• Bird Migration

Why do land birds migrate at night?

Birds’ instinct to migrate is largely influenced by sudden shifts in temperature, available daylight (photo period), moon phases and light tail winds. The evaluation of land bird migration determined that flying conditions for long-distance travel are most favourable under the cover of darkness. These favourable conditions include less potential for predation, cooler temperatures to help maintain body temperature and less inclement weather

How does migration influence bird-building collisions?

Artificial lighted structures can disorient night migrating birds as they tend to fly toward and hesitate to leave these lit areas.  As day breaks, birds quickly descend to the ground in search for vegetated habitat where they feverishly forage for food to replenish their depleted energy reserves.  This dramatic rise in the concentration of birds in built environments increases the potential for bird-building collisions.

The majority of land birds migrate at night. These include species like cuckoos, flycatchers, warblers, vireos, thrushes, orioles and sparrows.

Monitoring Weather Patterns to Predict Bird Migration

To help you prepare for what could be a busy night of migration, you need to look for a combination of the following 3 influencing factors:

Northerly Migration (March through May)

  • steady southerly winds
  • clear moon-lit nights
  • sudden increase in temperature

Southerly Migration (August through October)

  • steady northerly winds
  • clear moon-lit nights
  • sudden decrease in temperature

When all of these factors are present, step outdoors shortly after dusk and listen to the night sky. You’ll likely hear faint “peeps” from birds migrating overhead. Try using a spotting scope or binoculars to watch these birds as they fly past the face of the moon. You can go one step further by building your own microphone to record and document the number of calls and species of birds flying over your community. To learn how to build a microphone, visit Old Bird.

Photo by Bill Evans

Once you understand the nuances of weather patterns that trigger a birds’ instinct to migrate, you can make your own migration predictions. The below weather map by VENTUSKY offers an ideal visual interface of tools you can use to help you make these predictions.

TIP: High pressure systems rotate in a clockwise fashion and lows are counterclockwise.  For example, the leading edge of a high or the trailing edge of a low have the southerly winds that favor a strong migratory southerly flight that night.

Tools to Follow Migration and Report Collisions

Live Migration

BirdCast monitors bird migration activity through your region. Use real-time analysis maps to help you prepare for bird-building collisions on days following heavy nocturnal migration.

Report a Collision

Be on the lookout for bird-building collisions on days following heavy nocturnal migration (see BirdCast). Be sure to report these collisions into the Global Bird Collision Mapper (GBCM).

Stay informed.

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