Mechanical assembly of the logger showing the three PCBs (4 layer boards, FR4 substrate, thickness 0.8 mm), their interconnections, the locations of the sensors and circuit elements, and their physical positions relative to one another. Programming of firmware was achieved via five prominent pins of the primary interconnect using a PicKit3. Internal boards were protected by dipping in wax. Putty was used to prevent the battery from sliding back and forth within the PFA tubing which might otherwise cause spurious impacts to be transmitted to the accelerometer.
Top left: titanium electrodes and view of the sensor board. Top right: with pressure/temperature sensor attached through the slot in the titanium electrode (magnetometer also fitted). Bottom left: Top view showing the recess of the titanium electrode sealed with silicone. Bottom right: Extraction of the logger from the housing following recapture. Micro SD cards (15 × 11 mm) are intended to provide a sense of scale.
Flowchart showing the sequence of primary tasks performed by system firmware.
Examples of ECG traces captured during the migratory flight of a single goose. Signal quality was adequate despite the fact that flying lead electrodes adjacent to the heart were not used. Each trace covers 4 s and ECG has been upsampled by a factor of 8. Top: a clean signal, HR = 420 bpm. Middle: a noisier signal during ascending flight, HR = 440 bpm. Bottom: signal contaminated by motion artefacts close to take-off.
Heart-rate determined from post-processing of ECG covering the first few minutes of a lengthy flight.
The geomagnetic field after median filtering. Step changes were confirmed by accelerometry to be associated with episodes of flight. The prominent final flight was a southward trans-Himalayan crossing involving a 0.06 Gauss change in geomagnetic field intensity, a 12° change of latitude, and an estimated distance of 1300 km. The heart-rate plot of Fig. 4 covered the start of this 26 h flight.
Loggers within rugged housings were strapped and bonded to neck collars, internally lined here with foam strips in an attempt to improve coupling of flight movements from the neck to the accelerometer. These units were deployed on swans to collect accelerometry, temperature, and altitude measurements.
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