A radiotelemetry system for analyzing heart rate responses during playback experiments in blackbirds (Turdus merula )

Behavioural Processes, Elsevier

13 (1986) 3 1l-325

311

A RADIOTELPMETRY SYSTEMF'ORANALYZINGHEART RATE RESPONSESDURINGPLAYBACK FXPFRIMENTSIN BLACKBIRDS(Turdusmerula) PETER DIEHL (l), HANS-WOLFGANG MANFRED LijSCH (2)

HELB (l), UWE T. KOCH (1) AND

(1) Fachbereich Biologie der Universitat Kaiserslautern, Postfach D-6750 Kaiserslautern, FRG (2) Zentrale Elektronik-Werkstatt der Universitat Kaiserslautern, Postfach 3049, D-6750 Kaiserslautern, FRG (Accepted

3049,

10 July 1986)

AEiSTRACT Diehl, P., Helb, H.-W., Koch, U.T. and Losch, M., 1986. A radiotelemetry system for analyzing heart rate responses during playback experiments blackbirds (Turdus merula). Behav. Processes, 13: 311-325.

in

In acoustical stimulus-response tests on European blackbirds (Turdus merula) in cages and an outdoor aviary, alteration in heart rate (HR) was used to measure reaction strength. HR was measured by radiotelemetry. The miniature transmitters newly developed for this task had to fulfill the following requirements: Simultaneous recordings of HR in several interacting animals; uninterrupted transmission and of HR signals, sufficient range and battery life combined with low weight easy handling properties. The miniature transmitters successfully used in this experiment had a quartz-stabilized oscillator. They weighed between 4.1 and 5.2 g and had a range of 3 m and a lifetime of 72 hrs (circuit diagram, Fig.1). The transmitted signal corresponded to a unitary impulse representing the S-wave of the ECG (Fig. 4b). Implanted electrodes were used to record ECG potentials. The transmitter was carried by the birds like a small rucksack tied to their backs. Electrode implantation and transmitter installation are described in detail. HR signals stored on audio tape were later transformed to frequency curves on a chart recorder (Fig. 3, 4a). Typical HR response curves are shown (Fig. 5). Statistical analysis of the data was performed on a DEC-PDP-11 computer using a special set of programs. The system has been successfully used to provide answers to experimental questions not previously obtainable with classical methods. Key words: radiotelemetry, miniature transmitter, European blackbird, experiments, behavioural response, heart rate alteration, acceleration, ation, reaction strength, computer analysis system.

playback deceler-

INTRODUCTION Radiotelemetric data in animals experimental

without

apparatus

been developed, (Kolz et al., meters

methods

offer a very effective

the usual disturbances (Kimmich,

ranging

strategy

biological

due to the experimenter

1980). Therefore,

from tracking-transmitters

1978) to implantable

to obtain

and to the

a large variety

of systems has

using satellite

relay stations

systems measuring

several

physiological

para-

at the same time (Fryer et al., 1975).

Heart

rate

influences

(HR)

(e.g.,

of

Andersen,

Gessaman,

1979; Butler,

an

more

even

"emotional"

birds is affected

Berger et al.,

1980; Smith and Worth,

interesting

effects

1961;

by quite a

aspect

(Gabrielsen

of

1970; Aulie,

1980; Kanwisher

of this field

et al., 1977;

number

are

HR

physiological 1971; Flynn and

et al., 1981). Yet

alterations

Smith and Worth,

1980).

0376-6357/86/$03.50 0 1986 ElsevierSciencePublishersB.V. (BiomedicalDivision)

due

to

Special

312

attention Bilsing

has been directed and

Schneider,

experienced Parker,

during

1978;

Kanwisher

the approach

(Bilsing

et al.,

of a predator

(v.

and

Schicknick,

1978) and

fear,

Frisch,

1966;

1978;

mainly

as

Mueller

and

so far.

Yet

1980; Jones et al., 1981).

The

effects

of acoustical

on

HR responses

information very

helpful

(cf.

Thielcke,

in response to

to social relations

1970; Bergmann

the behavioural addition,

the

could also be evaluated. the evolution to

1984),

of these acoustical

special

including

some

system

newly

1. Possible

short-term

requiring

terms

to

be partially

could be used

value

of

the

these birds

concerning

experiments

of HR in

was necessary.

