Manual Versus Semiautomated Bioacoustic Analysis Methods of Multiple Vocalizations in Tricolored Blackbird Colonies

Abstract

Bioacoustic monitoring can reveal aspects of animal behavior as many species vocalize in association with certain behaviors. Despite this, bioacoustics remain infrequently used to monitor animal behavior due to lack of knowledge of how vocalizations relate to behavior and the challenge of efficiently analyzing the large acoustic datasets necessary to capture relevant behaviors. Vocalizations and associated behaviors have been previously established for the colonial tricolored blackbird Agelaius tricolor, but efficient analysis of the acoustic data remains a challenge. Previous work with tricolored blackbird acoustic data relied on manually listening to recordings, which is not practical on large scales. Using software to automatically detect vocalizations of interest has potential to reduce analysis time. However, automated detection is prone to errors often caused by faint vocalizations, overlapping calls, and background noise. Thus, incorporating components of manual and automated analysis of acoustic datasets remains essential. To address these challenges, we deployed autonomous recording units at three tricolored blackbird colonies from 2019 to 2021 and analyzed acoustic data using a manual and a semi-automated analysis method. Specifically, we used tricolored blackbird male song, male chorus, female song, hatchling call, nestling call, and fledgling call to determine the approximate timing of breeding stages and number of breeding attempts, or pulses, for each colony. We found that using a semi-automated approach was more time efficient than manual analysis, while using comparable numbers of recordings and obtaining equivalent information from the colonies. The odds of correct detections of vocalizations using the semi-automated method were generally lower for fainter vocalizations and colonies with high background noise. Overall, the semi-automated approach had tolerable rates of recall, precision, false positives, and false negatives. Our methodology adds to a growing body of literature addressing acoustic analysis, especially for colonial species and where questions of breeding phenology are important.

Tricolored blackbird survey methods

“…Most foraging occurs within 1 km from colony sites, but adults have been recorded foraging up to 8.6 km away (Hamilton and Meese 2006). We consider 5 km from the nesting colony as the most relevant distance within which to assess habitat conditions because it is consistent with typical foraging distances reported (Orians 1961;Crase and DeHaven 1977;Hamilton and Meese 2006;Wilsey et al 2019;Airola et al 2023a).…”

“…Direct Searching for Colonies.-A second strategy for locating colonies is to check suitable nesting substrates, especially previously used ones. Occupancy can often be determined at sites from the loud song choruses early in the season (Schackwitz et al 2020;Beedy et al 2023;Honig and Schackwitz 2023), swarming activity during settling and nest building, and by observing adults returning to colonies with food for nestlings. A caution for direct observation is that activity can be very low during the incubation period, such that activity at occupied colonies may be subtle and detected only by experienced observers or in later visits.…”

“…Colonies are considered successful when fledglings are observed at or near the colony or feces are seen in an empty nest. Monitoring via vocalizations also can be used to determine if young have reached fledgling age (Schackwitz et al 2020;Beedy et al 2023;Honig and Schackwitz 2023). Less direct evidence that indicates that a colony was likely successful includes repeated observations of adults feeding young at the colony over a 10-day period (Table 3; Beedy et al 2023).…”

“…Bioacoustic monitoring is a new tool that can provide detailed information on reproductive phenology and breeding success of tricolored blackbird colonies (Schackwitz et al 2020;Honig and Schackwitz 2023). The technique involves recording tricolored blackbird colonies and analyzing them to detect the timing of six vocalizations-male song, male chorus, female song, hatchling call, nestling call, and fledgling call (Honig and Schackwitz 2023).…”