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Waterfowl Responses to Zebra Mussels on the Lower Great Lakes

Birding • august 2002
1,2 Long Point Waterfowl and Wetlands
Research Fund Bird Studies Canada
P. O. Box 160
Port Rowan ON N0E 1M0
SP is the research director of the Long
Point Waterfowl and Wetlands
Research Fund. His work has focused
primarily on the ecology of waterfowl
in semi-arid environments and the
staging ecology of waterfowl in north-
temperate regions.
MLS is a Ph.D. candidate in Zoology
at the University of Western Ontario,
where he specializes in waterbird
research and the advancement of wet-
land conservation. His areas of inter-
est include waterfowl population
dynamics, socio-economic impacts on
wetland conservation, and landscape
Waterfowl Responses to Zebra
Mussels on the Lower Great Lakes
Scott Petrie1 and Michael L. Schummer2
Greater Scaup, Buffleheads,
Long-tailed Ducks, and other
waterfowl species that con-
centrate in large numbers on the
Great Lakes each winter are in dan-
ger of being poisoned by a novel
food source. The problem is present-
ed by a small creature with a
remarkable ability to concentrate
toxic substances found in lake
water—the zebra mussel.
The Great Lakes are widely
acknowledged to be one of the most
beleaguered ecosystems in North
America. Water pollution and shore-
line development are two of the bet-
ter- known affronts on this ecosys-
tem, but some ecologists consider
exotic plants and animals to be an
even greater threat. For better or for
worse, virtually every native species
in the Great Lakes has been impact-
ed by exotics, and waterfowl are no
The introduction of the zebra mus-
sel (Dreissena polymorpha) and closely
related Quagga Mussel (D. bugen-
sis)—hereafter referred to collectively
as zebra mussels—is a fairly recent
phenomeon, but it has already had
dramatic impacts on plants, animals,
and ecosystem processes of the Great
Lakes. It is tempting to view this
mussel invasion as a positive develop-
ment for waterfowl. Zebra mussels
provide a novel food source easily
exploited by certain species of water-
fowl. But the short-term benefits of an
increased food supply may be out-
weighed by the threat of food con-
tamination: as zebra mussels feed,
they accumulate in their tissues tox-
ins that may be passed up the food
Long-tailed Ducks are annual on the lower Great Lakes. They are uncommon at most times and at most places, but large concentra-
tions are sometimes noted both on migration and during the winter months. It is unknown whether Long-tailed Duck populations on the
lower Great Lakes are being affected by the zebra mussel invasion in the region.
waterfowl responses to zebra mussels 347
Great Lakes and their inhabitants.
Native mussels, which averaged ten
individuals per square meter prior to
zebra mussel colonization, have been
almost completely displaced by this
highly competitive, exotic species.
Influence on Diet and Distribution
In Europe, zebra mussels provide a
readily available source of food used
by certain species of waterfowl. These
waterfowl species are known to alter
movement patterns to take advantage
of zebra mussels, particularly in
recently invaded lakes. It is not sur-
prising that certain species of North
American waterfowl also have shifted
their dietary choices, as well as their
distributions, to take advantage of this
novel, yet easy-to-find, food source.
When a prey item becomes super-
abundant and is easily exploited,
waterfowl tend to concentrate their
foraging efforts on that food source.
Zebra mussels certainly fit this bill (no
pun intended). They now are much
more readily available than any other
invertebrate food source, their con-
sumption generally requires limited
search, and they are easy to eat.
From 1991 to 1995, the diets of 552
ducks of twelve species were sampled
from the Long Point, Lake Erie, water-
fowl check station to identify food
habits. Five of the twelve species ana-
lyzed had consumed zebra mussels,
but only Lesser Scaup, Greater Scaup,
and Buffleheads consistently incorpo-
rated zebra mussels in their diet.
Other species of diving ducks have
been reported to consume zebra mus-
sels: Common Goldeneye, Long-tailed
Duck, and White-winged Scoter,
according to research by D.J. Hamilton
and C.D. Ankney. Given their inability
Exotic Introductions
From the common carp (late 1800s),
to the Eurasian watermilfoil (1952),
and to one of the newest introduc-
tions, the round goby (about 1990),
the Great Lakes have endured their
share of exotic invasions over the past
200 years. Over 140 non-indigenous
species have invaded the Great Lakes
since the early 1800s. Some intro-
duced species compete strongly with
native fauna and flora, often resulting
in changes in community structure.
This competition ultimately can influ-
ence food web interactions and ecosys-
tem functioning. Few introductions,
however, have had a greater effect on
the lower Great Lakes ecosystem than
has the zebra mussel.
Zebra mussels are small (less than
one inch) clam-like invertebrates
native to European lakes. They were
introduced into Lake St. Claire, east of
Detroit, in 1986, apparently a result of
the discharge of larvae in ship ballast
water. Faced with limited competition,
zebra mussels rapidly increased in
numbers, expanding their range
throughout the lower Great Lakes.
They occur at densities from a few
hundred to ten thousand per square
meter on sandy, loamy, and vegetative
surfaces. In rocky areas, where the
mussels preferentially settle, densities
have reached 750,000 per square
The ability to expand rapidly and
colonize new areas (via free-swimming
larvae called veligers), coupled with
the extremely high densities at which
they can occur (they can adhere to
most surfaces, including each other),
has enabled zebra mussels to change
the entire dynamic of the lower Great
Lakes lake-bottom community.
