Canadian Report : An Achilles' heel for Bluebills
By Bob Bailey
I first saw where young lesser scaup were made in spring 1970, in the
Minnedosa- Erickson prairie pothole country, in southwestern Manitoba, and
it astonished me. I had grown- up hunting lessers and greaters on big
water. Bluebills were synonymous with inland seascapes, where rising plumes
of divers traded between distant, purple points of fading land. Scaup
looked strange in tiny ponds, and even stranger when I found my first scaup
nest on dry land. The startled hen paddled through the grass from her nest
near water. Her big webbed feet and short legs were way too far back for
land travel. I could have easily caught her with my hands.
Scaup Population Status
Greater and lesser scaup are counted together on breeding ground surveys,
although lessers are much more abundant. Greaters are most numerous in
Alaska, whereas lesser scaup breed from the prairies into the boreal forest,
and in northern river deltas. Population data used here is summarized in a
November 2004 Canadian Wildlife Service (CWS) report by Bruce Pollard and
Kathy Dickson.
Scaup have declined from a continental average of over 6 million breeding
birds in the 1970s to mid 1980s, to about 3.8 million in the last two years.
But the overall decline in scaup seems to break down into two problem areas:
the western boreal forest and the Canadian Prairies. Lesser scaup breeding
in the US portion of the prairies dropped from the early to mid- 1990s, then
rebounded to a higher stable level from the mid- 1990s to 2004. This higher
level is more than double the numbers of scaup breeding in the US portion of
the prairies in the 1960s and 70s. Similarly, scaup in Alaska have remained
at a fairly stable, high level since the 1960s.
The greatest decline in scaup numbers occurred in the boreal forest where
they dropped from around 4.3 million from 1970 to the mid 1980s, to 2.2
million in 2004. The boreal population seems to have stabilized over the
past 3 years. The Canadian Prairie population decreased from over 1 million
birds in the mid- 1970s to 80s, on a roller- coaster ride to around 340,000
in 2004.
Reasons for the Scaup Decline
Most experts concede that harvest has little to do with the declines
witnessed in scaup, and the information provided by Pollard and Dickson
report confirm that finding. Several biologists I interviewed question the
magnitude of the decline, pointing out that the breeding population surveys
are conducted for mallards, and occur too early to portray an accurate
picture for scaup. However, many biologists reflect what scaup hunters
already know, that bluebills are not as abundant as they once were.
Dr. Al Afton's research team at Louisiana State University is leading one of
the two principal avenues of research on the scaup decline. Afton's team
has shown dramatic decreases in "amphipods" or freshwater shrimp, used by
scaup during spring migration and on the southern prairies. Afton notes
that other food resources could become limiting with contamination of
wintering habitats, particularly following the clean- up operations in the
aftermath of recent hurricanes. These factors, coupled with direct risks
from ingestion of contaminants, may put female scaup in poorer body
condition for breeding, or introduce other impacts on reproduction.
Dr. Scott Petrie's team at the Long Point Waterfowl Research Foundation have
found elevated levels of selenium in both scaup species during the winter
and spring migration on Lake Ontario. Scaup are accumulating selenium by
feeding on abundant zebra mussels. Although elevated levels of selenium can
cause stress or death in waterfowl, it is unknown whether scaup visiting the
Great Lakes are able to eliminate the element prior to arrival on the
breeding grounds. Petrie's colleagues are investigating the impacts of
selenium on breeding scaup in Alaska.
Achilles heel for Scaup
Population data shows two major declines in scaup: in the western boreal
forest and on the Canadian Prairies. Doubling of the scaup population on
the US Prairies over the past four decades suggests dramatic differences may
exist between the US and Canadian Prairies for breeding scaup. Similarly,
the high yet stable populations of lesser and greater scaup in Alaska, would
suggest that the decline does not apply to that part of the scaup range.
"The problem is not the decline but the lack of scaup recovery" said Dr.
Dave Ankney, a retired waterfowl researcher from the University of Western
Ontario, "many other species declined much more than scaup in the mid 1980s,
but have rebounded to high levels." Since scaup are doing well in Alaska
and on the US Prairies, resource availability or selenium contamination may
not be preventing a recovery at this time. "You may have to look elsewhere
for solutions," he added.
I thought about my encounters with breeding scaup on the prairies of
Manitoba and Saskatchewan in the 1970s and early 80s. Scaup, like white-
winged scoters seemed to be just hanging on over vast stretches of the
prairies. As the prairie was cultivated and settled, new predators like the
fox, raccoon and skunk invaded the breeding habitats of these birds. If I
could catch a hen scaup or scoter nesting on dry land, imagine how easily a
fox could. The work of pioneers like Al Sargeant at the Northern Prairie
Research Center in North Dakota showed decades ago, how red fox could target
and destroy dozens of nesting mallards, certainly a greater challenge than
catching a poorly equipped aquatic bird out of water.
Al Afton mentioned the decline of scaup over the past 20 years on his study
area at Erickson Manitoba, some of the best scaup breeding habitat remaining
on the Canadian Prairies. When Al noted that scaup are highly philopatric
species (hens and their female offspring home the following spring to the
place they were born), a pattern for the removal of scaup by mobile new
predators began to take shape.
Eradication of nesting birds by newly- introduced predators is a well-
documented, world- wide phenomenon, caused by the impacts of human
settlement, cultivation and trade on the environment. Arctic foxes released
on the Aleutian Islands nearly eliminated the Aleutian goose, a small
relative of the Canada. A predator control program on the islands brought
Aleutians back from the brink and it has now be removed from the list of US
endangered species. Other birds threatened by predators expanding on the
heels of settlement, like shearwaters and oystercatchers nesting on the
beaches of east coast islands in the US, have been saved by predator
management.
