Ducks live on every continent except Antarctica, occupying habitats from Arctic tundra ponds to tropical mangroves, desert flood pools to open ocean shoals. The family Anatidae includes well over a hundred species, and their collective range covers an enormous variety of ecosystems. What ties them together is a dependence on water, but exactly what kind of water, and where, varies wildly depending on the species, the season, and the landscape.
Freshwater Wetlands and the Shallow-Water Preference
Most people picture ducks on a pond, and for good reason. Shallow freshwater wetlands are the single most important habitat type for dabbling ducks worldwide. Species like mallards, gadwall, pintails, and teal gravitate toward shallowly flooded areas with plenty of emergent vegetation rather than deep, open lakes. A study in western Tennessee found that four common dabbling duck species consistently selected moist-soil wetlands over deeper open-water or aquatic-bed habitats during winter, and that the ducks’ preferences tracked closely with shallow water depth, dense emergent plant cover, and high food energy availability.1The Journal of Wildlife Management. Habitat selection and activities of dabbling ducks during non‐breeding periods Deep, open water was actively avoided.
This preference for shallow, vegetated wetlands isn’t just a North American pattern. Research in southwestern Quebec showed that dabbling ducks strongly favored a habitat dominated by broken cattail cover with duckweed and water-milfoil underneath. Broods and adults were roughly four times more abundant per hectare in that habitat compared to the next best option.2Canadian Journal of Zoology. Habitat selection by dabbling ducks in the Baie Noire marsh, southwestern Quebec The common thread is structure: ducks need water shallow enough to tip forward and feed, with vegetation that provides food and cover from predators.
When multiple duck species share the same wetland, they often split resources to reduce competition. At an autumn stopover in a river delta, pintails and American wigeon fed almost exclusively on aquatic plants, while blue-winged teal and green-winged teal leaned heavily on invertebrates, and mallards opportunistically ate both.3Canadian Journal of Zoology. Resource partitioning among five species of waterfowl (Anas spp.) at an autumn migratory stopover This kind of diet splitting allows a surprisingly high density of ducks to coexist in a single marsh during migration staging.
Coasts, Estuaries, and Open Ocean
While dabbling ducks rule the inland marshes, sea ducks occupy a completely different world. The tribe Mergini, which includes scoters, eiders, long-tailed ducks, and mergansers, spends much of the year in marine environments along coastlines and sometimes well offshore. Along the eastern coast of North America, at least a dozen sea duck species overwinter in nearshore and offshore waters.4PubMed. Distribution patterns of wintering sea ducks in relation to the North Atlantic Oscillation and local environmental characteristics
What draws sea ducks to a particular stretch of coast usually comes down to food. In urbanized estuaries of the Pacific Northwest, herring roe was the strongest predictor of where sea ducks showed up, along with the presence of eelgrass beds, deeper water, and higher salinity.5Biological Conservation. Resource selection and space use by sea ducks during the non-breeding season: Implications for habitat conservation planning in urbanized estuaries Farther south, near Nantucket Island off Massachusetts, a winter concentration of long-tailed ducks on the order of 300,000 birds has been documented since the 1970s, with evidence of some aggregation there dating back to the late 1800s. Those ducks tracked concentrations of amphipods and clams at spatial scales up to about 30 kilometers.6Ecosphere. Spatial ecology of long‐tailed ducks and white‐winged scoters wintering on Nantucket Shoals These are not ducks dabbling in a park pond. They are diving birds riding ocean swells and foraging on the seafloor.
Arctic Tundra Breeding Grounds
Many of those same sea ducks that winter along temperate and subarctic coasts migrate north each spring to breed on Arctic tundra. The coastal plain of northern Alaska, for instance, hosts nesting king eiders, spectacled eiders, Steller’s eiders, and long-tailed ducks. King eider females pick nest sites close to water, often on small islands, favoring areas with willow cover for concealment.7The Journal of Wildlife Management. Strategies for Nest‐Site Selection by King Eiders
Tundra-nesting sea ducks show the same shallow-water preferences as their freshwater relatives, just in a much more extreme setting. On the Arctic tundra, all four species studied preferred shallow, vegetated wetlands over deeper lakes. They strongly favored wetlands dominated by the grass Arctophila fulva over sedge-dominated wetlands, even though the sedge wetlands were far more numerous and had more invertebrate biomass.8PubMed Central. Prey availability and foraging activity by tundra‐nesting sea ducks: Strong preference for specific wetland types The specific plant structure seems to matter more than sheer food quantity.
Breeding on the tundra after wintering at sea raises an interesting nutritional question: where do the nutrients for eggs come from? Isotope analysis of egg membranes from four Arctic-nesting sea duck species found that roughly 89 to 95 percent of the protein in their eggs came from freshwater food consumed on the breeding grounds, not from marine reserves carried in from the coast.9Ecosphere. Use of marine vs. freshwater proteins for egg‐laying and incubation by sea ducks breeding in Arctic tundra So even species that spend most of their lives at sea depend heavily on tundra wetlands to reproduce.
