Sex and plumage-type ratios of the Lesser Magellan Goose in
southern Chile
W .R . S IE G F R IE D . P .A .R . H O C K E Y . P .G . R Y A N an d A .L . B O S M A N
In tro d u ctio n
Methods
F o u r o f th e five species o f S o u th A m erican
sheldgeese (g en u s C hlo ëp h a g a) a re te rre s t­
rial g rass-eaters; th e ex cep tio n b eing the
K elp G o o se C. hybrida (D e la c o u r 1954).
T h re e o f th e fo u r te rre stria l species b reed
in so u th e rn P a tag o n ia, in cluding T ie rra del
F uego (Jo h n so n 1965; H u m p h re y et al.
1970). T h ey a re th e A sh y -h ea d ed G o o se C.
p o lio c e p h a la , R u d d y -h e a d e d G o o se C.
rubidiceps an d M agellan G o o se C. picta
w hich has tw o races, th e L esser M agellan
G o o se C. p. picta on th e S o u th A m erican
m ain lan d , an d th e G re a te r M agellan G o o se
C. p. leucoptera on th e F a lk la n d Islands.
T h e M agellan G o o se ex h ib its m ark ed
sexual plum ag e d im o rp h ism , b u t in the
o th e r tw o species th e sexes a re sim ilar. T he
L esser M agellan G o o se also differs from
the o th e r species in th a t ad u lt m ales p re se n t
a range o f c o lo u r p h a se s, fro m individuals
w ith co m p letely w hite u n d e rp a rts to birds
heavily b a rre d o r b lo tc h e d w ith black and
w hite. In the G re a te r M agellan G o o se, by
co n tra st, th e u n d c rp a rts o f ad u lt m ales
invariably a re p u re w hite. F em ales in g en ­
eral show little v a riatio n , b u t th e co lo u r of
the head o f th e L esser M agellan G o o se
ran g es b etw een un ifo rm red d ish and dull
grey cin n am o n (Jo h n so n 1965; B lak e 1977).
It has been know n fo r a long tim e th a t the
ex trem e co lo u r p h ases p re se n te d by the
L esser M agellan G o o se are m o re-o r-less
seg reg ated in d iffe re n t reg io n s a n d at dif­
fe re n t seaso n s; th e b a rre d ty p e s b ein g m ost
ab u n d a n t in th e south an d th e w hite type
in the n o rth (Jo h n so n 1965; H u m p h re y et
al. 1970). H o w ev er, q u a n tita tiv e d a ta su p ­
p o rtin g this a re scarce.
T his p a p e r su m m arises th e resu lts o f
co u n ts o f L esser M ag ellan , A sh y -h ead ed
an d R u d d y -h e a d e d G eese m a d e in th e
course o f m o to rin g o v e r som e 800 km o f
ro ad s in so u th ern C h ile, in cluding T ie rra
del F u eg o , d u rin g 17-23 N o v e m b e r 1985.
T hese ro ad sid e co u n ts gave q u an titativ e
d a ta on relativ e a b u n d a n c e , g ro u p size and
in te r-s p e c ific a s s o c ia tio n f o r all th r e e
species, an d sex an d p lu m ag e-ty p e ratios
fo r the L esser M agellan G o o se b etw een ca
51°S and 54°S, close to th e so u th e rn limit
o f th e ir b reed in g d istrib u tio n .
S held g eese w ere c o u n te d w h en e v e r seen
w ithin a p p ro x im ately 500 m o f th e ro a d sid e .
H en ce th e relativ e a b u n d a n c e o f sh eld g eese
is ex pressed as n u m b ers o f b ird s p e r k m 3.
T h e m ain ro u tes tra v e rse d e x te n d e d from
T o rre s del P ain e, in th e n o rth , via P u e rto
N ata le s an d P u n ta A re n a s, to F o rt B u ln es
in th e so u th ; from P u n ta A re n a s, across th e
B runsw ick P en in su la, to O tw ay S o u n d ;
from P u n ta A re n a s, a lo n g th e S traits o f
M ag ellan , n o rth -e a st to P u n ta D elg ad a;
a n d , on T ie rra del F u e g o , from P o rv en ir
n o rth -e a st to P u n ta E sp o ra (see F igure 1).
