Grebes are water birds that are known for their elaborate mating dances and floating nests. There are 22 species of grebes that can be found around the world, ranging from small pond-dwellers to large diving birds of open water. All grebes build nests near water, typically floating nests known as “nest platforms” that they anchor to emergent vegetation. The nest location and structure varies by species, as grebes have adapted to breed in different aquatic habitats.
Nesting Habitats
Grebes nest on quiet bodies of freshwater and saltwater. This includes ponds, lakes, marshes, estuaries, and sheltered bays. The specific nesting location depends on the species:
Ponds
Smaller grebes like the least grebe and little grebe nest on ponds. These grebes build nests attached to vegetation at the water’s edge or on floating mats of vegetation. Ponds provide dense cover and protection from waves.
Lakes
Larger diving grebes like the great crested grebe nest on lakes. They seek out quiet bays and inlets protected from wind and waves by emergent vegetation like reeds. Their floating nests are anchored to living plants or submerged woody debris.
Marshes
Shallow freshwater marshes are prime nesting habitat for pied-billed grebes and eared grebes. They construct floating nests attached to emergent plants like cattails, bulrushes, and reeds. The dense vegetation helps conceal the nests.
Coastal areas
Grebes that live along coasts, like the Western grebe and Clark’s grebe, nest in estuaries and sheltered marine bays. Their floating nests are anchored to plants like cordgrass and pickleweed that border the shoreline.
Tundra ponds
On the tundra, horned grebes and red-necked grebes nest next to small ponds that form during spring snow melt. These grebes build nests that float on water or sit very close to the pond edge amid low vegetation.
Nest Structures
All grebe nests serve the purpose of floating on water, allowing the sitting grebe to easily dive off the nest to escape predators. But the exact nest structure varies by species:
Mats of floating vegetation
Small grebes like least grebes construct the simplest nests – just a clump of floating dead plant matter and debris, anchored by living plants. The grebes actively pull vegetation together to create the mat.
Piles of wet plant material
Many small to medium grebes build nests from piles of wet plant material, especially reeds. The base often contains woody debris or a platform of reeds. More reeds are continuously added during incubation.
Mounds of vegetation on platforms
Larger grebes make sturdy nest platforms as foundations by piling together plant stems and debris. Cattails, reeds, sedges, and rushes are commonly used. On top of the platform they create a mound or cup shape from wet vegetation for the eggs.
Minimalist platforms
The Western and Clark’s grebes construct minimalist nests of just a small pile of stems as a platform, with sparse nesting material. But these exposed nests are very vulnerable in wind and waves.
Nesting Behaviors
Grebes exhibit some unique nesting behaviors related to their floating nests:
Anchoring the nest
Grebes anchor their nests to emergent vegetation. They incorporate live plants into the nest construction. This prevents the nest from drifting away as it floats.
Building nests near protective vegetation
Grebes select nest sites adjacent to tall, dense vegetation. The plants conceal the nest and shelter it from winds and waves that could destabilize the floating structure.
Adding nest material throughout incubation
Additional wet plant material is continuously added to the nest during incubation. This replaces material that gets waterlogged and sinks, helping the nest continue to float.
Frequent nest maintenance
One grebe, usually the female, remains on the nest at all times to prevent drifting. The incubating grebe often works on strengthening and rebuilding the nest throughout incubation.
Syncronized diving from the nest
Grebe pairs coordinate perfectly-timed dives off the nests when scared by predators. This makes the eggs less vulnerable to predators.
Timing of Nest Building
Grebes are spring and summer nesters. They build their nests at the following times:
Northern hemisphere
Most grebes in the northern hemisphere nest from April through August. They start nests shortly after ice-out on northern lakes and ponds. Nesting ends by late summer when their aquatic habitats start to freeze over again.
Southern hemisphere
Southern grebes like the hooded grebe nest from September through February. Their timing coincides with spring and summer in South America.
Migration
Grebes who migrate long distances, like the eared grebe, may not nest until May or June after arriving at breeding grounds. Migration delays nesting.
Altitude
At high altitudes, nesting is delayed until snow fully melts from mountain lakes, often not until June. Western and Clark’s grebes breeding at higher elevations have shorter nesting periods.
