J. Field Ornithol. 74(2):179–186, 2003
Effects of subcutaneous transmitter implants on
behavior, growth, energetics, and survival of
Common Loon chicks
Kevin P. Kenow,1,5 Michael W. Meyer,2 Francois Fournier,3,6 William H. Karasov,3
Abdulaziz Elfessi,4 and Steve Gutreuter1
U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road,
La Crosse, Wisconsin 54603 USA
Wisconsin Department of Natural Resources, 107 Sutliff Avenue, Rhinelander, Wisconsin 54501 USA
Department of Wildlife Ecology, 226 Russell Labs, University of Wisconsin-Madison,
Madison, Wisconsin 53706 USA
Department of Mathematics, University of Wisconsin-La Crosse, La Crosse, Wisconsin 54602 USA
Received 2 May 2002; accepted 16 September 2002
ABSTRACT. High rates of Common Loon (Gavia immer) chick mortality have been documented in Wisconsin,
especially on acidic lakes, but causes and timing of chick mortality are poorly understood. We modiﬁed and
evaluated a subcutaneous transmitter implant technique for Common Loon chicks using wild and captive reared
chicks. Results indicated that behavior, growth, energy expenditure, and survival did not differ signiﬁcantly between
chicks marked with miniature transmitters (mass 0.76 g, representing 0.8% of body mass at hatching) and
SINOPSIS. Efecto de transmisores implantados subcutaniamente en la conducta, crecimiento ener-
getica y supervivencia de polluelos de Gavia immer
Se han documentado, particularmente en Wisconsin, altas tasas de mortalidad en polluelos de Gavia immer
particular en lagos asiriﬁcados. Sin embargo, las causas y el perıodo de mortalidad no se entienden claramente.
Evaluamos un radiotransmisor modiﬁcado implantado subcutaniamente en polluelos cautivos y silvestres de la
especie antes mencionada (de masa de 0.76 g, representado 0.8% de la masa corporal al nacer). Los resultados
indican que la conducta, crecimiento, gasto energetico y supervivencia no vario signiﬁcativamente entre los polluelos
con radiotransmisores y un grupo control.
Key words: Common Loon, effects, Gavia immer, radiomarking, surgical implant, telemetry, transmitter implant
Annual recruitment rates of juvenile Com- (1992–2000), loon chick ﬂedging rates on low
mon Loons (Gavia immer) in Wisconsin were pH lakes were signiﬁcantly lower than on neu-
low (average 0.60 chicks ﬂedged per breeding tral pH lakes (M. Meyer, unpubl. data). Ele-
pair) in lakes studied by the Wisconsin De- vated mercury exposure and depressed prey
partment of Natural Resources (WDNR) from (ﬁsh) abundance have been implicated, but the
1992 to 2000 (M. Meyer, unpubl. data). De- causes and timing of chick mortality are poorly
spite inconsistencies in methods used, these understood.
rates are among the lowest productivity esti- Traditional observation studies have provided
mates reported for Common Loon populations only limited information on loon chick pro-
(McIntyre 1988). Common Loon productivity ductivity and have been ineffective in identify-
is lower on acidic lakes than on lakes with neu- ing the speciﬁc causes of mortality. Manage-
tral pH. Loons nesting on acidic lakes are ex- ment efforts to improve productivity and sur-
posed to elevated levels of dietary mercury vival of Common Loons cannot be effectively
(Meyer et al. 1995). Over an 8-yr period implemented until factors contributing to mor-
tality are better understood. Recent advances in
transmitter attachment techniques (Korschgen
Corresponding author. Email: kevin kenow@
usgs.gov et al. 1996a) have allowed biologists to obtain
Current address: Departement de biologie, Uni- data on movements, daily survival rates, and
