Shit happens … and persists: decay dynamics of capercaillie (Tetrao urogallus L.) droppings under natural and artificial conditions

Feces of wildlife species are commonly used indicators for species’ presence or relative abundance. These might however be biased due to inconspicuousness, due to rapid decay and disappearance, or due to high site-dependent variance in decay dynamics. Mapping of indirect signs is a frequently applied approach to study habitat use or distribution of grouse species. However, only a few studies addressed avian dropping decay up to now, and no study focused on dropping decay of European grouse species. Consequently, we conducted field surveys and greenhouse trials, studying time spans over which capercaillie ( Tetrao urogallus ) droppings persist and factors influencing the decay rates (i.e., habitat type, small mammal access, and precipitation regime). In the field survey, after an exposure of 98 days, only 6% of droppings ( n = 156) decayed completely and most droppings remained nearly unchanged. The decay rate was influenced by microsite conditions (i.e., vegetation and location), with lowest decay rates in areas with little ground vegetation or on tree stubs. Destruents were not found to play a major role in affecting decay rate. The greenhouse trial revealed the impact of precipitation on the decay rate of droppings ( n = 400): under high-amount and high-intensity precipitation regime droppings decayed faster compared to low-amount and low-intensity precipitation. The slow decay rate, and resulting long time period that they can be detected, therefore means that capercaillie droppings are a valid proxy for species’ occurrence.