In

(Diehl,

small

birds,

designing

the

had to be fulfilled:

without

should

disturbances

run in an outdoor

be

faithfully

were needed.

aviary

of

2.5

x

3

m,

animals

in

range of 2 - 3 m.

to measure

in

for ethological

of HR to single stimuli

recordings

interactions

of their HR alteration.

transmitters

general

by heterospecific

and recording

components,

responses

a transmitter

3. It was intended

and the communicative

required

requirements

thus continuous were

in

be

of HR alteration

by conspecifics

of sounds produced

for transmission

developed

the following

2. Experiments

and ethology

signals.

properties

transmitter,

recorded;

could

These results may also lead to new insights

the special

a

importance

sounds

1982). The measurement

of sounds produced

effects

been studied

and heterospecific

in bioacoustics

and Helb,

to the large variety

In

Due

on HR have rarely

in solving many problems

ascertain

signals.

stimuli

to conspecific

of two or more experimental

Therefore

same experimental

it had to be possible area

simultaneously

to run several without

mutual

interference. 4. In

order to rule out disturbances

weight 5. To

had to be sufficiently

allow

sufficient

experimental 6. The the

a battery

of data recording,

type of experimental

Lengthy

manual

suppression In

adaptation

situation,

methods

this

developed

analysis

programs

paper,

of the behaviour

by

the

transmitter,

its

low - below 5 - 10 % of body weight. of the animals life of several reduction

to the

transmitter

had to be tailored

raw data and to the requirements

in totally

we will describe

computerized and discuss

the

days was necessary.

and analysis

had to be avoided

and

as well as analysis

of the complicated

to

statistics. artifact

systems.

how and to which

degree

the

newly

system meets the above requirements.

MATERIALSAND METHODS 1. Experimental animals Experiments testing some of the system components (electrodes, transmitters, harness) as well as the actual stimulus-response tests were performed using European blackbirds (Turdus merula). A total of 10 birds (5 male, 5 female) were used. 5 birds had been caught in the wild as adults, whereas 5 had been hand-

313

raised. There were several reasons to choose the blackbird as experimental bird. It and its body weight (70 - 90 g) has a relatively low level of motor activity, weights which seemed to be attainable without extreme permits transmitter The most important reason for choosing blackbirds lies in the technical effort. fact that they belong to a class of bird species showing no obvious behavioural 1982, 1984). responses to playback of calls or single strophes (cf. Dabelsteen, This is in contrast to many other species of songbirds which feature a of behaviours in reaction to playback of calls or song quantifiable inventory strophes (cf. among others: Helb, 1973; Becker, 1976). It was, however, expected that blackbirds would show responses to calls and song strophes in form of HR alterations. 2. Electrodes The electrodes to be used for recording cardiac potentials had to be durable Needle electrodes simply inserted into the skin easy to apply to the birds. and 1980; Zimmer, 1982) turned out to be too loose. They either fell (Ferns et al., Thus, only the skin by their own weight or were plucked out by the birds. off satisfactory. An electrode similar to the one implantable electrodes were These electrodes successfully used by Stijhr (1982) was used in the experiments. which consisted of a 0.3 mm diameter stranded stainless steel wire (7 strands) teflon coated (Medwire, 316 SS 10T). The wire was pushed into a piece of was Detakta) and held in place by silicon rubber tubing (0.3 mm inner diameter, silicon rubber adhesive (Silastic). One end of the wire was then freed from the teflon and fed into an injection needle (0.3 mm inner diameter, coating This stainless steel tube was bent to a ring of 3-4 mm diameter, Plastipak). which was then pressed flat. The other end of the electrode wire was soldered to Electrode length depended on the site of an IC-socket contact pin (Carry). electrode placement: lo-13 mm for implantation at the right shoulder, and 50 or 40 mm for implantation at the left side of the abdomen or at the uropyge, respectively. 3. Transmitter 3.1. Circuit Transmitters currently used for telemetry on small animals (e.g., Stohr, 1982; Plonait and Biittner, 1984) have a free-running oscillator, which usually has rather poor frequency stability. This is in part due to the continuously changing capacitance between the transmitter and the animal's body. If several transmitters of this type were to be run simultaneously, the frequency bands must be far apart to maintain unambiguous assignments between transmitters and receivers. In addition, receivers would have to be continuously readjusted to the changing transmitter frequencies to ensure uninterrupted recordings. These properties of free-running oscillators would make them not very useful in experiments where simultaneous continuous recordings from several interacting animals are required. The use of transmitters with quartz stabilization would-5 be a solution to this problem, since they offer a frequency stability of 10 . However, these transmitters have a higher power consumption, require more space and are more difficult to modulate than free-running transmitters. The actual task of the transmitter design was to meet the requirements of size, weight and battery life with a quartz stabilized transmitter in spite of the above disadvantages. When selecting the transmitter frequency, a compromise between conflicting properties had to be made. On one side, a very high frequency (>lOO MHz) would have permitted a very small antenna. This, however, would have meant a very high energy consumption. This is due to the fact that quartz crystals operating in the fundamental oscillation mode are only obtainable with frequencies up to 30 MHz. Higher frequencies can only be achieved by operating the quartz at a higher odd harmonic of its fundamental frequency. Operation at the higher harmonics requires a higher energy input to achieve oscillation. In addition, an LC-filter circuit is needed to select the required harmonic component. We chose crystals operating between 27.5 and 27.9 MHz (3rd harmonic; details see Fig. 1) encapsulated into a package

