel Drechsler et al.
Figure 1. Different views on Ortmann’s funnel trap; picture of used collapsible nylon trap and study sites in Krefeld. (A) View
inside of Ortmann’s funnel trap: four half-cut inverted plastic bottles are inserted into the bucket. Swimmers (two foamed plastic
tubes) are fixed with an elastic plastic string through openings in the bucket. (B) Lateral view of Ortmann’s funnel trap. (C)
Ortmann’s funnel trap built with two tightly closed 0.33-l plastic bottles instead of the foamed plastic tubes at the upper part of the
bucket wall. (D) Exposed trap in a pond. (E) Top view of Ortmann’s funnel trap. Please notice that the lid has to provide enough
holes to allow oxygen transfer during exposure in the field. (F) Schematic illustration of a collapsible nylon trap used for the
comparative study. (G) Large pond and (H) ditch as typically sampled for amphibians with Ortmann’s funnel trap for the study
part in Krefeld (Germany).

An efficient funnel trap for amphibian monitoring 15
Ortmann et al. (2005) showed that funnel traps clearly
out-compete drift fences over short periods of time (14
days) as well in the long term (up to three years) when
monitoring crested newts (Triturus cristatus) in a Middle
European habitat (Baker, 1999). Indeed, funnel traps
have been shown to effectively catch different species
of amphibians, and especially newts during their aquatic
reproduction period (Fronzuto et al., 2000; Mölle et al.,
1998; Tucker, 1995; Wilson et al., 2002).
In this study, we present data for a new type of amphibian
funnel trap, the Ortmann funnel trap, which is designed
to catch newts and other aquatic amphibians. We
provide a detailed description of how to construct this
kind of trap and show with our data that the trapping of
aquatic amphibians is highly efficient with this new trap
type. Especially newts, in comparison to the commonlyused
collapsible nylon trap (also called the fish trap),
can be efficiently sampled. The Ortmann funnel trap can
be easily constructed for a low overall price, with items
available almost everywhere around the globe. Most
importantly, as one variant of this trap, it is completely
designed out of plastic items that have a smooth surface,
and it can be easily and exhaustively disinfected, thereby
limiting the possibility of spreading pathogens (e.g., Bd)
through the monitoring efforts (Johnson et al., 2003;
Garner et al., 2009).
Materials and Methods
Design and construction of the Ortmann funnel trap
Basically, the Ortmann funnel trap is a further development of the
single inverted bottle principle as designed and used by Griffith
(1985). The significant advances of our trap are the multiplication
of funnel openings while providing more space within a single
trap and the ability to swim, so that caught amphibians do not
drown (see Fig. 1A-D). Essentially, the Ortmann funnel trap is an
empty 10-l or 15-l paint bucket with four to five distinct openings
in which half-cut inverted 1.5l plastic bottles are inserted and act
as funnels. Counter-sunk in the respective habitat (e.g., a pond),
aquatic amphibians (adults and larvae) can easily enter the bucket
through the funnels, but have difficulties leaving it again.
In the following, we will describe the construction of the funnel
trap in detail. The bottom of the bucket as well as the lower part
of the bucket walls are perforated with little holes (smaller than 4
mm in diameter to avoid injuries to the larvae), as shown in Fig.
1A and Fig 1B. Holes in the size of a half-cut 1-l or 1.5-l bottle are
inserted into the wall of the paint bucket at different positions, as
shown in Fig. 1B, so that, in each hole, one inverted bottle can adequately
be inserted. Inserted bottles are then fixed with underwater-stable
glue at the contact zone of the bottle and at the wall of
the bucket. It is important that contact zones are absolutely clean
and fat-free before gluing them. Additionally, care has to be taken
that only underwater-stable glue is used (e.g., Soudal FixAll clas-
sic), as otherwise bottles will easily fall off. In order that the trap
can swim so that caught amphibians are able to gasp for breath,
two foamed plastic tubes are placed at the upper part of the bucket
wall fixed with a robust plastic string (see Fig. 1A-B). Since foam
offers a complex surface that might be difficult to disinfect, alternatively,
two tightly closed 0.33-l plastic bottles are installed
instead of the foamed plastic tubes at the upper part of the bucket
wall (see Fig. 1C-D). iv.). The accompanying lid of the bucket is
riddled with small holes to allow for oxygen exchange (see Fig.
1E), and it is used as a cover for the bucket during exposure.
