W ildfowl (1973) 24:1 5 -2 0
The use of small airplanes to gather swan data
in Alaska
J A M E S G. K I N G
A lask a is th e cen tre o f a b u n d a n c e fo r N o rth
A m erica’s nestin g sw ans. T h e W histling
Sw an Cygnus colum bianus columbianus
nests on th e tu n d ra o f w estern an d n o rth e rn
A lask a an d east to H u d so n B ay in C an a d a
w ith th e g reate st den sity o c c u rrin g o n th e
26.000 sq. m iles (67,340 sq. km ) o f th e
Y ukon R iver D elta. T h e T ru m p e te r Sw an
Cygnus Cygnus buccinator fo rm erly nested
th ro u g h o u t a larg e p o rtio n o f w estern
N o rth A m eric a b u t is now confined to a few
isolated locatio n s in o r n e a r th e R ocky
M o u n tain s an d to p o rtio n s o f th e fo rested
regions o f A lask a. T o d a y A la sk a hosts
ab o u t th re e -fo u rth s o f th e nestin g p o p u la ­
tio n o f T ru m p e te r Sw ans an d p e rh ap s
tw o -th ird s o f th e W histling Sw ans. T h ere
a re ab o u t 22,000 sq. m iles (56,980 sq. km )
o f T ru m p e te r h a b ita t in A la sk a a n d som e
72.000 sq. m iles (186,480 sq. km ) o f
W h istler h a b ita t. S tragglers from each
species a re o ccasio n ally fo u n d w ithin
th e ra n g e o f th e o th e r b u t essen tially th ey
use w e ll-sep arated b re e d in g a re a s (F ig­
u re 1).
D ow n th e years, n a tu ra lists h av e re ­
co rd ed o b serv atio n s o f sw ans in A la sk a b u t
b e cau se o f th e larg e te rrito rie s used by
sw ans a n d th e ir w ide ra n g e in th e w ilderness
it w as n o t p ossible fo r g ro u n d -b o u n d
o b serv ers to dev elo p a full p ic tu re o f sw an
d istrib u tio n . In 1954 th e first w aterfow l
b io lo g ist-p ilo t, H en ry A . H an se n , cam e to
A lask a an d it w as im m ed iately obvious
th a t sw ans, p e rh a p s m o re th a n any avian
species, len d them selves to study fro m th e
air. Sw an studies a re ju stified fo r th e ir
ow n sa k e b u t also p ro v id e a h an d y in d ic a to r
o f th e w ell-being o f all w aterfo w l in a given
h a b ita t. W h en sw an p ro d u ctiv ity is low
-A rc tic Slope
Whistling Swan
=
Cape
RomanzofY ukon
D elta
Ne Ison
Island
Bristol
Bay
I
1
100 miles
(161 km)
Figure 1. A pproxim ate swan breeding range
in Alaska.
Trumpeter Swan
16
James G. King
m ost o th e r species a re likew ise h aving a
p o o r season, a n d conversely. In th e p a st
17 years m an y sw an d a ta have accu m u lated
a n d cred ib le a ir survey m eth o d s h a v e been
developed. W e h av e sp en t m o re tim e in th e
d ev elo p m e n t o f tech n iq u es th a n in th e ir
ap p licatio n b e c a u se as y et no o n e h as been
assigned full tim e to sw an w ork.
T h e p u rp o se o f th is p a p e r is to d escrib e
tech n iq u es w hich if extensively applied
could resu lt in a m u ch b e tte r u n d e rsta n d in g
o f sw an p o p u la tio n dynam ics. It is h o p ed
th a t it will aid p e o p le p lan n in g a ir exp ed i­
tions in g ettin g m o re d a ta fo r th e ir tim e an d
m oney.
F ive survey m e th o d s a re described: (1)
com plete cen su s; (2) ra n d o m p lo t census;
(3) line tra n se c t su rv ey s; (4) ra n d o m flight
m eth o d s; (5) ex p lo ra to ry flight m ethods.
