Current data for many amphibian species are sorely lacking. About one quarter of named amphibian species are listed as Data Deficient by the IUCN, and this includes 114 of 172 species of caecilian! 

Amphibians may be secretive, nocturnal (night-active), diurnal (day-active), arboreal (tree-dwelling), aquatic (water-dwelling), fossorial (burrowing) and even switch between habitats at different stages of development.  For these, and other, reasons, field techniques designed to reveal the ecology and habitat requirements of amphibian species are myriad. 

There is no one standard method for sampling amphibians in the field. Instead, amphibian researchers develop tools for gathering baseline data as they gain insight into the behaviour and life history of their study species.  Standard practices that have been used include fencing in concert with pitfall traps, dip-netting, seining, ground-searches, funnel-traps, pipe-sampling, call surveying, the use of artificial cover objects, retreats and nesting sites and even hours of hard work with a pick and shovel.  Each approach comes with its own set of assumptions (and thus constraints) and it is not uncommon for a research program to utilise multiple methods.

For more information on the following survey techniques, please see the survey methods information in the general conservation pages:


Pitfall Traps
Call Surveying
Social Surveys

Pitfall Traps

Pitfall traps are usually buckets dug in to ground level and lined with moistened sponging. They are usually placed along solid fences or at the end of solid fencing. Amphibians move along fences at night and drop into the pitfalls, where researchers collect them from in the morning. Fence and pitfall arrays are often used at breeding ponds, but can also work well with species that are strictly terrestrial. Not very useful for strictly aquatic species, though.

Call Surveying

Call surveying involves walking amphibian habitat at night and listening for vocalizations. There are many limitations to call surveys, not the least of which it only samples animals that make calls, which are primarily male and adult frogs.

The Malagasy rainbow frog (Scaphiophryne gottlebei)

has a very distinctive call that may be heard speifically

during the rainy season.

Funnel Traps
Funnel traps are often used to sample larval or adult and aquatic amphibians.  Traps are cages with openings at either end that are shaped like funnels with the wider end at the entrance to the caging.  Traps are often baited.  Animals move into the funnels, travelling down to the narrow end and into the cage.  Once inside the funnel trap, animals generally stay at the edge of the cage and therefore cannot find the opening at the narrow end of the funnel.

Pipe-sampling
Pipe-sampling is done with, not surprisingly, a large piece of piping.  The pipe is ‘thrown’ into a pond or stream so that one open end of the pipe contacts the pond bottom.  The researcher then nets all amphibians out of the pipe.  Because the volume of the pipe is known, counts of amphibians found in several pipe “throws” can be extrapolated to estimate amphibian density.



Refugia Surveying
Artificial cover objects, retreats and nest sites are used to create refuges that amphibians use.  Boards on the ground may be used by terrestrial salamanders and small pieces of piping mounted on trees may be used by adult tree frogs: artificial nest sites of course provide a place for an amphibian female to deposit eggs or larvae.  One advantage of artificial sites is that amphibians can be surveyed without damaging natural sites, such as downed trees, tree hollows and burrows.  However, it is important to know how effective your artificial sites are with respect to natural sites otherwise counts made using artificial sites may be biased or inaccurate.


Exactly what question is being asked guides the methodology.  Amphibian populations may naturally fluctuate by the thousands and this even among developmental stages (think the number of eggs, then tadpoles you may see in a large pond as compared to the number of adults that produced the eggs).  Determining if population changes are atypical is a fundamental conservation question, and because of the inherent capability for amphibian populations to fluctuate wildly, a particularly prickly one to address.

 

Good estimates of amphibian population dynamics require long-term data sets, which are unavailable for the majority of amphibian species.  To bypass this shortcoming, researchers are moving towards comparative studies with specific a priori hypotheses.  For instance, if deforestation is deemed to be a potential threat to a forest-dwelling frog with direct development (development that involves no free-living aquatic larval stage), a research team may decide to select a set of forest patches, half suffering from deforestation and half not.  Within these patches, they may erect fenced arrays with pitfall traps located at the ends of the arms of the arrays and at the fulcrum of each pair of arms.  Because the species is a direct-developing one, there is no need to dip-net or seine water bodies for larvae, however, teams may perform time-constrained ground-searches for nests.

 

More recently, approaches are being used that bypass population size estimates entirely and instead focus on how the occupancy of habitat patches over broad geographic areas is correlated with presumed species threats.  These site occupancy techniques enable smaller numbers of researchers to gather large amounts of reliable data and examine area occupancy in a comparative manner.