Previously slow-growing, with limited
influence on ecosystem interactions,
that community now is dominated by
a single species that has transcendent
effects on the ecology of the lower
Exotic zebra mussels can reach astonishingly high densities in suitable environments in
the lower Great Lakes. On sandy, loamy, or vegetative substrates, they occur at densities
of a few hundred to ten thousand per square meter. On rocky substrates, densities as
high as three-quarters of a million per square meter have been recorded. In contrast,
native mussels average only ten individuals per square meter.
Birding • august 2002
to forage in deep water, and a normal
diet of vegetation during the non-
breeding period, it is not surprising
that dabbling ducks generally do not
consume zebra mussels.
At Long Point, there was a three-fold
increase in the number of waterfowl
staging there between 1986 (prior to
zebra mussel colonization) and 1997
(six years after colonization). Most of
this gain can be attributed to increased
numbers of Lesser and Greater Scaup
(Figure 1). In fact, the use of Long
Point by Lesser and Greater Scaup
together increased 92-fold between
1986 and 1997 (based on day-use cal-
culations), despite a substantial
decline in the North American popula-
tion of scaup during that time. Similar
increases in scaup use have been
reported for Lake St. Clair, as well as
for Points Pelee and Rondeau on Lake
These increases in scaup numbers
are most likely a consequence of more
birds gathering in these areas during
migration and of those birds then
remaining longer to consume zebra
mussels. Not only has the presence of
the mussels influenced the diets of
certain species of diving ducks on the
lower Great Lakes, but it also has
caused dramatic shifts in their distri-
butions and relative abundance during
Although no dietary studies have
been performed on diving ducks win-
tering on the lower Great Lakes since
the arrival of zebra mussels, we do
know that there have been major
changes in the wintering populations
of waterfowl since zebra mussel colo-
nization. One of the better long-term
sources of information on wintering
Great Lakes waterfowl numbers is an
extensive ground-based midwinter sur-
vey of the Canadian shoreline of Lake
Ontario, compiled by Bill Edmunds of
the Toronto Ornithological Club.
Numbers of Birds
Figure 1. This chart shows a steep rise in Lesser and Greater Scaup populations at Long
Point, which is on the northern shore of Lake Erie. Similar increases have been reported
for Lake St. Clair, as well as for Points Pelee and Rondeau on Lake Erie.
Numbers of Common Goldeneyes wintering on the lower Great Lakes have increased
appreciably in recent years. These recent population increases are probably tied to the
fact that the species is a known consumer of zebra mussels—which are a potentially
major food resource for wintering waterfowl.
waterfowl responses to zebra mussels 349
Numbers of Canada Goose and dab-
bling ducks (all species combined)
increased by 2.8- and two-fold, respec-
tively, between 1980 and 2000. But
numbers of diving ducks (all species)
increased nine-fold (Figure 2).
Actually, wintering diving duck num-
bers have been increasing exponential-
ly since 1991, around the time zebra
mussels arrived on Lake Ontario. This
substantial increase in overwintering
diving ducks can be attributed for the
most part to increased numbers of
Lesser Scaup, Greater Scaup, Long-
tailed Ducks, Common Goldeneye,
Buffleheads, White-winged Scoters,
and Common Mergansers, all of
which—with the exception of
Common Mergansers—are known to
consume zebra mussels. Higher winter
temperatures and reduced ice cover
associated with the recent warming
trend have in all likelihood con-
tributed to increased use of the lower
Great Lakes by these birds. However,
substantial increases in numbers of
staging and overwintering birds have
been primarily limited to those species
which consume zebra mussels, which
suggests that mussel availability is
quite possibly a primary factor influ-
encing these changes in distribution
and abundance.
Possible Adverse Impacts
Rather than consuming algae and
other food items that adhere to rocks
and plants on the lake bottom, zebra
mussels acquire their nutrition by fil-
tering suspended matter from the
water. Each zebra mussel filters several
quarts of water per day. It is this pro-
lific filtering capacity, combined with
the fact that the animals occur at such
high densities, that has enabled zebra
mussels to have such a profound effect
on lake ecology. This species has
increased water clarity on the lower
Great Lakes, diverted organic matter
from the water column to the bottom,
The Lesser Scaup, like other diving duck species, appears to have been a beneficiary of
the recent zebra mussel invasion of the lower Great Lakes. But the species may suffer in
the long run from eating too many zebra mussels. This hazard arises because of the fact
that zebra mussels bioaccumulate toxins that are passed up the food chain to predators
such as the Lesser Scaup. In particular, Lesser Scaup may be in danger of eating zebra
mussels that have been contaminated with cadmium, selenium, polychlorinated biphenyls,
and polynuclear aromatic hydrocarbons.
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
Numbers of Birds
Diving Ducks
Dabbling Ducks
Canada Geese
Figure 2. This chart shows across-the-board increases in waterfowl populations on the
Canadian shoreline of Lake Ontario. Note that numbers of diving ducks have been
increasing especially rapidly.
Birding • august 2002
altered foodweb interactions, and
influenced contaminant and nutrient
cycling. The uptake and subsequent
transfer of contaminants through the
food chain by these creatures is an
area of continuing research and con-
Because they filter particles indis-
criminately, zebra mussels incorporate
and accumulate into their tissues
water-associated contaminants—poly-
chlorinated biphenyls (PCBs), polynu-
clear aromatic hydrocarbons (PAHs),
and heavy metals (e.g., cadmium).
