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

Studies on the foraging ecology of wildlife species are of fundamental importance, as foraging decisions are closely linked to ecological key issues such as resource partitioning or population dynamics. Using Black grouse as a model system, we applied Fourier-transform infrared spectroscopy (FTIRS) to address some key questions in foraging ecology: (1) does FTIRS allow for determining plant taxa and plant parts? Can FTIRS suggest variation in digestibility of food and physiological mechanisms of consumers? (2) Can FTIRS be used to track changes in diets among populations? (3) Can FTIRS capture plants' phenology and shifts in diet? To answer these questions, we analyzed crop and gizzard contents of Black grouse via FTIRS looking for specific spectra and bands of plant taxa and plant parts. We compared spectral signals of undigested plant material and intestinal droppings, gained from wild-living birds and from aviaries. Our analyses yielded characteristic spectral fingerprints for several food plants and plant parts. Spectral fingerprints could differentiate between needles of J. communis and P. mugo and between fruits of J. communis, Sorbus sp., and Vaccinium sp. Spectral signals differed more between undigested material and crop samples than between crop and gizzard samples. Differences were more pronounced for berries than for needles. Apart from these differences, some fingerprints persisted for certain food items. The diverse foraging regime of wild-living individuals compared to captive Black grouse was reflected by spectral signals. Thus, FTIRS is a promising approach to explore variation in food choice of grouse species by means of non-invasively gained fecal samples.