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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Abstract

Common raven (Corvus corax; raven) abundance and distribution have increased in western North America in recent decades, facilitated by anthropogenic subsidies and other environmental changes. Electrical power transmission line structures provide nesting substrates for ravens. When these structures transect landscapes where natural nest substrates are limited, they may facilitate raven predation on eggs and juveniles of sensitive avian and reptile species. Little information is available regarding raven nest density trends on adjacent power lines or how raven territorial behavior influences spatial partitioning of nests, and hence, nest density. This knowledge would be valuable for managers of sensitive prey species who may be considering if interventions to reduce nesting are warranted. During 2014–2020, we conducted annual, repeated surveys for raven and buteo hawk nests along 272 km of electrical power transmission lines (69–233 kV) and 37 km of electrical distribution lines (12.5–13.8 kV) within a sagebrush (Artemisia spp.) ecosystem of southeastern Idaho, USA. Our objectives were to document annual raven nest trends on power lines and investigate spatial distancing between nests of conspecific ravens and those of ravens and raptors. We hypothesized that territorial raven pairs would maintain similar minimum distances between nearest-neighbor conspecific and raptor nests, as was observed in a study in western Idaho. Across the 7-year study, the number of occupied raven nests remained relatively stable (x̅ = 26.7, SD = 5.3, range = 20–30), and an assessment of past research on our site suggests this plateau in power line nesting occurred following increases during the past 2 or 3 decades. Occupied raven nests were never closer than 1,033 m (annual minimum distance ranged from 1,033–2,054 m), but raven nests and buteo hawk nests were occasionally as close as 200–500 m. Forty-three percent of ravens whose nearest nest was occupied by a ferruginous hawk (Buteo regalis) or red-tailed hawk (B. jamaicensis) pair werediffered, suggesting raven breeding pairs were less tolerant of conspecific pairs than they were of raptor pairs. Our study provides a method for monitoring raven nesting on power lines in semi-arid regions of western North America and an additional monitoring strategy to complement the more widely used point-count surveys to sample breeding and nonbreeding ravens.

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