Simple and inexpensive devices to measure heart rates of incubating birds

Heart rate is a useful physiological index for studies of stress, locomotion, and activity patterns. Measuring heart rates of birds without the need to handle individuals is desirable when trapping is problematic or may cause unwanted disturbance. Heart-rate recorders housed in dummy eggs offer an effective solution, but the usefulness of previously described devices is limited by their size, complex construction, and reliance on analog media. We constructed egg-based, heart-rate monitors through simple modifications of inexpensive, commercially available MP3 players and Bluetooth headsets. We compared the merits of each device during tests in the laboratory, an aviary, and the field in 2008. Field testing was undertaken at Presqu'ile Provincial Park, Ontario, Canada, where we recorded heart rates of Common Terns (Sterna hirundo), Caspian Terns (Hydroprogne caspia), and Ring-billed Gulls (Larus delawarensis). Birds incubated dummy eggs normally, with no differences in behavior (all P > 0.05) when incubating either wired (MP3 players) or wireless (Bluetooth) devices. MP3 devices were more reliable in the field. Bluetooth devices often lost pairing with laptop computers (33% of files analyzed contained no signal), produced files with more obscuring noise, and only two could be deployed simultaneously with a single computer; there was no limit on how many MP3 devices could be deployed simultaneously. Common Terns, the smallest of our three focal species, had significantly higher (P < 0.001) mean heart rates (268.6 ± 9.3 beats per min [bpm]) than either Ring-billed Gulls (198.0 ± 7.1 bpm) or Caspian Terns (204.2 ± 8.0 bpm). Heart rates of all three species were consistent with those reported or predicted from previous studies. The MP3 devices we describe provide investigators with a simple, inexpensive, and minimally invasive way to digitally record heart rates of birds of almost any size.