314

amplifier

Fig.

1. Circuit

BC 121 yellow 4700 pF, R2 1.2 M, coil:

L

diagram

C3 0.01 uF, R3 4.7 M, 2.2pH

bischofsheim).

of

(Siemens).

1 4 I I I

Schmitt

trigger

the

transmitter.

;

T

Capacitors:

I

Transistors:

(Jahre). Battery:

R8 100 k, Crystal:

B 3V lithium

Tl BC 201 yellow,

Cl, C6 0.22 uF 20V tantal

C4 3.3 pF, C5 18 pF (ceramic, R4,

oscillator

Resista).

Resistors:

R5, R7 47 k, R6 1 M, R9 180 Q 27.

..

T2-T5

(Ero-Tantal);

Rl lOM,

(Siegert).

MHz (Kristallverarbeitung

C2

HF

Neckar-

cell 70 mAh (Sanyo).

HC-45/U. The necessary filter assembly was kept small by using a miniature coil amplitude or frequency modulation is difficult in a quartz assembly. Since oscillator, a simple on-off modulation was used. The RF oscillator had to be switched on for about 20 ms each time a prominent voltage peak in the ECG was reached. This peak turned out to be the S-wave of the ECG. To achieve on-off control of the transmitter, the ECG signal (about 1 mV) amplifier had to be amplified to almost full battery voltage (3 V). The input described by Stohr (1982) in conjunction with a Schmitt trigger (T3 + T4) proved The capacitor C2 prolongs the time during which the RF adequate for this task. is switched on, so it can reach its maximum amplitude. oscillator In addition, the bandwidth of the transmitter signal is widened, which makes it a little easier to tune the receiver. The short switch-on time of the energy-consuming RF oscillator helps in attaining a long battery life of the transmitter. On the receiver side, commercial shortwave receivers can be used. Demodulation of the on-off transmitter signal was achieved by adding an auxiliary oscillation with a frequency deviating by 1 kHz from the transmitter frequency. This mixing produces an oscillation pulse in the audible range which can be recorded on a tape recorder for later analysis. 3.2 Construction of the transmitter The transmitter was built from subminiature components as used in hearing aids, so that the whole circuitry including the lithium battery (3 V, 70 mAh, could be accommodated on an epoxy printed circuit board 32 x 9 x 0.5 mm. Sanyo) The components were soldered together under a microscope using a 5 W miniature soldering iron (Ersa) and solder wire 0.5 mm thick. The cables for connection to see Fig. 2) were made from highly flexible the electrodes (Ca, Cn; stainless silicon rubber isolated) as used in heart pacemakers steel wire (double coiled, for humans. They had a length of IO-15 mm and 1.4 mm diameter. A miniature connector made from a single contact of an IC socket was used to make the connection to the electrodes.

315

Schematic drawing of the transmitter, including silicon rubber Fig. 2. encapsulation, fixed to the harness. B = battery, Ca = active electrode connection, Cn = neutral (reference) electrode connection, El = electronics, En = encapsulation, H = harness, Q = quartz.