T h e first tw o tech n iq u es a re th e m ost
p ro m isin g fo r th e exclusive study o f sw ans
an d resu lt in a census. T h e last th re e are
w ays o f re co rd in g m eaningful sw an d a ta
w hile engaged in w o rk o n o th e r species
b u t resu lt ra th e r in an index th a n in a
census. P re-p la n n in g is in each case th e key
to p ro d u cin g co n sisten t u seab le reco rd s.
Safety, visibility, speed an d ra n g e are
im p o rta n t co n sid eratio n s in selecting a
p ro p e r a irp la n e fo r b ird surveys. A float
p la n e is safest fo r w o rk in extensive w ilder­
ness area s; high w ing airp lan es a ffo rd th e
best visibility; single engine airp lan es
cruise a t acce p ta b ly low speeds a n d a 6o r 7-h o u r ra n g e affo rd s th e b est tim e utility.
T h e C a n a d ia n -b u ilt D e H av ilan d B eaver on
a m p h ib io u s floats is a seven place, single
engine, h ig h w ing p la n e w ith 7-h o u rs ran g e
a t 100 m p h (160 k m /h r). It is a satisfacto ry
p la n e fo r surveys b u t is p o o r fo r catching
flightless b ird s fo r b an d in g . T h e U .S .-built
C essna 180 a n d C essn a 185 a re th e m ost
v ersatile p lan es fo r all ph ases o f sw an w ork.
T hese a re five p lac e p lan es w ith ad e q u ate
ran g e an d a re m o re m an o e u v e ra b le on th e
w ater th a n th e la rg e r B eaver.
T h e choice o f season fo r a ir surveys is
d ep en d en t o n th e ty p e o f in fo rm atio n
so u g h t an d p e rh a p s th e q u ality o f th e
te rra in . In th e N o rth , sw'ans sc a tte r to
te rrito rie s as th ey arriv e o n th e p a rtially
thaw 'ed nestin g ran g e. W hen d istu rb ed
d u ring in c u b a tio n som e A m erican sw ans
will get o ff th e ir n ests a n d h id e b eh in d
th e m o r n earb y cover. T h e first m o n th to
6 w eeks a fter h a tc h in g is th e m o st difficult
tim e fo r surveys as th e y o u n g te n d to
cluster closely w ith p a re n ts in th e th ick est
cover they can find. In th e last 2 o r 3 w eeks
b efo re fledging th e y o u n g are q u ite larg e
an d a re freq u e n tly seen in o p en w-ater and
W h istlers o ften graze o r lo a f o n th e o pen
tu n d ra . A fte r fledging th e b ird s b egin to
leave th e n estin g te rrito rie s a n d g a th e r in
p re-m ig ratio n flocks. T hey can th e n b e
c o u n ted o r p h o to g ra p h e d from th e a ir b u t
o n e can no lo n g e r d eterm in e th e ir re la tio n ­
ship to th e nestin g h a b ita t. T h e surveys
h erein d escrib ed a re useful fro m th e on set
o f in c u b a tio n to th e tim e o f fledging.
L en sin k (1973) has show n th a t th e
stru c tu re o f th e p o p u la tio n changes som e­
w h a t as su m m e r pro g resses. I f only one
a n n u al survey is p ossible th e last 3 w eeks
b efo re fledging w ould p ro b a b ly b e th e best
tim e. In A lask a we get th e b est in fo rm atio n
fo r eith er species in late A ugust.
T o c o u n t eggs in th e nest req u ires flying
a t less th a n 100 ft (30 m ). W ith th e u n aid ed
eye sw ans can b est b e fo u n d fro m an eleva­
tio n o f 4 0 0 -5 0 0 ft (120-150 m ) a lth o u g h
it m ay b e n ecessary to b e lo w er fo r b ro o d
cou n ts. S om e p eo p le p re fer to w o rk from
a b o u t 1,000 ft (300 m ) w ith b in o cu lars.