They do this much more readily than
do native Great Lakes bivalves. These
contaminants can subsequently be
passed up the food chain to waterfowl
that consume the mussels. This ulti-
mately could compromise waterfowl
reproductive output or survival. For
instance, reproductive success in cap-
tive Tufted Ducks fed contaminated
zebra mussels was 60 percent less than
that of individuals fed less-contaminat-
ed mussels, according to research by
W.C. de Kock and C.T. Bowmer.
Waterfowl surveys on the breeding
grounds indicate that the continental
population of Lesser and Greater
Scaup declined from a high of eight
million birds in 1972 to 3.7 million in
2001. However, the bulk of this
decline has occurred since the mid-
1980s, around the time zebra mussels
began colonizing the Great Lakes.
United States harvest data also suggest
that the proportion of juveniles and
adult females in the Lesser Scaup pop-
ulation has declined over the last two
decades. This implies that both female
survival and breeding or fledgling suc-
cess have declined. Furthermore, there
has not been an increase in the num-
ber of scaup taken by hunters, and
populations of most other species of
diving ducks have been increasing
during the period of scaup decline.
Considering the increased use of the
Great Lakes by scaup, plus a diet shift
toward zebra mussels, scaup could be
acquiring unhealthy contaminant bur-
Studies to date have indicated that
PCB and DDE burdens in staging and
wintering Lesser and Greater Scaup on
the Great Lakes are below the known
effect levels for waterfowl. However,
selenium has been detected in the ele-
vated-to-potentially-harmful range in
most birds collected from Lakes
Ontario, Erie, St. Clair, and Michigan.
Elevated selenium levels (more than
ten parts per million, dry weight) can
impair reproduction; yet higher levels
(more than 33 parts per million) actu-
ally can cause mortality, according to a
1996 study by G.H. Heinz. Selenium is
a semi-metallic trace element occur-
ring naturally in some soils; it is also a
byproduct of smelting operations and
other industrial activities. Although
selenium is nutritionally required by
birds in very small amounts, it is high-
ly toxic in greater quantities.
Selenium can rapidly increase in
aquatic organisms, particularly in filter
feeders such as zebra mussels. Field
studies show that bottom-zone inverte-
brates can accumulate 20 to 370 parts
per million of selenium and still main-
tain stable, reproducing populations.
These levels are somewhat alarming as
reproduction in Mallards is impaired at
a dietary concentration of just nine
parts per million. It has been recom-
mended by A.D. Lemly that three parts
per million is the toxic threshold for
selenium in aquatic food-chain organ-
isms consumed by fish and wildlife.
Selenium concentrations quickly build
up in tissues when birds are intro-
duced to a selenium-contaminated
diet. Selenium is also quickly excreted
from the body when birds are removed
from a selenium source. Females use
the egg as a route of selenium excre-
tion, and high selenium burdens can
impair reproduction.
It is difficult to speculate at the present time about the eventual impacts of the zebra
mussel on waterfowl populations that winter on the Great Lakes. Zebra mussels present
a superabundant resource for Buffleheads and other species. But zebra mussels have
greatly destabilized foodweb dynamics and contaminant cycling in the lower Great
Lakes, with potentially harmful long-term effects on waterfowl populations.
Hamilton, D.J. and C.D. Ankney. 1994.
Consumption of zebra mussels
Dreissena polymorpha by diving
ducks in Lakes Erie and St. Clair.
Wildfowl 45:159–166.
Heinz, G.H. 1996. Selenium in birds.
pp. 447–458 in: W.N Beyer, G.H.
Heinz, and A.W. Redmond-Norwood,
eds. Environmental Contaminants in
Wildlife: Interpreting Tissue
Concentration. SETAC Special
Publication Series. Lewis Publishers,
Boca Raton.
Herbert, P.D.N., B.W. Muncaster, and
G.L. Mackie. 1989. Ecological and
genetic studies on Dreissena polymor-
pha (Pallas): a new mollusc in the
Great Lakes. Canadian Journal of
Fisheries and Aquatic Sciences
Lemly, A.D. 1996. Selenium in aquatic
organisms. pp. 427–445 in: W.N.
Beyer, G.H. Heinz, and A.W.
Redmond-Norwood, eds.
Environmental Contaminants in
Wildlife: Interpreting Tissue
Concentration. SETAC Special
Publication Series. Lewis Publishers,
Boca Raton.
Mitchell, C.A. and J. Carlson. 1993.
Lesser Scaup forage on zebra mussels
at Cook Nuclear Plant, Michigan.
Journal of Field Ornithology
Petrie, S.A. and R.W. Knapton. 1999.
Rapid increase and subsequent
decline of zebra and quagga mussels
in Long Point Bay, Lake Erie: possible
influence of waterfowl predation.
Journal of Great Lakes Research
Prince, H.H., P.I. Padding, and R.W.
Knapton. 1992. Waterfowl use of the
Laurentian Great Lakes. Journal of
Great Lakes Research 18:673–699.
Wormington, A. and J.H. Leech. 1992.
Concentrations of diving ducks at
Point Pelee, Ontario, in response to
invasion of zebra mussels, Dreissena
polymorpha. Canadian Field
Naturalist 106:376–380.
waterfowl responses to zebra mussels 351
Because of the rapid rate of uptake
and excretion, birds collected on the
Great Lakes that show elevated seleni-
um burdens quite possibly acquired
those burdens while foraging on the
Great Lakes. Even if selenium inputs
to the lower Great Lakes have not
increased substantially over the past
fifteen years, zebra mussels—through
filter feeding and bioaccumulation—
may have concentrated selenium in
their tissues, thereby increasing the
availability of this trace element to
waterfowl that consume them. Due to
the large numbers of scaup staging on
the lower Great Lakes and Mississippi
River, where zebra mussels are readily
available, selenium intake may be a
factor in the decline of these species.