To provide mechanical protection, the earlier versions of the transmitters were embedded in silicon rubber (RTV HB, Hobby-Technik). In later models a polymer coating (455 D, Wacker-Chemie) that was applied by immersion was preferred because of its reduced weight. A piece of stainless steel wire (8 cm long) proved to be sufficient as antenna. The battery was partly kept free from coating to solder the cable on the battery and to simplify battery changes. To put a transmitter into service, the battery was connected to the circuit by soldering. A total of 5 transmitters were built and used in the experiments (Diehl, 1984). Their size was 33 x 10 x 7.5 mm and they weighed between 4.1 and The range of the transmitter was 3 m. 5.2 g, depending on the type of coating. Battery life was approximately 3 days. 4. Harness In the literature, some methods for fixing a transmitter on a bird are described (e.g., Cochran et al., 1967; Bray and Corner, 1972; Martin and Bider, 1978; Raim, 1978). Most of them did not seem adequate for our experiment, since we needed a simple method to fix the transmitter to the bird rapidly and reversibly but firmly. Our design follows that of Godfrey (1970), who used a similar "harness" to fix a tracking transmitter (5 g) on American woodcocks. We cut a harness, adapted in size to the blackbird, from a domestic rubber glove. It weighed 0.6 g and looked somewhat like a bolero-vest. The transmitter was glued to the harness with Silastic adhesive. 5. Signal reception The transmitter signals were received with a shortwave receiver (Kenwood R600). In laboratory experiments a wire wound around the cage served as antenna. For experiments in the outdoor aviary, the wire antenna was put inside the aviary and tuned to the transmitter frequency. 6. Data recording and reduction HR signals from the receiver were recorded on track 1 of a stereo tape recorder (Uher 4200 report monitor) at a tape speed of 4.7 cm/s. Track 2 was used record the acoustic stimuli played back by a tape recorder (Uher 4000 report ::,, event marks, and additional comments made by the experimenter. In a first stage of analysis, the 1 kHz impulses representing the ECG S-wave were filtered

316

+-J

input

Dl.D2=1N4448

I

IK

I_ ~‘

O.lb+

_ T

+ i~356

Circuit Fig. 3. diagram of the frequency-to-voltage converter (F/U) (instantaneous frequency measurement). At each input pulse, a linear ramp is started. The next impulse reads the ramp height into a sample-and-hold, then resets the ramp. S&H voltage thus is proportional to time between impulses. The analog divider converts this to a voltage proportional to instantaneous frequency. and fed into a Schmitt trigger (Fig. 3). The trigger level was continuously checked with an oscilloscope and adjusted to maintain optimum signal-to-noise A monostable circuit was used to block spurious impulses directly ratio. following a trigger impulse. The digital signal thus gained was fed into a frequency-to-voltage converter. It used a linear ramp to produce a voltage proportional to the time elapsed between two impulses. This voltage U was stored in a sample-and-hold circuit and then transformed into l/U using an analog divider circuit. Thus, the output voltage was a linear function of the input frequency. At each heartbeat the output voltage was set to a new voltage representing the instantaneous frequency of the previous heartbeat interval. The accuracy of the circuit was on the order of 1 %. The output of the instantaneous frequency meter was connected to a chart recorder running at 2.5 mm/s (Hellige He 16). An interfacing amplifier with continuously variable offset and amplification was used to calibrate the chart recorder. a tape was used For calibration, containing synthetically produced sequences of impulses with known frequencies. In general, the system was calibrated such that a HR change of 1 beat/s corresponded to an excursion of 10 mm on the chart recorder (cf. Fig. 4a). 7. Data evaluation First, reaction curves produced by the chart recorder were carefully inspected. Maxima, minima, and inflections were marked by hand. The time and amplitude coordinates of these marked points were then fed into a DEC-PDP 11-03 computer using a digitizer tablet (Houston Instruments) which had been previously calibrated. Additional data about the type of stimulus, the experimental bird, were etc. in by hand. a set of 35 variables was stored for each Thus, typed