T h e w id th o f th e p a th o f o b serv atio n d e­
p en d s o n th e a ltitu d e . B efore startin g lineal
surveys it is w ell to m easu re th e d istan ce
b etw een tw o a p p ro p ria te la n d m a rk s an d
fly o v er th e m several tim es to accu sto m th e
eye to th e d e sired lim its. Pieces o f ta p e can
b e p lace d on th e w indow a t eye level an d on
th e w ing s tru t to aid in d eterm in in g th e
w id th o f o b serv a tio n s from any given a lti­
tu d e .
Com plete census
In 1968 w e m a d e a co m p lete co u n t o f
T ru m p e te r Sw ans on th e ir e n tire A lask a
b reed in g ran g e. T h e census w as d o n e in
A ug u st w hen th e y o u n g w ere n o t yet
fledged b u t w ere larg e en o u g h to b e easily
seen; 124 h o u rs in th e a ir w ere req u ired .
P lanes w ere flow n at a b o u t 500 ft (150 m)
b u t it w as som etim es n ecessary to dip dow n
to c o u n t b ro o d s. P rio r to each flight, m aps
w ith a scale o f 1:63,360 w ere stack ed in
o rd e r. A ll th e sw an h a b ita t on each m ap
w as co v ered b e fo re p ro ceed in g to th e next.
T h e o b serv er in th e rig h t h a n d se at m ark ed
th e ex act flight p a th o f th e a irp la n e w ith
p encil o n th e m ap . T h e p recise lo c a tio n o f
each sighting w as m ark ed w ith a d o t and
n u m b e red co nsecutively o n each m ap. On
th e m arg in w ere n o ted th e n u m b e r o f
b ird s, a d u lt o r y o u n g ; b ird s in flight being
distin g u ish ed b y th e le tte r F.
T his survey resu lte d in an a c tu a l co u n t
o f 2,848 b ird s, 32% o f w hich w ere cygnets
(H an se n et al., 1971). T h e tru e p o p u la tio n
w as b elieved to b e so m ew h at h ig h er since
Use o f airplanes to gather swan data
so m e low den sity T ru m p e te r h a b ita t w as
m issed an d b ecau se so m e sw ans conceal
them selves. In spite o f th ese k now n d e­
ficiencies, th e census stan d s as a g o o d
b aselin e fo r co m p ariso n w ith fu tu re counts.
T he m ost im p o rta n t fe a tu re o f th is ty p e of
co u n t is th e reco rd in g o f th e ex act flight
p a th so th a t fu tu re o b serv ers will know
exactly w here sw ans w ere n o t seen as well
as w h ere th ey w ere. T his is th e item m o st
often neglected in a ir surveys.
A lth o u g h th is c o u n t w as a n a tte m p t to
cover th o ro u g h ly a very larg e a re a it is n o t
alw ays necessary to ex am in e th e en tire
ran g e o f a species to g et useful in fo rm a tio n
on density, p o p u la tio n stru c tu re an d p ro ­
ductivity. T h e tec h n iq u e could b e applied
to key p o rtio n s o f sw an h a b ita t. T hus,
Sladen h as m ad e com p lete co u n ts in th e oil
d ev elo p m en t a reas o f A lask a ’s A rctic Slope
w h ich w ill sh o w th e effect o f su ch d istu r­
b a n c e on d istrib u tio n a n d p ro d u ctiv ity .
A Ju n e co u n t d u rin g in c u b a tio n follow ed by
an A ugust c o u n t w o u ld re su lt in a m o re
co m plete p ic tu re o f a lo cal p o p u la tio n an d
its p ro d u ctiv ity . M o nthly o r even w eekly
surveys w ou ld b e b e tte r still. By careful
flying it is p o ssib le to c o u n t clutch sizes
b u t as som e b ird s sit tig h te r th a n o th ers a
co m plete co u n t o f eggs in a given area
w ould be difficult to achieve w ith o u t having
to lan d . O f co u rse any survey is en h an ced
if it can b e re p e a te d y e ar a fte r y ea r to give
long te rm averages a n d tre n d s.
