Alaska to New Zealand and Polynesia: Trans-hemispheric Migrations of Shorebirds Followed Using a New Implantable Satellite Transmitter
Until recently, the size of the smallest satellite transmitter suitable for implantation into birds weighed 42 g, limiting deployment to birds weighing greater than 840 g (at 5% of body weight) or 600 g (at 7% of body weight). In June of 2005 and 2006, using a new satellite transmitter weighing about 24 g (1.9×1.6×4.2 cm, with a 23 cm antenna), transmitters were implanted into the right abdominal air sacs of bristle-thighed curlews (Numenius tahitiensis) and bar-tailed godwits (Limosa lapponica), captured on their Alaskan nesting grounds. An anesthetic combination of propofol, bupivacaine, and lidocaine was used. Hyperthermia was a complication, but all birds survived anesthesia and surgery. For implanted birds, mean loading ratios (transmitter weight/body weight × 100%) were bar-tailed godwit: 6.7% (range: 6.4–7.5%), and bristle-thighed curlew: 6.0% (range: 5.5–6.2%).
In 2005, all five transmitters implanted in godwits failed due to premature battery failure just prior to migration but two of the five implanted godwits were identified subsequently on the wintering grounds in Australia and New Zealand and again in 2006 on the nesting grounds in Alaska. In 2006, four bar-tailed godwits and eight bristle-thighed curlews were implanted. Three godwits and seven curlews were tracked during migration to overwintering sites in the South Pacific or until signals stopped. Calculated nonstop flight durations and distances were up to 8.3 days and 9,725 km for curlews and 9.6 days and 10,800 km for godwits. Godwits may have the longest nonstop migration of any land bird.