317

t I

-10

ti

t

t I

0

tt’

t

1’

n t

I

I

10

20

I

,

t

Is1

30

Fig. 4. Typical time course of HR response to presentation of song strophes and calls. The black bar shows onset and (a) Chart record of the F/U converter output. duration of the test stimulus (T). 12 characteristic points used in the computer evaluation are marked in the response curve: A = amplitude values; t = time of occurrence of characteristic points; 01, 011, 0111 = zero-crossing No I, II, III; i1, iI = inflections No I and II. (b) Direct recording of the transmitter signals. Each oscillation pulse resulting from the S-wave of the ECG is marked as a vertical bar. The relevant information of the transmitted signal lies in the distance between the individual pulses.

experimental situation. The data input program was designed to ensure that elements located in the same position of the data array always corresponded to the same experimental variable. The data were which analyzed by means of a specially developed program, allowed the user to select one or several variables from each data set, perform operations upon them, The calculations and produce histograms of the results. involving the selected variables not restricted to addition or were multiplication. In fact, any mathematical procedure feasible in Basic programming could be performed on the variables. To achieve this, a sector in the program (set-up in DEC-BASIC 11) was left open for the user. After loading the program, the user defined the mathematical operations to be performed by inserting new lines, for example X = SQR (A* + B* + C*), into the program. At runtime, the dummy variables A, B, C were given the values of the selected variables, and the result, X, was put into the distribution routine. In addition, program lines containing selective conditions could be inserted. Thus, it was possible to extract only experiments with certain birds from the data pool for evaluation. The histogram section plotted a graph on a plotter and printed mean, standard deviation and number of experiments in the distribution. The binwidth and the scale of the distribution could be adjusted to the needs of the analysis.

EXPERIMENTAL

PROCEDURE

Electrodes were implanted one day before the actual stimulus-response experiments. For the subcutaneous implantation of the electrodes, complete anesthesia of the birds was necessary. The blackbirds were anesthetized by injection of 0.3 to 0.35 ml of a 1:3 mixture of Nembutal (Ceva) and NaCl in physiological concentration into the flight muscle. This corresponds to an anesthetic concentration of 7 - 8 mg/lOO g body weight. Normally, the anesthesia lasted about 30 minutes. If the operation time was prolonged, an additional 0.1 -

318

0.3 ml of the anesthetic solution was injected during the operation. To implant the active electrode, an incision of 3 mm length was made in the Using a wire probe, a channel directed skin at the cranial end of the scapula. The electrode was then pushed into towards the head was formed under the skin. the channel with the wire probe. When the electrode was properly placed anterior to the cranial end of the scapula and even a little further into the neck region, material ring was sutured to the skin using surgical suture the electrode from (Ethicon). only the electrode connector protruded After proper placement, the skin. The skin incision was then closed using tissue adhesive (Histoacryl blue, B. Braun). For cage experiments, the reference electrode was positioned at the lower left rib-bow. For outdoor cage experiments, the reference electrode was placed dorsally just anterior to the uropyge. In both cases, the skin incision was made end of the scapula. electrode was at the caudal Otherwise, the reference implanted in the same way as the active electrode. still In most cases, the transmitter was placed on the bird while it was anesthetized. It sufficed to place the wings through the widely expandable holes of the vest. Then, the electrode connectors were plugged in the appropriate transmitter connectors. After rearranging the feathers, the bird would carry the transmitter like a tight fitting rucksack. It was also possible to mount the transmitter on an awake bird, e.g. when the battery had to be changed. This procedure could be finished in 30 seconds. After recovery from anesthesia, the bird was transferred to the outdoor aviary or the cage. The cage was placed in an otherwise empty laboratory. The bird was observed from a neighbouring room through a viewing port.

RESULTS 1. Transmitter

compatibility

Preliminary

experiments

experimental birds

birds

sat

placement around

with transmitter

with transmitters

quietly

on

transmitter.

After about one hour,

feed.

From

this time on,

fly

with

without

the animals

range

of

weight

plumules

The

hand-raised animal

one

extensively

began to hop around deviations

In the outdoor

on their backs without

occurring

was observed

aviary,

hour

their

the The after

feathers

on parts of

in the cage and in their

the to

behaviour

the birds were able to

signs of impairment.

in body weight naturally

electrode

which were outside

from one week to

only in the cranial

the tips of the feathers

were lost during

The

vest

implantation

the maximum

another

(12

9).

part of the transmitter-

were broken.

