Abstract
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.
Highlights
Migration behavior has evolved in many species of birds to take advantage of seasonally available resources in temperate regions to increase reproductive success (Pulido, 2007; Ramenofsky and Wingfield, 2007)
Investigations have concentrated more on describing details of spring migration than autumn migration (Able, 1972; Buskirk, 1980; Gauthreaux, 1999), and most studies have been conducted on the northern Gulf coast (Gauthreaux, 1971; Gauthreaux and Belser, 1998; Gauthreaux, 1999)
We found that peak passage in spring occurred between 2000 and 0300 h, as migration traffic rate (MTR) remained stable throughout the night, and was considerably lower during crepuscular and diurnal hours (Figure 4)
Summary
Migration behavior has evolved in many species of birds to take advantage of seasonally available resources in temperate regions to increase reproductive success (Pulido, 2007; Ramenofsky and Wingfield, 2007). Each year millions of birds migrate vast distances between their breeding and wintering areas to benefit from seasonal environments (Moore et al, 1993; Alerstam et al, 2003; Pulido, 2007; Ramenofsky and Wingfield, 2007), but we are still far from understanding many aspects of this important life cycle phase in birds. Most information on bird migration in this region comes from anecdotal observations or volunteer-driven surveys
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