Ficure 1. Two oscilloscope tracings of chirping field
“crickets (oscilloscope dial multiplier = 5). Two
horizontal scale units = 0.0010 seconds. Fre-
quency = 6000 cycles/second.

fe TT
Le,
aan

Ficuns. 3. Tracing of a portion of the sound spectrum of
& the Tockh Electra showing the Jow fre-
quency carrier wave (about 400 cycles/seconds)
with superimposed intermittent high frequency
waves of 6,000 cycles/second. For this tracing,

the oscilloscope multiplier is 8, and 1.25 hori-
zontal scale units = 0.0010 seconds.

Ficure 4. Fast trace of Electra sounds (multiplier = 2).

Ficune 2. Faster trace of field cricket sounds (multiplier =
2). Five horizontal scale units = 0.0010 sec-
onds. Note the head and shoulder wave form

appearance of the thrce waves forming triplet
sets.

Five horizontal scale units = 0.0010 seconds.
Compare the wave form of these Electra trip-
lets, with those of the crickets in figure 2. The
oscilloscope sweep setting is identical in figure 2
and figure 4. Note that the individual triplets
in this Electra tracing, receive a slight base-
line distortion in accordance with whether or
not the slow wave is descending or ascending,


The following is a sample quote taken from
notes of the field observers: “When the Elec-
_ tra was about halfway down the taxiway from
the terminal, the sound became more noticeable.
We noticed a relatively large flock of starlings
rise up from the side of the runway. The birds
maintained an airborne position to the rear
(downwind) of the plane during its ground
operation, at a height above the ground of less
than 100 feet, with an angle of elevation of 45°
from the ground with reference to the Electra.
Birds seemed confused; flocks dipped and dived
in various directions, but maintained their same
telative position with refercence to the aircraft.
During take-off, the birds followed the plane a

of the runway.” .

Tt was observed (S. R. M.) that a large num-
ber of singing field crickets sound strikingly
similar to a taxiing Electra. This is particularly
so when one drives along a country road in the
late summer at about 20-30 mph and experi-
ences the fusion of individual cricket sounds into
a sustained chorus, ‘Starlings have been ob-
served to cruise at 20-30 mph, and would ex-
perience a similar sustained exposure to the
cricket sound sources,

These observations seemed to justify further
| study. The Electra sound spectrum and that of
field crickets were recorded on an Ampex Model
970 tape recorder and fed into a Hughes “mem-
oscope” oscilloscope model 105, for analysis.
| Crickets’ chirping was found to be a mixture of
two frequencies, namely 6000 and 2000 cycles
per second (Figs. 1 and 2), and appears to con-
sist of sets of three main vibration waves, The
center wave of this triplet has'a greater ai ip-
litude than the other waves, giving’a “Head
; and shoulder” appearance to the triplet. The
Electra sound (Figs. 3 and 4) has a slow carrier

high frequency waves of 2/1000ths to 6/1000ths
of a second duration, superimposed intermit-
tently, at a rate of 100 to 300 per second. This
intermittent high frequency wave has the same
“Ttead and shoulders’ appearance (Figs, 4) and
is practically identical in frequency and wave
form to that of the crickets. This explains the
chirp or twitter in the Electra sound, which is
mentioned earlier in this paper.

short way and then settled back along the side -

wave Pte cycles per second), with pulses of -

DISCUSSION

The Lockheed L-188 Electra was first flown
on December 6, 1957, It is used for short and
medium-range commerical transport ( 66-99
passenger). The L-188C model has four Alli-
son 591-D13_ single-shaft turboprop engines,
each rated at 3,750 e. h. p.

Starlings in the U. S. now number in the
hundreds of millions. We are experiencing a
starling population explosion, a curious conse-
quence of the placement in New York’s Central
Park of 100 starlings by the Englishman, Eugene
Schieffelin, in 1890 and 1891 (Reference 5).

A large proportion of the diet of starlings
(almost half) consists of crickets and other in-
sects (Reference 7). Phonoreception in birds
is highly developed, and provides for both ac-
curate localization of sound and excellent fre-
quency discrimination (Reference 3, page 490).
These facts, coupled with the need of migrating
starlings (as in the long north to south trips in
the fall) for considerable amounts of food, en-
able the starling to learn to locate food by hom-
ing on singing insects.

Field crickets sing a great deal in the Midwest
and South during the late summer and early
fall mating period. Fields of singing crickets
can set up a din which exceeds the seventy deci-
bels of sound intensity common to busy streets
(Reference 3, page 473).

For reasons not yet clear to ornithologists, a
certain per cent of the birds in the Northeast
who customarily ‘migrate to the South in the
winter, miss the fall signal and overwinter in
the Northeast (See Reference 12 for a discussion
of bird nigration, with particular reference to
newly expande(i’ species in a new geographic
area), For these stay-at-homes, the first cold-
snap is quite a shock, in that the insects dis-
appear, by and large, leaving the birds a meager
available food supply. It probably takes several
weeks for these birds to discover new and ad-
equate food sources for the winter, In the
process, numbers die in the. cold of starvation.
Should an early fall snow appear, the food situa-
tion for the starling beconies particularly acute.