In

and transmitter

addition,

some

placement.

Skin

were not observed. showed

birds

carried

where

zone,

irritations

This

changes

to the feathers

carrying

about

they rearranged

of

results:

in place for up to 75 days.

None of the birds showed changes

Damage

this time,

they showed no obvious

transmitters.

the transmitter

held the transmitter

During

One bird (male 3) plucked

vest.

from animals

led to similar

one of the bars in the cage for

of the transmitter.

the

dummy tags and observations

in operation

male

strong variability

pulled

the electrodes

in the acceptance out within

was not used in the experiments.

the electrodes

the surrounding

tissue.

for 4 months.

of the

a day on

On the

other

electrodes.

several hand,

By this time, the electrodes

A

occasions. female

104

had grown into

319

2. Reliability of the transmitter the system was capable

By and large, rupted

recording

disturbed

the

atmospheric trigger in

the

There were,

of HR.

of

reception

circuits.

orientation

changes

in the quality

between

experimental

of the received

The

electrodes

were placed

muscle

potentials

was

The

the requirement

a few

effects

most

common

originating

was

via the Schmitt

birds and antenna

to

suppress.

only led

to

The minor

signal. due

no disturbance

Only extreme

wing flapping

(such

to catch the bird in the cage) produced

strong muscle

signals

HR recordings

sometimes

disturbance

from other transmitters

were more difficult

in such a way that almost

observed.

of uninter-

that

out to a large degree

Signals

busy 27 MHz band sometimes

variable

attempts

signals.

which could be filtered

noise,

and other filtering rather

HR

of fulfilling however,

as

to

during

that

made

impossible.

The most prominent IC-connector

cause of system

and the electrode

or 2 days, thus impairing

wires.

long-term

failure was the soldered These connections

joints between

sometimes

the

broke after

1

experiments.

HR[b/s]

a

b

C

I

,

I

-10

I

0

I

10

I

I

20

30

.

t

kl

Fig. 5. Typical heart rate curves in response to acoustical stimuli: T = duration of the stimuli; stimuli start at t = 0. (a) Response to a conspecific song strophe; this type of response curve is most often found. (b) Response to a conspecific call. (c) Heterospecific song strophe thrush, Turdus philomelos) is presented: no reaction can be seen. (The (song arrows in (b) and (c) point to artifacts.)

320

3. Sample HE recordings A

series

acoustical time

of

typical

HR response

stimulus-response

course

of

acceleration

followed

acceleration,

the system returns

by

5b shows a HR response a technical Here,

in

to the presentation

deceleration

of

phase is

to the initial

observed.

or a different

In Fig. 5c, a heterospecific

in the HR to the test stimulus

examples

of HR response

response

parameters

three

different

conspecific

to an alarm call: a pure acceleration.

disturbance. response

no

a

as recorded

is shown in Fig. 5. Fig. 5a shows the typical

tests,

the HR response

curves,

curves and the results

song:

After

a

an

second

new HR level. Fig. The arrow points to

song strophe

is presented.

can be observed.

of the statistical

see Diehl and Helb (1986a), Helb and Diehl

For

further

analysis

of the

(1986).

4. Data analysis The

stimulation response

yielded

stimulus-response the

experiments

curves.

transcription

response

took

only

3

parameters.

experiment, diskette

it

plotting

was

data

statistical involving

inflections

possible

file.

analyses

selection

Using

and marked

the

of the distribution distribution

results

(Diehl,

chart

a very large variety

curves,

was

recorder fact

in various ways, and points

number

the

of

(such

of

calculation

a

per

single

criteria,

One "statistical

of derived

of one of these quantities

on

selective

it

additional

parameters

to store the data of all 1000 tests

of reaction

months

lies in the

curve and to type in

restricted

were drawn from the same data base.

of 1200 different published

to

3

acoustical

levels) were put into the computer,

one response

Due

to the graphs

Since only characteristic

and initial

min to digitize

experimental

by inspection

and corrected.

of

about 650

part of the data analysis

of these chart recorder

classified

can be detected minima,

over a period

containing

The most time-consuming

The advantage

that they can be readily

as maxima,

1000 tests,

the raw data on the tape recorder

of

curves.

artifacts

using 8 blackbirds

curves from about

quantities

all run'

9

and the

took only 3 min.

