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 L5A 3V3, Canada; Quinton
Instrument Company, St. Louis, MO 63103 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 mo 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
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 mo 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 yr) adverse effects.2 However, long-term effects on reproduction and health have not been
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