Forests and Tree-Cavity Nesters
Not all ducks live in open landscapes. The wood duck of North America is a forest species that nests in tree cavities, sometimes high above the ground in mature hardwoods near water. Finding a suitable cavity isn’t easy. A survey of nearly 5,000 trees in South Carolina found that only about 14 percent of identified potential cavities were actually suitable for nesting wood ducks, and suitable cavities were most common in stands of oak, gum, and cypress.10The Journal of Wildlife Management. Occurrence of natural tree cavities suitable for nesting wood ducks across South Carolina forest types
In Minnesota, researchers inspected over 7,800 trees and about 1,200 potential cavities, finding that only 19 percent met the size and structural criteria for wood duck nesting. For every one-centimeter increase in trunk diameter, the odds of a tree having a suitable cavity went up about 7 percent. Dead and declining trees were dramatically more likely to contain usable holes than healthy trees.11Forest Ecology and Management. Forest inventory attributes predict the occurrence of cavities suitable for nesting by Wood Ducks (Aix sponsa) This means that clean, intensively managed forests with all the dead wood removed are poor wood duck habitat, even if there is water nearby. The birds need old, decaying trees.
Similar cavity-nesting ducks exist elsewhere in the world. The mandarin duck of East Asia, a close relative of the wood duck, also nests in tree hollows near rivers and forested lakes. Australia’s maned duck uses hollows as well. The pattern of dependence on mature forest with standing dead wood repeats across continents.
Mountain Rivers and High Elevations
Some ducks have adapted to environments that seem almost hostile to waterfowl. The torrent duck of South America lives in fast-flowing Andean rivers with steep gradients, rapids, and powerful currents. Surveys in central Chile found that torrent ducks specifically selected river sections with the highest density of rapids, steepest slopes, and fastest water velocities.12Waterbirds. Habitat Selection by Torrent Ducks (Merganetta armata armata) in Central Chile: Conservation Implications of Hydropower Production These are the stretches of river that most other waterbirds avoid entirely.
Torrent ducks range from near sea level to well above 3,000 meters in the Andes. Populations at different elevations show physical differences that reflect their conditions. Comparing birds from approximately 1,500 meters and 3,500 meters in Peru, researchers found that the high-altitude population had significantly longer, denser down feathers, likely an adaptation to colder ambient temperatures at elevation.13bioRxiv. Down Feather Structure Varies Between Low- and High-Altitude Torrent Ducks (Merganetta Armata) in the Andes Their contour feathers didn’t differ, suggesting the insulation change is specifically in the innermost plumage layer.
Deserts and Ephemeral Wetlands
Australia offers one of the more surprising duck stories. Much of the continent’s interior is arid, and surface water appears and vanishes unpredictably with erratic rainfall. Australian ducks like the grey teal have evolved a nomadic lifestyle in response. Rather than migrating on a fixed seasonal schedule the way Northern Hemisphere ducks do, grey teal make long-distance movements seemingly triggered by rainfall and flooding events, flying distances up to 1,200 kilometers across the dry interior to reach newly inundated wetlands.14Ibis. What drives long‐distance movements in the nomadic Grey Teal Anas gracilis in Australia? Some flights matched up with rain or flooding at the destination, but others landed the ducks on small wetlands in regions with very little water, suggesting not all movements are perfectly targeted.
The Pacific black duck, another Australian species, responds to heavy rainfall in arid ecosystems by dramatically increasing nocturnal flight. After a major rain event in one study, the proportion of flight occurring at night spiked to nearly 90 percent in the first days after rain, with the total distance traveled per 24-hour period surging as well.15Scientific Reports. Heavy rainfall triggers increased nocturnal flight in desert populations of the Pacific black duck (Anas superciliosa) In a more stable, well-watered ecosystem, the same species showed no such response. The behavior appears to be a specific adaptation to exploit short-lived flood pulses in unpredictable environments.
Island Endemics and Tiny Ranges
At the opposite extreme from globe-spanning species like the mallard, some ducks occupy vanishingly small ranges. The Laysan duck is native to the Hawaiian Archipelago but was driven off most islands after mammalian predators arrived. For roughly 150 years, the entire species was confined to Laysan Island, a speck of land just 4.1 square kilometers in size. To reduce extinction risk, 42 wild birds were eventually translocated to Midway Atoll, another predator-free low-lying atoll of about 6 square kilometers.16The Journal of Wildlife Management. Demographic variation, reintroduction, and persistence of an island duck (Anas laysanensis) The species doesn’t naturally disperse between distant Hawaiian islands today, so without human intervention it would remain trapped on whatever island it happened to survive on.
The Laysan duck is far from the only island-bound species. Madagascar, New Zealand, and various Indonesian islands each harbor endemic ducks with extremely restricted ranges. These species are disproportionately threatened because a single catastrophic event on their island, whether a cyclone, an introduced predator, or a disease outbreak, can wipe out the entire population at once.
