This research examined nocturnal and diurnal bird migration using an automated marine radar system during three autumn (August 15 to November 17) and three spring (March 15 to June 1) periods in 2007–2010 along the lower Texas coast. We quantified migration timing, magnitude, and flight altitudes for over 14 million targets during 16,360 h of radar operation. Autumn migration was prolonged in contrast to spring migration, which was concentrated within a four-week period in mid–April to mid–May. Mean migration traffic rate in autumn averaged 1,186 targets km-1 h-1 and was 46% greater than spring. Migration traffic rates at our northern site were at least 62% higher than at our southern site. We found bird passage to be similar between diurnal and nocturnal periods in autumn, but predominately nocturnal (68% of targets) in spring. Mean flight altitudes were 10-33% higher in spring than autumn. Our results confirm that the lower Gulf coast of Texas is a significant migration corridor concentrating millions of birds during migration. This new information on temporal and spatial dynamics of migration provides guidance for the placement and operation of wind power developments to reduce the risk to migratory birds along the lower Texas coast.
Key words: Bird migration, coast, flight altitude, marine radar, migration traffic rates, Texas, wind power.
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