Abstract

Telemetry is an essential tool for the study of wild bird populations, which has stimulated active research in methods for attachment of transmitters to birds. External attachments have been frequently associated with adverse effects on behavior, flight, metabolism, reproduction and survival, and problems with damage to, or loss of the instrument. Surgical implantation of transmitters was developed as a means to reduce the adverse effects of external attachments and to increase retention rates of the instruments.^5,10 Recently, the development of a technique permitting abdominal implantation of the transmitter body with a percutaneous antenna allowed for maximal efficiency of signal transmission.⁶ Further miniaturization of transmitters occurred simultaneously with the development of surgical implantation techniques allowing the technique to be used on incrementally smaller birds. Conventional very high frequency (VHF) transmitters suitable for abdominal implantation now weigh about 20 g and have a 1–2 year working life. Satellite transmitters weigh 35–60 g and have working lives of 4–12 months, depending on what duty cycle is programmed.

In Alaska, satellite and conventional transmitters have been surgically implanted into diving seabirds and sea ducks, birds that have poorly tolerated transmitters attached externally using harnesses or glue and anchors. From 1993 through 1999, more than 600 conventional VHF and satellite transmitters with percutaneous antennas were surgically implanted into nine species (Table 1). Implanted transmitters have proven to be very successful in sea ducks but have been less useful in seabirds. Satellite transmitters have been implanted into birds as small as 550 g and conventional transmitters have been implanted into birds weighing as little as 450 g.

Implanted miniaturized satellite transmitters were first used in spectacled eiders (Somateria fischeri) in Alaska and Siberia.¹¹ Although the transmitters were expected to last 12–13 months, they all failed in as little as 3 months, due to the spontaneous self-discharging that occurred due to the intolerance of the lithium batteries to the elevated body temperatures of birds. However, these transmitters were successfully used to locate gender-specific molting areas in the Beaufort Sea.¹¹ In an unexpected and still unexplained manner, one transmitter that had failed several months earlier, reactivated briefly in mid-winter, giving several locations in the center of the ice sheet south of St. Lawrence Island. A plane was sent to investigate and found nearly the entire population of spectacled eiders, over-wintering in small pools of open water, kept ice-free by the birds themselves.¹²

Seabirds such as common murres (Uria aalge), thick-billed murres (U. lomvia) and tufted puffins (Fratercula cirrhata) have been implanted with satellite transmitters, but results have been erratic. Besides the same battery life limitation experienced in all birds, transmitter problems with alcids have been with abandonment of nests,⁷ pressure effects on the transmitter, mortality of implanted birds, and apparent effect of signal duty cycle on the birds.³ Particularly interesting has been the observation that birds implanted with transmitters programmed to transmit frequently (short duty cycle) die faster and more frequently than birds implanted with transmitters programmed to transmit less frequently (long duty cycle).³ Notwithstanding the problems, implanted transmitters have proved useful in determining seasonal movements of these birds in their pelagic habitat.⁴

Surf scoters ( Melanitta perspicillata) and white-wing scoters (M. fusca) were implanted with satellite transmitters during a stopover in Prince William Sound during their northward migration. About 40% of the implanted birds were lost within 2 weeks of surgery, while the birds were still in Prince William Sound. Mortality after the birds left Prince William Sound was negligible. Recovery of remains indicated that predation by bald eagles was the cause of death. Observation of newly implanted birds suggested that the birds sequestered themselves away from the main flock, thereby attracting the attention of predators.

More than 300 harlequin ducks (Histrionicus histrionicus) were implanted with VHS transmitters as part of a study that determined that the Exxon Valdez oil spill continues to adversely affect over-winter survival of this species.² Because of the large number of transmitters deployed over 3 years, and the philopatry of the birds, allowing individual birds to be recaptured more than once, we were able to detect and examine several effects of implanted transmitters. A change in transmitter design from a spherical unit to a cylindrical one was responsible for the birds pulling a large proportion of the transmitters out through the body wall.⁹ We determined that the birds did not die following loss of the transmitter because of the fibrous scar tissue surrounding the transmitters prevented the entrance of seawater into the coelomic cavity. Implanted transmitters did not affect the annual survival rate of ducks, as recapture rates of implanted birds were identical to those of banded but not implanted birds.¹ This indicates that implanted radios offer an unbiased method for estimating survival of harlequin ducks. Intraoperative and immediate (14 days) post-release mortality was reduced from 7.2% in the first year to 1.5% in subsequent year by alterations in anesthetic and surgical technique.⁸

Table 1

Summary of abdominal implantations of conventional and satellite transmitters with percutaneous antennas into sea ducks and seabirds in Alaska, 1993–1999.

Literature Cited

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