For these reasons, the Long Point
Waterfowl and Wetlands Research
Fund began an intensive study of
dietary intake, contaminant burdens,
and body condition of spring and fall
staging Lesser and Greater Scaup on
Lakes Ontario, Erie, and St. Clair in
1999. Birds collected by the Canadian
Wildlife Service in 1985 (prior to
zebra mussel colonization), as well as
birds collected throughout the fall of
1999 and spring of 2000, plus the
zebra mussels themselves, are being
analyzed for burdens of heavy metals
and trace elements, including seleni-
um. This study will enable us to
determine conclusively if Lesser and
Greater Scaup are acquiring
unhealthy burdens of selenium (or
any other heavy metals or trace ele-
ments) while staging on the lower
Great Lakes, and if contaminants are
in fact acquired through zebra mussel
We know that zebra mussels pro-
vide a readily available, easily
exploitable food source, and that cer-
tain species of waterfowl will change
their movement patterns to exploit it.
But we are as yet uncertain if this
novel food item is in fact toxic to its
dinner guests.
Further Reading
For further details on some of the
studies mentioned in the article, along
with additional information on zebra
mussels, we recommend the following
Brieger, G. and R.D. Hunter. 1993.
Uptake and depuration of PCB 77,
PCB 169, and hexachlorobenzene by
zebra mussels (Dreissena
polymorpha). Ecotoxicology and
Environmental Safety 26:153–165.
Custer, C.M. and T.W. Custer. 1996.
Food habits of diving ducks in the
Great Lakes after the zebra mussel
invasion. Journal of Field
Ornithology 67:86–99.
de Kock, W.C. and C.T. Bowmer. 1993.
Bioaccumulation, biological effects,
and foodchain transfer of contami-
nants in the zebra mussel (Dreissena
polymorpha). pp. 503–533 in: T.F.
Nalepa and D.W. Schloesser, eds.
Zebra Mussels: Biology, Impacts, and
Controls. Lewis Publishers, Boca
Fisher, S.W., D.C. Gossiaux, K.A.
Bruner, and P.F. Landrum. 1993.
Investigations of the toxicokinetics
of hydrophobic contaminants in the
zebra mussel (Dreissena polymor-
pha). pp. 465–490 in: T.F. Nalepa
and D.W. Schloesser, eds. Zebra
Mussels: Biology, Impacts, and
Controls. Lewis Publishers, Boca
Gillis, P.L. and G.L. Mackie. 1994.
Impact of the zebra mussel,
Dreissena polymorpha, on popula-
tions of Unionidae (Bivalvia) in Lake
St. Clair. Canadian Journal of
Zoology 72:1260–1271.
Griffiths, R.W., D.W. Schloesser, J.H.
Leach, and W.P. Kovalak. 1991.
Distribution and dispersal of the
zebra mussel (Dreissena polymorpha)
in the Great Lakes region. Canadian
Journal of Fisheries and Aquatic
Sciences. 48:1381–1388.
... There is also evidence that the wintering populations for 21 of 44 waterfowl species monitored through the Christmas Bird Count increased between 1966 and 2013 (Soykan et al. 2016). This increase may be due to a northward shift in wintering range that has been observed among mallard (Brook et al. 2009; but see Green and Krementz 2008), American black duck A. rubripes (Link et al. 2006, Brook et al. 2009, Robertson et al. 2017, and other diving and dabbling duck species (Petrie andSchummer 2002, La Sorte andThompson 2007). ...
... Changes in winter distributions of dabbling duck species have been well documented in eastern North America (Petrie and Schummer 2002, Link et al. 2006, Brook et al. 2009, as has the impact of climate on waterfowl movement during migration (Schummer et al. 2014, Notaro et al. 2016). However, our study is the Between 1968 and 2011, we found that peak autumn migration occurred 11-18 days later for four of six focal species, the equivalent of 3-5 days/decade. ...
... American black duck American green-winged teal Gadwall Blue-winged teal American wigeon the observed delays in migration (this study) and northward shifts in winter distributions reported elsewhere from the 1970s and onward (Petrie and Schummer 2002, Link et al. 2006, Brook et al. 2009, Robertson et al. 2017). Additional factors that could explain the later migration include, but are not limited to, increased food availability from agricultural resources such as waste grain and corn (Stafford et al. 2010, Pearse et al. 2012, the introduction of exotic species as an abundant food source like the zebra mussel Dreissena polymorpha in the Great Lakes (Petrie and Schummer 2002), and supplemental feeding in wildlife refuges (Palumbo et al. 2019) near breeding territories or at staging sites. ...