T h e shelcfgeese on th e ro u te b e tw een T o r­
res del P aine an d P u n ta A re n a s w ere su r­
v eyed only o n ce, b u t th e so u th e rn ro u tes
w ere trav elled m o re fre q u e n tly . In such
cases, h o w ev er, th e surveys w ere restricted
to se p a ra te days. A to tal o f 310 en c o u n te rs
w ith sh eld g eese w ere re c o rd e d in th e ex ­
te n d e d ro a d -strip , co v erin g 808 km .
S h e ld g e e s e w e re o b s e rv e d c a re fu lly ,
using b in o cu lars an d tele sc o p e s, an d th eir
b e h a v io u r, in term s o f feed in g , nestin g and
asso ciatio n b e tw een sexes, w as re co rd ed .
T h e b ird s' h a b ita ts a n d any association
b etw een th e b ird s an d d o m estic livestock
w ere also rec o rd e d . T h re e c ate g o ries o f
m ales w ere recognised b ased on th e e x ten t
o f b arrin g on th e ir u n d e rp a rts: co m p letely
w h ite ; in t e r m e d ia te ; a n d . c o m p le te ly
b a rre d . D e lac o u r (1954) im plies th a t belly
c o lo u r o f im m a tu re s reflects th e a d u lt
co lo u r p h a se , an d thus th e p resen ce of
im m a tu re a n d su b -a d u lt b ird s in flocks
should n o t bias analyses o f p lu m ag e-ty p e
ratio s. F em ales w ere also g ro u p ed in th re e
c a te g o rie s , b a se d o n h e a d c o lo ra tio n :
greyish cin n am o n ; in te rm e d ia te ; a n d , re d ­
dish cin n am o n . B irds w ere classified as
'in d e te rm in a te ' w hen p o o r light, c o v er o r
som e o th e r fa c to r p re v e n te d th em from
being c ateg o rised accu rately . B irds w ere
a d ju d g e d to be p a ire d w hen individual
m ales an d fem ales a sso ciate d an d m oved
closely to g e th e r, usually w ithin a m e tre of
each o th e r. In som e flocks it w as n o t p o ssi­
ble to d e term in e p a ire d /u n p a ire d ratios:
such flocks w ere used only in analyses o f
sex ratio an d g ro u p size.
15
W ild fo w l 34 (I4SX ): 15-21
16
Fig. 1.
W .R . S iegfried, P .A .R . H o ck ey, P .G . R ya n a n d A .L . B osnian
Map of the study area in southern Chile. D otted lines indicate routes taken during surveys.
Results
R elative abu n d a n ce
T o tals o f 1,941 (9 5 % ) L esser M agellan, 78
(4 % ) A sh y -h e a d e d a n d 20 (1 % ) R u d d y ­
h e a d e d G e e se w ere re c o rd e d . T h e L esser
M agellan G o o se w as m ark ed ly m o re a b u n ­
d a n t in th e n o rth o f th e survey a re a (T o rres
del P aine to P u e rto N atale s) a n d in n o rth ­
e rn T ie rr a d e l F u e g o th a n e lse w h e re .
R u d d y -h e a d e d a n d A sh y -h e a d e d G ee se
Table 1.
w ere u n c o m m o n in all th re e a re as (T ab le
1). H ig h est d en sities o f th e A sh y -h ead ed
G o o se w ere fo u n d on th e B runsw ick P en in ­
sula, n o rm ally in asso ciatio n w ith ind ig­
e n o u s fo rest p atch e s. Several pairs w ere
fo u n d b re e d in g alo n g th e in te rm itte n tly
fo re sted R io S an Ju a n to th e so u th o f F o rt
B ulnes. T h e R u d d y -h e a d e d G o o se w as
m o st a b u n d a n t, a lth o u g h still ra re , in th e
g rasslan d s o f n o rth e rn T ie rra del F u eg o ,
w h ere th e A sh y -h e a d e d G o o se w as ab sen t.