The hen scaup's exceptional vulnerability to new predators on the prairies
would make it one of the first ducks to disappear as the land was cultivated
and settled. As invading predators picked off hens, daughters and nests
on portions of the breeding range over time, there would be no survivors to
home to the area. Unlike other species like blue- winged teal, scaup hens
are highly philopatic, so there would be no reservoir of nomadic breeding
females, shifting with changing patterns of water availability across the
prairies each spring. For example, if all the hen teal were killed by
predators (but even foxes would have trouble catching every teal) in any
given spring on a section of breeding habitat, there could be twice as many
teal appear on the area the following spring, if the water conditions are
favorable. But in the case of scaup, once the hen and her daughters are
removed, that is the end of the breeding legacy on that part of the nesting
grounds.
Canvasback hens are also highly philopatric, and closely related to scaup.
But cans did recover since the mid- 1980s, setting new population records
and remaining at a fairly high, stable level. Canvasbacks are also divers,
and would be extremely awkward and easy to catch on land, however, they seem
to have solved this problem by mostly nesting over water. Redhead hens,
like breeding teal are nomadic, following the spring water, yet like
canvasbacks, redheads build their nest over water, as does the ruddy duck.
Redheads, canvasbacks and ruddy ducks may be plagued in some areas by
raccoon predation, but they are virtually invulnerable to capture by foxes.
So why wouldn't hen scaup solve the predation problem by nesting over water
like the other species? It takes a species time to adapt to new situations
and new predators. The arrival of foxes, raccoons and skunks on the
prairies is very recent and these predators are extremely efficient at
removing ground nesting birds and their eggs. This is perhaps why so
relatively few scaup were recorded in the earliest surveys on the prairies-
they were the first birds to be reduced substantially by invading predators.
The vulnerability of scaup to new predators and their early disappearance on
the prairies seems to fit with the observed increase of scaup on the US
prairies, since the mid- 1990s. The US prairie scaup increase coincided
directly with the establishment of millions of acres of grasslands under the
Conservation Reserve Program (CRP) in the mid- 1980s. Where sufficient
upland nesting cover exists (and we are talking millions of acres of grass
under CRP), scaup are not as easily found, even by new predators. This idea
may also explain why scaup are doing well in Alaska, but it doesn't explain
the downward trend observed in the heart of the western boreal forest.
I looked at the ringneck population data to see if ringnecks could shine
some light on the fading fortunes of scaup in the boreal forest. The
ringneck is a similar- sized diving duck, which overlaps the heart of the
scaup breeding range in the western boreal forest. Ringneck populations
have more than doubled since 1980 on the US Prairies, and are steadily
rising to new heights in Alaska - basically the same pattern exhibited by
scaup in these regions. Ringnecks have fluctuated widely over the past 5
decades on the Canadian Prairies. Ringneck numbers have often been higher
than NAWMP goal levels on the Canadian Prairies, but they now appear to be
falling. However, in contrast to scaup, ringnecks have dramatically
increased since 1990 in the western boreal forest.
Several potential differences in the breeding biology of scaup and ringnecks
may explain the opposite trends for these species in the boreal forest.
Ringnecks tend to nest over water, on floating bogs in boreal habitats,
whereas scaup prefer nesting on land. As noted for diving ducks on the
prairies, even a small difference in the propensity of each species to nest
over water, could produce big dividends in brood production and population
growth. The second principal difference is the attentive behavior of
ringneck hens, which tend to remain with their broods until the young can
fly. Scaup hens often abandon their ducklings earlier, even at the downy
stage. Scaup hens tend to concentrate their nests and newly- hatched young
scaup often gather in large "gang- broods" like Canada geese, with few hens
watching over them.
The nesting and brooding differences between scaup and ringnecks may not
amount to much for each population if all things had stayed the same in the
boreal forest. However, the influences of humans, climate change and other
factors are pervasive in the forest, and may have some negative implications
for scaup and ringneck populations. There has been a huge continent- wide
growth of gull populations, with marine species moving inland and others
establishing larger colonies on inland waterways. Thirty years ago I
observed gulls preying on ducklings and young coots on a daily basis while
conducting waterfowl research in the western boreal forest. Native
residents commented on the new abundance of gulls. Herring gulls and ring-
billed gulls are numerous in the lake and forest country, and they are
highly efficient at capturing ducklings, particularly where guarding hens
are absent, and the broods frequent open water. There is a possibility that
changes in predator abundance in the forest may also be influencing these
species, and changes may also be occurring too quickly for scaup to adapt
their nesting and brooding behavior.
A lifetime of biological puzzles has taught me that there is seldom a single
cause to a problem and often several potential solutions, especially dealing
with populations of birds over a continent. It has also taught me that
predation is not a peripheral pressure on duck populations, as it can shape
the distribution and abundance of many species.
Drs. Frank Rowher and Elizabeth Loos at Louisiana State University have been
conducting predator management research on the prairies of North Dakota with
Delta Waterfowl over the past 6 years. Rowher says, "when we found our
first scaup nest 6 years ago, all the students came over to look at it, so
they could say they actually saw a scaup nest in North Dakota. But this
year, a master's (MS) student who needed to find in the order of 200 scaup
nests for his study, found them on our area in record time, completing his
field work weeks ahead of schedule. The growth in the scaup breeding
population on the predator managed areas here has been phenomenal. Another
student working on his MS a few years earlier, worked hard with twice as
many assistants and got fewer than half that number of nests in two years,
in what had been some of the best scaup breeding habitat in Manitoba."
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Topic: Scaup & Ringbill Report (Read 3826 times)