Full-text available
Delays in waterfowl autumn migration have been widely reported by hunters and ornithologists throughout North America. The implications of such delays are vast, with potential effects on the efficacy of population management, reduced social and economic opportunities, and reduced resource availability by overuse and over-grazing in key staging areas. In this study, we tested for changes in autumn migration timing for six abundant species of dabbling ducks in southern Ontario, Canada. We applied generalized linear mixed models to test for effects of year and climate indices El Niño Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) on the Julian date of peak abundance as observed during aerial surveys conducted throughout the lower Great Lakes. Our analyses revealed delays of 11–18 days between 1968 and 2011 for four of six focal species: mallard, American black duck, American wigeon and gadwall. La Niña and El Niño events had no effect on migration timing for American black duck, American green-winged teal or American wigeon, while an increase in the annual NAO index resulted in a delayed migration for American wigeon. There was an NAO:ENSO interaction for mallard and gadwall migration; an increase in NAO advanced peak migration dates during La Niña events. However, an increase in NAO delayed migration for gadwall during the neutral phase of the ENSO and delayed migration for both species during El Niño events. Blue-winged teal and American green-winged teal showed no change in migration timing. Given that climate forecasts indicate continued positive-value phases, the autumn migrations for mallard, American black duck, gadwall and American wigeon may become increasingly delayed. Wildlife managers should use all available data, including from standardized aerial surveys, citizen science and climate models to inform and direct adaptive population management, hunting regulations, wildlife emergency response and habitat conservation.
... The distribution of scaup from autumn through spring has shifted substantially in the past 2 decades with some of the greatest increases in abundance and residency time occurring in the Great Lakes region , Afton and Anderson 2001, Petrie and Schummer 2002. These shifts and increases have largely been related to increased abundance of invertebrate foods directly or indirectly resulting from colonization of the Great Lakes by invasive zebra (Dreissena polymorpha) and quagga mussels (D. bugensis; Hamilton and Ankney 1994, Austin et al. 2000, Schummer et al. 2008). ...
... These shifts and increases have largely been related to increased abundance of invertebrate foods directly or indirectly resulting from colonization of the Great Lakes by invasive zebra (Dreissena polymorpha) and quagga mussels (D. bugensis; Hamilton and Ankney 1994, Austin et al. 2000, Schummer et al. 2008). In addition, substantial declines in ice cover on the Great Lakes during the same period likely increased access to these abundant food resources and potential residency time of scaup in the Great Lakes region (Petrie and Schummer 2002, Assel et al. 2003, Duguay et al. 2006, Wang et al. 2012). Our analysis of the eastern survey area indicates that scaup using these important wintering and staging areas of the Great Lakes are grossly underestimated in the WBPHS because nearly 50% of our marked scaup migrated ahead of the survey and settled in Quebec, from the northern boundary of the WBPHS to approximately 58.58N. ...
... Scaup are highly nomadic during winter and change wintering locations to follow food resources (Baldassarre 2014). For example, migrating Scaup increased 10-fold on the Great Lakes following introduction of Dreissena polymorpha (Pallas) (Zebra Mussel; Petrie and Schummer 2002). We suspect that increased abundance of Scaup at GSB resulted from similar changes in food abundance following Superstorm Sandy, but research on benthic food densities and consumption by Scaup are needed to better understand relationships between the changes in Scaup abundance and their food resources at GSB. Due to these changes in food resources, climate, or other untested causes, Scaup populations that use the Atlantic flyway may be shifting their wintering ranges. ...
... As in Europe (Suter 1982, Stanczykowska et al. 1990), scaup and other North American diving ducks have altered their migratory (Wormington andLeach 1992, Petrie andSchummer 2000) , and feeding habits (Mitchel and Carlson 1993, Mazak et al. 1997 in response to the invasion of the zebra mussel in the lower Great Lakes. Using exclosures, found that diving ducks reduced the biomass of zebra mussels by 57% during the fall migratory period off Point Pelee in western Lake Erie, Canada. ...
One of the proposed explanations for the recent continental decline in Lesser Scaup (Aythya affinis) populations is that females experience lower survival or reproduction resulting from exposure to contaminants in their diet of exotic bivalves during migration and over winter. In 1999, we collected eggs and females from five sites in the boreal forest of Canada and Alaska and four sites in Canadian parkland. We analyzed eggs from 60 clutches and ten nesting females for toxic metals, selenium, 19 pesticides and other organochlorines, and 43 polychlorinated biphenyl (PCB) congeners. The highest organochlorine concentration we measured was 1.5 μg g−1 ww of DDE in eggs. The highest mercury concentration was 1.8 μg g−1 dw in liver. The highest cadmium concentration was 6.2 μg g−1 dw in kidney. The highest selenium concentrations measured were 1.6 μg g−1 ww in eggs, and 5.3 μg g−1 dw in liver. All are well below thresholds known to cause embryotoxic and other effects in other bird species. Though sample sizes were small and did not include the entire breeding range or nonbreeders, our results provide no evidence to support the hypothesis of contaminant-induced effects on egg hatchability and female health. However, recently published concentrations of selenium in zebra mussels (Dreissena polymorpha) and Asian clams (Potamocorbula amurensis), predominant foods on staging areas, are sufficient to induce other sublethal effects, and possibly mortality if eaten by scaup for extended periods. ¿Son Preocupantes las Concentraciones Actuales de Contaminantes en los Huevos y Hembras Reproductivas de Aythya affinis? Resumen. Uno de los argumentos propuestos para explicar la disminución reciente de las poblaciones continentales de Aythya affinis es que como consecuencia de la exposición a contaminantes presentes en su dieta de bivalvos exóticos durante la migración y el invierno, la supervivencia o reproducción de las hembras es reducida. En 1999, colectamos huevos y hembras en cinco sitios ubicados en bosques boreales de Canada y Alaska y en cuatro sitios en parques canadienses. Analizamos los metales tóxicos, selenio, 19 pesticidas y otros organoclorados y 43 congéneres de bifenil policlorado (PCB). La concentración más alta de organoclorados que medimos fue de 1.5 μg g−1 (peso fresco) de DDE, en huevos. La concentración más alta de mercurio fue 1.8 μg g−1 (peso seco), en hígado. La concentración más alta de cadmio fue 6.2 μg g−1 (peso seco), en riñón. Las concentraciones de selenio más altas fueron 1.6 μg g−1 (peso fresco) en huevos y 5.3 μg g−1 (peso seco) en hígado. Todas estas medidas están por debajo de los niveles que causan efectos embriotó xicos y de otros tipos en otras especies de aves. Aunque los tamaños muestrales fueron pequeños y no incluyeron todo el rango de distribución reproductivo ni aves que no se estaban reproduciendo, nuestros resultados no proveen evidencia para apoyar la hipótesis de que existen efectos inducidos por los contaminantes sobre la capacidad de eclosionar de los huevos y la salud de las hembras. Sin embargo, las concentraciones de selenio en los bivalvos Dreissena polymorpha y Potamocorbula amurensis, alimentos predominantes en áreas de escala migratoria, son suficientes para inducir otros efectos no letales y posiblemente la muerte si son consumidos por A. affinis por períodos prolongados.
