M oult m igration of Lesser Snow Geese
K E N N E T H F. A B R A H A M
Salomonsen (1968) classified m oult m igra­
tion of w aterfow l according to the age, sex,
and reproductive status of participants, the
num ber of individuals involved, and the
relative locations of the m oulting and
breeding areas of the population. Those of
several species of geese involve primarily
the non-breeding segm ent of the popula­
tion (but see K rohn & Bizeau 1979) and
m oult areas usually lie to the north of the
breeding areas. The num ber of participants
varies am ong species and populations, and
in response to seasonal and dem ographic
changes.
In N orth A m erica, m oult m igrations of
C anada G eese Branta canadensis and
E m peror G eese A n ser canagicus have been
described (Sterling & D zubin 1967; K rohn
& Bizeau 1979; B lurton Jones 1972). C on­
vincing evidence of m oult m igration by
other N orth A m erican goose populations,
including Snow G eese A nser caerulescens,
was lacking at the tim e of Salom onsen’s
(1968) review, but he reported its possible
occurrence in the W rangel Island Snow
G oose and B rent G oose Branta bernicla
populations (Salom onsen 1968; U spenski
1960, 1965).
In this paper, I describe an annual moult
m igration of Lesser Snow G eese A . c.
caerulescens from a breeding colony at La
Pérouse Bay, M anitoba, C anada.
Study area and methods
The biology of Lesser Snow G eese has
been studied since 1968 at a breeding col­
ony at La Pérouse Bay, M anitoba
(58° 30'N , 94° 25'W ) (Figure 1). Activities
are m onitored from spring arrival until
approxim ately four weeks after peak
hatch; geese are captured and banded at
that tim e. C oloured leg bands with unique
alphanum eric codes have been attached to
approxim ately 2,000-3,000 geese annually
since 1972. This perm its identification of
individuals by observation at a distance
with the aid of binoculars or telescopes.
O bservations of yearling and adult non­
breeding geese have been m ade in most
years of the study, but these w ere intensi­
fied in 1976-1978. O bservations of be­
haviour and distribution w ere m ade from
portable hides in 1976, and from a perm a­
nent live-in tow er in 1977 and 1978. In
1976, eight fem ales w ere trap p ed on nests
and coloured with feath er dyes at m id­
incubation. T heir eggs w ere rem oved to
sim ulate p redation, and the subsequent
m ovem ent of these ‘failed b reed ers’
throughout the colony area w ere m oni­
tored. A erial surveys w ere m ade during
th e late hatch period in 1976-1978 to d eter­
mine the presence and distribution of non­
productive geese.
Results
N on-productive geese at La Pérouse Bay
had three options: leave the breeding area
on a moult m igration, or rem ain and moult
either dispersed am ongst flocks of produc­
tive adults with goslings, or in segregated
flocks. T he evidence sum m arized below
indicates that the m ajority m ake a moult
m igration, but th at some do join adults and
young. T here is no evidence for the local
presence of m oulting flocks of only non­
productive geese.
T he m ajority o f yearlings and non­
breeding adults rem ain at La Pérouse Bay
for four to six w eeks until around m id­
hatch. D uring this period, they use a great
variety of habitats within or n ear the
periphery of nesting areas. Virtually all
non-defended space in th e colony is used.
Individual yearlings and sibling groups
were often closely associated with their
parents during egg-laying and early incuba­
tion. L ater, these and adult non-breeding
pairs congregated in flocks of up to 400
birds. T he geese whose 1976 nests were
destroyed joined these groups of non­
productive geese within hours of nest loss.
T he eight m arked pairs were sighted 40
times during the two w eeks after nest loss;
31 tim es they w ere in flocks which aver­
aged 59 birds (range 3 —400), 60% of which
were yearlings.
By the late incubation period there was a
noticeable increase in flock size and in
local m ovem ents, presum ably associated
with prem igration restlessness. G round
counts of non-productive geese at La
Pérouse Bay im m ediately prior to hatch
gave estim ates of 3,700 in 1976, 5,000 in
89
W ildfowl 31 (1980): 89-93
90
Kenneth F. A braham
Figure 1. Location of La Pérouse Bay breeding colony and the McConnell River area where La
Pérouse Bay non-productive snow geese were caught after moult migration.
1977, and 1,500 in 1978 (Table 1). The
large num ber in 1977 was due to the p re­
sence of m any failed and non-breeders that
year. The sm aller num ber in 1978 reflects
both low production in 1977 and a general­
ly successful nesting season in 1978.
