Zooplankton are tiny animals that drift in the ocean’s water column. They include a variety of organisms like copepods, krill, jellyfish larvae, rotifers, and fish larvae. Zooplankton are a key part of ocean food webs and are eaten by many larger animals. This raises the question – do birds eat zooplankton?
Do Seabirds Eat Zooplankton?
Yes, some seabirds do eat zooplankton. Seabirds that are known to consume zooplankton include:
– Penguins
– Puffins
– Auks
– Murres
– Murrelets
– Shearwaters
– Petrels
– Storm petrels
– Phalaropes
– Gulls
– Terns
– Skimmers
– Frigatebirds
– Tropicbirds
– Boobies
– Cormorants
– Pelicans
Many of these seabirds are pursuit divers, meaning they chase and catch prey underwater while swimming. Their diets consist mainly of small fish, squid, and crustaceans, but they regularly supplement this with nutritious zooplankton like krill and other large zooplankton species.
Some examples:
– Little penguins feed on krill, copepods, and amphipods.
– Atlantic puffins eat copepods, amphipods, and krill.
– Rhinoceros auklets consume large amounts of krill.
– Cassin’s auklets eat krill, copepods, amphipods, and pteropods.
– Common murres eat copepods and euphausiids.
– Xantus’s murrelets eat copepods and crab larvae.
– Sooty shearwaters consume amphipods, krill, and other crustaceans.
– Wilson’s storm petrels eat copepods and larval stages of crustaceans.
– Red phalaropes feed on zooplankton like copepods.
– Kelp gulls eat krill, amphipods, crab larvae, and other zooplankton.
– Caspian terns consume fish larvae and small crustaceans.
– Black skimmers sometimes eat zooplankton.
– Great frigatebirds occasionally prey on jellyfish.
– Blue-footed boobies feed on small schooling fish as well as krill and other zooplankton.
– Brandt’s cormorants consume krill, crab larvae, amphipods, and other small crustaceans.
– Brown pelicans eat fish along with some zooplankton like crab larvae.
In cold, highly productive polar waters, zooplankton often make up a major part of seabird diets during certain times of year. But even in tropical and temperate oceans, pursuing zooplankton can provide an efficient source of nutrition for many seabirds.
Do Shorebirds Eat Zooplankton?
Most shorebirds don’t directly consume zooplankton from the water column. However, some shorebirds do opportunistically feed on stranded zooplankton that washes up on beaches. This includes species like:
– Sanderlings
– Ruddy turnstones
– Red knots
– Dunlins
– Western sandpipers
– Least sandpipers
– Plovers
– Oystercatchers
These small shorebirds pick invertebrates out of piles of washed up kelp, seaweed, and debris that accumulates at the high tide line on beaches. This material can contain small crustaceans like copepods, beach hoppers, larval crabs, shrimp, and other zooplankton that were swept in with the tides. For example, western sandpipers probe for amphipods and other tiny crustaceans in seafoam accumulated on shorelines.
While most shorebirds don’t directly filter-feed on zooplankton in the water, they will opportunistically pick through strandlines to consume whatever small aquatic invertebrates get left behind.
Do Other Waterbirds Eat Zooplankton?
Some other waterbird groups like loons, grebes, herons, storks, and flamingos also consume zooplankton at times. Examples include:
– Red-throated loons eating krill and small crustaceans.
– Eared grebes consuming copepods.
– American white pelicans feeding on crayfish and brine shrimp.
– Wood storks eating small fish, amphibians, and crustaceans.
– Greater flamingos filter-feeding on algae, diatoms, and small invertebrates like copepods.
However, most of these species get the bulk of their nutrition from larger prey like fish, frogs, aquatic insects, or vegetation. Zooplankton generally make up a minor supplementary part of their diet. Groups like ibises, rails, cranes, and ducks are not significant zooplankton consumers.
Do Land Birds Eat Zooplankton?
Land birds do not directly consume zooplankton, since zooplankton live suspended in aquatic environments. However, some inland bird groups like swallows and swifts will occasionally eat aerial plankton.
Aerial plankton are tiny flying insects and arthropods that get passively carried by wind currents high up in the air. This includes organisms like aphids, leafhoppers, spiders, mites, and beetles. Groups like swifts, swallows, nightjars, and flycatchers will aerially hawk aerial plankton while in flight. But this is limited to temporary concentrations of small winged insects rather than marine zooplankton.