... Decreased weather severity is hypothesized to account for delays in waterfowl migration to southern latitudes during autumn and winter (Petrie and Schummer 2002, Kaminski et al. 2005, Brook et al. 2009, Reilly 2017. Although timing of autumn migration by dabbling ducks in North America is primarily influenced by the combined influences of 1) changes in day length (i.e., photoperiod); 2) habitat availability; 3) weather severity; and 4) physiological differences among species (Calder 1974, Bellrose 1980, Newton 2008, Baldassarre 2014, all these ducks must migrate to southerly locales at some threshold weather severity during the nonbreeding period (Calder 1974, Bellrose 1980, Newton 2008, Schummer et al. 2010, Baldassarre 2014). ...
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Annual distributions of waterfowl during the nonbreeding period can influence ecological, cultural, and economic relationships. We used previously developed Weather Severity Indices (WSI) that explained migration by dabbling ducks in eastern North America and weather data from the North American Regional Reanalysis to develop an open-access internet-based tool (i.e., WSI web app) to visualize and query WSI data. We used data generated by the WSI web app to determine whether the weather known to elicit southerly migration by dabbling ducks had changed, from October to April 1979 to 2013. We detected that the amount of area in the Mississippi and Atlantic Flyways with weather severe enough to cause southerly migration decreased during 1) October–December for American wigeon (Mareca americana), green-winged teal (Anas crecca), and northern shoveler (Spatula clypeata); 2) December–January for mallard (A. platyrhynchos), American black duck (A. rubripes), and northern pintail (A. acuta); and 3) February–April for mallard, American black duck, gadwall (M. strepera), American wigeon, green-winged teal, and northern shoveler. Results were consistent with prior research indicating that weather causing autumn and winter migration of dabbling ducks has become increasingly mild in the past 3 decades. The WSI web app enables users to query daily data and maps by species and by Flyway, Joint Venture, Landscape Conservation Cooperative, and State. We encourage those with corresponding data on participation and satisfaction by waterfowl enthusiasts (i.e., birders and hunters) to test for relationships with the WSI because of the implications for conservation funding, especially if autumn and winter weather severity continues to become increasingly mild as predicted.
... There, during the nonbreeding season, Herring Gulls coexisted with large flocks of Aythya ducks numbering from 50,000 individuals in the early 1990s to more than 350,000 in 2000 (Ross et al. 2005). According to Petrie and Schummer (2002), this increase in the number of ducks resulted from the introduction and subsequent expansion of the zebra mussel population, which began in the mid-1980s. However, during winter and early spring in the lower Great Lakes, fish and garbage continued to be the main food in the gulls' diet as no mussel remains were found in their pellets (Ewins et al. 1994). ...
... We interpret our results in the interest of inspiring further investigation but caution that results are based on small sample sizes. Diving duck use of the Great Lakes as a staging and wintering site has increased in recent decades, potentially because of increased food abundance, decreasing ice cover, or their combination (Custer and Custer 1996, Petrie and Knapton 1999, Petrie and Schummer 2002, Schummer et al. 2012. The Great Lakes thaw slower during spring than nearby smaller bodies of water such as rivers and shallow lakes (Assel 2005); this effect on habitat availability may have caused some of the results we saw for the scaup migrating through the eastern survey area. ...