versite de Moncton, Moncton, New Brunswick E1A
´ causes of mortality of ducklings (Korschgen et
3E9, Canada. al. 1996b) using subcutaneously implanted
J. Field Ornithol.
180 K. P. Kenow et al. Spring 2003
transmitters. The objectives of our study were weighed each chick, measured body length
to develop a radio-marking technique to deter- (from the anterior tip of the bill to the posterior
mine the causes and timing of loon chick mor- tip of the pygostyle of the outstretched chick),
tality from hatching to ﬂedging, and evaluate attached a web-tag (Haramis and Nice 1980),
the effects of the radio-marking technique on and held the chicks in a brooder until they were
behavior, growth, energy expenditure, and sur- released. The chicks were radiomarked with a
vival of the chicks. miniature radiotransmitter (model BD-2T, Ho-
lohil Systems, Ltd.) following procedures adapt-
METHODS ed from Korschgen et al. (1996a). Transmitters
had an average mass of 0.76 g, measured about
This study was conducted during 1998 in 4.7 7.3 14.0 mm, and had a life expec-
conjunction with ongoing studies of Common tancy of 21 d. The transmitters were implanted
Loon productivity. The study area encompassed subcutaneously in the chicks within a few hours
lakes over a 4400 km2 area in Oneida, Vilas, of hatching. Handling and care of the chicks
Forest, and Iron counties in northern Wiscon- and surgical techniques were approved by the
sin. Because loon productivity appears related Animal Care and Use Committee of the Upper
to lake pH, study lakes were selected from Midwest Environmental Sciences Center.
among lakes that were either low-pH (4.9–6.0) Transmitters were implanted while the chicks
or intermediate/neutral-pH ( 6.0). Some tech- were under a general anesthetic. Transmitters
niques were developed during pilot studies in were disinfected in a 10% bleach solution for
1997. about 30 min, rinsed with distilled water, and
Egg collection and incubation. Shore- stored in chlorohexidine diacetate solution until
line areas of lakes within the study area were surgery. Anesthesia was induced by passing a
searched for loon nests following the methods concentration of 3.0 to 5.0% isoﬂurane in ox-
of Titus and VanDruff (1981). Frequent visits ygen at a ﬂow rate of about 1.25 l/min using
to loon territories allowed us to determine the an out-of-circuit, agent-speciﬁc vaporizer and a
date of nest initiation (ﬁrst egg laid) within 2 mask. A surgical level of anesthesia was main-
days. Each egg was assessed for viability (Mi- tained with a 1.0–3.0% concentration of isoﬂu-
neau and Pedrosa 1986), measured (length and rane in oxygen.
width) with digital calipers, weighed, and Each loon was placed on its ventral surface
marked with a unique number using a Sharpie and held with its legs straight out. When the
permanent marker. loon lacked eye or toe-pinch reﬂexes, the sur-
We collected one egg from each nest follow- gical site was prepared immediately posterior to
ing 10–14 d of incubation. The collected egg the nape along the dorsal midline of the inter-
was randomly selected from among the ﬁrst or scapular region. Adjacent down was wetted to
second egg laid. Water-ﬁlled (37 C) plastic eggs expose the incision site and the site was disin-
(83 57 mm, 125 g) were painted to match fected with 1% povidone-iodine solution. An
the color of Common Loon eggs and substi- 8–10 mm incision was made immediately pos-
tuted in place of the eggs removed from the terior to the nape along the dorsal midline of
nest. Collected eggs were transported in insu- the interscapular region. A 2.80-mm OD
lated coolers heated (37 C) with water bottles (2.00-mm ID, 80 mm length) cannula (distal
or in temperature-controlled coolers. Distur- end open with smooth edges, modiﬁed by
bance of the nest and surrounding vegetation grinding) was inserted into the incision and
and the duration of the visit were kept to a used to separate skin from underlying muscle
minimum. posteriorly from the incision, forming a pocket
Eggs were hatched in incubators and peri- between the skin and muscle for placement of
odically checked for viability. Target incubator the transmitter. The pocket was extended pos-
conditions were 37.5 C dry-bulb and 29.4– teriorly to the synsacrum. The distal end of the
30.6 C wet-bulb (RH 56–60%). Pipped eggs cannula was placed in position at the point
were transferred to a hatcher. Target hatcher where the antenna was to exit, and a stainless
conditions were 37.2 C dry-bulb and 33.3– steel tube with sharpened end (1.47 mm OD,
34.4 C wet-bulb (RH 76–82%). 0.90 mm ID, 100 mm length) was fed poste-
Radiomarking. Following hatching we riorly through the proximal end of the cannula
Vol. 74, No. 2 Radio Transmitters and Common Loons 181
until it punctured the skin. The cannula was placed the radio-marked chick and any sibling
removed by backing it out over the stainless chicks in a paper envelope made of a single
steel tube. The transmitter antenna (0.63 mm hand towel (ﬁnished size about 19 13 mm).