B ased o n rela tiv e a b u n d a n c e o f th e geese
Relative abundance of three species of sheldgeese in southern Patagonia, November 1985.
Survey route
T orres del Paine - P uerto N atales
Puerto N atales - P unta A renas
P. A renas A irport - P unta D elgada
Brunswick Peninsula
Porvenir - Punta E spora
A rea
Mean density of birds per krrr
surveyed
(km 2) Lesser Magellan A shy-headed
R uddy-headed
G oose
Goose
G oose
150
188
240
88
142
4.03
0.99
0.99
1.18
5.35
0.04
0.06
0.04
0.26
< 0.01
0.00
0.06
0.00
0.03
0.00
Lesser Magellan geese in Chile
17
Table 2. Percentage frequency of group size and the proportions (percentages) of paired birds in
the Lesser Magellan Goose in three regions of southern Patagonia, November 1985.
Region
North
C entral
South
G roup size
2
3—10
> 10
67
60
71
20
IS
IS
14
22
10
Sample
Proport ion of paired birds N um ber of pairs observed
size
with broods of small
(no. groups) Males Fem ales Overall
young
66
62
168
65
44
52
species, th re e regions w ere reco g n ised a
posteriori w ithin o u r study area : N o rth
(T o rre s del P ain e - P u e rto N a ta le s); C e n ­
tral (m ain lan d so u th o f P u e rto N ata le s);
an d . South (T ie rra del F u eg o ) (F igure 1).
T hese regions w ere used in su b seq u e n t
analyses.
G roup size
G ro u p sizes o f A sh y -h e a d e d a n d R u d d y ­
h e a d e d G eese v aried b e tw e e n o n e a n d 24
an d o n e an d eight b ird s, respectively. D ata
bases fo r th ese tw o species a re to o sm all to
allow fu rth e r statistical analysis aim ed at
revealing any g eo g rap h ical d ifferen ces in
gro u p size.
In th e L esse r M agellan G o o se , g ro u p size
ran g ed b etw een tw o an d 152 birds. In all
regions, a g ro u p size o f tw o w as m ost
fre q u e n t (T ab le 2) a n d in only o n e instance
did th ese o b se rv a tio n s n o t re la te to p re ­
sum ed m ated p airs. T h e re w as a ten d en cy
fo r g roups to be larg est in th e C e n tra l region
w h ere density w as low est (T a b le s 1 an d 2),
co rresp o n d in g w ith a low er p ro p o rtio n o f
p aired birds in this reg io n . H o w e v e r, g roupsize freq u en cy w as n o t significantly dif­
fe re n t betw een th e regions (X 2= 6 .0 5 , d f=
4, P > 0 .0 5 ).
Sex ratio a n d p lu m a g e types
Sex ratio s o f th e L esser M agellan G o o se
w ere very close to p arity in all th re e regions:
N o rth , m ales = 5 2 .2 % ; C e n tra l, m ales =
95
45
55
77
45
53
5
0
1
4 7 .7 % ; a n d , S o u th , m ales = 5 2 .5 % .
T h e re w as a clea r latitu d in a l cline in m ale
p lu m ag e-ty p e freq u en cy , w ith w hite birds
p re d o m in atin g in th e N o rth an d b a rre d bellied b ird s in th e S o u th . In te rm e d ia te
type b ird s w ere m o re fre q u e n t in th e N o rth
an d C e n tra l regions th a n in th e S o u th (X 2=
29.28, d f= 2 , P C 0 .0 0 2 ) (T a b le 3). T h e p a t­
te rn am o n g fem ales was less obvious. T h e re
was a clear g ra d ie n t o f g re y -h e a d e d bird s,
d e c r e a s in g to w a r d s h ig h e r la t it u d e s ,
alth o u g h in te rm e d ia te fem ales w ere n u m e r­
ically d o m in an t in all reg ion s a n d b ecam e
increasingly so in th e S o u th (T ab le 3). T h e
p ro p o rtio n o f p a ired re d -h e a d e d fem ales in
th e C en tral region w as g re a te r th a n ex ­
p e cte d (X 2= 10.34, d f= 2 , P c O .O l). T hese
tre n d s a re reflected in th e freq u en cy d istri­
b u tio n s o f th e p lu m ag e-ty p e co m b in atio n s
o f p a ired b ird s in th e th re e regions (T ab le
4).
