What Drives Golden Eagles to Use Roads in Winter?

What Drives Golden Eagles to Use Roads in Winter?

Background & Objective

Roads pose a dual-edged trade-off for scavengers: they offer easy carrion (roadkill) but also carry high collision risk. This study examined how both intrinsic traits (age, sex, migratory strategy) and extrinsic conditions (snow depth, prey availability, roadkill density, season timing) jointly shape golden eagles' (Aquila chrysaetos) selection of areas near roads during winter—a period when eagle-vehicle collisions peak.

Methods

Researchers used GPS telemetry data from 51 golden eagles (175 individual-winters) tracked across Wyoming, USA, from 2014–2023. They applied a Resource Selection Function (RSF) framework with generalized linear mixed models, comparing used vs. available locations within Brownian Bridge–derived winter home ranges. Intrinsic hypotheses (sex, age, movement strategy) were tested first, followed by extrinsic hypotheses layered on the top intrinsic model.

Key Findings

• No effect when factors ignored: A baseline model with only distance-to-road showed no overall avoidance or selection of roads.
• Sex effect: Males were 14.2× more likely than females to select areas near roads.
• Age effect: Adults were 15–16× more likely than subadults (all three subadult classes) to select roadside areas.
• Snow depth (strongest factor): This extrinsic variable had the greatest explanatory power. During high snow depth (>17.9 cm), eagles were 17× more likely to select areas near roads than during snow-free periods.
• Secondary extrinsic effects: eagles also favored roadside areas when primary prey (cottontail) availability was low, later in winter, and where roadkill density was lower (likely reflecting lower traffic/collision risk trade-offs).

Significance

Failing to account for these interacting factors would have masked meaningful patterns—the naive model suggested no road preference at all. The results imply that adult and male eagles, and periods of deep snow, represent priority contexts for mitigation (e.g., roadkill carcass removal) to reduce collision mortality, particularly relevant given a documented 28% decline in Wyoming's golden eagle population.

Source: 

Photo: By © Giles Laurent, gileslaurent.com, License CC BY-SA, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=142133890