Effects of subcutaneous transmitter implants on behavior_ growth

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					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
unmarked chicks.

   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@                                                    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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                                                          LIFSON, N., AND R. M. MCCLINTOCK. 1966. Theory of
AEBISCHER, N. J., P. A. ROBERTSON, AND R. E. KEN-             use of the turnover rates of body water for measur-
    WARD. 1993. Compositional analysis of habitat use         ing energy and material balance. Journal of Theo-
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