diameter with 1.40 mm diameter base) was in- The top of the envelope was stapled closed. The
serted into the anterior end of the sharpened envelope was easily ripped open by the chicks,
tube until it appeared at the posterior end of especially after it had been wetted by moisture
the tube. The tube was removed from the chick from the nest substrate or returning adult. We
through the antenna exit site. The transmitter monitored the nest from a distance with bin-
was pushed through the incision into the pock- oculars or a spotting scope to conﬁrm that nest-
et and placed completely posterior to the inci- ing adults accepted the chick.
sion ( 4 mm) such that it did not place pres- Captive rearing. Six Common Loon
sure on the incision after it was closed. The chicks were reared in captivity following the
incision was inspected and closed with two techniques of J. Pichner (pers. comm.), Pichner
mattress stitches per Korschgen et al. (1996a). and DonCarlos (1986), and Barr (1996). These
After surgery, pure oxygen was administered chicks were artiﬁcially incubated and hatched.
until the loon’s respiratory rate returned to nor- Three of the chicks, selected at random, were
mal. We physically restrained the loon until it radio-marked. Chicks were held indoors in 0.7
demonstrated control of head and neck and was 2.9 m raceways that contained about 25 cm
able to assume an alert posture. of water, a resting platform, and a brooder light
The implant technique reﬂected pilot work until they were about 30 d old. Room lighting
we conducted in 1997, when we radio-marked was maintained at an approximate 16L:8D
eight loon chicks using a similar, but larger (1.5 light cycle. Chicks were transferred to 48-m2
g, 5.1 8.4 19.5 mm, 35-d life) transmitter outdoor ponds ﬂooded to a depth of approxi-
and released the chicks to their natal nests. mately 0.6 m and equipped with a resting plat-
Mortality among those chicks was high (20-d form and brooder. A constant supply of well
survival rate of 0.25), with most deaths occur- water (approximately 12 C) was supplied to the
ring within 1.4 d. Those deaths suggested to us raceways and outdoor ponds. Chicks were fed
that the implant procedure was disrupting the ﬁsh (primarily rainbow trout [Salmo gairdneri])
waterprooﬁng of the chick’s down. Transmitter ad libitum. The size of ﬁsh provided was in-
retention was also problematic as all three of creased gradually from an average of 1.0 g on
the chicks that survived past 15 d lost their day 1 to 20.0 g by week 8. The diet was sup-
transmitters within 6–11 d after release. Based plemented with thiamine and multivitamins.
on an examination of chicks that had lost their Records detailing thermal environment, body
transmitters, it appeared that migration of the mass, condition, development, food consump-
transmitter due to rapid body growth (10-fold tion, and behavioral development were main-
increase in mass in 20 d), coupled with pressure tained daily for each individual.
necrosis of overlying tissue, contributed to the Behavior evaluation. Observations of ra-
transmitter loss. In 1998, we used a smaller dio-marked and unmarked chicks were con-
transmitter and modiﬁed the implant technique ducted using an instantaneous sampling pro-
to keep the surgical procedure as ‘‘dry’’ as pos- cedure (Altmann 1974). Observations of sibling
sible and using only a few drops of saline so- chicks in the wild and among broodmates
lution to part down at the implant site and then reared in captivity were made simultaneously.
