Atmospheric trajectories and spring bird migration across the Gulf of Mexico

Abstract

We examined the relationship between the longitude of peak arrival of trans-Gulf migrants on the northern coast of the Gulf of Mexico in spring and wind trajectories over the Gulf at three different altitudes (500, 1,500, and 2,500 m above ground level). We used data from 10 WSR-88D radars (weather surveillance radar-1988-Doppler) from Brownsville, Texas, to Key West, Florida, to record the time and longitude of peak arrival on the northern Gulf coast for four spring migrations (2001)(2002)(2003)(2004). We used the National Oceanic Atmospheric Administration Air Resources Laboratory HYSPLIT transport and dispersion model at the READY Web site to generate backward, 24-h atmospheric trajectories based on archived atmospheric data for each trans-Gulf flight. The trajectories began at the geographic location where radar indicated the greatest concentrations of arriving migrants. Although the longitude of peak arrival varied, peak densities of most trans-Gulf migrants arrived on the northern coast near longitude 95°W. Regression analyses showed that the relationship between the longitude of peak trans-Gulf arrival and the direction of atmospheric trajectory was significant but weak at the 500-m level, where few migrants occurred, and was insignificant for the 1,500-and 2,500-m altitudes, where migrant densities were greater. We conclude that winds aloft over the Gulf have little influence on the longitude of peak trans-Gulf arrival on the northern coast of the Gulf of Mexico, and we speculate that the arrival pattern may reflect the transGulf migration pathways that evolved during the Last Glacial Maximum.

Avian Resources of the Northern Gulf of Mexico

“…On a small spatial scale, habitat (amount and quality, prey availability) is critical, while on a broader scale, weather and winds become critical (Moore 2000a). Wind patterns are generally favorable for birds to migrate across the Gulf in the spring, usually determined by studies with radar (Gauthreaux 1971(Gauthreaux , 1999Gauthreaux et al 2006). Migration patterns are not static, but shift from year to year and season to season, depending upon prevailing winds (Barrow et al 2005).…”

“…Analyzing data from 10 radar stations from Key West, Florida to Brownsville, Texas, Gauthreaux et al (2006) showed that in the spring: (1) northbound migrants approached the northern Gulf Coast at between 1,000 and 2,500 m above ground; (2) the longitudes of peak arrivals were similar over the 4-year period (near longitude 75 west, northern Texas/western Louisiana); (3) wind trajectories over the Gulf of Mexico had relatively little influence on the longitude of peak arrival; (4) the longitude where the greatest density of trans-Gulf migrants arrived on the northern coast was relatively constant from year to year; and (5) on occasion, strong winds or storms displaced migrants, but migrants seemed to have a preferred route they followed. These conclusions suggest that conservation efforts should concentrate on the preferred routes and landing locations.…”

“…While radar is used to determine patterns of migration across the Gulf (Gauthreaux et al 2006), data from banding stations are used to assess ecology of migrants, including timing (Moore et al 1990;Marra et al 2005), stopover duration (Moore and Yong 1991), and habitat use (Moore et al 1990). Stable isotope techniques are used to connect the wintering and breeding grounds of Nearctic-Neotropical migrants (Hobson and Wassenaar 1997;Hobson et al 2007;Hobson 2005;Kelly 2006b;Langin et al 2009).…”

“…The four flyways of North America join in the Gulf of Mexico. Many migrants pass through central Veracruz, while others from the Mississippi and Atlantic flyways migrate directly across the open waters of the Gulf (Moore 2000a;Gauthreaux et al 2006).…”

Migratory navigation in birds: new opportunities in an era of fast-developing tracking technology

“…Migration over ocean and land may also differ in the availability of navigational cues, such as detectable stable visual landmarks. Tracking studies across different types of topography will enable researchers to relate corrective navigation following wind (Klaassen et al, 2010) or any natural displacement to surface features below, environmental barriers as well as wind speeds (Gauthreaux et al, 2003;Gauthreaux et al, 2006). Detailed knowledge of wind conditions at sample locations and flight altitudes may be needed for these analyses.…”