Illuminating the Nocturnal Habits of Owls with Emerging Tagging Technologies

Abstract

Owls play important cultural, ecological, and indicator roles throughout the world. Yet owls’ cryptic behavior has led to uncertainties about their basic ecology, including foraging, communication, and functional roles within the community, and potentially hindered the implementation of effective conservation measures. Here we demonstrate the potential for next‐generation GPS tags capable of recording high‐precision, minute‐by‐minute locations paired with other technologies to resolve some of these uncertainties. We combined high‐precision GPS tagging data with infrared (IR) video recorded by arboreally‐mounted cameras at 5 spotted owl (Strix occidentalis) nest sites in the Sierra Nevada, USA to provide a uniquely detailed examination of owl foraging patterns. Our approach allowed us to identify the precise time and location of 54 predation events and prey identity. We also used high‐precision GPS tags with on‐board audio recorders to map the vocal activity of 8 individuals by matching the time of vocalizations in the audio data to GPS locations recorded at one‐minute intervals. The combined spatial and acoustic data revealed that nonbreeding males had the most widespread territorial vocal activity (i.e., producing 4‐note territorial calls), while females provisioning fledglings displayed extensive nonterritorial vocal activity (i.e., producing many contact calls). Thus, the GPS‐tag technologies we employed can provide opportunities to better understand owl foraging, communication, territoriality, and population dynamics. The methods we describe are time‐ and resource‐intensive but can be paired with techniques that are more applicable at landscape scales, such as stable isotope analyses, LiDAR‐based habitat analyses, and passive acoustic monitoring to link local processes to broad‐scale ecological patterns. Therefore, our approach could be applied to many species whose behavior inhibits direct observation. © 2021 The Wildlife Society.

Breeding status shapes territoriality and vocalization patterns in spotted owls

“…Territory size and vocal behavior commonly fluctuates throughout the breeding season in avian species and has been observed to be highly variable between individuals (Odum and Kuenzler 1955, Anich et al 2009, Whitaker and Warkentin 2010, however few studies directly examine variation in territoriality and vocal behavior between breeding and non-breeding individuals during the breeding season (but see Barnes and Belthoff 2008). Even fewer have been able to examine territory size and vocal behavior in such a wide-ranging and cryptic species like the spotted owl with the high precision we achieved, highlighting the utility of acoustic/GPS tags for addressing such questions (Wood et al 2021). The heterogeneity in territory size and vocal behavior that we observed between breeding and non-breeding spotted owls raises interesting questions regarding space use and Figure 6.…”

“…Our study combined extensive background knowledge of spotted owl vocalization types and their meaning (Forsman et al 1984) with cutting‐edge tagging technologies (Wood et al 2021), leading to new insights regarding spotted owl vocal behavior and life history trade‐offs – along with the future potential to study many other aspects of owl behavior as well. We discovered that spotted owl vocal behavior and territoriality is strongly linked to breeding status, suggesting that population density and space‐use are fluid across the landscape even for a site‐faithful, highly territorial species.…”

“…We investigated how life history constraints might affect territoriality and vocal behavior within a territorial species, the California spotted owl ( Strix occidentalis occidentalis , hereafter ‘spotted owl'), using acoustic/GPS tags that provided high‐resolution, minute‐by‐minute location and audio data. Spotted owls are an ideal study species because their territorial vocalizations and various call types are well documented and easily identifiable, with novel acoustic/GPS tags developed and optimized for this species offering a unique opportunity to study their vocalizations at unprecedented levels of detail (Wood et al 2021). Further, spotted owls are a focal species for the development of regional‐scale, passive acoustic‐based population monitoring programs (Wood et al 2019a, Duchac et al 2020) but their wide‐ranging and cryptic nature has made it difficult to study their vocal behavior at an individual level until now (Wood et al 2021).…”

“…Spotted owls are an ideal study species because their territorial vocalizations and various call types are well documented and easily identifiable, with novel acoustic/GPS tags developed and optimized for this species offering a unique opportunity to study their vocalizations at unprecedented levels of detail (Wood et al 2021). Further, spotted owls are a focal species for the development of regional‐scale, passive acoustic‐based population monitoring programs (Wood et al 2019a, Duchac et al 2020) but their wide‐ranging and cryptic nature has made it difficult to study their vocal behavior at an individual level until now (Wood et al 2021). This is the first study to deploy acoustic/GPS tags on an owl species in the wild, and thus exemplifies the type of fine‐scale information that can be gained when this technology is applied to novel taxa.…”

Forest heterogeneity outweighs movement costs by enhancing hunting success and fitness in spotted owls

“…Based on owls found as part of the aforementioned surveys, we captured 31 spotted owls (24 males and 7 females) in 2019 and 2020 for GPS tagging using noose poles, pan raps and "hand capture" methods (Wood et al, 2021). Owls were selected opportunistically for tagging based on the accessibility of the nest for video-monitoring (see below) and the likelihood of recapture to remove transmitters.…”