applying a small amount of 1% povidone-io- Behavior of the wild chicks was recorded at 30-
dine solution with a Q-tip along the incision s intervals for a 1-h period for 1 to 3 d after
site. With these modiﬁcations, the chick’s down release. Behavior of captive-reared chicks was
was left dry and ﬂuffy at the end of the surgery recorded on 15 d during the ﬁrst 22 d after
except for the immediate area of the incision hatching. Chick behavior was classiﬁed accord-
site. ing to Evers (1994) as resting, feeding, loco-
Chick release. Radio-marked loon chicks motion, brooding, or preening. Behavior of
were returned to natal nests as soon as possible captive birds fell primarily in the categories of
after hatching to enhance imprinting on the resting, locomotion, or preening. We also char-
parents (Korschgen et al. 1996b). To restrain acterized the spatial relationship of wild-reared
chicks in the nest until the parent returned, we chicks to the adult as on adult’s back, under
J. Field Ornithol.
182 K. P. Kenow et al. Spring 2003
adult’s wing, on water 1 m from adult, on Gompertz growth models that included a ran-
water 1 m from adult, or on nest. For captive dom effect for asymptotic size and assumed the
chicks, we recorded whether the chick was on repeated measurements were serially correlated
the brooding platform or in the water at each with the correlation inversely proportional to
observation. We treated behavioral observations the time interval between measurements.
as compositional data (Aebischer et al. 1993) Determination of chick mortality and
and conducted multivariate analysis of variance survival rates. Radio-marked loon chicks
(MANOVA) on additive log ratio-transformed were located one to several times daily. Trans-
data to test for effects of radio-marking on be- mitters were thermistor-regulated for remote
havior of radio-marked and unmarked chicks. monitoring of loon chick body temperatures
Determination of daily energy expendi- and served as a mortality cue. Dead birds were
ture and growth. Daily energy expenditure recovered as quickly as possible. Determination
of radio-marked and unmarked loon chicks was of the cause of death was based on recovery
determined using the doubly-labeled water location of the carcass and/or transmitter and
(DLW) method (Lifson and McClintock 1966; related evidence. Fresh carcasses were submitted
Nagy 1980). We increased background enrich- for complete pathological examinations, includ-
ments of 18O and deuterium in wild and captive ing selected diagnostic and histopathology stud-
chicks via injection at 10, 21, and 35 d. CO2 ies to check for viruses, bacteria, and parasites.
production was calculated using the change in Because the transmitters had a limited life, we
O and deuterium enrichment between blood recaptured chicks at night and replaced expiring
samples collected at the time of enrichment and transmitters. The transmitter implant technique
2 to 3 d later. Energy expenditure (kJ/d) was was similar to that used with day-old chicks.
calculated from CO2 production assuming an Transmitter removal and implantation of re-
energetic conversion factor of 25.7 J/mL CO2 placement transmitters was completed in a sin-
for a ﬁsh diet (Ricklefs 1974; Nagy 1983). gle surgical procedure. Chicks were returned to
Wild-reared loon chicks were captured using within the visual range of parents following sur-
nightlighting techniques (Evers 1993). At each gery and the next day we conﬁrmed that chicks
capture, chicks were weighed to the nearest 0.1 had rejoined their parents.
g, measured to obtain indices to structural size Survival of control and radio-marked chicks
(e.g., body length), and the transmitter site was was determined by visual observations. The sib-
assessed for external evidence of histological re- ling chick served as a control when available (in
actions. Details pertaining to the injection of some cases, the egg that remained in the nest
the DLW solution, blood collection, prepara- was depredated). Chicks were visually located
tion and analysis of plasma samples, and cal- daily. Survival rates of radio-marked and un-
culation of energy expenditure are provided in marked loon chicks were calculated using the
Fournier et al. (2002). We analyzed energy ex- Kaplan-Meier approach (Kaplan and Meier
penditure data using analysis of covariance 1958). A log rank 2 test was used to test for
(ANCOVA), adjusted for body mass as a co- differences between the survival of radio-
variate to determine differences between radio- marked and unmarked chicks.
marked and unmarked groups and between
wild and captive birds. Body mass and ﬁeld RESULTS
metabolic rate values were log-transformed.
