Grebes are unique waterbirds that are found on lakes and rivers across North America. They have specialized feathers that help them float high on the water and give them a lightning fast diving ability. Grebes have fascinating feeding behaviors and diets that allow them to thrive in their aquatic environments.
What do grebes eat?
Grebes are carnivorous birds that feed on a variety of small aquatic prey. Their diet consists mainly of fish, amphibians, and invertebrates. The specific diet of a grebe depends on the species, habitat, season, and availability of prey. Here are some of the main items in a grebe’s diet:
Fish
Fish make up a large portion of a grebe’s diet during the breeding season and in winter. Grebes are able to swallow fish whole underwater. Some common fish consumed include minnows, sticklebacks, sunfish, carp, catfish, and perch. The size of fish eaten ranges from 1 to 6 inches long.
Invertebrates
Grebes eat a wide array of invertebrates including insects, mollusks, crustaceans, worms, and aquatic larvae. Common invertebrate prey are water beetles, backswimmers, water boatman, crayfish, shrimp, leeches, insect larvae, snails, and freshwater mussels. These are caught by diving underwater.
Amphibians
Amphibians like salamanders and tadpoles are readily eaten by grebes when available. Grebes will consume frog eggs and adults frogs as well. Amphibians provide a good source of protein.
Plants
While grebes mostly eat animals, they occasionally supplement their diet with some vegetation. Some plant material eaten includes roots, stems, leaves, algae, seeds, and plant debris. This vegetation is incidentally ingested when catching small prey.
How do grebes catch their prey?
Grebes have several key adaptations that help them expertly catch prey underwater:
Streamlined body shape
A grebe’s fusiform shape and squat posture in the water reduces drag and allows them to dive and swim fast. Their bodies are evolved for rapid acceleration underwater.
Strong feet
Large feet placed far back on the body provide powerful propulsion for quick bursts of speed during dives. Toes have wide lobes of skin for paddling efficiently.
Flexible neck
A grebe can snake its long, flexible neck down to snatch up unsuspecting prey below. Their necks bend to help scan the water and strike from different angles.
Sharp beak
Grebes have a narrow, pointed beak ideal for spearing and holding onto slippery prey like fish. Sensitive beak tips help locate prey by touch when diving.
Stealth hunting
Grebes swim low in the water and dive suddenly without splashing to surprise prey. Their feathers trap air pockets for buoyancy and noiseless plunging.
Specialized hunting techniques
To make the most of their adaptations, grebes utilize various specialized hunting techniques:
Pursuit diving
If grebes spot prey from the surface, they will submerge and swiftly pursue it underwater in a high-speed chase. Pursuits may go as deep as 60 feet down.
Bottom feeding
Grebes dive down to the lake bottom and probe sediment with their beak searching for buried prey like crayfish. They can feel prey moving using sensitive beak tips.
Feather gathering
Grebes will gather floating feathers into a pile then grab any small invertebrates or larvae that may be caught with the feathers.
Surfacing with prey
After catching fish or large prey underwater, grebes swim back up partially emerging to manipulate and swallow their meal at the surface.
When and where do grebes feed?
Grebes forage for food at specific times and places to increase success:
Early morning and late afternoon
Low light conditions in morning and evening make it easier for grebes to ambush light-sensitive prey. Many insect hatches also occur at these times.
Open water
Grebes hunt for fish and invertebrates in open water areas without dense vegetation. More prey availability and better diving access.
Along weed beds
Beds of aquatic plants and algae harbor abundant insects and small fish. Grebes forage intensively along these weed line edges.
Shallow zones
Shallow water with good light penetration provides ideal habitat for tadpoles, small fish, and larvae. Allows grebes to hunt by sight.
Seasonal variations in diet
The diet of grebes changes throughout the year as prey availability shifts. Here are key seasonal differences:
Summer
– More insects like dragonflies, damselflies, water beetles
– Tadpoles and frog eggs
– Young fish and minnows
Fall
– Crayfish become more important
– Leeches and snails are eaten
– Small shrimp are consumed
– Some plant material ingested
Winter
– Mainly fish like perch, sunfish, and carp
– Crustaceans still taken like freshwater shrimp
– Will eat carrion fish and scraps
Spring
– Fish like minnows and sticklebacks predominate
– Amphibian eggs and larvae are key prey
– Early hatches of aquatic insects taken
Variation between grebe species
While all grebes are piscivorous divers, their diets differ in prey composition:
Western grebe
Small fish predominate like minnows, sticklebacks, and killifishes. Also take good amounts of crayfish and aquatic insects.
