by Steve Tillmann
Beavers are nature’s aquatic engineers. They fell trees and shrubs, excavate mud for cement and build elaborate dams and lodges. In doing so, beavers create wetlands essential not only to their colonies but to a rich variety of life. In our part of the west, beaver activities can transform bare, scoured river and stream channels with little permanent water and vegetation into enduring riparian “Serengeti” wetland complexes rich in biodiversity. Many species of plants, invertebrates, fish, birds and animals depend on wetlands created by beavers. One bird that has much in common with the beavers and has benefited greatly over the centuries from the efforts of this furry engineer is the Wood Duck (Aix sponsa).
Smaller in stature than other ducks but with unmatched beauty, the Wood Duck or “woodie” is considered one of North America’s most beautiful waterfowl. Though found in many regions of the US today, wood ducks, like beaver, were once on the path to extinction.
Their shared story of persecution, the beaver prized for its fur, meat and scent glands and the wood duck for its delicate meat, is also a shared story of redemption and recovery.
By the early 1900’s wood duck populations crashed due to habitat loss and unregulated market hunting. Beaver populations had already been decimated by this time due to relentless hunting and trapping the previous century. As beaver populations were wiped out, the ponds and backwaters wood ducks needed also disappeared. A hundred years ago the situation was dire for the wood duck but hope was on the horizon.
The Migratory Bird Treaty Act of 1918, with specific protections for wood duck, including closed hunting seasons until 1941, may have saved this species from extinction. In response to this legislation, wood duck numbers soon started to rebound. But it was dedicated conservation efforts launched on public and private lands to protect wetland habitats and encourage beaver colonization that boosted the recovery of both species.
To understand how beavers benefit wood ducks let’s look at basic habitat needs (Food/Water, Cover & Space) for these ducks and how beaver activities influence each.
Food & Water Availability
As its name implies, wood ducks inhabit woodland lakes, rivers, streams and ponds that offer a diverse range of food for adult birds and their young. Woodies are “surface feeders” and need slower moving water of beaver ponds and still waters to feed effectively. This is especially true for ducklings that require insects, aquatic invertebrates, small fish and other high-protein animal material to fuel their early and rapid growth and for egg-laying female ducks in the spring .
Beaver dam and lodge building activities create food sources for wood ducks through the following:
- Dam and lodge building deposit tree and shrub biomass into the stream channel and along with mud excavated to cement these structures, nutrients are released into the water. These nutrients are mostly retained in the beaver pond wetland complex rather than simply flowing downstream. This leads to increased biodiversity and more food for wood ducks;
- Dams raise water levels and flood nearby vegetation. This expands food opportunities, especially for young wood ducks that can swim to glean insects from the water and the stems of a greater range of plants.
- Dams slow stream flow and allow pools and ponds to form. Slow moving water allows for richer diversity of aquatic invertebrates and plant growth than fast-moving riffles. In addition, ducklings (and adult wood ducks) can safely navigate slow water without expending energy required to negotiate rapid currents.
- Beaver lodges typically have underwater food caches comprised of stems, leaves and other vegetation. These sub-surface food storage areas promote algae growth and concentrate a myriad of invertebrate food sources accessible to adult wood ducks and their young.
Reduced water flow rate and nutrient recharge are tremendous beaver benefits and create diverse food sources within wetland communities. Many species benefit and wood ducks are no exception here. Without beaver dams to “slow-the-flow”, water in river and stream channels may simply be flowing too fast for food to be available for wood ducks.
Cover For Feeding, Resting & Nesting
Wood ducks are prey for animals and raptors. They require wetlands where they can feed, loaf and raise their young in safety. Beaver activities create protective cover and space by:
- Flooding existing woody vegetation – Flooded areas with tree and shrub cover allow wood ducks to feed and rest on the water or shore with protection from the sides and from above. This is especially important for ducklings as they forage before learning to fly and for migrating adults that need to rest and recover during their journey.
- Promoting tree growth for nesting – Wood ducks are “cavity-nesters” and require trees with naturally occurring cavities or those made by woodpeckers as close to water as possible. Beaver dams increase water recharge to the surrounding landscape and aquifer. Over time, this promotes permanent tree cover of sycamore, cottonwood and other large riparian tree species. These trees have naturally occurring cavities big enough for wood ducks and can grow close to or at the water’s edge which reduces the distance to water that ducklings must travel after hatching.
- Creating snag nest trees – A second way wood ducks create nest cavities is by inundating trees that die and become “snag” trees. Snags are attractive to woodpeckers for excavating nests of their own and later for other cavity nesting species. Snag trees can form close to or even in the water. Nest cavities in snags surrounded by water provide additional protection from climbing predators like raccoons and opossum.
Enduring Space To Live
Beaver activities can exponentially expand wetland habitat area and its permanency. This means more food, cover and reproduction potential for wood ducks when compared to seasonal water channels. Wetland size matters to wood ducks but so does how long these areas retain surface water. Beaver pond complexes can hold water long after temporary riparian zones run dry and are often the sole source of year-round wetland habitat in arid regions. For example, a primary reason wood ducks are often year-round residents in San Luis Obispo County is a credit to our hard-working beaver colonies along the Salinas River. These beavers and their pond network help preserve wetlands through dry periods of the year when wood ducks would otherwise have to leave the area.
Beavers create space for other species to live. That’s a fact. Though the total area colonized by beaver may be small the impact is huge. By some estimates, wet areas, including those colonized by beaver, comprise less than 1% – 2% of the landscape in the western US. Yet it’s also estimated that more than 80% of all wildlife species in this region depend upon wetlands.
Because of their importance as ecosystem engineers, the role of beaver should be encouraged in western wetland management at every opportunity.
In closing, beavers and wood ducks have been next-door riparian neighbors for millennia. They both need wetlands for their survival. They’ve both suffered persecution to the brink of extinction and both species continue to recover together. Theirs is a shared history we can learn much from in understanding connections between and within all living systems. So, head out to your nearest beaver pond. Take a look around. Get wet and explore and learn more about how beavers benefit wood ducks and so much more. And if you do see a wood duck feeding, resting or raising its young, chances are a beaver was there to help out somewhere along the way.