Body mass of radio-marked and unmarked We collected and incubated 19 Common
chicks reared in captivity was measured daily Loon eggs in 1998. All of the eggs hatched and
and body length was measured every 3 to 5 d. 12 of these chicks were radio-marked and re-
Males and females were pooled for analyses as turned to nests, one chick was returned un-
sex-related differences in growth were found to marked, and six chicks were reared in captivity.
be minimal until about day 42. Logistic and Average mass of the radiomarked chicks was
Gompertz growth curves were ﬁt to the ﬁrst 38 99.4 6.8 (SD) g. The duration of the surgical
d of these data and assessed for goodness of ﬁt. implant procedure averaged 9.4 min (range
We determined that the Gompertz function 7 to 11 minutes) including induction of anes-
provided a superior ﬁt to the data based on ¯
thesia (x 5.6 min) and actual surgery (x ¯
Akaike’s Information Criteria (AIC). We ﬁtted 3.8 min). Two of 12 (17%) transmitters im-
Vol. 74, No. 2 Radio Transmitters and Common Loons 183
Fig. 1. Percent of time wild unmarked and radio-marked Common Loon chicks were observed resting,
swimming, brooding, feeding, and preening, and percent of time chicks were on an adult’s back, under an
adult’s wing, on the water 1 m from an adult, and on the nest at northern Wisconsin study lakes, June
planted at hatch were lost, providing a 21-d ior of radio-marked vs. unmarked chicks.
retention rate of 0.79 using the Kaplan-Meier Paired observations (3626 observations totaling
approach. Eight replacement transmitters (re- 30.2 h) of four sets of chicks lended themselves
placed at average age of 21 d; range 10 to 29 to further analysis. While time activity budgets
d) were all retained through ﬂedging. varied signiﬁcantly (MANOVA; Wilks’
Chick release. Radio-marked chicks were 0.001, F 18.11, P 0.03) among loon
released to nests within 11 h of hatching (x ¯ broods, radio-marked and unmarked chicks did
6.3 h, range 3 to 11 h). On our approach not differ (MANOVA; Wilks’ 0.25, F
to a nest, tending adults varied in their reaction 1.00, P 0.61) in the proportion of time the
from slipping off the nest and quietly remain- chicks spent resting, locomoting, brooding,
ing within 5 m of the nest to ﬂushing, vocal- feeding, and preening (Fig. 1). Similarly, while
izing, and moving several hundred meters from the spatial relationship of chicks to adults varied
the nest. Tending adults returned to nests and (MANOVA; Wilks’ 0.0001, F 234.87,
assumed incubating/brooding posture within 3 P 0.001) among broods, radio-marked and
to 77 min (x ¯ 22.3 min). In two cases, the unmarked chicks did not differ (MANOVA;
radio-marked chick was released to nests where Wilks’ 0.25, F 1.00, P 0.61) in po-
the sibling egg had been depredated but the sitioning with respect to adults (Fig. 1).
adults continued to incubate the plastic dummy We collected 10,800 behavioral observations
egg. In three instances, the control chick had on three radiomarked and three unmarked loon
hatched. Through observation we conﬁrmed chicks in captivity totaling 45 h (Fig. 2). Ob-
that all of the restrained radio-marked and con- servations were analyzed for two time periods,
trol chicks escaped the paper towel envelope when chicks were 8 d old and when they were
and were accepted by the adults. 8 d old. Time activity budgets did not vary
Behavior evaluation. We collected between radio-marked and unmarked chicks
10,484 behavioral observations on 11 radio- (MANOVA; Wilks’ 0.16, F 1.71, P
marked and eight unmarked loon chicks in the 0.50) or with age category (MANOVA; Wilks’
wild totaling 87.4 h. During these observations 0.12, F 2.54, P 0.43). While the
we observed no impairment of radio-marked proportion of time spent in the water differed
chicks and no marked differences in the behav- with age (ANOVA; F 21.635, P 0.02),
J. Field Ornithol.
184 K. P. Kenow et al. Spring 2003
Fig. 2. Percent of time captive unmarked and radio-marked Common Loon chicks were observed resting,
swimming, and preening, and percent of time chicks were on a brooding platform or on the water in a
laboratory setting at the Upper Midwest Environmental Sciences Center, June 1998.
