Analyses of Black Grouse (Tetrao tetrix) faeces with infrared spectroscopic methods

Abstract

In recent years, the Fourier transform infrared spectroscopy (FT-IR) was used to assess the diet, digestibility or nutritional values of food items of ruminants. However, it has never been used to analyse the diet of grouse species. Commonly used methods have so far been direct observations of birds and microscopical analyses of droppings. The sample preparation and comparison of microscopical analyses is a highly time-consuming procedure. The comparison is based on morphological structures of epidermal cells, like the shape of cells, stomata or trichomes. In contrast, the sample preparation for the FT-IR and the subsequent measuring is simple and quickly done. We investigated the diet of Black Grouse (Tetrao tetrix L.) in two study areas with infrared spectroscopic methods comparing summer and winter droppings' content with plant reference material. The study areas are located in the provinces of Salzburg and Upper Austria, Austria. In our study, samples were measured in the mid-and nearinfrared range. We tried to determine the dominating content of faecal samples at species, genera or family level or at least to assign samples to one of four main plants groups (i.e. woody plants, heathers, herbs and grasses). Our results showed a dominance of Larix decidua within the group of woody plants in both areas and, within the group of heathers, a dominance of Calluna vulgaris and Rhododendron hirsutum in one study area. Partially, our results are in marked contrast to other studies conducted in the Alps, as Vaccinium myrtillus was not detected in the samples. For further methodological studies, faecal sampling over larger areas, larger samples of plant reference material (including seeds and other parts of plants at different seasons), taking more samples per dropping and synchronous comparisons of microscopic analyses as well as FT-IR spectroscopy, are recommended.

From plants to feces: pilot applications of FTIR spectroscopy for studies on the foraging ecology of an avian herbivore

“…Thus, our study provided good indications, that both plant species and plant parts like fruits, leaves or needles might be determined via FTIRS. This outcome is consistent with first FTIRS analyses of food plants of Black grouse by Url et al (2015). One prerequisite for non-invasively tracking food choice of grouse via feces is, that initially identified spectral fingerprints of food plants or plant parts are subsequently not significantly modified during digestion.…”

“…For ultimate statements on the applicability of FTIRS for a non-invasive determination of food items of grouse species and for comparisons among populations, spectral signals of undigested plant material have to correspond to signals of intestinal droppings. First FTIRS analyses of Url et al (2015) provided an indication of this assumption, but direct links between undigested plant material and intestinal droppings were missing. In our study, FTIR spectra of dropping samples gained from aviaries and those of field samples yielded a distinct separation of these two dropping groups in terms of PCA scores.…”

“…Moreover, FTIRS provides an opportunity to assess hypotheses related to the physiological mechanisms of herbivory, using feces as the in vivo window to plant-herbivore interactions. So far, Url et al (2015) applied FTIRS to compare band positions and band heights of intestinal droppings of Black grouse (Tetrao tetrix L.) and undigested reference plant material, both collected in the field. However, the "true" content of droppings with a more detailed classification of plant taxa or plant parts (buds, shoots, leaves, fruits, and seeds) was not addressed within this pilot study.…”