Migration path annotation: cross-continental study of migration-flight conditions

The movements of animals are an important indicator of how they interact with and use land resources in sustainable ways. Thus, the study of how migratory patterns change due to external environmental influences may provide an indication of a species’ ability to survive in the event of rapid climate change. Mandel et al. (2008) created a study that tested the flight patterns of three geographically separate populations of turkey vultures to ascertain which topographical and weather variables created a shift in movement. For purposes of the study, movement was defined as the straight-line distance between two points and navigation was recorded based on the hourly deviations a bird’s flight pattern relative to their seven prior recorded hours. The birds were tagged and monitored with a GPS network that fed into a gridded data set that allowed researchers to observe the birds’ movements. From these they could visualize predictable error rates and global patterns. The researchers found that the movement of east and west coast turkey vultures was influenced by the topography of the land that they flew over. For all three populations of birds, horizontal wind speed was the largest factor in the deviation of migratory paths; however, the effect on each population differed. West coast birds had an increased deviation in high winds, but their flight path was not directly impacted by the direction of the wind. East coast birds flew in the straightest path when the wind strength was at either the low or high end. Conversely, whereas coastal birds responded to both slope and thermal soaring, interior birds only used thermal soaring. – Adriane Holter
Mandel, James T., Bohrer, Gil, Winkler, David W., Barber, David R., Houston, C. Stuart, Bildstein, Keith T. Migration path annotation: cross-continental study of migration-flight response to environmental conditions. Ecological Society of America, Vol 21. Issue 6.

          Turkey vultures direct their flight by identifying a thermal zone and then soaring through that zone on an air current. This method of flight is crucial for the species to use the least possible amount of energy. In order to determine how turkey vulture migration might be impacted by climate change, the authors of the paper studied topography and weather variables alongside the flight patterns of turkey vultures. The conclusion of the research determined that these factors do change the way that turkey vultures migrate.
          The birds in the two coastal locations, southern California and eastern Pennsylvania, experienced higher levels of turbulence kinetic energy (TKE) in the air as they flew through mountain ranges. TKE refers to the amount of friction in the air current surrounding the birds. A higher level of TKE signifies more friction in the air, which negatively impacts the birds’ ability to coast in the air with the minimum possible energy output. In response to the TKE levels around the mountains, the birds flew in slope patterns that reflected the shape of the mountain ranges to provide protection from wind. Internal continental birds, from central Saskatchewan, did not encounter much TKE because they flew through an area that was flat and did not need to change their flight patterns to avoid it. In addition, internal continental birds did not respond to thermal patterns. This research thus implies that changes caused to topography and weather due to climate change has the potential to alter the way that regional populations of a bird species move and interact wit their surroundings. 

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