What are Winkler Samples?

Winkler samples are an efficient method of sampling leaf litter ants. The method involves sifting bulk samples of leaf litter and rotten wood by agitating them vigorously in a bag above a coarse mesh screen. Litter arthropods are concentrated in the finer "siftate" that passes through the screen. Arthropods are then extracted from the siftate by a passive extraction method, in which the siftate is placed in thin mesh sacks and then suspended and enclosed within an outer cloth "Winkler bag." The Winkler bag tapers to a cup of ethanol. After loading the sample the Winkler bag is closed at the top and suspended in a sheltered location. Arthopods fall from the litter and accumulate in the ethanol, and the sample is taken off after 3 days.

Methodological variations involve how the bulk litter is selected. A "MaxiWinkler" sample involves a subjective selection of litter to sift, and is not based on a particular area or volume of bulk litter. The person taking the sample moves through the habitat selecting pockets of moist litter. These accumulations of litter and rotten wood occur between buttresses, along the sides of rotten logs, around dead stumps, and in soil depressions. When approximately 6l of siftate is obtained, the material is placed in a cloth bag and returned to the lab or field camp to be suspended in a Winkler bag.

A "miniWinkler" sample involves sifting the litter from a one square meter quadrat. The litter and dead wood in the quadrat are first aggressively minced with a machete. Then the litter is sifted until all the litter in the quadrat is sifted or 2l of siftate are obtained, whichever comes first. When there is more than enough litter to produce 2l of siftate, the different kinds of litter in the quadrat (e.g. leaves on soil versus litter from a rotten log) are subsampled so that all are represented (a somewhat subjective process that attempts to include the diversity of litter types found in the quadrat). Quadrats are placed according to a protocol of transects, grids, stratification, randomization, or other procedures. Thus the method is much less subjective and less dependent on the habits of the sifter. However, miniWinkler samples are less efficient than maxiWinklers in terms of species capture per unit of effort.

At each field site two transects of miniWinkler samples were be taken. Each transect was 245m long and contained 50 quadrats at 5m spacing. Starting point and direction of transect were chosen subjectively, attempting to keep the transect within a habitat patch. If the patch was too small, or an impassable area was encountered, the transect changed direction or was broken into more than one segment.