The assembled trap can now be used but should be fixed with the
help of a plastic string fixed by a tent peg to avoid uncontrolled
drifting. According to our experience, the use of plastic strings
is strongly recommended since other material has been gnawed
by rodents and/or has a higher risk of rotting if traps are used
continuously.
Application of Ortmann’s funnel trap under
natural conditions
Altogether, 140 funnel traps were used during 150 inspections,
each from March to July in 2004, 2005 and 2006 to monitor 28
stagnant water bodies for crested newts in a former flooding area
of the Rhine River near the town of Krefeld, Germany (coordinates:
51°19`5`` N, 6°39`17`` E). Inspected water bodies ranged
from small to large ponds (Fig. 1G), but also included ditches
(Fig. 1H). Depending on the size of the respective pond/ditch,
four to 38 traps were applied per inspection and traps were tried
to be distributed equal distances from each other and across the
respective body of water. On average, traps were exposed for 48
hours. Each individual was recorded regarding its species status
and developmental state (i.e., larva or metamorphosed). After registration,
all of the individuals were released directly into the
water where they have been formerly caught.
Comparing the efficiency of Ortmann’s funnel trap
with a collapsible nylon trap
In a recent study carried out in two distinct study areas in the east
of Hamburg in Germany (53°37`16`` N, 10°11`36`` E; 53°28`34``
N, 10°6`36`` E), we showed that collapsible nylon traps (also
commonly called fish traps; see Fig. 1F) can be efficiently used
for monitoring crested newts (Triturus cristatus; Bock et al.,
2009). To test for the efficiency of the Ortmann’s funnel trap, we
directly compared the catching success for crested newts of both
trap types in a competitive setup and in a separate counter setup
in the same study sites near Hamburg. In the competitive setup,
Ortmann’s funnel traps (four to five circular openings of about
1 cm in radius) and collapsible nylon traps with the size of 25 x
25 x 43 cm (LxWxH) covered with 5-mm mesh-gauze and two
round (2.75 cm radius) openings were simultaneously exposed
for 24 hours in eight distinct ponds in April 2009. To test for the
efficiency of a specific trap without the competing influence of
the other trap type, we used each trap type at separate occasions in
the same pond (counter setup). This way, we were able to test for
the catching ability of the two different trap types in five counter
setups in four different ponds. Supplementary Table 1 provides
an overview of all of the catching occasions for the competitive
and counter setups.

16
The number of caught newts in the different setups and different
trap types were broken down to determine the number of caught
newts per trap type and the catching efficiency in relation to the
size of the trap openings.
Since trapped individuals can potentially escape through the trap
openings in the case of collapsible nylon traps (Bock et al., 2009),
we compared the escape rate of trapped individuals for both trap
types. Therefore, we monitored the presence of caught newts over
a 24-hour period using the same approach as described in Bock
et al. (2009). In short, traps were controlled every two hours for
newts, and every present newt was recorded by its individual ventral
spot pattern and placed back in the trap. This way, it is possible
to monitor the presence or escape of caught newts.
Data analysis
The program SPSS (Version 15.0.1 © SPSS Inc.) was used to
perform Chi-squared and contingency tests for the nominal data.
T-tests and ANOVA were used for the metric data. Before performing
the T-tests, metric data were tested for a normal distribution
using a Kolmogaroff-Smirnoff test that was also performed in
SPSS.
Results
During a monitoring period of crested newts (Triturus
cristatus) from 2004 to 2006 in the area of Krefeld
(Germany), we caught 5,687 crested newts, 36,683
common newts (Lissotriton vulgaris), 20,615 Alpine
newts (Mesotriton alpestris), 40,692 common toads
(Bufo bufo) and 7,661 pool frogs (Rana esculenta) by
the application of the newly designed Ortmann funnel
trap (see Fig. 2). The observed mortality of amphibians
caught inside the traps was almost zero.
Ortmann’s funnel trap showed a considerably higher
catch-efficiency both in the number of caught newts
per trap (Fig. 3a) and in the number of caught newts
Axel Drechsler et al.
Table 1. Results of competitive trap tests for crested newts in a study site near Hamburg (Germany). Specific number of caught
newts per trap type during simultaneous application of collapsible nylon trap versus Ortmann’s funnel trap across eight distinct
ponds (A-H). The date of inspection, identification of ponds (pond ID), corresponding values of the chi 2 test (chi 2 -value, P-value),
total number of caught newts (N) and the number of caught newts per trap type are provided (n. c. = not calculated).
