Golden eagles regularly use gravity waves to soar: new insights from high-resolution weather data

Area of Science:

• Ornithology
• Atmospheric Science
• Bioenergetics

Background:

• Soaring flight reduces metabolic costs for birds by using atmospheric energy.
• Previous studies lacked high-resolution atmospheric data, limiting understanding of soaring adaptability.
• The role of gravity waves in bird soaring has been largely unexplored.

Purpose of the Study:

• To investigate the flexibility of soaring flight in response to complex atmospheric dynamics, including gravity waves.
• To characterize updraught sources used by golden eagles in the European Alps.
• To provide a new perspective on environmental energy availability for soaring birds.

Main Methods:

• Utilized high-resolution atmospheric analysis.
• Employed high-resolution global positioning system (GPS) tracking data.
• Analyzed soaring segments of golden eagles (Aquila chrysaetos) in the European Alps.

Main Results:

• Golden eagles were found to repeatedly use gravity waves as an updraught source (at least 19% of soaring segments).
• Thermals were the primary energy source, but gravity waves and orographic lifting dominated during winter.
• Identified gravity waves as a significant, previously underappreciated, updraught source for soaring birds.

Conclusions:

• Soaring birds exhibit flexibility in utilizing various atmospheric energy sources.
• Gravity waves play a crucial role in avian soaring, particularly in winter or resource-scarce conditions.
• Understanding these updraught dynamics is key to comprehending landscape connectivity for soaring birds in complex topographies.