Random plot census
T h ere is usually a p ra c tic a l lim it to th e size
o f a p o p u la tio n o r a b reed in g ra n g e th a t
can be covered by a co m p lete census. In
th e case o f W histling Sw ans w ith a p o p u la ­
tio n th irty to fo rty tim es g re a te r th a n
T ru m p eters sca tte red o v er a ra n g e several
tim es larg er, a co m p lete census w ould b e
exhausting an d d o u b tless a w aste o f tim e.
R esults o f eq u al v eracity c o u ld b e achieved
by a ra n d o m p lo t c o u n t. In this m eth o d
th e en tire a re a is g rid d ed in to p lo ts o n a
m ap o f suitab ly d e tailed scale. T h irty or
m o re p lo ts a re selected a t ra n d o m fo r actu a l
census. T h e size o f th e p lo ts sh o u ld b e such
th a t som e sw ans o c cu r o n each . O n th e
Y ukon D elta, L en sin k h as fo u n d (p erso n al
co m m u n icatio n ) th a t 4-sq. m ile (10-36 sq.
km ) p lo ts a re su itab le fo r W histlin g Sw ans.
W7h ere densities are low er, larg er plots
w ould b e need ed . Sam pling e rro r can be
d eterm in ed by sta n d a rd p ro c e d u res fo r
analysing sim ple o r stratified ra n d o m
sam ples. P lo t census can b e d o n e at
17
in terv als w hile th e b ird s a re o n te rrito ry ,
a n d ca rrie d o v er a p e rio d o f y ears w o u ld be
m ost valu ab le.
W e h av e n o t as y e t se t u p any co n sisten t
W histling Sw an sam p lin g by th is m ethod.
W e did use th e m eth o d o v e r a 31,000-sq.
m ile (80,000 km 2) a re a in so u th e a st A lask a
to d e term in e th e b reed in g p o p u la tio n of
B ald E agles H aliaeetus leucocephalus.
By sam p lin g th irty p lo ts fro m 488, w e
d ete rm in e d a p o p u la tio n o n te rrito ry o f
7,287 ± 25% w ith 95% confidence. W e
used a p lo t size o f 65 sq. m iles (166 sq.
km ) in this case b u t w ere req u ired to fly
only th e co astlin e a n d riv e r valleys in
each p lo t. T his survey to o k 32 h o u rs o f air
tim e in a single en ain e flo at p la n e (K ing,
1972).
Line transect surveys
F o r th e p a st 18 y ears th e A lask an breed in g
p o p u la tio n o f duck s h as b een surveyed
from th e a ir by a system o f lineal tran sects.
T his ty p e o f survey is d escrib ed by Crissy
(1957) an d M artin so n & K aczy n sk i (1967).
T h e tran se c ts a re m ark e d o n d etailed m aps
an d a re flow n a t 100 m p h (160 kp h ) a t an
elev atio n o f 100 ft (30 m ) ab o v e th e te rra in .
T h e p ilo t o n th e left an d an o b serv e r o n th e
rig h t rec o rd all w aterfo w l o b serv atio n s
w ithin ¿-m ile (201 m ) o f each side o f th e
p lan e . E a c h o b serv er uses a p o rta b le ta p e
re c o rd e r. T h e re su lt o f e ach 16-mile (26 km )
segm ent is a census o f 4 sq. m iles (10-36
sq. km ). T h e d a ta a re co n v erted to an
e stim ate o f p o p u la tio n w ithin th e to tal
sq u are m iles o f th e h a b ita t. C onfidence
lim its can b e d ete rm in e d as fo r a sim ple
ra n d o m sam ple.