T he large, m obile flocks so evident im ­
m ediately prior to the com m encem ent of
hatch were absent each year during the
post-hatch period. The idea that they
might simply alter their behaviour (i.e.
becom e flightless and thus less visible to
ground observers) was tested by aerial
surveys. No flocks of non-productive geese
were located in any year. Boag (1974) had
earlier shown th a t geese w ithout young
com prised less th an 2% of the adult and
sub-adult geese in post-hatch flocks p ho to ­
graphed during aerial surveys. J. A . Smith
(pers, com .) also found this to be true
during ground observations in 1977.
Small
num bers
of Snow
G eese
w ere observed in flocks of m oult m igrant
C anada G eese in each year from 19761978. M oult m igrant geese of both species
passed over L a Pérouse Bay flying in a
northw esterly direction on 16-20 June
1976, 14-17 June 1977, and from 19-29
June 1978. Some flocks of m igrating geese
in 1978 landed on the bay shore; later
these, and others which did not land, flew
out of sight over H udson Bay. A lthough
the Snow G eese with them may have ori­
ginated far south of La Pérouse Bay, these
observations provide positive evidence of
moult m igration. T he disappearance of the
prom inent flocks discussed above occurred
at the same tim e as the C anada G oose
M oult migration o f Lesser Snow Geese
91
Table 1. Summary of La Pérouse Bay banding data from 1972-1978 and estimated number of
non-productive geese. N um bers given for banding include only m ass-capture drives in which all geese
w ere handled.
1972
N um ber of yearlings in
11
banding drives
N um ber of yearlings plus
985
adults in banding drives
M
Percent yearlings
‘ E stim ated num ber of non­
productive geese present
before hatch
tE stim ate d num ber of non­
productive geese m oulting
at La Pérouse Bay
Estim ated num ber and percent
of total non-productive geese
making a m oult m igration
1973
17
1974
31
1975
1976
1977
1978
13
50
98
14
1,800
1,513
1,257
593
1,005
1,558
5-4
0-9
3-2
1-4
5-2
1-3
3,700
5,000
1,500
348
388
258
3,352
(90-6)
4,612
(92-2)
1,242
(82-8)
1972-1978
average
_
2-7
90-3
* A erial survey in 1976, ground surveys in 1977 and 1978.
t A n estim ated 23, 34, and 17 percent of post-hatch population at La Pérouse Bay was handled in
mass capture drives in 1976,1977, and 1978 respectively. T hese estim ates thus represent the num ber
of captured yearlings adjusted for proportion of colony handled, plus 2% of the adjusted num ber of
adults (Boag 1974 and see text).
m igration during m id-June each year.
In 1976, the feather-dyed ‘failed breed­
ers’ rem ained close to their nest sites until
hatch, then began to range th e entire col­
ony as hatch approached. T hey w ere last
sighted on 20 June 1976, again at the same
tim e m oult m igration was noted. A lthough
it is difficult for ground observers to dis­
tinguish an actual departure flight from
local m ovem ents, and thus establish the
exact date of the m igration exodus from
the colony area, the observations above
provide strong circum stantial evidence for
a m oult m igration of La Pérouse Bay Snow
G eese.
Banding data collected from 1972 to
1978 at La Pérouse Bay is sum m arized in
T able 1. No flocks consisting only of non­
productive geese w ere observed or cap­
tured. T he proportion of yearlings in the
captured sam ple (excluding goslings)
varied from 0-9 to 5-4% . E ven in the year
o f highest num bers (1977), this yields an
estim ate of only 388 non-breeders, or 10%
of the estim ated pre-hatch num bers. Thus,
about 90% of La Pérouse B ay’s non­
productive geese leave the area to moult.
A continued attachm ent to parents prob­
ably encourages som e yearlings to remain
at the colony for the wing m oult. O f a small
sample of 10 yearling geese, whose parents
w ere identifiable and known to nest during
the year, 4 w ere captured in th e same flock
as their parents.
Conclusive evidence of m oult migration
is provided by the case history of a female
Snow G oose from La P érouse Bay banded
as a gosling in 1975. D uring the period of
14 May to 4 June 1977, she was sighted on
seven days in a nesting area of the colony.
She showed no attachm ent to a nest site,
and her behaviour was inconsistent with
th at of known nesting birds although she
was with a m ate. It can be concluded that
she was a non-breeder th a t year, as are
m ost 2-year-old Snow G eese (Finney &
C ooke 1978). Seven w eeks after the final
sighting at La Pérouse Bay, she was cap­
tured during her wing m oult in a flock of
non-prodüctive Snow G eese near the
M cConnell River, N orthw est T erritories,
250 km to the north (Figure 1). She re­
turned to La Pérouse Bay in 1978 and
nested th ere, successfully raising four
young. A n o th er 65 geese banded at La
Pérouse Bay betw een 1969 and 1976 were
captured near the M cConnell River in
1977.
