f ie ldstudyfeature - Long Point Waterfowl

Forêt boréale
du Nord
Life’s a Journey
Prairie du
Nord
Grands
Lacs
Article by
Côte
atlantique
Scott Petrie and Kerrie Wilcox
Photos: Ron Ridout
I
Spring migration begins as the Tundra Swans depart
from the Atlantic coast wintering grounds throughout
February. The swans do not arrive at their breeding grounds
until mid-May to mid-June, over 100 days later. On average,
our transmitter-equipped swans were found to spend about
50% of their annual cycle in staging areas (29% in spring,
23% in fall) and used four distinct staging regions during
migration: the Atlantic coast, Great Lakes, northern prairies,
and boreal forest (see map of North America).
f you want to track a Tundra Swan, first you have to catch it.
That seems reasonable enough, but rather hard to rationalize
after hours of crouching in a snowy ditch on the edge of a
windy field in the mind-numbing cold. The evening before, we had
positioned rocket nets at the field boundary between winter wheat
and corn. We knew the swans had been recent visitors, feeding on
the wheat and waste grains.
Eventually, our patience paid off. A flock of Tundra Swans
glided onto the field. The birds moved slowly and purposefully
through the wheat toward the corn, intent on consuming important
calories for the long trip north to the breeding grounds. As the
swans moved into range, we launched the rocket nets and sprang
into action as they fell over 15 birds. Success! Once in the nets, the
swans become quite docile and cooperative. Each one is measured,
weighed, sexed, and banded or, in the case of a special few,
outfitted with a satellite transmitter so we can track their journey to
their Arctic breeding grounds and, with any luck, back south to
their wintering grounds.
The Tundra Swan is the most widespread and numerous
species of swan in North America. The eastern and western
populations of this species are distinct. The eastern population is
known to migrate through Long Point (their point of capture for
this study) and surrounding parts of southern Ontario as the birds
make their extensive annual migration between their Atlantic coast
wintering areas and Arctic breeding grounds. Little is known,
however, about the birds’ activities at stopovers along the way.
Bird Studies Canada’s Long Point Waterfowl and Wetlands
Research Fund (LPWWRF) initiated a Tundra Swan research
program in 1998 to investigate the chronology of spring and fall
migration and the relative use of terrestrial and aquatic habitats at
key stopover areas. Since 1998, the
movements of 12 transmitterequipped swans have been tracked
for varying periods to provide
insight into the duration of
migration stopovers and habitat use
along their journey.
Long Point was chosen as a
suitable capture site for this study
because Tundra Swans use its vast
wetlands extensively during
migration. In fact, mean peak fall
counts (which provide a minimum
estimate of swan use) at Long Point
have increased to 7.9% of the
eastern population in the 1990s
from 0.7% in the 1970s.
Once swans are fitted with a
transmitter, their locations are
Spring and fall locations and migration routes of satellite-tracked Tundra Swans, identifying
four important staging regions, 1998–2000.
Routes migratoires printanières et automnales des Cygnes siffleurs munis d’un émetteur
satellites de 1998 à 2000. Les quatre principales régions contenant les haltes migratoires sont
identifiées sur la carte.
On average, our transmitter-equipped swans were found
to spend about 50% of their annual cycle in staging areas.
FEATURE
FIELD STUDY
tracked by three ARGOS satellites that continuously orbit the
Earth 850 kilometres above its surface. Each time they pass
overhead, the satellites detect the transmitters across a 5000kilometre path, picking up the frequency from a particular
transmitter. This information is converted to a geographical
coordinate (latitude and longitude) and relayed to a ground
station in the United States, and then to our computers via email shortly after the satellite’s pass.
So, why does spring migration take over 100 days when
the actual total flight time to complete the journey is only
about 115 hours? A lengthy spring migration may be a
Le voyage des Cygnes siffleurs
Nous ne connaissons encore que très
peu de choses sur la migration des
Cygnes siffleurs de la population de
l’Est (Cygnus colombianus
colombianus) ainsi que sur leur écologie
lorsqu’ils effectuent des arrêts
migratoires. Entre 1998 et 2000, 12
cygnes portant un émetteur satellites,
soit attaché à leur cou sous forme de
collier ou à leur dos à l’aide d’un
harnais, ont été suivis durant leurs
trajets migratoires à partir de Long
Point, située le long du lac Érié, une des
plus importantes aires de repos pour
cette espèce au printemps et à
l’automne. Le suivi satellitaire, de
même que les inventaires aériens, ont
permis de confirmer que la région de
Long Point constituait la dernière halte
migratoire d’importance pour les cygnes
en route vers le sud à l’automne et la
première halte migratoire au printemps.