A ssum ing th a t so litary m ales in d icated
actively b re e d in g b irds, th e re w as no d iffer­
en ce in th e ir a b u n d a n ce relativ e to th e
o cc u rre n c e o f m a te d , b u t n o t activ ely
b re e d in g , m ales in each o f th e th re e regions
(X 2 = 2 .8 6 , d f= 2 , P > 0 .0 5 ). Sim ilarly, th ere
w as no differen ce b etw e e n p lu m ag e-ty p e
ratio s o f b re e d in g m ales a n d m ate d m ales
in th e S o u th re g io n (X 2= 2 .9 2 , d f = 2 ,
P > 0 .0 5 ), o r b e tw een sim ilar ratio s o f w hite
an d in te rm e d ia te m ales in th e N o rth region
(X 2= 0 .0 6 , d f = l , P > 0 .0 5 ). S am ple sizes for
b a rre d m ales in th e n o rth e rn reg io n , an d
fo r all p lu m ag e-ty p es in th e C e n tra l region
w ere to o sm all fo r statistical analysis.
Table 3. Percentage frequency of three plumage types in male and female populations of the Lesser
Magellan Goose in three regions o f southern Patagonia, November 1985.
Region
N orth
C entral
South
M ales
Plum age-types
W hite Interm ediate Barred
61
27
12
32
30
19
7
43
69
N
127
153
317
Fem ales
Plum age-types
Greyish Interm ediate Reddish
33
14
8
51
57
72
16
29
20
N
70
169
307
18
W .R . Siegfried, P .A .R . H o ck ey, P .G . R yan a n d A .L . B osnian
Table 4. Percentage frequency of the nine possible plumage-type pairings of the Lesser Magellan
Goose in three regions of southern Patagonia, November 1985.
Region
Male plum age-type
W hite Interm ediate Barred
N orth
female
plumage
type
Total
C entral
female
plumage
type
Total
South
female
plumage
type
Greyish
Interm ediate
Reddish
Greyish
Interm ediate
Reddish
Greyish
Interm ediate
Reddish
Total
12
16
3
41
10
2
9
7
0
62
33
5
31
53
16
100
5
0
0
16
19
17
0
5
38
21
24
55
5
52
43
100
3
0
1
5
17
51
1
1
21
9
18
73
4
73
23
100
A ssociatio n s betw een species
O f th e o b serv ed A sh y -h e ad e d a n d R u d d y ­
h e ad ed G e e se , 70% an d 6 0 % , respectively,
o ccu rred in asso ciatio n w ith g ro u p s o f L es­
se r M agellan G e e se . In instan ces w here
A sh y -h ead ed G e e se (A ) o ccu rred w ith L es­
se r M agellan G e e se (L ), th e n u m b e rs o f th e
tw o species in th e flocks w ere c o rre late d
positively (n A = 0 .0 7 n L + 1 .4 1 , r= 0 .8 9 , d f=
8 , P C 0 .0 0 1 ).
In all th re e reg io n s, m o st g ro u p s o f th e
L esser M ag ellan G o o se w ere n o t asso ciated
w ith d o m estic an im als (T ab le 5). T o clarify
this relatio n sh ip , th e in cid en ce o f d o m estic
livestock w as n o te d b e tw ee n P u n ta D elg ad a
and P u n ta A re n a s, a n d in T ie rra del F uego.
