IntroductionWorldwide, 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).

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,

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

Axel Drechsler1, Daniel Bock2, Daniel Ortmann3 and Sebastian Steinfartz1*

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

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.

Axel Drechsler et al. 14

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 commonly-used 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 ad-equately be inserted. Inserted bottles are then fixed with underwa-ter-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, al-ternatively, 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 (coordi-nates: 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 re-gistration, 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 trapIn 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.

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 ven-tral spot pattern and placed back in the trap. This way, it is pos-sible 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 perfor-ming the T-tests, metric data were tested for a normal distribution using a Kolmogaroff-Smirnoff test that was also performed in SPSS.

ResultsDuring 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

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<0.01; see Table 1). Only in one case (pond F), a marginally higher number of crested newts (five individuals) were caught by the collapsible nylon trap in comparison with the Ortmann trap (two individuals). In pond B, no newts were caught at all by either type of trap. The calculated catch-efficiency in relation to the size of the funnel (in the case of Ortmann’s funnel trap) or the trap (in the case of collapsible nylon trap) openings resulted in a distinctly higher number of individuals caught by the Ortmann funnel trap in seven out of eight ponds (see Fig. 3b). Additionally, if traps were applied solely in the same pond at different dates (hereafter called counter trap tests) Ortmann’s funnel trap clearly out-competed the collapsible nylon trap. In four out of five of these comparisons, significantly more newts were caught by Ortmann’s funnel trap than by the collapsible nylon trap (P<0.01; see Table 2). As newts can not only enter a trap, but also evidently escape from it (see Bock et al., 2009 for collapsible nylon traps), we tested for the escape rate of caught newts from the two trap types by observing how long a specific individual stayed in a trap during a 24 h period. Newts remained in the Ortmann funnel trap

Axel Drechsler et al. 16

Date PondID

Chi2-value P N Crested newts in collapsible nylon trap/ Ortmann’s funnel trap

03.04.2009 A 9.846 0.002 26 5/2104.04.2009 B n. c. - 0 0/007.04.2009 C 18.963 0.000 54 11/4308.04.2009 D n. c. - 13 0/1309.04.2009 E 3.769 0.052 13 3/1010.04.2009 F n. c. - 7 5/215.04.2009 G 7.860 0.005 86 30/5617.04.2009 H 14.297 0.000 37 7/30

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 chi2 test (chi2-value, P-value), total number of caught newts (N) and the number of caught newts per trap type are provided (n. c. = not calculated).

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

An efficient funnel trap for amphibian monitoring 17

Figure 2. Number of larval and adult individuals per amphibian species (in thousands) caught in the years 2004-2006 with Ort-mann’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).

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’ contributionsDO 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.

AcknowledgementsThe 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 Landschaftsbehör-de 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 Landschaftsbehör-de Krefeld kindly provided permission to carry out this study.

Axel Drechsler et al. 18

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 chi2 tests (chi2-value and corresponding P-value), number of trapped newts in total (N) and number of trapped newts in collapsible nylon traps (Ncollapsible nylon traps) and Ortmann’s funnel trap (NOrtmann’s funnel trap).

Date PondID

Chi2-value P-value

NTotal Ncollapsible nylon traps NOrtmann’s funnel trap

15.04.2009 5 not applied 16.04.2009

I 21.564 0.000 39not applied 34

25.04.2009 14 not applied 16.04.2009

I 8.333 0.004 48not applied 34

16.04.2009 9 not applied 22.04.2009

J 3.000 0.083 12not applied 3

16.04.2009 3 not applied 17.04.2009

K 8.895 0.003 19not applied 16

22.04.2009 3 not applied 25.04.2009

L 23.059 0.000 34not applied 31

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<0.01) are marked by an asterik.

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An efficient funnel trap for amphibian monitoring 21

Accepted by Miguel Vences

Pond ID Number of collapsible nylon

traps

Number of Ortmann funnel

traps

Date

A 10 6 03.04.2009B 8 5 04.04.2009C 3 2 07.04.2009D 6 5 08.04.2009E 10 5 09.04.2009F 10 5 10.04.2009G 4 2 15.04.2009H 10 2 17.04.2009I 5 0 15.04.2009I 0 3 16.04.2009I 10 0 25.04.2009J 0 0 16.04.2009J 4 2 22.04.2009K 4 0 16.04.2009K 0 2 17.04.2009L 3 0 22.04.2009L 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.