Clark’s grebe
Specialize in small fish under 5 inches like minnows and perch. Crustaceans like crayfish are important prey as well.
Red-necked grebe
The most varied grebe diet including fish, amphibians, leeches, snails, shrimp, and aquatic insects. Opportunistic feeders.
Eared grebe
Mainly small fish like fathead minnows and mosquitofish. Also prey heavily on aquatic invertebrates like shrimp and beetle larvae.
Digestion and feeding rates
Here are some key facts about the grebe digestion process and feeding patterns:
High metabolism
Grebes have very fast metabolisms to power their active diving and foraging. Their digestion is rapid.
Frequent feeding
Grebes need to eat very frequently, up to every 30 minutes during the day. Some spend over 80% of daylight hours feeding.
Flexible stomach
The stomach can distend greatly to accommodate large prey items like fish that are swallowed whole. Stomach size increases 25% when full.
Rapid digestion
Grebes digest small fish fully in 1-2 hours. Larger fish may take 4-6 hours to fully digest. This allows grebes to feed continually.
Caeca function
A pair of intestinal dead-end pouches called caeca likely help break down chitin from insect prey. These special chambers enhance digestion.
Grebe Species | Average Weight Eaten Daily |
---|---|
Western grebe | 25-30% body weight |
Clark’s grebe | 20-25% body weight |
Red-necked grebe | 35-40% body weight |
Eared grebe | 30-35% body weight |
Feeding territory and sociality
Grebes exhibit some interesting territorial behaviors related to feeding:
Solitary feeders
During the nonbreeding season, grebes are solitary and maintain individual feeding territories free from competition.
Defended territories
Grebes defend prime feeding patches against intrusions from rivals. Disputes may escalate to physical confrontations.
Nocturnal feeding
At night, territorial boundaries break down and grebes may feed socially in groups at concentrated food resources.
Cooperative feeding
On migration and at wintering sites, large flocks of grebes will work together to drive fish into shallower water to feed communally.
Synchronized swimming
Synchronized swimming by pairs and flocks concentrates small fish to allow more effective group feeding.
Parental feeding of young
Grebe chicks require extensive parental care and feeding:
Fed by both parents
Male and female grebes share brooding duties and provide extensive fish meals to their begging chicks.
Fed whole fish
Chicks are fed whole, live fish by the parents. Young chicks may be helped handling larger fish but quickly learn to swallow themselves.
Frequent feeding
Grebe chicks beg incessantly and are fed very frequently, sometimes hourly, throughout the day. This intense feeding continues for 2-3 months.
Diving from nest
Parent grebes may dive directly from the nest to catch fish to bring back. Some chicks even make their first dives from the nest.
Nocturnal feeding
On some lakes, grebe parents conduct nearly all feeding at night to avoid diurnal predators. This allows safe chick provisioning.
Threats to grebes from diet
Despite their adept fishing skills, grebes face some threats related to their dietary needs:
Pollution
Pollution from pesticides, heavy metals, and industrial chemicals can accumulate in prey fish eaten by grebes. Can cause poisoning.
Habitat loss
Wetland drainage and degradation reduces food availability. Grebes depend on healthy, productive wetlands.
Overfishing
Depletion of fish stocks by human overfishing lowers grebe feeding success and breeding rates. Need abundant small fish.
Invasive species
Introduced fish, crayfish, and bullfrogs may outcompete and prey on native species grebes rely on for food.
Climate change
Warmer water and declining water levels can dry up wetland feeding habitat and reduce fish populations. Limits prey availability.
Conclusion
In summary, grebes are remarkable divers and fish eaters. They employ specialized hunting techniques and adaptations to feed on a variety of aquatic prey. Grebes maintain feeding territories but may also cooperate and synchronize to locate abundant fish schools. The diet varies by species, season, and location. Grebe conservation requires protection of wetland habitats and fish populations that these unique waterbirds depend on. Their specialized piscivorous diet allows them to occupy an important aquatic niche, but also makes grebes vulnerable to environmental changes that threaten their food supply. Further research and grebe friendly management policies are needed to ensure grebes can continue their amazing feeding behaviors and flocking dances into the future.