T h e fo llo w in g g ro u p fre q u e n c ie s w ere
reco rd ed : L esser M agellan G o o se only =
173; sh eep only = 77; ca ttle only = 2; geese
an d sh eep = 11; a n d , g eese a n d cattle = 5.
T h ese d a ta suggest th a t th e re m ay in d eed
be a positive asso ciatio n b e tw een g eese an d
c a ttle , b u t th e sam p le is to o sm all fo r
Table 5. Percentage frequency of association
between groups of the Lesser Magellan Goose and
domestic livestock in three regions of southern
Patagonia, November 1985.
Region
North
C entral
South
Frequency of association
No.
None W ith sheep W ith cattle records
92
81
95
5
8
5
3
11
0
66
62
168
T otal
n = 58 pairs
n = 58 pairs
n=151 pairs
statistical testin g . F o r sh e e p , h o w ev er, th e
o b serv ed fre q u e n c ie s o f asso ciatio n are
very d iffe re n t from th o se ex p e c ted (assu m ­
in g in d e p e n d e n c e , X 2= 1 0 8 .1 3 , d f = 2 ,
PcO.OOl), d e m o n stra tin g a cle a r n egative
rela tio n sh ip b e tw e e n th e p resen ce o f sh eep
an d L esser M ag ellan G e e se , w hich m ay be
d u e to a v o id an c e o r su b tle d ifferen ces in
h a b ita t re q u ire m e n ts. T h e re w ere m ark ed
latitu d in al d ifferen ces in th e h a b ita ts used
by th e L esser M agellan G o o se w hich reflect
h a b ita t av ailab ility (T a b le 6 , X 2 = 7 7 .5 7 ,
d f= 4 , PcO.OOl).
Table 6. Percentage frequency of habitat utilisa­
tion by the Lesser Magellan Goose in three regions
of southern Patagonia, November 1985.
North
Region
C entral
G rassland
Scrub
W ater associated
37
33
30
76
4
21)
89
3
8
No. records
66
55
160
H abitat
South
Discussion
L esser M ag ellan G eese in C hile lay eggs in
N o v e m b e r (Jo h n so n 1965), th e re fo re th e
m id -N o v em b er surveys should have coin ci­
d e d w ith th e in cu b atio n p h ase. H o w ev er,
alth o u g h m o re th a n h alf o f th e b ird s w ere
p a ire d , sing le m ale s a ssu m ed to have
in cu b atin g m a te s h id d en from view co m ­
L esser M agellan geese in C hile
prised only 5% o f all m ales re c o rd e d , and
only six p airs w ere re c o rd e d w ith sm all
young. T h u s, w hile no c o m m en t can be
m ade on th e p ro p o rtio n o f b re e d in g birds
in th e p o p u la tio n s su rv ey ed , it can be assu ­
m ed th a t d a ta on g ro u p size, sex ra tio ,
a b u n d an ce an d g eo g rap h ical d istrib u tio n
are relatively free o f biases w hich m ight
have o ccu rre d if a large p ro p o rtio n o f th e
p o p u latio n w as b re ed in g at th e tim e o f the
surveys.
R elative abundance
T h e in fo rm atio n on th e relativ e ab u n d a n c e
o f th e R u d d y -h e a d e d , A sh y -h ea d ed and
L esser M agellan G eese in so u th e rn P a ta ­
gonia p resen ts a p a tte rn sim ilar to th o se
re p o rte d in th e m o re re c e n t lite ra tu re
(H u m p h re y et al. 1970). In effect, the
L esser M agellan G o o se o u tn u m b e rs its tw o
cong en ers by tw o o rd e rs o f m a g n itu d e , w ith
the R u d d y -h e ad e d G o o se now o ccurring
w ith som e reg u larity only in T ie rra del
F uego and so u th e rn B u e n o s A ire s P ro ­
vince. In T ie rra del F u eg o , o u r survey
included nine R u d d y -h e ad ed G eese o u t of
a to tal o f 775 sh eld g eese, acco u n tin g for
1 . 2 % , in co m p ariso n to < 0 . 1 % ( 6 in 6000)
rec o rd e d in 1973 (K ing 1981).