there was no signiﬁcant effect of radiomarking 0.626), treatment (radio-marked vs. un-
(ANOVA; F 0.470, P 0.54). marked; F 0.524, P 0.509), and interac-
Daily energy expenditure and growth. tion effects (F 0.387, P 0.567) were not
Problems with sample analyses and inability to signiﬁcantly different among chicks 35 d old.
consistently recapture wild chicks limited our We did not detect differences in asymptotic
calculations of daily energy expenditure of 10- mass ( 21 2, P 0.16), instantaneous growth
d old wild and captive chicks and 21-d old wild rate ( 21 2.6, P 0.11), or inﬂection point
chicks. Energy expenditures of wild radio- ( 21 3.0, P 0.08) between radio-marked
marked birds averaged 6 to 10% higher than and unmarked captive chicks. In addition, we
those of unmarked birds when comparing did not detect an effect of radio-marking on
paired sample means at ages 10 (6%), 21 body length (P 1 for asymptotic mass, in-
(10%), and 35 (7%) d (Fig. 3). Two-way AN- stantaneous growth rate, and inﬂection point).
COVA indicated that energy expenditure Chick mortality and survival rates. We
among sources (wild vs. captive; F 0.278, P monitored the daily survival of 12 radio-
Fig. 3. Energy expenditure (kJ/d) of unmarked and radio-marked Common Loon chicks that were captive-
reared or monitored in the wild at northern Wisconsin study lakes, June and July 1998.
Vol. 74, No. 2 Radio Transmitters and Common Loons 185
marked and nine unmarked chicks. One of the of the chicks that survived past 15 d lost their
radio-marked chicks was eliminated from the transmitters within 6 to 11 days. Comparable
analysis as the timing of the fate of its sibling size transmitters (1.5 g) have been used with
was not determined. At the end of the ﬁeld day-old ducklings (about 4% of body mass)
season, eight radio-marked chicks and six un- without signiﬁcant retention problems (Korsch-
marked chicks remained alive. Contributing gen et al. 1996a). One cannot assume that spe-
causes of mortality of the radio-marked chicks cies with closely related body conﬁgurations
were attack by an intruding adult loon of a sin- will tolerate a comparable transmitter. A spe-
gle 1-d-old chick, aquatic predator (e.g., large cies-speciﬁc assessment of transmitter attach-
ﬁsh) of a 1-d-old and an 11-d-old chick, and ment techniques is needed.
infestation of intestinal parasites of a 38-d-old Subcutaneously implanted transmitters have
chick. The 80-d survival rate did not differ (log also proved effective in identifying causes of
rank 21 0.01, P 0.92) between radio- mortality. Careful monitoring of transmitter
marked (0.69 0.15 [SE], N 11) and un- temperature, and consequently chick body tem-
marked chicks (0.67 0.16, N 9). perature, can lead to the timely recovery of
chick remains and associated evidence following
DISCUSSION death. In our investigations of loon chicks, we
were able to link mortality to disease and pred-
The modiﬁed transmitter implant technique ators, the latter including the Bald Eagle (Ha-
we describe shows promise to determine the liaeetus leucocephalus), ﬁshers (Martes pennanti),
causes and timing of mortality and the daily and ﬁsh. Krementz and Pendleton (1991)
survival rate of Common Loon chicks from found that implanted transmitters provided
hatching to ﬂedging. We observed no signiﬁ- more accurate information on causes of mor-
cant differences in behavior, growth, energy ex- tality in ducklings than did externally attached
penditure, and survival between radio-marked transmitters.
