Migrating birds avoid flying through fog and low clouds.

Area of Science:

• Ornithology
• Meteorology
• Ecology

Background:

• Weather conditions significantly influence bird migration patterns.
• The specific impact of fog and low clouds on migrating birds remains poorly understood.
• Fog avoidance may stem from visual impairment or altered soaring conditions.

Purpose of the Study:

• To investigate the influence of fog and other weather variables on diurnal soaring bird migration intensity.
• To determine if fog affects bird passage rates at a key migratory bottleneck.

Main Methods:

• Utilized X-band radar to record bird movements, capable of detecting birds within fog.
• Collected local meteorological data, including fog, wind speed/direction, and air temperature.
• Analyzed bird passage rate (tracks/hour) in relation to weather variables and time of day.

Main Results:

• Fog was identified as the most significant factor reducing bird migration intensity.
• Birds were observed to actively avoid flying into fog.
• Wind direction also influenced migration intensity, with specific effects from tailwinds and crosswinds.

Conclusions:

• Fog presents a major impediment to diurnal soaring bird migration.
• Meteorological conditions, especially fog, have substantial consequences for bird migration navigation, path length, and energetics.
• Understanding fog's impact is crucial for assessing migratory bird behavior and conservation needs.