A fte r an initial in crease at th e tu rn o f th e
ce n tu ry , w hich m ad e it o n e o f th e co m ­
m onest sheld g eese in n o rth e rn T ie rra del
F uego (S cott 1954), th e R u d d y -h e a d e d
G o o se d ecre a se d d ram atically a fte r th e
1950s to an estim ate d p o p u la tio n o f few er
th an 1,000 birds on T ie rra de F u eg o in the
late 1970s (R u m b o ll 1975; K ing 1981). T he
p o p u la tio n has b e e n classified as “e n ­
d a n g e re d " (K ing 1981), w ith th e m ain fac­
to rs fo r its d ecrease b eing given as: p e rse c u ­
tion by m an (egg d estru c tio n an d sh o o tin g );
p re d a tio n by th e in tro d u c e d P a tag o n ian
G rey Fox D usicyon griseus', a n d , co m ­
p etitio n w ith d o m estic sh e e p fo r fo rag e.
T h e allegation th a t sh eep d ep riv e th e sh e ld ­
geese o f fo rag e is u n su b sta n tia te d (S u m ­
m ers 1985).
C attle w ere in tro d u c e d in to so u th e rn
P atag o n ia d u rin g th e m iddle o f th e n in e ­
te e n th cen tu ry a n d sh e e p som e 25 years
la ter. T h e extensive cattle in d u stry d eclined
to w ard s th e e n d o f th e c e n tu ry a n d , sh eep
ranching e x p a n d e d to co v er m ost o f the
a rea o ccupied to d ay . D u rin g th ese ch an g es,
forests w ere cle a re d , b u rn e d a n d c o n v erted
to grasslands. W e h y p o th esise th a t th e
co m b in atio n o f fo rest c learin g (th a t c o n ­
19
tin u es to d a y ) an d cattle ra n ch in g fav o u red
an initial in crease o f th e R u d d y -h e ad e d
G o o se . T h e L esse r M agellan G o o se p re ­
sum ably b e n e fited th ro u g h th ese actio n s as
w ell. It is su g g ested , h o w ev e r, th a t th e
A sh y -h e ad e d G o o se m ay have d ecreased
w ith th e d estru c tio n o f th e fo rest, since it
a p p e a rs th a t th e species b re e d s m ainly in
fo re st clearings th a t a re asso ciated w ith
p o n d s an d o th e r w e tla n d s (Jo h n so n 1965;
H u m p h re y et al. 1970, p ers. o b s.). T h e
sh o rt cro p p in g o f v e g e ta tio n by th e sh eep
(C raw shay 1907; S u m m ers a n d D u n n e t
1984), a n d p e rh a p s by ra b b its (Jak sic an d
Y an ez 1983), possibly initially b en efited
tw o o f th e th re e sp ecies o f sheld g o o se.
H o w ev e r, it m ay also have re su lte d in th e
g ro u n d b eco m in g d rie r a n d ch an g es o ccu r­
ring in th e co m p o sitio n o f th e grassy v e g e ta ­
tio n as w ell as an e n c ro a c h m en t o f sem iarid a d a p te d scrub a t th e ex p en se o f grass
cover. It w ould follow th a t a ch an g e in b o th
th e q u a n tity an d q u ality o f th e grass co v er,
a n d n o t c o m p e titio n w ith sh eep fo r forage
(S u m m ers an d G riev e 1982), has b e en a
m a jo r fa c to r c o n trib u tin g to th e recen t
d ecrea se o f th e R u d d y -h e a d e d G o o se in
so u th e rn P atag o n ia. O th e r m a jo r factors
a re u n d o u b te d ly p e rse c u tio n a n d th e in tro ­
d u ctio n o f p re d a to rs. T h e L esser M agellan
G o o se m ay be less selective in its feed in g
a n d nestin g re q u ire m e n ts th a n th e R u d d y ­
h e a d e d G o o se a n d , c o n se q u e n tly , has no t
(yet) b ee n so affected by th e se relatively
re ce n t chan g es in h a b ita t. S u m m ers an d
G riev e (1982) fo u n d th a t G re a te r M agellan
G e ese in th e F a lk lan d Islan d s co n su m ed a
g re a te r diversity o f v eg e ta b le m aterial th an
did R u d d y -h e a d e d G e e se , b u t sam p le sizes
fo r th e la tte r w ere sm all. A lien m eadow grasses Poa spp. d o m in a te d th e d iets of
b o th sp ecies, an d a b u n d a n c e o f Poa w as
re la te d to th e activities o f sh eep .