It is understandable why, under conditions
such as these, a sound which simulates a field
fecund with singing crickets, would have a
strong appeal for hungry starlings. Curiously,
the elimination of certain arbage dumps could
potentially aggravate the Bod stortage of these
nonmigrating starlings.

The common field cricket is a leaping or-
thopterous insect of the family Gryllidae, genus

| Gryllus. The male cricket’ produces sounds
through rubbing together his forewings which
contain little files and scrapers (Reference 2,
page 62). Other types of crickets, such as the
. snowy tree cricket, produce characteristic, easily
| recognized, tunes, This latter cricket is known
as the “temperature cricket,” since it varies its
tempo, but not pitch, with temperature. The
number of notes per minute, plus forty, divided
by four, gives a rough estimate of the tempera-
ture in degrees Fahrenheit. The pitch of cricket
sounds doesn’t change very much with
changes of temperature, since the pitch is deter-
mined by the mechanical characteristics of the
exoskeleton. The tempo changes with tempera-

ture, since the cricket is cold-blooded, and its’

metabolic rate increases with increasing envi-
ronmental temperature.

Insect music has been recorded by other
workers (Reference 9), and they have noted
that the field cricket chirps, lasting for a fraction
of a second, consist of three pulsations, each
pulsation consisting of a slur, with the! pitch
somewhat lower at the beginning and end of
each chirp. Our findings confirm this past
work. Also, crickets produce pure-tone sounds,
in contradistinction’ to other insects, such as
katydids, and the over-all pitch of the cricket
chirp is in a range about one octave above the
highest note on the piano (Reference 6 page
1442),

It is a curious fact that sounds produced by.

a number of mechanical devices have been
noted to accidentally simulate very closely the
singing of crickets.” For example, it has been
observed that the sounds of crickets are almost
identical to the tinklings of little bells used by
Far East priestesses in sacred dances (Reference
10). The shuttle used by weavers operating
certain types of looms, has accidentally pro-
duced tones which closely imitate the sounds of
crickets (Reference 2, page 72), The faraway
jingling and ringing of the old-fashioned bridle

bit simulates the song of the cricket, as does an
electric bell heard from a distance (Reference
11).

Within the above framework, we begin to see
a basis for the starling-Electra relationship, and
the major reason why, as noted by other persons
(Reference 4, page 2) the autumn period
in the Northeast is the most hazardous time for
Electra bird ingestion.

CONCLUSIONS

The Electra sound spectrum contains an
audible chirp which appears identical in fre-
quency and wave form to the chirp of field
crickets.

Field observations of bird activity in the
vicinity of the airport during Electra opera-
tions, strongly indicate an attraction of starlings
and possibly other birds to the sound of the
Electra. :

Since over 402 of the starling’s diet consists of
insects (crickets, grasshoppers, etc.), it seems
reasonable to assume that the starlings are at-
tracted to the Electra by being misled into the
belief that there is a feta of crickets at the
source of the Electra noise.

RECOMMENDATIONS

Since starlings are rapidly multiplying in the
United States and the severe consequence of
bird ingestion by a commercial carrier was
clearly demonstrated by the October 4, 1960
Boston crash in which sixty-two persons died;
and'since this study has shown that starlings are
quite likely attracted by the chitp in the Electra
sound spectrum, consideration should be given
to taking steps to eliminate the sound frequen-
cies in’ these aircraft responsible for this chirp.
ing noise. This.could probably be done through

Felatively minor structural changes in the Elec-

tra power plant package, or a change in the
Electra’s taxiing rpm.

The changes could encompass (1) the elim-
ination of the positive soviotropic vibrations,
(2) masking of the positive sonotropic vibra-
tions, (3) addition of frequencies which repel
starlings (negative sonotropism), or (4) other
means which do not involve modification of the
Electra (e.g., sound decoy of starlings to sites
other than the airports, etc.),

-4-


AD->Fo ale

doin reiiininanba aie

- dre EFFECTS
)MMERCIAL

AiR TRANSPORT SOUND
ON BIRDS

FEDERAL AVIATION AGENCY

Civil Aeromedical Research Institute
AERONAUTICAL CENTER
OKLAHOMA CITY, OKLAHOMA

MARCH 1962



In planes non-modified along the above lines,
particular caution must be exercised during the
autumn period in the Northeast, since this
would be the time of the predicted greatest
affinity for the Electra by the starlings.

ACKNOWLEDGMENTS

The authors wish to acknowledge the assist-

ance given by Mr. J. D. Gamer and Mr. E. B.
McFadden in field observations, and Mr. Jack
Earley for the oscilloscope analysis,

REFERENCES

1. Heilbrunn, L. V., An Outline of General Psysiology,
Second Edition, Revised, W. B. Saunders Co., Phila-
delphia, 1943.

2, Stillson, Blanche, Wings, Insects-Birds-Men, Bobbs-
Merrill Co., New York, 1954.