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Identifying environmental metrics specific to lesser scaup (Aythya affinis; scaup) spring migration chronology may help inform development of conservation, management and population monitoring. Our objective was to determine how environmental conditions influence spring migration of lesser scaup to assess the effectiveness of the Waterfowl Breeding Population and Habitat Survey in accurately estimating scaup populations. We first compared peak timing of mallard (Anas platyrhynchos) and scaup migration from weekly ground surveys in North Dakota, USA because the Waterfowl Breeding Population and Habitat Survey is designed to capture annual mallard migration. As predicted, we detected that peak timing of scaup and mallard migrations differed in 25 of 36 years investigated (1980–2010). We marked scaup with satellite transmitters (n = 78; 7,403 locations) at Long Point, Lake Erie, Ontario, Canada; Pool 19 of the Mississippi River, Iowa and Illinois, USA; and Presque Isle Bay, Lake Erie, Pennsylvania, USA. We tested the assumption that our marked scaup were representative of the continental population using the traditional survey area by comparing timing of migration of marked birds and scaup counted in the North Dakota Game and Fish Department survey. We detected a strong positive correlation between marked scaup and the survey data, which indicated that marked scaup were representative of the population. We subsequently used our validated sample of marked scaup to investigate the effects of annual variation in temperature, precipitation, and ice cover on spring migration chronology in the traditional and eastern survey areas of the Waterfowl Breeding Population and Habitat Survey, 2005–2010. We evaluated competing environmental models to explain variation in timing and rate of scaup migration at large-scale and local levels. Spring migration of scaup occurred earlier and faster during springs with warmer temperatures and greater precipitation, variables known to influence energy budgets and wetland availability. Our results suggest that surveys designed to index abundance of breeding mallards is imprecise for estimating scaup abundance, and inaccurate at estimating breeding population size by survey stratum.
... There, during the nonbreeding season, Herring Gulls coexisted with large flocks of Aythya ducks numbering from 50,000 individuals in the early 1990s to more than 350,000 in 2000 (Ross et al. 2005). According to Petrie and Schummer (2002), this increase in the number of ducks resulted from the introduction and subsequent expansion of the zebra mussel population, which began in the mid-1980s. However, during winter and early spring in the lower Great Lakes, fish and garbage continued to be the main food in the gulls' diet as no mussel remains were found in their pellets (Ewins et al. 1994). ...
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Niche construction can lead to coevolutionary episodes and greater specialization, and can have implications for the evolution of biological diversity, so understanding how individuals adjust their behavior to conspecifics and heterospecifics over changing social and environmental gradients presents an interesting research problem. The objective of our study was to test the hypothesis that mixed flocks of gulls and diving ducks congregate as a result of interacting over food. Ducks are vectors that carry zebra mussels (Dreissena polymorpha) up from the bottom of a water body, and gulls consume this type of food. We investigated the interactions of 2 gull species with 3 benthivorous duck species—Common Pochard (Aythya ferina), Tufted Duck (A. fuligula), and Greater Scaup (A. marila)—in the Szczecin Lagoon, Poland. We found that the presence of gulls in duck flocks was closely correlated with foraging by ducks. Eighty-four percent of foraging duck flocks (>5% of the flock members were foraging) and 52% of nonforaging duck flocks (<5% of the flock members were foraging) were accompanied by gulls (Fisher's exact test, P = 0.008). The odds ratio showed that every 10% increase in the number of foraging ducks doubled the chance of gulls being present (odds ratio of 10% unit change = 2.058). We defined the relationship between the size of the foraging duck flock and the number of gulls present in it; the number of gulls rose with increasing numbers of ducks in the flock. All our findings confirmed that this gull–duck co-occurrence was the result of interaction over food (commensalism or interspecific kleptoparasitism). We showed that the diet of gulls in the Szczecin Lagoon changed dramatically when Aythya ducks made their appearance; after duck arrival, gull pellets contained almost exclusively mussels. Our results reveal that the trophic relationship between zebra mussels and the studied bird species is not just a straightforward one between predator and prey.
... This novel, readily available food source permitted scaup to shift from native foods to a diet dominated by dreissenid mussels (Custer and Custer 1996, Petrie and Knapton 1999, Badzinski and Petrie 2006a. Since dreissenid mussels have become prevalent there also has been a substantial increase in the number of scaup staging and wintering on the LGL in some years (Wormington and Leach 1992, Petrie and Knapton 1999, Petrie and Schummer 2002, despite the continental population decline (Allen et al. 1999, Wilkins et al. 2005. For example, waterfowl days (each day a bird spends in the given area) for scaup in the Long Point area on Lake Erie increased from 38,500 in 1986, before dreissenid mussel colonization, to 3.5 million in 1997 (Petrie and Knapton 1999). ...
Le Service canadien de la faune d’Environnement et Changement climatique Canada n’effectue aucun relevé régulier de sauvagine dans les limites du parc marin du Saguenay–Saint-Laurent (Québec, Canada) comme tel, mais il dispose néanmoins de données provenant de 2 inventaires plus globaux pouvant aider à dresser un portrait sommaire de sa fréquentation par ce groupe d’oiseaux. La partie du Saguenay comprise dans le parc n’apparaît pas comme un lieu d’importance pour la sauvagine, et ce, à aucun moment de l’année. En revanche, les sections de l’estuaire moyen et maritime du Saint-Laurent sises dans le parc présentent un intérêt certain pour la sauvagine, puisqu’elles sont fréquentées, selon la période de l’année, par des centaines, voire des milliers d’individus pour des durées variables. Certaines espèces ne font qu’y passer en migration, tandis que d’autres y restent pour plusieurs mois : en été, les eiders à duvet ( Somateriamollissima ) pour la nidification ou des milliers de macreuses ( Melanitta spp.) pour la mue; en hiver, les garrots ( Bucephala spp.). L’intérêt de la partie estuarienne du parc marin du Saguenay–Saint-Laurent réside vraisemblablement dans les aires d’alimentation et de repos qu’elle offre à la sauvagine.