Discussion
N on-productive Snow G eese from the La
Pérouse Bay, M anitoba colony m ake an
annual m oult m igration in mid- to late June
after a 4 to 6 w eek residence at the colony.
T he num ber and age of individuals in­
volved varies, but may have included as
92
Kenneth F. A braham
many as 4,600 birds in 1977. A t least some
of the geese m igrate 250 km northw ard.
Thus the num bers, age and reproductive
status of participants, and the direction of
the m igration are in agreem ent with known
m oult m igrations for other A nser and
Branta species (Salom onsen 1968).
M oult m igrations involving other breed ­
ing colonies of Snow G eese are suspected
but have not been docum ented. In the
eastern arctic population, no m oulting con­
centrations of non-breeders have been re­
ported at locations rem ote from breeding
areas, although Brace et al. (1978) and
C. D. A nkney (pers, com .) have suggested
that some non-breeders from the M cCon­
nell R iver colony m igrate to other areas to
m oult. It is know n only that many non­
breeding geese m oult near the large breed ­
ing colonies at the M cConnell River, on
Southam pton Island, and on Baffin Island
(M anning 1942; Cooch 1958; Barry 1962;
H anson et al. 1972; K erbes 1975; Brace et
al. 1978). For the w estern arctic popula­
tion, U spenski (1965) and B arry (1967)
reported that the non-breeding geese did
not return in spring to the colonies at
W rangel Island, Siberia, and A nderson
River and Kendall Island, N W T, respec­
tively. King (1970) and King & Hodges
(1979) located m oulting Lesser Snow
G eese near T eshekpuk Lake, on A laska’s
arctic slope, approxim ately mid-way b e­
tw een the W rangel Island and w estern
Canadian breeding areas. The decreasing
num bers of Snow G eese m oulting there in
the 1970s (D erksen et al. 1979) suggests a
link with the W rangel Island colony which
has been declining (D zubin 1979). H ow ­
ever, banding d ata (King & H odges 1979)
suggest ties with both breeding areas. The
small num ber of geese m eans that this is
not the only m oulting location for non­
breeders from those colonies. B arry (1967)
had previously rep o rted concentrations of
non-breeding Snow G eese on the north
end of Banks Island (Thom sen R iver and
Castel Bay).
T he significance of m oult m igrations in
the life history of geese is not yet com plete­
ly understood, although several explana­
tions have been proposed (Salom onsen
1968). The data from La Pérouse Bay show
that some mixing of Snow G eese from
different colonies occurs as a result of
m oult m igration. This may also be the case
at o th er eastern arctic colonies and the
A laskan m oulting area. W hether the mix­
ing is tem porary, or p erm anent and leading
to genetic exchange betw een colonies, has
im portant im plications. For exam ple, D zu­
bin (1979) suggested th at mixing during the
moult could have contributed to recent
increases in the frequency of blue phase
Snow G eese in w estern N orth A m erica.
These findings and lack of inform ation
about the m oulting areas of the large east­
ern arctic population underscore the need
for further studies of m oult m igration.
Acknowledgements
I am grateful to D r F. C ooke for allowing m e to
analyse data from La Pérouse Bay banding and
for m uch helpful criticism and discussion of this
paper. I thank R. F. H ealey for m any construc­
tive com m ents, and J. C. D avies, P. M ineau and
J. A. Sm ith for reviewing earlier drafts and
D . A braham for typing all drafts of the paper.
R. K. Brace and G . H . Finney of the Canadian
Wildlife Service provided the inform ation on
birds captured n ear the M cConnell R iver in 1977
for which I am grateful. T he a uthor received a
grant for a study of non-productive Snow G eese
from the W ildlife M anagem ent Institute and the
A m erican Petroleum Institute. The La Pérouse
Bay Snow G oose p roject is a continuing study
funded by the C anadian W ildlife Service and
National R esearch Council o f Canada.
Sum m ary
Over 90% of the yearling and non-productive
adult Lesser Snow G eese A n se r c. caerulescens
from the La Pérouse Bay colony annually par­
ticipate in a m oult m igration during m id-June,
after a 4-6 w eek residence. Some of them
undergo m oult 250km to the north, at the
M cConnell R iver, N orthw est T erritories. The
occurrence of m oult m igration at o th er Lesser
Snow G oose breeding colonies is suspected but
not yet docum ented. F u rth e r study is required to
locate m oult areas of non-productive geese and
to ascertain the significance of intercolony mix­
ing.
M oult m igration o f Lesser Snow Geese
93
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