Sw ans h av e b een re c o rd e d o n th is survey
fo r th e p a st 14 y ears as 107 o f th e segm ents
fall w ithin th e b reed in g ran g e o f th e W hist­
ling Sw an. A lth o u g h analy sis o f th is sw an
d a ta h as n o t b een ex h au stiv e we have som e
p re lim in ary
findings
th a t
show th e
a d v an tag es a n d w eaknesses o f this te c h ­
nique.
A d v an tag es include:
(1) A n index o f p o p u la tio n flu ctu atio n s
o v er a p erio d o f y ears is d erived
th a t w ould show th e o c c u rren ce of
d ra stic changes in th e b reed in g
p o p u la tio n . N o u p w a rd o r dow n w ard
tre n d is o b vious in A la sk a th u s fa r
(T ab le 1).
(2) It is a g o o d m eth o d fo r stratifying
sw an h a b ita t by m e a n density p e r
sq u are m ile. F ig u re 2 show s how line
tra n se c t d a ta is u sed to stratify
18
James G. King
Figure 2. T he Y ukon D elta showing location
of each of the 65, 16-mile line transect survey
segments. The num ber below each segm ent is
the 16-year average num ber of swans seen there
th e h a b ita t on th e Y ukon D elta,
p ro v id in g a g o o d basis fo r lan d use
an d m a n a g e m e n t decisions.
(3) A ro u g h e stim a te can b e m ad e o f th e
sw ans o n te rrito ry th a t a re likely to
re p ro d u c e (b reed in g p o p u latio n ).
W eaknesses include:
(1) T h e survey w as designed to sam ple
duck s, so lack s th e p recisio n o f a
survey specially p lan n ed fo r sw ans.
(2) T h e o b serv ers m u st ju d g e th e ¿-m ile
o b serv a tio n
sw ath
an d
m ake
acc u ra te
o b serv atio n s
w ith o u t
benefit o f circling o r going b a c k to
rech eck .
(3) A t som e tim es th e survey is d o n e
u n d e r cloudy skies an d a t o th ers
b rig h t sun causes w a ter g lare th a t
in terferes w ith visibility.
(4) It is difficult to an aly se th e d a ta w ith ­
o u t benefit o f c o n c u rre n t g ro u n d
studies p a rtic u la rly o f sw an breeding
b eh a v io u r. W e are n o t su re how
m an y sw ans a re m issed. It is n o t yet
kno w n w h a t p ro p o rtio n o f single
sw ans a c tu a lly re p re se n t a p air,
th a t appear to b e on territory. The dotted lines
group areas according to density, low averaging
from trace (t.)-3 , m edium 4 -8 and high 9-18.
a n d w hich a re tru ly lo n e birds.
L acking p recise d a ta , single birds
h av e b e e n co n sid ered a p a ir in th e
final analysis (T ab le 1). T his m ay be
m o re a c c u ra te th a n co u n tin g tw o
single sightings as a p a ir b u t th e re is
still an u n reso lv ed bias.
(5) T h e survey do es n o t m easu re clusters
o f n o n -b reed in g b ird s accu rately .
(6) T h e survey w o u ld b e im p ro v ed by
b eing rep e a te d in late A ug ust to
m easu re actu a l p ro d u c tio n o f young.
W e m u st co n c lu d e th a t th e line tra n se c t
m e th o d by itse lf gives a relatively su p e r­
ficial p ic tu re o f a sw an p o p u la tio n an d th a t
th e in c u b a tio n p erio d is n o t th e b est tim e
to d o such a survey. W hen a d etailed study
o f a p o rtio n o f th e sw an p o p u la tio n is
ca rrie d th ro u g h a n e n tire seaso n , th e long
term tra n se c t survey in fo rm atio n already
g ath e red will b eco m e m o re v aluable.
