Supplementary material for "Intraguild interactions shape vocal output and diel activity patterns in sympatric forest owls"

1. Competition and intraguild predation among sympatric predators may force smaller, subordinate predators to reduce interactions with larger, dominant species via restricted spatial or temporal activity (Acquiescence hypothesis). On the other hand, dominant predators may also actively exclude subordinate competitors through frequent vocal and physical aggression (Exclusion hypothesis). While mechanisms of spatial avoidance have been well-demonstrated across taxa, evidence for temporal avoidance, especially across the diel cycle among non-mammalian predators remains limited. 2. Using data from long-term passive acoustic monitoring, we assessed the effects of intraguild interactions on the vocal activity of owls in Southern Bohemia, Czech Republic. We quantified vocal output, bout durations, and the diel vocal activity patterns in a predator guild consisting of four co-occurring forest owl species: Ural Owl (Strix uralensis), Tawny Owl (Strix aluco), Boreal Owl (Aegolius funereus), and Pygmy Owl (Glaucidium passerinum). 3. Using Generalised Linear Mixed Models, we found that Boreal Owls significantly reduced vocal output in the presence of Tawny Owls, probably to reduce predation risk. Generalised Additive Mixed Models indicated that all four species shifted their diel vocal activity patterns in the presence of dominant or competitor species. The diel shifts suggested avoidance (Boreal with Tawny Owl, Tawny with Ural Owl, Pygmy with both Tawny and Ural Owls), and interference (Ural with Tawny Owl) among owl species. However, the vocal activity of the Boreal Owl was largely unchanged in the presence of the Ural Owl. 4. Our findings demonstrate that intraguild interactions not only affect overall acoustic signalling effort in owls but also result in fine-scale temporal redistribution of vocal activity, which may act as a mechanism facilitating coexistence. Furthermore, our results provide mixed support for the Acquiescence and Exclusion hypotheses, indicating that these effects were not merely associated with a size-structured dominance hierarchy but instead reflected species-specific ecological relationships. While further research is required to assess whether such changes in vocal behaviour are associated with fitness or mortality risk, our findings have important implications for monitoring programmes and may also be broadly applicable to predator guilds.