P lum age variation
T h e o ccu rren ce o f m ale L esser M agellan
G ee se in tw o co lo u r p h a ses, w hite versus
b a rre d , a n d th e se p a ra tio n o f th ese phases
alo n g a n o rth -so u th axis h as b e e n know n
fo r a long tim e (D e la c o u r 1954; H u m p h rey
et al. 1970). It is so m ew h at su rprising,
h o w ev er, th a t th e re has b e e n little in v esti­
g atio n o f its ev o lu tio n a ry origin an d o f th e
facto rs resp o n sib le fo r th e p h e n o m en o n .
G re a te r M agellan G o o se fem ales a p p a ­
ren tly d o n o t no rm ally b re e d until th ey are
tw o y ears o ld , an d m ales usually delay on set
20
W .R . S iegfried , P .A .R . H o ck ey, P .G . R yan a n d A .L . B osnian
o f b reed in g until th e y a re th re e y ears old
(S u m m e rs 1 9 8 3 a ). C o m p a ra b le in f o r ­
m atio n is n o t av ailab le fo r th e L esser
M a g e lla n G o o s e . T h e p r e s e n t d a t a ,
h o w ev er, d e m o n s tra te th a t b ird s o f all th re e
plum age ty p es b elo n g in g to b o th sexes
o ccu rred as a p p a re n tly m ate d m em b ers o f
p a irs, an d as p a re n ts o f b ro o d s. C learly,
th e n , w e have a situ a tio n e ith e r o f v ariatio n
in fully ad u lt p lu m ag e (tru e co lo u r p o ly m o r­
phism ) o r o f c e rta in in dividuals b eing able
to b re e d successfully w hile n o t yet having
full definitive a d u lt p lu m ag e. It is n ecessary
to p ro v id e a c a v e a t h ere in ad m ittin g th a t
o u r ratio s o f fem ale p lu m ag e ty p es m ight
n o t be free o f e rro r, since varying c o n d i­
tio n s o f light in te n sity c o u ld have affected
o u r ju d g e m e n t in distinguishing b etw een
sh ad es o f h ea d c o lo u r, an d h e a d c o lo u r
itself m ay ch an g e b e tw een m o u lts, w hich
can be irre g u la r (S u m m ers 1983b).
B ased o n th e d a ta fo r g ro u p size, and
incidence o f p a irs an d p a re n ts w ith b ro o d s
(T ab le 2), it a p p e a rs th a t b reed in g sta rte d
e a rlie r in th e n o rth -w e ste rn th a n in th e
so u th -ea stern a re a s o f so u th e rn P atag o n ia.
T h e n o rth -w e ste rn area is g en erally m o re
m esic, w ith relativ ely m any sm all lak es and
o th e r w etla n d s, an d is m o re v aried to p o g ­
ra p h ic a lly th a n th e so u th -e a s te rn a re a
w hich has a lo n g e r estab lish ed an d m o re
intensive system o f do m estic livestock g raz­
ing. D o e s th is suggest th a t th e n o rth ­
w estern a re a , in w hich w h ite-p h ase m ales
p re d o m in a te , p ro v id es relativ ely su p e rio r
b reed in g h a b ita t fo r th e L esser M agellan
G o o se? T h is q u estio n c a n n o t b e an sw ered
at p re s e n t, b u t existing ecological th e o ry
w ould be satisfied if th e L esser M agellan
G o o s e 's d e n se n o rth -w e s te rn b re e d in g
p o p u latio n co n sisted m ainly o f o ld e r ex ­
p erie n c e d b ird s ex p lo itin g o p tim al h a b ita t,
causing y o u n g er su b o rd in a te in dividuals to
trav el fa rth e r so u th w h ere h a b ita t is less
su itab le a n d b re e d in g occurs later. T h is, o f
c o u rse, begs th e q u e stio n o f ag e-re la te d
p lum ag e ty p e s, p a rtic u la rly in th e case o f
fem ales.