3. Prosser, C. Lad (Editor), Comparative Animal Phy-
siology, W. B. Saunders Co., Philadelphia, 1950.

4, Aldrich, J. W., Robbins, C.’S., and Dykstra, W. W.,
Bird Hazard to Aircraft, Wildlife Loaflet 429, United
States Department of the Interior, Jannary 1961.

5. “Starling Menace Rises in Jet Age”, The New York
Times, Tuesday, May 23, 1961.

6. Glasser; Otto (Editor), Medical Physics, The Year Book
Publishers, Chicago, 1944.

7. Kalmbach, Edwin Richard, “Economic Value of the
Starling in the U. S.", U.S. Department of Agricul-

FAA AC 62.2577

8.

9.

10.

iL

Lex

ture Bulletin 868, U. S. Government Printing Office,
1921. (Kalmbach authored additional pamphlets; one
in 1922 on “Food Habits of Starlings”).

Regen, J., “Hearing in Gryllus,” Sitzungsh Akad, Wiss.
Math-Nat., K1. 1, Wien, 132: 81-88, 1923.

Lutz, Frank E., A Lot of Insects, G. P. Putnam’s
Sons, New York, 1941.

Priest, Alan, “Insects: ‘The Philosopher and the Butter-
fly”, The Metropolitan Museum of Art Bulletin,
Vol. 10, No. 6, 1952.

Hearn, Lafcadio, “Insect Musicians of Japan,” Exotics
and —Retrespectices, Little, Brown and Co., Bos-
ton, 1908.

Sauer, E. G. F., “Further Studies on the Stellar Orien-
tation of Nocturnally Migrating Birds”, Psychologische
Forschung, Vol. 26, No. 3, 224-244, 1961.



SONOTROPIC EFFECTS
| OF COMMERCIAL AIR TRANSPO:

JOHN J. SWEARINGEN, M.S.
Chief, Protection and Survival Branch
Civil Aeromedical Research Institute

and

STANLEY R. MOHLER, M.D,

DIRECTOR

Civil Aeromedical Research Institute

{ . FEDERAL AVIATION AGENCY me
AERONAUTICAL CENTER

i CIVIL AEROMEDICAL RESEARCH INSTITUTE

! OKLAHOMA CITY, OKLAHOMA

March 1962



SONOTROPIC EFFECTS
OF COMMERCIAL AIR TRANSPORT SOUND
ON BIRDS

John J. Swearingen, M.S, and Stanley R. Mohler, M.D.
\
\

The Electra sound spectrum contains an audible chirp which appears identical in
frequency and wave form to the chirp of field crickets. Field observations strongly indicate -
that the sound of the taxiing Electra exerts an attraction for starlings, and possibly other
birds, particularly in the fall in the Northeast, when insects suddenly become less plentiful.
The implications of this attraction, “positive sonotropism”, for air safety, are discussed,

Recommended approaches to alleviating this type of bird hazard are presented. oy

INTRODUCTION

In the fall of 1960, there were two major in-
cidents in the Northeast U. S. (one severe crash
and one aborted take-off) when Lockheed
Electras ingested large numbers of starlings, On
other occasions, large flocks of starlings gather-
ing around Electras soon after engine starting,
have forced the pilot to stop the engine to pre-
vent bird ingestion.

Sounds from inanimate devices have been ob-
served to exert a marked attraction for various
animal species, For example, fish have been at-
tracted by certain musical notes (Reference 1,
page 618), and female crickets have been at-
tracted by the telephone transmitted sounds of
male crickets (Reference 8). Similarly, a/high
frequency sound simulating the flight séng of
the female mosquito has been broadcast in the
Cuban swamps te attract male mosquitos
(Reference 2, page 54). For centuries, bird
watchers have attracted birds by twisting’ a

rosin-coated pewter peg within a small birch- ©

wood block (the Audubon Bird Call, by Roger
Eddy, Newington, Connecticut), Also, bird
watchers make a high-pitched sound by kissing
“the back of their hand (“squeaking”), which
_ attracts birds.
One of us (J. J. S.) noticed a twittering sound
mixed with the other sounds generated by the
Electra, and suspected that this relatively high

frequency twitter in the Electra sound spec-
trum may for some reason actually attract star-
lings to the aircraft.

FINDINGS

Initially, to determine whether Electra sounds
attract starlings, teams of investigators were
assigned to field positions near the ends of the
Tunway at a major airport (Will Roger Field,
Oklahoma City). These teams, equipped with
binoculars and portable tape records, observed
and recorded notes describing bird flight pat-
terns and activity during aircraft take-offs and
landings. All major types of aircraft were moni-
tored, including Lockheed Constellations,
Douglas DC-6'’s and DC-7’s, Viscounts, Bocing
707s, Convair! 880’s, Lockheed Electras, an
other heavy and light aircraft.

The numerous observations made during
December 1960, and periodically throughout
1961, indicate that during some portions of the
year (when the natural sources of food for birds
are scarce), starlings in the vicinity of an airport
appear tobe attracted by, or highly disturbed
hy, something in the sound spectrum of the
Electra. The sound generated by other turbo-
jet, turboprop, or conventional aircraft, did not
induce a recognizable pattern of response in
the starlings,

~1l-