and unmarked chicks. However, we note that We suspect that most telemetry attachment
energy expenditures of wild radio-marked birds methods have some negative effects. When
averaged 6 to 10% higher than those of un- planning avian telemetry studies, biologists ﬁrst
marked chicks. The small sample size may have must consider the impacts of attaching a trans-
precluded detection of a signiﬁcant effect at 35 mitter to a bird as it relates to the objectives of
d. Only one other published study has assessed their study. Evidence to support use of a par-
the ﬁeld metabolic costs of radio-marking birds. ticular technique should be age and species-spe-
Klaassen et al. (1992) also reported a higher ciﬁc and address effects on behavior, growth,
(7.3%), but non-signiﬁcant, daily energy ex- energetics, and survival. Researchers should
penditure for Common Terns (Sterna hirundo) weigh published evidence in lieu of conducting
equipped with transmitters glued to the skin of their own evaluation. When necessary, evalua-
the interscapular region. Subcutaneous trans- tions should be incorporated into telemetry
mitter implants, similar to those used in our studies and include both ﬁeld and captive work.
study, in Mallard (Anas platyrhynchos) ducklings Because chick survival is strongly related to the
in an open-circuit respirometer did not signif- chick-adult bond immediately following hatch-
icantly affect net heat production (Bakken et al. ing, we recommend controlled measurement of
1996). If the difference in energy expenditure assembly behavior of chicks released some dis-
between wild radio-marked and unmarked loon tance from the adult(s) or systematic ﬂushing
chicks was real in this study, there was no in- of the adult to observe chick following behav-
dication that the birds consequently modiﬁed ior.
their behavior. We also recommend that investigators con-
The attachment technique offered good sult with appropriate veterinary or wildlife pro-
transmitter retention: initial transmitters (im- fessionals to assist with selection of techniques
planted at hatching) had a 21-d retention rate and to obtain the training needed to correctly
of 0.79. All replacement transmitters were re- attach or implant transmitters. The subcuta-
tained through ﬂedging. This performance was neous implant technique described here should
a marked improvement in retention over the be used only by experienced individuals after
1.5-g transmitter used in 1997 when all three they have received proper training, have dem-
J. Field Ornithol.
186 K. P. Kenow et al. Spring 2003
onstrated competence in the technique, and KLAASSEN, M., P. H. BECKER, AND M. WAGENER. 1992.
have the necessary equipment and supplies in Transmitter loads do not affect the daily energy ex-
penditure of nesting Common Terns. Journal of
hand. Field Ornithology 63: 181–185.
KORSCHGEN, C. E., K. P. KENOW, W. L. GREEN, M. D.
SAMUEL, AND L. SILEO. 1996a. Technique for im-
This project was funded by the Wisconsin Depart- planting radio transmitters subcutaneously in day-
ment of Natural Resources and the Upper Midwest En- old ducklings. Journal of Field Ornithology 67:
vironmental Sciences Center. We thank R. DeWald, J. 392–397.
E. Lyon, K. A. Kroc, M. L. Meier, L. E. McColl for ———, ———, ———, D. H. JOHNSON, M.D. SAM-
assistance with ﬁeld observations and loon chick care; UEL, AND L. SILEO. 1996b. Survival of radio-marked
C. E. Korschgen for guidance and logistical support; L. Canvasback ducklings in northwestern Minnesota.
Johnson for providing veterinary consultation; J. Pich- Journal of Wildlife Management 60: 120–132.
ner for consultation on captive rearing methods; and F. KREMENTZ, D. G., AND G. W. PENDLETON. 1991.
P. Meyer, L. E. Holland-Bartels, and two anonymous Movements and survival of American Black Duck
reviewers for providing reviews of the manuscript. and Mallard broods on Chesapeake Bay. Proceed-
ings of the Annual Conference of the Southeastern
Association of Fish and Wildlife Agencies 45: 156–
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