Grebes are waterbirds that are well adapted for swimming and diving underwater. They have lobed feet with long toes that allow them to efficiently propel themselves through the water. Their bodies are streamlined and their feathers are waterproof, allowing them to stay submerged for long periods of time. So the quick answer is yes, grebes do swim underwater.
How do grebes swim underwater?
Grebes have several adaptations that enable them to swim and dive underwater effectively:
- Their feet are located far back on their bodies, near their tails. This gives them more power and thrust when swimming.
- Their toes have flat lobes that act like flippers under water. Grebes can rotate their toes to position the lobes vertically for diving or horizontally when swimming along the surface.
- They have dense, waterproof plumage that helps reduce buoyancy underwater. Their feathers trap air against their bodies to help insulate them in cold water.
- Grebes have flexible vertebrae in their necks, allowing them to snake their necks into a tight S-shape when diving. This reduces drag and helps them plunge through the water head first.
- Their nostrils close underwater, and grebes can hold their breath for extended periods, up to a minute or more while diving.
- Their eyes are adapted to see well underwater. They have flat corneas and the ability to adjust the lens shape to focus under water.
By combining these adaptations, grebes are able to “fly” through the water. They propel themselves with their powerful feet and streamlined bodies, using their wings for steering and stabilizing underwater. Some species do a running dive from the surface to help give them an initial burst of speed as they swim downwards on a dive.
How deep can grebes dive?
Different grebe species are capable of diving to different maximum depths. Some examples include:
- Western grebes – can dive to depths over 30 meters (100 feet).
- Great crested grebes – typically dive to depths of 10-30 meters (30-100 feet).
- Little grebes – dive to depths around 3 meters (10 feet) or less.
The maximum diving depth depends on the species and water clarity. In clear open water, grebes are capable of diving to deeper depths. Western grebes in particular have been recorded diving to depths over 45 meters (150 feet) in clear lakes in the western United States.
In turbid or murky water, grebes are limited to shallower dives since visibility decreases. They usually do not dive much past 30 meters even in clear water, since light diminishes greatly at those depths. This limits their ability to see and hunt underwater.
How long can grebes stay submerged?
Most grebes can stay underwater for 1-3 minutes during a single dive. Larger grebe species with greater oxygen storage capacity can remain submerged for longer periods. Some timing examples for different grebe species include:
- Little grebes – average dives of 30-90 seconds
- Eared grebes – 1-2 minutes
- Great crested grebes – 1-3 minutes
- Western grebes – over 5 minutes
The longest recorded single dive for a western grebe is just over 5.5 minutes. However, this is an extreme case. Most dives tend to be shorter, in the 1-3 minute range even for larger grebe species.
Grebes are able to remain underwater for these extended periods due to:
- Slowing their heart rate to conserve oxygen
- Having higher than average hemoglobin and myoglobin concentrations in their blood and muscles to store more oxygen
- The ability to tolerate increased lactic acid levels that result from oxygen deprivation
When diving for extended periods, grebes surface slowly and take time to recover. They may need to pause and rest on the water surface before making another long dive.
How fast can grebes swim underwater?
Grebes are speedy swimmers underwater. Different species have been clocked at the following underwater speeds:
- Little grebes – 2-5 mph (3-8 km/h)
- Eared grebes – around 5 mph (8 km/h)
- Great crested grebes – 5-6 mph (8-10 km/h)
- Western grebes – 6-8 mph (10-13 km/h)
The fastest underwater swimming by grebes is done by the western grebe, which has been recorded swimming as fast as 8.5 mph (13.6 km/h) in short bursts when diving. This speed matches or exceeds the underwater swimming speeds achieved by some marine mammals like dolphins.
In comparison, human Olympic swimmers only reach maximum underwater speeds around 3 mph (5 km/h). So grebes are much faster swimmers under the water’s surface than people are!
Grebes achieve these fast swimming speeds thanks to their streamlined shape, powerful feet, and ability to propel themselves with their wings like they are flying through the water.
Why do grebes dive and swim underwater?
Grebes spend so much time diving and swimming underwater because it allows them to efficiently hunt and find food. Reasons why grebes dive include:
- Catching small fish and aquatic invertebrates like crayfish
- Foraging for vegetation and roots along the bottom
- Evading predators like eagles, foxes, and coyotes when threatened
- Escaping rough weather conditions on the water surface
- Reaching nesting sites and retrieving sunken nesting material
Additionally, some courtship activities like presenting nesting material to mates occur underwater. Grebes perform elaborate courtship rituals and mating displays featuring synchronized swimming and diving.
Since grebes live their entire lives on the water, diving underwater to feed, hide, breed, and travel comes naturally to them. Their adaptations for swimming and diving allow grebes to thrive in their aquatic environment.
What kinds of aquatic habitats do grebes inhabit?
Grebes are most commonly found on freshwater inland wetlands such as:
- Lakes
- Rivers
- Marshes
- Ponds
But some grebe species can also be found in coastal marine habitats such as:
- Estuaries
- Bays
- Inlets
And even far out at sea when migrating. The key requirements are calm, open water for swimming and diving, and abundant prey available below the surface. Vegetation like reeds or rushes along the water’s edge provide nesting material and cover.
During the winter some grebes will migrate to more sheltered large bodies of water that don’t freeze over. Others may stay in more exposed waters if they have enough open area for swimming and diving.
Freshwater Habitats
Most grebes prefer freshwater lakes, ponds, and wetlands. Some examples:
- Pied-billed grebes – small ponds and marshes
- Little grebes – lakes, rivers, and freshwater marshes
- Great crested grebes – large freshwater lakes and ponds
These freshwater settings provide habitat for fish and invertebrates that the grebes feed on. Shallow water areas are especially productive for finding food.
Coastal Marine Habitats
Some grebes inhabit brackish or saltwater areas along coastlines, such as:
- Western grebes – estuaries and bays
- Clark’s grebes – coastal inlets
- Red-necked grebes – sheltered saltwater bays
The abundance of small fish and invertebrates to dive for make these protected coastal waters attractive to grebes.
Pelagic Ocean Habitats
When migrating over long distances, some grebes traverse large stretches of open ocean. For example, eared grebes migrate from inland lakes where they breed all the way to the Pacific ocean to overwinter.
While not their preferred habitat, grebes are capable of diving into deeper offshore waters in search of food when necessary during migration. But they seek out more sheltered coastal or inland wetlands when possible.
Conclusion
In summary, grebes are highly specialized waterbirds that are well adapted for diving and swimming underwater. Their lobed feet, streamlined bodies, and dense waterproof plumage allow grebes to swim at fast speeds, dive to depths up to 30 meters, and stay submerged for several minutes when hunting for food. Grebes inhabit a variety of aquatic habitats, but prefer calm freshwater lakes, ponds, marshes and sheltered coastal bays where they can easily dive from the surface and find fish, invertebrates, and vegetation underwater. Their ability to maneuver and forage underwater helps make grebes successful in the aquatic environments they call home.