3D coordinates of the foraging flights of wild black skimmers

Published Jul 30, 2024 on Dryad. https://doi.org/10.5061/dryad.tmpg4f573

Data files

Jul 30, 2024 version files 44.36 MB

Abstract

Birds commonly exploit environmental features such as columns of rising air and vertical windspeed gradients to lower the cost of flight. These environmental subsidies may be especially important for birds that forage via continuous flight, as seen in black skimmers. These birds forage through a unique behavior, called skimming, where they fly above the water surface with their mandible lowered into the water, catching fish on contact. Thus, their foraging flight incurs the costs of moving through both air and water. Prior studies of black skimmer flight behavior have focused on reductions in flight cost due to ground effect but ignored potential beneficial interactions with the surrounding air. We hypothesized a halfpipe skimming strategy for skimmers to reduce the foraging cost by taking advantage of the wind gradient, where the skimmers perform a wind gradient energy extraction maneuver at the end of a skimming bout through a foraging patch. Using video recordings, wind speed, and wind direction measurements we recorded 70 bird tracks over four days at two field sites on the North Carolina coast. We found that while ascending the skimmers flew more upwind and then flew more downwind when descending, a pattern consistent with harvesting energy from the wind gradient. The strength of the wind gradient and the flight behavior of the skimmers indicate that the halfpipe skimming strategy could reduce foraging costs by up to 2.5%.

This dataset contains the XYZ coordinates of black skimmers foraging flight tracks taken in 5 different recording sessions. The flights were recorded using three video cameras, videos were synchronized the scene was calibrated and aligned using the DLTdv (Hedrick, 2008) application on MatLab. The tracks were smoothed using a 4-pole digital Butterworth low pass filter with a cutoff frequency of 0.5 Hz. We found that while ascending the skimmers flew more upwind and then flew more downwind when descending, a pattern consistent with harvesting energy from the wind gradient.

Description of the data and file structure

For each CSV file the columns represent the XYZ coordinates for each tracked point, so that the first three columns will contain XYZ (in that order) coordinates for point one, columns 4-6 will be the second point, and so forth. For all files ‘NaN’ is a missing data point on a track. Missing data results from one or more cameras not capturing the moving or static object being tracked.

Here is what you will find for each file and some extra information: