Pitfall trap designs to maximize invertebrate captures and minimize captures of nontarget vertebrates

Abstract

Pitfall traps containing a preservative have become the standard method of sampling for epigeal invertebrates such as carabid beetles and cursorial spiders. However, they often result in high levels of mortality for small mammals and amphibians. We compared the carabid, spider, and vertebrate captures within five pitfall trap types (conventional trap, funnel trap, shallow trap, Nordlander trap, and the ramp trap) to determine the trap type that would reduce vertebrate incidental catch without compromising the capture of invertebrates. We also examined the effect of a mesh screen over pitfall traps on carabid beetle and vertebrate catches. All modifications to the conventional trap design resulted in a reduction in both small mammal and amphibian captures. The shallow pitfall trap and the funnel trap captured a carabid beetle and spider fauna similar to that captured by the conventional trap. The species compositions of the ramp trap and the Nordlander trap were different from those of the other trap types, but these traps were more efficient, capturing more species per individual captured. The ramp trap appeared to be the method of choice for sampling epigeal spiders. Thus, the choice among trap designs for invertebrates depends on the objectives of the study. However, an alternative to the conventional trap design should always be considered to reduce small mammal mortality.Résumé-Les pièges à fosse contenant un liquide de conservation constituent la méthode standard pour la récolte d'invertébrés épigées, tels que les coléoptères carabidés et les araignées coureuses. Cependant, leur usage entraîne souvent de fortes mortalités de petits mammifères et d'amphibiens. Nous avons comparé les récoltes de carabes, d'araignées et de vertébrés dans cinq types de pièges à fosse (modèle ordinaire, en entonnoir, à forme surbaissée, type Nordlander et à rampe) afin de déterminer le type de piège qui permette de réduire les captures accessoires, sans minimiser la récolte d'invertébrés. Nous avons aussi examiné l'effet d'un grillage au-dessus du piège sur les récoltes de carabes et de vertébrés. Toute modification du modèle ordinaire entraîne une réduction des captures de petits mammifères et d'amphibiens. Les pièges à forme surbaissée et en entonnoir récoltent une faune de carabes et d'araignées semblable à celle du piège ordinaire. La composition en espèces des récoltes au pièges de type Nordlander et à rampe diffère de celle des autres types, mais ces pièges sont plus efficaces et capturent un plus grand nombre d'espèces par individu. Le piège à rampe semble être la méthode privilégiée pour l'échantillonnage des araignées épigées. Le choix d'un type de piège pour la capture des invertébrés dépend donc des objectifs de l'étude. Cependant, on doit toujours envisager l'utilisation d'un modèle de rechange au piège ordinaire afin de réduire la mortalité des petits mammifères.[Traduit par la Rédaction] 233 Fig. 3. Dendrogram based on the relative Bray Curtis similarity measure and weighted average cluster analysis describing the s...

The ant (Hymenoptera: Formicidae) communities of the central interior of British Columbia: Adaptations to a temperature-constrained environment.

“…The lack of vertebrate bycatch recorded for the Laurent pitfall traps of our study confound any certain conclusions here, however. It is likely that the smaller cup sizes used in our study as compared other work (Lemieux and Lindgren 1999;Pearce et al 2005) contributed to the reduction in vertebrate bycatch. Additional and extensive use of the Nordlander design in the other experiments detailed in this dissertation were also free of vertebrate bycatch.…”

“…Other studies have shown considerable benefits of the Nordlander design in this regard, however. Although vertebrate bycatch using the Nordlander design has been reported (Lemieux and Lindgren 1999;Pearce et al 2005), two points are relevant. First, the entrance holes in both of these studies were 13 mm in diameter because of interest in capturing large carabid beetles, as contrasted with 6-mm in this experiment, intended for the capture of ants.…”

“…Lemieux and Lindgren (1999) report that only a single vertebrate was captured in the Nordlander design, as compared to 13 in the Laurent design. Pearce et al (2005) reported that only 5% of total vertebrate captures occurred in the Nordlander design when compared to Laurent and funnel style pitfall traps. Thus, the literature establishes an advantage to the Nordlander in this regard, and it is likely, although not established here that the smaller openings used in our study would be even more efficacious.…”

“…The Nordlander pitfall trap (Nordlander 1987;Lemieux and Lindgren 1999;Pearce et al 2005) may provide a solution to this problem. As designed for this study, the only access is through the 6-mm holes, which should be large enough for all ants but too small to allow for vertebrate bycatch.…”

“…Further, there is little standardization in pitfall trap design, and discussion relating to tailoring the design to a particular fauna is lacking. Vertebrate bycatch is commonly a problem with the traditional Laurent design leading to both ethical issues and the spoilage of trap contents by vertebrate remains (Pearce et al 2005). …”