A total

plots were made from the data base and used in the

1984; Diehl and Helb,

1986a).

DISCUSSION 1. Electrodes

and implantation

The bipolar tioning

electrodes

the reference

ly good signals.

most prominent

ECG

recordings

or near the uropyge

(1976), we found in on-line

signal of the ECG is the S-wave

with electrodes

potentials

rings was firm enough, avoided

along "lead II" (Sturkie,

on the abdomen

As stated by Sturkie

the

from muscle

were positioned

electrode

in this position

(cf. Sturkie,

1974; Kuhn,

methods

sewing

equal-

recordings

electrode

gave the smallest

1963). Subcutaneous

so that more complicated

(e.g., Sawby and Gessaman,

in this

1976). Posiyielded

that

position.

disturbances

of the electrode

of implantation

1981, pers. comm.).

could be

321

The

small

electrode the

deformations

were plugged

solder

joints.

experimental

birds,

simplification Nembutal although 100

%

occurring

together

may have contributed

To reduce

this technical

and the time and effort

of the electrode

the dose required higher

design

required

transmitter

and

fatigue

disturbances

in

of

for implantation,

the

further

is planned.

for sufficiently

than recommended

of

to the premature

difficulty,

a sodium-pentabarbiturate,

(Ceva),

(Parke-Davis)

when the connectors

proved an adequate

anesthetic,

deep and long anesthesia

by Kronberger

did not meet the requirements

(1978).

The

with respect

about

was

anesthetic

Ketanest

to the duration

of

the

anesthesia. Although could

be

we did not use a gaseous advantageous

because

anesthetic

such as Halothan,

it offers very precise

control

think

we

it

of the

anesthesia

either

too

(cf. Bilo et al., 1972).

2. Construction The

ECG

(Thompson

transmitters

et al.,

and Amlaner, lifetime

was

Tupaia,

described Studier

1968;

1980;

transmitter

of

of the transmitter

Gessaman,

too

short

built

presented

another

5 m and a lifetime

is that of Plonait

1980;

(Ferns

by Stohr

in the literature

and Howell,

Smith and Worth,

et

al.,

1980).

difficulty.

Although

of 3 - 5 months,

because

short time recordings

of HR in several

is one of the prominent

lifetime

present

an

outweighed Since become

important

development available

version,

still

weight

of3g.

smaller

birds.

The weight on

disadvantage stability

which

This makes

different

observed (1980)

of transmitter

bird species

quantifiable Kanwisher

unobjectionable. body

weight

et

Cochran as

Transmitter

disturbances, al.

transmitter reached

Siegfried

(1981) regarded

in songbirds.

by

components

performance.

a lifetime

far

have A

new

of 40 days at

of longer duration

of

of disturbance

(1973) and Amlaner et al.

transmitter

et al. (1967) even considered

tolerable

and

did not

and are

to 5.5 - 7.0 %

degrees

and Sargeant whereas

The

weight

the

a on

body

loads in this range have been used

with very variable

Greenwood

so far,

new electronic

amounted

(nor

system.

to plan experiments

and harness

birds.

Boag (1972),

and

it possible

in

for simultaneous

of our transmitter

in the experiments

the

the

ECG

1.5 g, and has a range

for the higher

properties

stage,

the

birds (or other animals).

reasons

of the quartz

help to improve

in the developmental

weight

These

exception, of

it is not quartz-stabilized

interacting

of our system was begun,

of the experimental

behaviour.

of

of our transmitter.

by the improved

single

1984), it would not be suitable

quartz-stabilization shorter

or their battery

recording

it weighs

heavy

et al., 1977; Ball

1980),

The

(1982) for the telemetric

and Biittner,

were

1969; Gabrielsen

Studier

(1977), weights

transmitters and

of

Howell

normal

et al. (1978)

of

Gessaman 5

%

as

weighing

15 %

(1969)

used

322

transmitters

weighing

the bats naturally The natural we

as much as 40 % of body weight

exhibited

weight

weight

changes

fluctuations

occurring

in our blackbirds

found that none of the birds carrying that all birds showed normal

and were

not

disturbed

measurements

below values found in the literature

that

This conclusion values

the transmitter

Helb and Diehl,

does not disturb

also

supported

by

In addition,

1985b).

the transmitter

supports 1985a;

the birds (Diehl and Helb,

the

the view 1986b;

1986).

