Breeding status shapes territoriality and vocalization patterns in spotted owls

Abstract

Vocal territory defense can vary within a species due to many factors such as sex and breeding status, influencing territory size and thus population density across a landscape. Therefore, understanding what influences variation in territorial vocalizations can help to illuminate trade-offs between territoriality and other life history demands, which benefits our general understanding of animal ecology as well as helps to inform emerging passive acoustic monitoring approaches. Here, we investigated how sex and breeding status affected territoriality and vocal behavior in the California spotted owl Strix occidentalis occidentalis in the Sierra Nevada, California, USA, using highresolution acoustic/GPS tags. We discovered that territorial vocal behavior was related to breeding status and to a lesser extent sex. Breeding owls with fledged young had a less diverse vocal repertoire, produced fewer and quieter territorial calls, and typically called only when close to their nest. Males were also more likely to engage in territorial calling than females. Breeding spotted owls also maintained significantly smaller territories -but utilized larger home ranges -than non-breeding individuals. Our results suggest that breeding spotted owls may reduce their investment in territorial behaviors to mitigate the demands and risks associated with rearing young. Further, our results have important implications for the passive acoustic monitoring of spotted owls and, more broadly, highlight the utility of using multiple call types to detect species of interest.

Using bioacoustics to enhance the efficiency of spotted owl surveys and facilitate forest restoration

“…With respect to the detection night criterion, our rationale was to identify a set of thresholds for the number of nights with spotted owl detections that maximized the probability of detecting occupied territories (true positives), and minimized the number of false positives to avoid triggering unnecessary active follow‐up surveys (Reid et al 2021). With respect to the ARU deployment duration, our rationale was that acoustic detections from a shorter deployment duration would provide more time for acoustically assisted active surveys and thus increase the likelihood of detecting and locating territorial owls early in the breeding season (May was as early as was feasible in our study area) before they become less vocal, shift activity centers, and range over wider areas later in summer (Forsman et al 1984; Reid et al 2021, 2022). For ARU deployment durations shorter than the full recording period of 5 weeks, we removed acoustic data from the dates that were latest in the season (e.g., for a unit that was deployed from 15 May to 22 Jun, a 3‐week simulated deployment used data from 15 May to 5 Jun).…”