The recent development of a technique permitting implantation of satellite and conventional radio transmitters into the abdomens of birds relies on passing the antenna through the body wall to enhance transmission strength and quality.6 The fistula created by the passage of the antenna could represent a route for contamination of the abdomen. The developers of the technique adapted a collar from percutaneous devices or artificial organ implants placed in human beings. The collar consists of plastic or silicone tubing, sized to fit the diameter of the base of the antenna, surrounded by a layer of Dacron plush fabric (Vas-Cath, Mississauga, Ontario, Canada; Quinton Instrument Company, St. Louis, MO, USA). The antenna collar remains inside the abdomen, abutting the body wall. In theory, the antenna collar serves to seal the antenna fistula, initially serving as the matrix for a blood clot. Within days, fibrotic tissue encapsulates the transmitter and the antenna collar and the associated cells and collagen form a permanent seal. Encapsulation is completed within about 1 month following surgery, but the exact progression of its formation has not been determined in birds.6 However, mammalian studies are available.1,5,7 A secondary function of the antenna collar is to provide a structure through which a single interrupted suture can be placed. In most cases, this single suture is the only means of anchoring the transmitter in the body of the bird until encapsulation occurs.
We have implanted more than 600 birds with transmitters using percutaneous antennas equipped with the antenna collar. All birds are released as soon as they have fully recovered from anesthesia. Few implanted birds are ever recaptured. When implanted birds are recaptured, they usually cannot be sacrificed for examination because they are an ongoing part of a population being studied or because they are a threatened species (e.g., spectacled eiders, Somateria fischeri). However, in one project concerned with determining if the effects of the 1989 M/V Exxon Valdez still affected over winter survival of harlequin ducks (Histrionicus histrionicus), we recaptured many implanted ducks in subsequent years of the study.3 We were able to recover failed or expired transmitters and the antenna collars from a small number of ducks. Fabric collars were recovered from antennas of implanted radio transmitters that had been in place for 12 months in ten harlequin ducks. Both the transmitters and the antenna collars were entirely covered with a fibrous capsule with adhesions to internal organs. In all of the collars examined, there was a foreign body reaction. Histologically there was a mild (one duck), moderate (six ducks), or severe (three ducks) inflammatory reaction (heterophils, lymphocytes, and plasma cells) that was most severe in the fabric adjacent to the plastic tube to which the fabric was attached. In some samples, there was a rim of degranulated heterophils at the collar-tissue interface. Bacteria were present in eight of the ten collars examined, with bacterial colonies especially prevalent along the fabric-plastic interface. It was not possible to determine if the bacterial contamination extended the full length of the collar. However, the encapsulation of the transmitter and collar probably contained such contamination, preventing development of peritonitis. Indirect evidence of the effectiveness of this barrier was seen when harlequin ducks pulled some of the transmitters out through the skin.9 Few if any of these birds died, probably because the fibrous encapsulation contained the influx of seawater when the transmitters were extracted.
Hematologic and serum chemical analysis of blood taken from six birds at the time of transmitter implantation and again at transmitter removal showed no indications of a chronic system effect of the implant. Our results show that the collars were not excluding bacteria, as originally expected, but acted primarily to stabilize the transmitter. Although bacteria were found in the antenna collars, the ducks contained the infection. In human implant literature, it is also thought that the collars do not necessarily act as a barrier to infection, but stabilize the implant, thus preventing the piston-like movement that would tend to spread the infection deeper into the tissue.11 The foreign body reaction begins within a few hours following surgery and likely persists for the life of the implant.4,8 Not all bird researchers believe that antenna collars are necessary. One study in captive mourning doves (Zenaida macroura) described subcutaneous and abdominal implantation of transmitters with percutaneous antennas that were not equipped with Dacron collars.10 The snug fit between the skin and the antenna formed a seal that appeared to work well in this non-aquatic bird. However, until additional research is done, we will continue to use collars on all percutaneous antennas. A mark-recapture analysis of harlequin ducks with and without transmitters found no differences, indicating that abdominal implantation of transmitters in this species has no short-term (1–2 years) adverse effects.2 However, long-term effects on reproduction and health have not been examined.
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