Migration Corridors and Flyways
The global distribution of ducks at any given moment depends heavily on the season. Most Northern Hemisphere species are migratory, breeding in the higher latitudes during summer and shifting south or to coasts for winter. Tracking studies across Asia using GPS transmitters have mapped major flyway structures in detail, confirming that the Central Asian and East Asian-Australasian Flyways are spatially distinct corridors used by multiple Anatidae species. Bar-headed geese in the Central Asian Flyway concentrated at high-elevation lake stopovers along the eastern Qinghai-Tibetan Plateau, while ruddy shelducks split into two separate corridors suggesting distinct populations.17PubMed Central. Mapping migratory flyways in Asia using dynamic Brownian bridge movement models
Global mapping of waterfowl richness shows that migratory species dominate the regions with the highest species counts. In mid-latitude areas with the greatest waterfowl diversity, the overwhelming share of that diversity consists of migratory species.18Wiley Online Library. Seasonality drives global‐scale diversity patterns in waterfowl (Anseriformes) via temporal niche exploitation Seasonal variation in plant productivity was the strongest predictor of breeding-season species richness globally, while winter warmth and moisture drove non-breeding concentrations. In short, ducks pile into places where the food supply is seasonally booming.
Fine-scale GPS tracking has also revealed how ducks move within landscapes on a daily basis. Three species of dabbling ducks tracked at 30-minute intervals showed distinct daily patterns of moving between patches, giving researchers a much more detailed picture of how ducks connect different wetland sites within a region over a single day.19PubMed Central. GPS tracking data reveals daily spatio-temporal movement patterns of waterfowl
Shifting Winter Ranges Under Climate Change
Duck distributions aren’t static. Over the past several decades, warming winters have pushed some species’ ranges noticeably northward and eastward. A study spanning three decades of waterbird monitoring across Northwest Europe found strong northeastward shifts in the wintering ranges of three common species, correlating with an increase of about 3.8°C in early winter temperatures in the northeastern portions of their range. Abundance grew exponentially in those warming northeastern areas while declining at the southwestern margins.20PubMed. Rapid climate driven shifts in wintering distributions of three common waterbird species
Similar patterns have emerged in the midwestern United States, where six decades of survey data show shifts in the winter ranges of several duck species. The causes are complex and species-specific: habitat loss and degradation, changing land use, agricultural practices, and climate change are all playing a role simultaneously.21U.S. Geological Survey. 60 years of data show shifts in the winter ranges of three duck species in the Midwest A duck population that historically concentrated in Louisiana marshes during January might now linger farther north if mild winters keep northern wetlands ice-free. This shuffling matters for local economies, hunting seasons, and the wetland habitats themselves, which evolved with certain levels of duck use.
Ducks Where They Don’t Belong
Humans have also moved ducks around the globe, sometimes with serious consequences. The North American ruddy duck was brought to wildfowl collections in the United Kingdom in the 1940s and 1950s, and birds soon escaped into the wild. The feral UK population grew from about 20 wintering birds in 1962 to nearly 6,000 by 2000.22Biological Invasions. Genetic studies facilitated management decisions on the invasion of the ruddy duck in Europe From there, ruddy ducks spread to continental Europe, eventually being recorded in 22 countries across the western Palearctic, with viable breeding populations establishing in Belgium, the Netherlands, France, and Spain.23Biological Invasions. Towards the European eradication of the North American ruddy duck
The problem wasn’t just competition. Ruddy ducks readily hybridized with the white-headed duck, a globally endangered species restricted to parts of the Mediterranean and Central Asia. Hybrids were first recorded in Spain in 1991, and the ruddy duck appeared to have a competitive mating advantage. The species was recognized as the single most significant threat to the white-headed duck’s survival.24DigitalCommons@University of Nebraska – Lincoln. CONTROL AND ERADICATION OF THE NORTH AMERICAN RUDDY DUCK IN EUROPE A continent-wide culling program followed, one of the largest coordinated efforts to eradicate an invasive bird species in history. The ruddy duck story illustrates how easily ducks can establish themselves in new regions when given a foothold, and how an animal perfectly at home in one part of the world can become a crisis in another.
Gaps in Protection
Keeping ducks on the landscape long-term depends heavily on whether their key habitats fall inside protected areas, and many don’t. An analysis of duck protection across the Western Palearctic found a stark geographic gradient: critical sites in Western Europe were far better protected than those in Eastern Europe, the Middle East, and Central Asia. The problem is that the least-protected regions are where duck populations are currently the largest, and they are also among the areas where ducks are expected to increase in the future as climate change pushes ranges northward and eastward.25Biodiversity and Conservation. Ready for climate change? Geographic trends in the protection status of critical sites for Western Palearctic ducks In other words, the places ducks are moving toward are the places with the weakest safety net.
Even where protected areas do exist, their effectiveness depends on how closely they are clustered. Mallards fitted with transmitters in the midwestern United States were about three times less likely to move between two wildlife sanctuaries for every additional 10 kilometers of distance separating them. Larger sanctuaries attracted more transitions, but the dominant factor was simply how far apart they were.26Scientific Reports. Proximity among protected area networks promotes functional connectivity for wintering waterfowl A network of small, well-spaced refuges may serve wintering ducks better than a handful of large, isolated ones if the spacing allows daily movements between them. For wildlife managers designing protected-area networks, the lesson is that connectivity between wetlands matters as much as the size of any individual site.