Il a été noté que les oiseaux possèdent
une bien meilleure condition physique
quand ils arrivent sur les côtes de
l’Atlantique tard à l’automne que
lorsqu’ils en repartent au printemps. Le
temps qu’ils passent à s’alimenter dans
les champs agricoles de la région de
Long Point et ailleurs dans le sud de
l’Ontario leur permet donc sans aucun
doute d’accumuler les réserves de gras
nécessaires pour poursuivre leur trajet vers
les Prairies aux États-Unis et au Canada.
En quittant la région de Long Point au
printemps, les cygnes traversent
rapidement le Michigan et le Wisconsin
pour atteindre le Dakota du Nord, le
Manitoba et la Saskatchewan, où ils
s’arrêtent pour une longue période afin
d’emmagasiner de nouvelles réserves. Les
réserves de gras qu’ils accumulent lors de
cette seconde halte leur permettront de
produire les oeufs qui seront pondus à leur
arrivée sur leur territoire de nidification.
Il a été possible de déterminer que les
cygnes munis d’un émetteur satellites
avaient atteint différents sites de
nidification situés dans l’Arctique : le
delta du fleuve Mackenzie au Yukon, l’île
Victoria et le golfe de la Reine-Maude au
Nunavut et les côtes de la baie d’Hudson
au Manitoba et au Nunavut. Bien que les
oiseaux se déplacent en général sur des
distances de moins de 500 km entre
chaque étape de leur trajet migratoire entre
la côte Atlantique et les Prairies, il a été
noté qu’ils voyageaient sur des distances
beaucoup plus grandes lors de leurs
derniers déplacements vers les sites de
nidification. Un oiseau a ainsi déjà
franchi 1900 km sans s’arrêter entre le
nord de la Saskatchewan et le delta du
fleuve Mackenzie.
En moyenne, la migration printanière
dure de 3 à 4 mois durant lesquels les
cygnes passent autant de temps que
possible dans les champs agricoles afin
de bénéficier au maximum d’une source
de nourriture riche et abondante. Les
cygnes, qui ne se nourrissaient
auparavant que de plantes aquatiques,
ont commencé à utiliser les champs
vers le milieu des années 50. Ce
changement de comportement leur a
permis de réduire leur dépendance par
rapport aux habitats aquatiques pendant
la migration, un changement qui permet
probablement d’expliquer
l’augmentation du nombre de cygnes et
les modifications qui ont été apportées
à leurs habitudes et à leurs routes
migratoires. Comme les Cygnes
siffleurs passent près de la moitié de
leur vie dans les haltes migratoires, on
comprend aisément l’importance
d’assurer la protection de ces sites ainsi
que le besoin de continuer à étudier leur
écologie durant cette période.
Photos: Ron Ridout
4
BIRDWATCH CANADA
SPRING 2002, NUMBER 19
5
The Breeding Grounds
Our satellite-tracked swans bred on the
western shore of Hudson Bay, Victoria
Island, Queen Maude Gulf, Mackenzie
River and the Mackenzie River Delta. They
arrived at the breeding areas between midMay and mid-June and departed between
late August and late September. The total
time spent in or near their breeding areas
ranged from 76 to 140 days.
Since it takes from 102 to 117 days to
raise cygnets to an age at which they can
successfully migrate, swans that spent
in good condition when they arrive and
therefore have less need to linger and
store nutrients.
Most of our satellite-tracked swans
migrated almost directly from southern
Ontario to northern Chesapeake Bay.
From Maryland, they made numerous
stops along Chesapeake Bay as they
migrated south to North Carolina. While
in southern Ontario in fall, Tundra
Swans at Long Point fed primarily in
aquatic habitats as opposed to the
agricultural fields that they primarily
used in the spring (see maps of Long
Point). Information provided by satellite
tracking suggests that swans continue to
feed in aquatic areas in Maryland, but
feed more in agricultural areas as they
move south through Virginia and into
North Carolina. This may be due to
declining availability of submerged
aquatic vegetation as winter progresses,
or may simply reflect a dietary
preference for waste corn in late winter.
relatively short periods of time in their
breeding areas were probably unsuccessful
breeders that departed early. Two of the
swans remained in breeding areas for at
least 112 days, suggesting that they both
bred and raised broods successfully.
Fall Migration
Tundra Swans tend to use similar
migratory pathways during spring and fall.
Some noticeable differences exist,
however, in habitat use at staging areas, as
well as in the amount of time spent in each
of the major staging regions. The swans
migrated more quickly in fall, possibly
because of rapidly advancing winter
conditions, whereas in spring their progress
is more likely delayed by ice cover and the
need to gain fat for reproduction.