A lin e tra n se c t survey designed speci­
fically fo r sw ans sh o u ld b e p la n n e d so som e
sw ans o c c u r o n every tra n se c t. I t m ig h t be
flow n so m ew h at h ig h er th a n a d u c k survey
p e rm ittin g a w id er survey p a th .
Use o f airplanes to gather swan data
Table I.
19
WTiistling Swan spring population in Alaska from 1958 to 1971 (excluding the Arctic
Slope) as determined from 107 line transects
1958
1959
1960
1961
1962
1963
1964
64,000
59,000
79,000
79,000
56,000
64,000
50,000
1965
1966
1967
1968
1969
1970
1971
62,000
52,000
43,000
50,000
75,000
69,000
61,000
14-year average 62,000; range 43,000-79,000.
(Figures from Cham berlin, M artinson & Clark, 1971).
R andom flight method
W hen m aking ro u tin e flights acro ss sw an
breed in g h a b ita t v alu ab le d a ta can be
o b tain ed by reco rd in g every sw an seen.
N ests an d clu tch sizes can b e re c o rd e d in
this fashion. It is n ecessary only to fly
low enough fo r sw ans to b e easily seen.
T he o b serv er n eed n o t d ire c t th e p a th o f
flight, b u t if he can th e q u ality o f b ro o d
counts, flock c o u n ts, an d egg co u n ts are
im p ro v ed . If such flights can b e m a d e at
least once a w eek, a g o o d p ic tu re o f sw an
p ro d u ctiv ity
and
ju v e n ile
m o rtality
th ro u g h o u t th e nestin g seaso n can be
q b tain ed .
T he b est ex am p le o f th is ty p e o f survey is
from th e Y uk o n D e lta w h ere th e sta ff o f
C larence R h o d e N a tio n a l W ildlife R ange
hav e reco rd ed sw an d a ta on ro u tin e flights
since 1963 (L ensink, 1973).
T he ad v an ta g es o f this m e th o d a re th a t
no cost is involved as p eo p le a re travelling
anyw ay an d o b serv atio n s fro m differen t
areas can b e c o m p ared if th e trip s w ere
m ad e a t a b o u t th e sam e tim e o f year.
E xploratory flight method
A n a irb o rn e bio lo g ist m u st d e v o te som e
tim e to explorin g h a b ita t new to him to get
th e ‘feel’ o f th e c o u n try befo re he can set up
m eaningful surveys. T h e v alu e o f th e
o b serv atio n s m a d e o n su ch trip s can be
e n h an ced if o b serv atio n s a re reco rd ed
system atically. W e have fo u n d th a t o v er th e
tu n d ra h a b ita t w e can use th e tech n iq u es
o f th e line tra n se c t m e th o d to arriv e at
ro u g h estim ates o f sw ans o n th e b reed in g
g ro u n d s. O b serv atio n s a re m a d e in a co n ­
sisten t sw ath a n d d ivided a t fixed tim e
intervals. E fforts sh o u ld b e m a d e to reach
every p a rt o f a given h a b ita t an d n o t to
spend to o m u ch tim e in any o n e area . It is
n o t necessary to fly straig h t lines. W e have
used th e ¿-m ile (201 m ) o b se rv a tio n sw ath
and 10 m in u te in terv als w hich a t 96 m ph
(155 kph) gives us six sam ples o f 2 sq. m iles
(5-18 sq. km ) fo r e a c h h o u rflo w n . W ith one
o b serv er th is p erm its th e rec o rd in g o f all
A n a tid a e and o th e r m ed iu m sized b ird s. If
sw ans only are to b e re c o rd e d a w ider
o b serv atio n sw ath could b e covered from a
h ig h er altitu d e . T h e co v erage is d o u b led o f
co u rse if th e re is an o b se rv e r o n each side o f
th e p lan e. A figure fo r th e n u m b e r o f birds
p e r sam p le can b e e x p an d ed to th e to ta l
a re a covered. By th is m e th o d we estim ated
th e re w ere 800 sw ans o n th e 23,000 sq. miles
(59,570 sq. km ) o f w aterfo w l h a b ita t o f th e
A rctic Slope in 1966 (K ing, 1970).