Date Pond
ID
Chi 2 -value P N Crested newts in collapsible nylon
trap/ Ortmann’s funnel trap
03.04.2009 A 9.846 0.002 26 5/21
04.04.2009 B n. c. - 0 0/0
07.04.2009 C 18.963 0.000 54 11/43
08.04.2009 D n. c. - 13 0/13
09.04.2009 E 3.769 0.052 13 3/10
10.04.2009 F n. c. - 7 5/2
15.04.2009 G 7.860 0.005 86 30/56
17.04.2009 H 14.297 0.000 37 7/30
in relation to the size of the funnel openings (Fig. 3b)
when compared with collapsible nylon traps in a study
site near Hamburg carried out in 2009. In detail, if
applied simultaneously in the same pond (i.e., under
competitive conditions) considerably more newts were
caught by Ortmann’s funnel trap than by the collapsible
nylon trap in six out of eight independent pond-setups.
In four cases (ponds A, C, G and H), this difference was
highly significant (P

An efficient funnel trap for amphibian monitoring 17
significantly longer than in the collapsible nylon traps
(ANOVA: F=15,800; df=2; p=0,000; n=112), thereby
demonstrating that amphibians might escape more
easily from the collapsible nylon traps.
Discussion
In the face of world-wide declining amphibian
populations, the effective sampling and trapping of
amphibians is a basic issue, as monitoring and sampling
specific populations is normally the first step in
addressing the reasons for and mechanisms of declining
amphibian populations (Collins and Crump, 2009).
During spring-field surveys of three consecutive years
in a typical Middle European amphibian habitat, a single
person (DO) was able to trap with Ortmann’s funnel
trap more than one hundred thousand larval and adult
individuals of five distinct species (Figure 2; see also
Ortmann, 2009). This catching success demonstrates
the enormous power and efficiency of this trap type to
monitor aquatic amphibian species. The first funnel trap
that was used for catching amphibians was designed
by Griffith (1985) and represented a plastic bottle with
an inverted bottleneck so that the newts could easily
enter the bottle, but have difficulties in leaving it again.
High catching-efficiency, low material costs and the
simple engineering of this kind of trap was contrasted
by its disadvantages, such as a short application period
limited to a few hours (due to the potential drowning
of amphibians) and the complicated discharging, i.e.,
removal of individuals from the inside of the bottle.
Other kinds of applied funnel traps (Jahn and Jahn,
1997 and Kupfer, 2001) were either complicated to
handle and/or suffered from short exposure times (see
Schlüpmann, 2006).
By combining the high catch efficiency and low
material costs of single funnel traps while avoiding
their disadvantages (short application periods and
complicated discharging), Ortmann’s funnel trap is
a major improved tool for sampling and monitoring
aquatic amphibian species (Fig. 1A-E). As shown by our
data, the Ortmann funnel trap is ideally suited to catch
adult and larval newt species in ponds of quite different
sizes (see Figures 1G-H). Larvae of anurans have been
equally well trapped, whereas the relative catching
success of adult anurans is lower when compared to the
larvae (see Fig. 2). When comparing the catch efficiency
of crested newts under competitive (see Fig. 3 and Table
Figure 2. Number of larval and adult individuals per amphibian species (in thousands) caught in the years 2004-2006 with Ortmann’s
funnel trap in Krefeld (Germany). Values are shown for crested newts (Triturus cristatus), common newts (Lissotriton
vulgaris), Alpine newts (Mesotriton alpestris), pool frogs (Rana esculenta) and common toads (Bufo bufo).

18
1) or counter-conditions (see Table 2), Ortmann’s funnel
trap clearly out-competed the collapsible nylon trap that
is commonly used for surveying aquatic amphibians.
Although we have applied the Ortmann funnel trap only
in stagnant waters, we think that it should also work
well under running water conditions (e.g., streams) as
long as the funnel openings are below the water level.
