Complex behaviour in complex terrain - Modelling bird migration in a high resolution wind field across mountainous...

Area of Science:

• Ornithology
• Ecological Modeling
• Bioenergetics

Background:

• Mountainous terrain presents significant energetic challenges for migratory birds.
• Wind patterns are critically altered by topography, impacting flight behavior and energy expenditure.

Purpose of the Study:

• To investigate the influence of wind and topography on nocturnal passerine migration behavior.
• To assess the energetic costs of different flight strategies for crossing the Jura Mountains.

Main Methods:

• Utilized a novel framework of mathematical models simulating bird behavior (wind drift compensation, flight height adaptation, obstacle avoidance).
• Employed a mesoscale weather model for high-resolution wind field predictions.
• Simulated nocturnal passerine migration using weather radar data for initial bird densities and vertical distributions.

Main Results:

• Migration over complex terrain is the most energetically costly flight strategy.
• Wind is the primary factor influencing energy expenditure in the birds' preferred flight direction.
• Combined effects of wind and orography concentrate migratory birds in favorable lowland areas north of the Jura Mountains.

Conclusions:

• Understanding the interplay of wind, topography, and bird behavior is crucial for predicting migration routes and energetic costs.
• Complex terrain significantly increases the energy demands of bird migration.
• Favorable wind conditions in lowlands attract concentrated migratory bird populations during autumn migration.