Surgical implantation and evaluation of heart rate transmitters in captive bighorn sheep

A surgical approach was developed for implantation of transmitters to monitor heart rate of bighorn sheep (Ovis canadensis) with an objective of discrete long-term, long-range data collection. We surgically implanted Telonics model HR400 transmitters on the dorsolateral thorax of 15 captive adult bighorn sheep ewes in April-May and October-November 1995. No complications or marked impairment of function were associated with the surgery; however, a transmitter was passively expelled from one ewe 19.5 mo post-implantation. Twelve of 15 transmitters remained functional > or = 1 yr, while three failed 3.5 to 4.5 mo following implantation. Heart rate data collected from the transmitters using a Lotek SRX_400 telemetry receiver/datalogger equipped with W9 EVENT_LOG accurately reflected heart rate as measured with electrocardiogram tracings. Line of sight signal range was at least 800 m in 95% (37/39) of collections made from standing ewes, while data could be collected reliably (74%; 29/39) to 600 m from bedded ewes. When a reliable long-lasting inconspicuous telemetry system is required, we believe that this approach holds promise for success in free-ranging as well as captive ungulates.