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Dreissena polymorpha has established a population in Lakes St. Clair and Erie, likely as a result of ballast water discharge. The Lake St. Clair population was polymorphic at 73.9% of the loci examined; individual heterozygosities averaged 31.6%. This high level of genotypic diversity indicated that the population was founded from a substantial number of individuals and did not undergo a bottleneck subsequent to founding. The population is reproducing with peak densities >200 individuals.m-2. Juvenile settlement occurs in late July and August with veliger larvae preferentially settling on the shells of live mussels. The species appears likely to become a dominant member of the shallow water benthos throughout the lower Great Lakes. -from Authors
The European zebra mussel has recently invaded North America and is now well established in Lake Erie. Since 1988, larger-than-usual flocks of eight species of diving ducks were observed at Point Pelee during autumn migration. Maximum one-day counts of the principal species, lesser scaup Aythya affinis, were up to 90 times historical counts. The ducks also remained in the area for a longer-than-normal period. The ducks actively feed on zebra mussels. The availability of a new food source has led to this recent change in autumn migratory behaviour by several species of diving ducks. -from Authors
Zebra mussels (Dreissena polymorpha) invaded the Great Lakes in the mid-1980s and quickly reached high densities. The objective of this study was to determine current consumption of zebra mussels by waterfowl in the Great Lakes region. Feeding Lesser Scaups (Aythya affinis), Greater Scaups (A. marila), Canvasbacks (A. valisineria), Redheads (A. americana), Buffleheads (Bucephala albeola) and Common Goldeneyes (B. clangula) were collected in western Lake Erie and in Lake St. Clair between fall and spring, 1992-1993 to determine food habits. All 10 Redheads, 97% of Lesser Scaups, 83% of Goldeneyes, 60% of Buffleheads and 9% of Canvasbacks contained one or more zebra mussels in their upper gastrointestinal tracts. The aggregate percent of zebra mussels in the diet of Lesser Scaups was higher in Lake Erie (98.6%) than in Lake St. Clair (54.4%). Zebra mussels (aggregate percent) dominated the diet of Common Goldeneyes (79.2%) but not in Buffleheads (23.5%), Redheads (21%) or Canvasbacks (9%). Lesser Scaups from Lake Erie fed on larger zebra mussels (x̄ = 10.7 ± 0.66 mm SE) than did Lesser Scaups from Lake St. Clair (x̄ = 4.4 ± 0.22 mm). Lesser Scaups, Buffleheads and Common Goldeneyes from Lake Erie consumed zebra mussels of similar size.
Distribution and density of two introduced dreissenid species of mollusks, the zebra mussel Dreissena polymorpha and quagga mussel D. bugensis, were monitored in the Inner Bay at Long Point, Lake Erie, 1991–1995. Since populations of certain waterfowl species have been reported to alter their dietary intake and migration patterns in response to the ready availability of zebra mussels, the percent occurrence of zebra mussels in the diet of 12 duck species (552 birds) was studied concurrently, and several spring and fall aerial waterfowl surveys were flown between 1986 and 1997 (n=75), to document changes in duck populations at Long Point. The first reproductive population of zebra mussels on the bay most likely appeared in 1990. After an initial rapid increase in density and colonization of the Inner Bay, zebra mussels began to steadily and consistently decline in absolute numbers, density per station and occupied area. Mean density per station in 1995 was 70% less than in 1991, the first year of rapid colonization, and 67% less than in 1992, the year of peak abundance in the bay (P
Dreissena polymorpha (Pallas), a small mussel common throughout most of Europe, was discovered in June of 1988 in the southern part of Lake St. Clair. Length-frequency analyses of populations from the Great Lakes and review of historical benthic studies suggest that the mussel was introduced into Lake St. Clair in late 1986, probably as a result of the discharge of ballast water from an ocean-crossing vessel. Following the 1990 reproductive season, Dreissena populations ranged from the head of the St. Clair River, through Lake St. Clair, the Detroit River, Lake Erie, the Welland Canal, and the Niagara River to the western basin and southern shoreline of Lake Ontario. Isolated populations were found in the St. Lawrence River and in harbours in Lakes Huron, Michigan, and Superior. The rapid dispersal of this organism has resulted from its high fecundity, pelagic larval stage, bysso-pelagic drifting ability of juveniles, and human activities associated with commercial shipping, fishing, and boating (research and pleasure). Virtually any waterbody that can be reached by boaters and fisherman within a few days travel of the lower Great Lakes, particularly Lake Erie, seems to be at risk of being invaded by this nuisance species.
Literature on habitat and limiting factors of waterfowl in Great Lakes wetlands and deep water habitats is reviewed; more than 30 species of waterfowl use coastal habitats at some time during the year. Waterfowl use of the Great Lakes has declined dramatically from presettlement times; the obvious cause is human encroachment on coastal wetlands and destruction of river delta and embayed wetland complexes. Loss of wetland habitats from diking and filling above the average water level constitutes a permanent habitat loss, especially during high water cycles. The greatest number of species and individuals use 15 concentration areas during the spring and fall migratory periods when use by diving ducks, sea and stiff tailed ducks, and swans and geese predominates. Lesser numbers of species use the coastal wetlands for breeding. Large concentrations of dabbling ducks, primarily mallards (Anas platyrhynchos) and American black ducks (A. rubripes), and mergansers (Mergus spp.) are found on ice-free areas during winter. Wetland habitats have become more favorable, due to human modifications, to dabbling duck species found in the prairie habitats of North America. Mallards have become the most numerous species breeding in coastal wetlands along with a concomitant decline in black ducks, which may be a consequence of introgression. Habitat modifications, degradation, and loss have great potential to affect existing waterfowl populations negatively and to point the way toward future research.