To prevent the spread of Bd through monitoring and
research efforts from one habitat to another, laboratory
and field equipment should be efficiently disinfected
(Johnson et al., 2003; Woodhams et al., 2003; Young
et al., 2007; Pessier, 2008; Garner et al. 2009). As
compared to other commonly applied traps that all harbor
complex and structured surfaces (e.g., nets or foam)
that potentially complicate the efficient disinfection
of traps in the field, the possible construction of
Ortmann’s funnel trap (completely out of plastic items
with smooth surfaces) (see Fig. 1C) should enhance
efficient disinfection. Since it has been shown that high
concentrations of disinfectants (e.g., bleach) have a
negative impact on tadpoles and zooplankton (Schmidt
et al., 2009), this kind of construction could also favor
the application of lower concentrations of disinfectants
to eliminate pathogens.
Conclusion
We describe a new kind of efficient amphibian trap that
can be constructed quite easily at low costs with items
available all over the world. Applied to aquatic habitats,
and allowing exposure of the trap openings under water,
this item will catch larvae and adult amphibian species
in high amounts. Its pure construction out of smooth
plastic parts should allow for efficient and reliable
disinfection in the field.
Authors’ contributions
DO invented the trap. SS designed the overall study.
Field surveys in Krefeld were carried out by DO. DB
performed the comparative study and the corresponding
data analysis. AD, DB and SS drafted the manuscript. All
of the authors read and approved the final manuscript.
Acknowledgements
Axel Drechsler et al.
Table 2. Results of counter trap tests (collapsible nylon traps versus Ortmann’s funnel trap) for crested newts (Triturus cristatus)
in the same pool at different dates in a study site near Hamburg (Germany). Provided is the information on the date, pond ID,
results of chi 2 tests (chi 2 -value and corresponding P-value), number of trapped newts in total (N) and number of trapped newts in
collapsible nylon traps (N collapsible nylon traps ) and Ortmann’s funnel trap (N Ortmann’s funnel trap ).
Date Pond
ID
Chi 2 -value Pvalue
NTotal Ncollapsible nylon traps NOrtmann’s funnel trap
15.04.2009
16.04.2009
I 21.564 0.000 39
5 not applied
not applied 34
25.04.2009
16.04.2009
I 8.333 0.004 48
14 not applied
not applied 34
16.04.2009
22.04.2009
J 3.000 0.083 12
9 not applied
not applied 3
16.04.2009 K 8.895 0.003 19 3 not applied
17.04.2009
not applied 16
22.04.2009 L 23.059 0.000 34 3 not applied
25.04.2009
not applied 31
The authors thank Dieter Gaumann (University of Siegen) for the
improvement of the Ortmann funnel trap, Jutta Sandkühler from
the Stiftung Naturschutz Schleswig-Holstein, Sven Baumung
from NABU, Andrea Funke from the Untere Landschaftsbehörde
Krefeld and Wolfram Hammer for their help and cooperation.
The Behörde für Stadtentwicklung und Umwelt in Hamburg, the
LANU of Schleswig-Holstein and the Untere Landschaftsbehörde
Krefeld kindly provided permission to carry out this study.

An efficient funnel trap for amphibian monitoring 19
Figure 3a/b. Comparison of catch-efficiency of crested newts between Ortmann’s funnel trap and collapsible nylon trap applied
simultaneously in the same pond. (A) Estimated average number of caught newts calculated per single Ortmann funnel trap versus
single collapsible nylon trap across eight distinct ponds (A-H). Catch-efficiency was higher in Ortmann’s funnel trap than in the
collapsible nylon trap in six ponds. (B) Catch-efficiency of Ortmann’s funnel trap and collapsible nylon trap in relation to the size
of trap-openings (number of crested newts per square centimetre). Significant differences (P

20
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An efficient funnel trap for amphibian monitoring 21
Pond ID Number of collapsible nylon
Number of Ortmann funnel
traps
traps
A 10 6 03.04.2009
B 8 5 04.04.2009
C 3 2 07.04.2009
D 6 5 08.04.2009
E 10 5 09.04.2009
F 10 5 10.04.2009
G 4 2 15.04.2009
H 10 2 17.04.2009
I 5 0 15.04.2009
I 0 3 16.04.2009
I 10 0 25.04.2009
J 0 0 16.04.2009
J 4 2 22.04.2009
K 4 0 16.04.2009
K 0 2 17.04.2009
L 3 0 22.04.2009
L 0 3 25.04.2009
Appendix 1. Overview of application of traps used to test for catch-efficiency of crested newts (Triturus cristatus) between the
collapsible nylon trap and the Ortmann funnel trap in study sites near Hamburg. Information is provided on pond ID, number and
type of applied traps, and the date.
Date
Accepted by Miguel Vences