How does the weather affect migration? |
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Weather is one of the chief external influences on migration. Cool air masses moving south in the fall can trigger migratory flight. Cool air brings high pressure, low or falling temperatures and winds moving in the direction of flight and clear skies. If the cool air meets warmer air, clouds, precipitation and fog may result. Fog, especially, causes birds to descend to the ground and cease migration. Sudden changes in the weather can be disastrous for birds. In the spring a warm, moist mass of air (low pressure with higher or rising temperatures) moving north over the Gulf of Mexico can start a wave of migrating birds to move northward from the American Tropics or southern United States. A southward moving cold front meeting such a warm air mass can result in heavy rains and high winds. This can stop migration immediately or within 24 hours. These spring "fallouts" or "groundings" of migrants may occur when the migrating birds literally fall into sheltered areas seeking food and refuge. This can be disastrous if the migrants are forced down into the ocean drowning thousands of birds. Resumption of southerly winds and rising temperatures starts migration northward again. |
Instructions for observing nocturnal bird migration by moon-watching
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In North America and Europe, research has demonstrated that the majority of migrating birds fly at night. The predominant theories explaining why some passerines migrate by night in North America and Europe—to avoid predation, to take advantage of greater atmospheric stability and celestial navigation clues, and to use cooler temperatures to dissipate body heat – could be applied to any other migration system. Consequently, we predict that a large proportion of South American migrants also fly at night. Normally, nocturnal migrants fly at heights where they are not visible to us. However, by watching the disk of the full moon with a telescope in spring or autumn, from time to time you can see birds crossing the disk of the moon. The number of birds counted in a given time interval is proportional to the intensity of bird migration. However, numbers are not directly proportional to intensity; observations are influenced by the height distribution of the birds and the visibility according to distance and the position of the moon. With good visibility and a telescope of 20-30x magnification, nocturnally migrating birds can be recorded at altitudes up to 1500m. With the methods outlined below, intensity and flight directions can be recorded simultaneously.
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| Full Moon dates for 2009 2009 Sep 4 16:05 Fri 2009 Oct 4 06:11 Sun 2009 Nov 2 19:15 Mon 2009 Dec 2 07:33 Wed 2009 Dec 31 19:15 Thu Full Moon dates 2010 2010 Jan 30 06:19 Sat |
Check The Moon Feeds, when your next planning hunt
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