All these findings

support

tests

stimulus-response experiments

is

reductions,

that the birds

that in some cases were clearly

(Diehl and Helb,

that birds will sing while carrying

However,

were 10 %. In addition,

showed weight

These facts indicate

behaviour.

which yielded

of HR at rest,

observation

transmitters

by the transmitter.

species.

in a bat

up to 40 %.

the acceptability

generally

of this radiotelemetric

(Diehl,

especially

1984),

1986a) or conspecific

of song (Diehl and Helb,

vs.

method

in

in

playback

heterospecific

calls (Diehl and Helb, in prep.).

3. Data storage and evaluation The

preliminary

Kanwisher

et al.,

storage 1978;

amount of heterogeneous (cf.

e.g. Zimmer,

tively

and

the

of the experimental

1984) permits

Evans et al., data in a shorter

1982). In addition, signals

data on tape (cf.

the acquisition

time than with on-line

tape-recorded

can be processed

among

others,

of a large

chart

recorders

data can be evaluated

electronically

(filtering)

selec-

to

reduce

artifacts. Compared (Zimmer,

to

the

1982;

converter) precision

recording

Bastian,

measured (cf.

and manual measuring

1984),

HR greatly

Kanwisher

chart

simplify

et al.,

1978;

Since HR values can be read directly HR alterations

can be recognized

of the heartbeat

(missing

The the

fine details

present

impulse

per

battery

life. Where

ordinate these

investigations. heartbeat

values,

cases,

The

reduced

reduction

the energy

strong arrhythmias

average

and Searcy,

1980; Stohr,

F/U-

1982).

tendencies

Small and short-term

as well as external

of

variations

artifacts

(cf.

of the ECG were not needed

of the transmitted

requirements

yielded

signal

and thus

large variations

arises as to the definition

calculated

(by

increased

and can be spotted with ease.

in the QRS waveform

some difficulty

the

arrhythmias)

heartbeats

while offering

as amplitude-time-functions,

reproduced

contained

Dooling

individual

of the electronically

the evaluation

at first glance.

beats,

Fig. 5b, c) are faithfully

records

of

from two consecutive

in

to

one

increased

the

of consecutive

HR

of the "true" HR. In ordinate

values

was

taken as the actual HR. The vast amount of data would have been almost computer. typed-in

The digitizing experimental

of manually

parameters

preprocessed

impossible

to analyze

HR reaction

turned out to be a sensible

without

curves along compromise

a

with

between

323

all-manual

very

impulses

by computer.

to

complicated

suppress

of the reaction

measurements

tape recorder

screen

analysis,

the latter method,

the data for different

all kinds of artifacts.

appropriate

curves and the direct

Using

This preselection,

since the raw results

analysis

HR response however,

of ethological

the

of

it would have been and

types

is essential

experiments

to

for an

can rarely

be fit into a rigid scheme. The 1985 the

results

of experiments

a,b) show that radiotelemetric effects

and meanings

of the methods Apart

of a first series

from

reactions

experiments

HR recordings

1984;

can yield new

of songs and calls in blackbirds.

will allow experiments

of juvenile

(Diehl,

with smaller

songbird

with adult male and female

birds and interactions

between

birds,

Diehl and

Helb,

insights

about

Further species we

improvements in the field.

intend

these different

to

study

groups.

ACKNOWLEDGPMENTS We would like to thank Prof. Dr. E. Tretzel for the generous support of the radiotelemetry program, and Dipl.-Ing. W. Baus for his continuous interest in the development and construction of the transmitters. A large contribution was made by Dr. W. Stohr (Bayreuth) and Dipl.-Biol. H.-V. Bastian (Tiibingen), who helped with unstinted advice. Finally, we gratefully acknowledge the support of several companies that reduced our development costs by donating some of the material required. We also thank Mrs. G. Seidel and Mrs. S. Watt for typing the manuscript and Dr. M.A. Biederman-Thorson (Oxford) for correcting our English manuscript.

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