Although swans were found to spend
limited time staging in the northern boreal
forest region in spring (an average of 14
days), they spent relatively long periods
there in fall (32–49 days). The availability
of submerged aquatic vegetation in boreal
forest wetlands would be higher in fall,
after the summer growing period, than in
spring. Tundra Swans fledge at a smaller
proportion of their adult mass than is the
case with geese and are still growing when
they leave their breeding areas. Therefore,
increased time spent in the northern boreal
forest in fall, relative to spring, is probably
due to continued growth requirements and
the limited stamina of juveniles, and
Transmitters were first placed on the swan’s back. It was later found that they worked
better when affixed to the plastic collar.
Les émetteurs ont d’abord été attachés au dos des cygnes. On constata par la suite qu’il
était plus efficace de les attacher sur le collier de plastique.
FEATURE
amount of time that Tundra Swans spent in
the boreal forest region in spring, we
suggest that they already have ample fat
stores and remain in this region only until
weather conditions enable them to
complete the migration.
The availability of agricultural grains
and winter wheat has become a major
influence on the migration schedule of
Tundra Swans, especially in spring.
Whereas Tundra Swans spend 40% of their
time during spring migration in the northern
prairies and 27% in the Great Lakes region,
they spend only 15% of their time in the
northern boreal forest region. Their
migration pattern enables them to consume
large quantities of agricultural grains
(especially corn) that have a high
carbohydrate content that gets turned into
fat reserves.
FIELD STUDY
function of food depletion in wintering
areas, the ready availability of agricultural
grains and winter wheat in spring staging
areas, the need for juveniles to migrate
slowly, or the need for the swans to arrive
on their breeding grounds soon after spring
thaw with ample fat reserves, which they
need in order to reproduce.
Tundra Swans lose body mass
throughout the winter and are still in
relatively poor condition when they arrive
in southern Ontario in early March. The
distance between Tundra Swan wintering
areas in North Carolina and southern
Ontario is at least 1000 kilometres, and it is
an additional 1500 kilometres to their next
major staging region in the northern
prairies. Time spent consuming waste corn
and submerged aquatic plants in the lower
Great Lakes region would enable swans to
acquire the fat they need to continue
migrating to the northern prairies.
In late March and early April, satellitetracked swans migrated west from the
Great Lakes to the northern prairies where
they spent from 25 to 45 days. This
extended stay on the prairies, combined
with the need to arrive in breeding areas
with ample fat reserves and the fact that the
swans still have between 900 and 2000
kilometres left to migrate, suggests that
swans probably acquire substantial fat
reserves for migration, as well as for
reproduction, while staging on the
northern prairies. Based on the limited
Summing Up
Tracking the movements of
individual
birds has significantly
Spring (triangles) and fall (circles) locations of satellite-tracked Tundra Swans
contributed to our understanding of
at Long Point.
seasonal variations in habitat use and the
Localisations des Cygnes siffleurs dans la région de Long Point au printemps (triangles)
migrational movements of the eastern
et à l’automne (cercles).
Tundra Swan population. While Tundra
possibly to the need for adults to replenish in spring. Tundra Swans that stop in Swans tend to maximize the time they
nutrients used during reproduction and southern Ontario in fall do so for about three spend in agricultural fields in spring,
flight-feather moult.
weeks. Large numbers of swans in the they are more dependent on large
After leaving the northern boreal eastern population also stage on the upper wetlands in fall. Also, conservation of
forest, satellite-tracked birds staged on Mississippi River in fall for three or four staging habitats is critical for the eastern
large inland wetlands in central and weeks. The amount of time swans spend on population since swans spend half their
southern Saskatchewan. Use of these the lower Great Lakes and upper lives migrating between Atlantic coast
wetlands at that time can be attributed to the Mississippi River in fall is probably wintering areas and Arctic breeding
swans foraging primarily on submerged dictated primarily by weather, as swans are grounds.
aquatic plants during fall migration. Tundra
Swans spent less time (21 days on average)
in the northern prairie region during fall
migration than during spring migration (37
days on average), a difference that may
simply be due to the fact that, after
spending a prolonged period of time in the
northern boreal forest in fall, they have
limited time to remain on the prairies
before freeze-up.
One satellite-tracked swan made the
arduous trek from the northern prairie
region to North Carolina, a distance of
2895 kilometres, within four days.
Movements of this swan on the breeding
grounds suggest that she did not breed
successfully. Migrating without immature
swans in tow may have enabled this bird to
make such an extensive and rapid journey.
Some evidence, however, indicates that
Tundra Swans routinely travel longer
Photo: Ron Ridout
Can you spot the collared swan?
distances between staging areas in fall than
Pouvez-vous trouver le cygne portant un collier?
Photos: LPWWRF
6
BIRDWATCH CANADA
Photo: Ron Ridout
SPRING 2002, NUMBER 19
7