N o tw ith sta n d in g th e p reced in g sugges­
tio n s a n d qualificatio n s, it w ould seem th a t
th e L esser M agellan G o o se d o es in d eed
ex h ib it tw o , o r m o re , ’defin itiv e’ co lo u r
p h ases, at least in fully ad u lt m ales. T h e
d a ta , th u s, serve to reaffirm a previously
n o ted ten d e n c y fo r p u re w h ite m ales to
p re d o m in a te in th e n o rth an d b a rre d m ales
in th e so u th , o f so u th e rn P a ta g o n ia (H u m ­
p h re y et al. 1970). T h e d a ta also p o in t, for
th e first tim e , to a d e c r e a s e in th e
in te rm e d iate -p lu m a g e ty p e in acco rd with
th e n o rth to so u th g ra d ie n t. T h e situ atio n
in N o v e m b e r 1985 w as so m ew h at d ifferen t
to th a t in M arch 1953 (S cott 1954) w hen
w hite m ales acco u n te d fo r alm o st 50% o f
m ales o n th e m ain lan d a ro u n d P u n ta A re ­
nas, b u t well u n d e r 1% in T ie rra del F uego.
T h e re is also a seg reg atio n o f plu m ag e types
o v e r a c o m p arab ly n arro w la titu d in al range
o n th e w in terin g g ro u n d s in A rg en tin a
(M artin et al. 1986), w ith b a rre d birds
do m in atin g alo n g th e co ast, a n d w hite birds
do m in atin g in lan d to th e n o rth . B earin g in
m in d o u r re se rv a tio n c o n cern in g h e ad co lo u r, o u r d a ta suggest th a t th e re m ight
b e a n o rth -so u th cline in th e d istrib u tio n of
a t least greyish cin n am o n fem ales on th e
b re ed in g g ro u n d s as w ell. G iven th e sta te
o f o u r kno w led g e at p re se n t, we c a n n o t
im p ro v e on th e sp ecu latio n o f H u m p h rey
et al. (1970) th a t, p rio r to th e arriv al o f
E u ro p e a n se ttle rs an d sh e e p , th e tw o c o lo u r
ph ases o f th e L esser M agellan G o o se m ight
have b een “ . . . m o re se p a ra te d eco lo g i­
cally d u rin g th e b re e d in g season a n d th a t
this se p a ra tio n m ay have dim in ish ed d u rin g
th e p ast 75 o r 100 y ears b ecau se o f changes
in th e e n v iro n m e n t b ro u g h t a b o u t by
s h e e p .”
Acknowledgements
This paper is based on part of the FitzPatrick
Institute’s 25th A nniversary E xpedition to Chile.
The work was supported by the South African
C SIR and the University of Cape Town. We
thank D r Ja n e t K ear and an anonym ous referee
for their com m ents on the m anuscript.
Summary
Sex ratios in sheldgeese, especially the Lesser
Magellan G oose Chloëphaga p. picta were de te r­
m ined from roadside counts over 800 km in
southern Chile and on T ierra del Fuego. They
were close to parity. Males with white underparts
predom inated in the north and those with barred
underparts in the south. T here may also be a
north/south cline in the greyish-headed females
versus those with reddish heads. T he interactions
with o ther species of sheldgeese and with cattle
and sheep are discussed.
Lesser Magellan geese in Chile
2!
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Prof. W .R. Siegfried, Dr P.A.R. Hockey, Peter G. Ryan and Dr Alison L. Bosnian. FitzPatrick
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