Asynchrony between regions
The same species may nest at very different times across its range. Regional conditions and latitude influence nest timing, which may vary by months.
Duration on the Nest
The amount of time grebes spend incubating on their floating nests depends on:
Clutch size
Grebes lay between 2 to 12 eggs. Larger clutches take longer to incubate, keeping grebes on their nests for longer periods.
Incubation period
Incubation ranges from 23 days for small grebes to 29 days for large grebes. Longer incubation results in more days spent nesting.
Nest loss
Grebes who lose nests to waves, wind, or predators must completely rebuild their nests and re-lay eggs. This extends the nesting phase significantly.
Renesting
Most grebes renest after nest failure, remaining in nesting mode for an extended duration. They may attempt to nest repeatedly.
Double brooding
Some grebes, like eared grebes, produce two successful broods per season. This results in a very prolonged nesting period spanning several months.
Differences Between Grebe Species
While their nesting behaviors share many similarities, grebes do have differences when it comes to types of nesting habitats, nest structures, and nesting timeframes.
Large vs. small grebes
Large grebes nest in expansive lakes and marine bays while small grebes use ponds and marshes. Large grebes build sturdy nest platforms and small grebes use frail floating vegetation mats.
Coastal vs. inland grebes
Coastal grebes use estuarine plants like cordgrass for nest anchoring and building. Inland grebes rely on freshwater vegetation like cattails and reeds. Wave action impacts nests in coastal areas.
Northern vs. southern grebes
Northern grebes wait for ice-out in spring while southern grebes nest during regional summers. Different plant species are also used based on geography.
Migration patterns
Migratory grebes nest later after arriving at breeding sites. Non-migrants initiate nesting sooner based on local conditions.
Grebe Species | Habitat | Nest Materials | Nesting Period |
---|---|---|---|
Western grebe | Large lakes | Small platform of stems | May – August |
Little grebe | Ponds and marshes | Floating mats of vegetation | April – July |
Hooded grebe | Tundra ponds | Pile of vegetation anchoring to land | October – January |
Threats to Nesting
Grebes face several threats to successful nesting:
Wave action
Waves can break up floating nests or detach them from anchoring plants. Grebes avoid nesting where exposure to waves is high.
Wind
Strong winds can push floating nests into open water or pile debris onto nests. Windy periods often cause nest flooding or abandonment.
Predators
Predators like gulls, mink, and racoons readily eat grebe eggs. Adults aggressively defend nests from approaching predators.
Water level changes
Falling or rising water levels can detach anchored nests or leave them stranded out of water. Stable water levels are key.
Boats
Motorized boat wakes create waves that flood or damage nests. Grebes avoid nesting where boating activity is frequent.
Human disturbance
Nest abandonment may occur due to repeated human intrusions near nests. Grebes are sensitive to disturbance.
Invasive species
Invasive plants species replace native vegetation used for nest anchoring and cover. Invasive predators also threaten nesting success.
Conservation and Management
Several management strategies help protect and restore grebe nesting:
Preserving wetlands
Wetland protection provides grebes intact habitat for nesting. Draining or filling of wetlands removes key habitat.
Managing water levels
Providing stable water levels through dam management or other measures helps maintain nesting conditions.
Eradicating invasive species
Removing problem plants like European frogbit improves conditions for native vegetation that grebes rely on for nest structures.
Establishing protected areas
Reserves with restricted access limit human disturbance of nests. Patrolling helps prevent detrimental activities.
Altering recreational uses
Zoning off sensitive nesting areas from motorized boats helps reduce damaging waves from wakes.
Habitat restoration
Restoring degraded wetlands through revegetation and hydrological improvements recreates nesting habitat.
Nest platforms
Artificial nest platforms made of tethered mats of vegetation provide additional nest sites if natural sites are lacking.
Conclusion
Grebes are remarkable water birds that build unique floating nests in a variety of wetland habitats. While grebe species exhibit differences, they share common nesting behaviors like diving from nests and continuous maintenance of the floating platforms. Threats like waves, predators, and human disturbance jeopardize their delicate nests, requiring conservation measures focused on protecting aquatic habitat and mitigating risks. With appropriate management, grebes can continue their mesmerizing nest building and mating rituals into the future.