Discussion
T he foreg o in g m eth o d s can be ‘ta ilo re d ’ to
tim e a n d b u d g eta ry lim itatio n s. P ro b ably
th e m o st im p o rta n t fe a tu re o f th e A lask a
w o rk h as b een con sisten cy in p lan n in g and
rec o rd in g so th a t y e a r can b e co m p ared to
y e a r an d a re a to area. If we co n tin u e
a c cu m u latin g d a ta in th is fashion we will
even tu ally p iece to g e th e r a g o o d p ic tu re o f
sw an p o p u la tio n d y n am ics on th e b reed in g
range.
I f a irb o rn e bio log ists w o rk in g full-tim e
o n sw ans w ere av ailab le, th e rep e ate d
survey o f sam p le p lo ts w o u ld b e th e m ost
ad v an ta g e o u s m eth o d . T h e m a jo r effort
sh o u ld b e a co m p lete ra n d o m p lo t survey
co n d u cte d in A ug u st to d ete rm in e p ro ­
du ctiv ity . B efore an d a fte r th is, p o rtio n s of
th e a re a could b e ex am in ed at w eekly or
bi-w eekly in terv als to d ete rm in e arriv al
d a tes, te rrito ry size, o n se t o f nest building,
egg laying, clu tch sizes, h atch in g dates,
m o rtality ra te s, b ro o d m o v em en ts, fledging
d ates, fall flocking p a tte rn an d exodus fro m
th e b reed in g a re a . A co m b in a tio n o f p lo t
co u n ts an d ra n d o m flights m ig h t w o rk best.
A ir surveys c a n n o t an sw er all th e q uestions
o f sw an b iology an d g ro u n d w o rk will be
essen tial to learn a b o u t feeding h ab its,
g e n eral b e h a v io u r, an d causes o f m o rtality .
Som e asp ects o f sw an b e h a v io u r from y ea r
20
James G. King
to y ear will re q u ire m ark in g in d ividual
b irds as d esc rib e d by Sladen (1973).
A n aerial te a m assigned full tim e to
sw an w o rk co u ld p ro b a b ly d o a lo t o f
g ro u n d o b se rv a tio n . Sw ans d u rin g th e ir
a n n u al m o u lt o r p rio r to fledging can easily
be cau g h t fo r m ark in g by use o f a flo at a ir­
plan e.
A lth o u g h this re p o rt relates entirely to
th e use o f a irp lan es w e assu m e th a t th e
m eth o d s d escrib ed could b e m odified to
use from a h elico p ter.
W e co n clu d e th a t th e full u n d e rsta n d in g
o f sw ans o n th e b ree d in g g ro u n d s req u ires
th e use o f lig ht a irc ra ft fo r surveys as well
as g ro u n d access.
Acknowledgments
Those who have contributed to swan survey
m ethods in A laska include: H. H ansen, C.
Lensink, W. Sladen, P. Shepherd, D. Spencer,
R. Richey, J. B artonek, A. Thayer, S. Olson,
R. Trem blay, J. Branson, L. Johnson. Jack
Hodges provided th e stratification shown in
Figure 2.
Summary
Single engine airplanes have been used in Alaska
for swan population counts over the past 17
years. Five different m ethods have been dev­
eloped: ( 1) com plete census; (2) random plot
census; (3) line transect surveys; (4) random
flight m ethod; (5) exploratory flight m ethod. The
first two m ethods are recom m ended when full
tim e can be devoted to swan w ork. The last three
are used when the flight is prim arily for other
purposes.
References
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H ansen, H . A., Shepherd, P. E. K., King, J. G .,
& Troy er, W . A. 1971. The T rum peter Swan
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King, J. G . 1970. The swans and geese of
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Jam es G . King, Bureau o f Sport Fisheries and
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