Overall, marine and freshwater zooplankton do not directly contribute to the diets of terrestrial bird groups like songbirds, raptors, gamebirds, and ratites that live on land. Only aquatic birds that frequent marine habitats like seabirds consume zooplankton with any regularity.
Why Do Some Birds Eat Zooplankton?
There are several reasons why certain seabirds and waterbirds eat zooplankton:
- Highly nutritious – Zooplankton like krill are packed with protein, lipids, calories, and micronutrients like omega-3 fatty acids.
- Easy to catch – Birds can scoop up or filter-feed on dense swarms of slow-moving zooplankton.
- Abundant food source – Areas like polar seas have massive zooplankton biomass.
- Provides variety – Zooplankton complement other prey like fish or squid.
- Feed chicks – Some seabirds provision nestlings with nutrition-rich zooplankton.
- Targeted seasons – Zooplankton pulses are exploited during breeding time.
The combination of accessibility, abundance, and nutritional value makes seasonally gorging on zooplankton advantageous for many seabirds. This allows them to take advantage of zooplankton as a temporary food source when available.
How Do Birds Catch Zooplankton?
Seabirds and other zooplanktivorous waterbirds use a variety of hunting strategies to catch zooplankton, including:
- Diving – Penguins, auks, cormorants dive and pursue krill underwater.
- Surface seizing – Terns and gulls snatch zooplankton from the surface while swimming.
- Plunge diving – Boobies, tropicbirds, petrels plunge dive from air into water to catch prey.
- Filter feeding – Flamingos, some ducks pump water through modified bills to filter out zooplankton.
- Aerial hunting – Swifts and swallows scoop up aerial plankton and insects while in flight.
- Scavenging – Shorebirds pick out stranded zooplankton from beach deposits.
Specialized morphological adaptations like modified bills, tactile senses, or plunge diving abilities allow birds to effectively exploit zooplankton when available. This allows them flexibility to take advantage of ephemeral zooplankton populations.
Challenges Birds Face When Eating Zooplankton
While zooplankton can be a valuable food source, birds also face some challenges when targeting them:
- Small size – High energy required to scoop up dense concentration of tiny organisms.
- Mobility – Zooplankton patches are scatter, requiring searching.
- Seasonality – Zooplankton abundance changes throughout the year.
- Distribution – Zooplankton congregate in certain ocean areas more than others.
- Night feeding – Some zooplankton migrate to surface at night.
- Competition – Other predators compete for same zooplankton resources.
- Overfishing – Human fisheries can deplete zooplankton stocks.
- Climate change – Ocean warming, acidification can impact zooplankton.
Birds need effective hunting strategies and metabolic capabilities to contend with the challenges of capturing tiny fast moving zooplankton. Declining zooplankton abundance due to overfishing or climate change can also negatively impact seabird populations.
Key Zooplankton Groups Eaten by Birds
Some of the main types of zooplankton preyed upon by seabirds include:
Krill – Krill are shrimp-like crustaceans and a major component of zooplankton biomass in oceans worldwide. Major krill species eaten by seabirds include Antarctic krill, Pacific krill, and Northern krill. Penguins can eat up 500 grams of Antarctic krill per day.
Copepods – Copepods are tiny marine crustaceans, with over 10,000 species identified. They are the most abundant animal group on earth and an important zooplankton food source for many seabirds.
Amphipods – Amphipods are a type of small crustacean related to shrimp and sand fleas. Birds pick them out of kelp wrack on beaches or capture them from the water column.
Euphausiids – Euphausiids are close relatives of krill with nearly 90 species identified. They are consumed by many tubenoses seabirds.
Other crustaceans – Birds also eat larval stages of crustaceans like crab, shrimp, lobster, crayfish, barnacles, and isopods.
Fish larvae and eggs – Larval fish and fish eggs are vulnerable prey for many seabirds.
Jellyfish and salps – Gelatinous zooplankton like jellyfish, comb jellies, and salps are eaten by some birds.
Pteropods – Pteropods or “sea butterflies” are tiny swimming sea snails. Their fragile aragonite shells make them sensitive to ocean acidification.
Larvaceans – Larvaceans are tadpole-like marine chordates in the zooplankton. Their houses can aggregate marine snow particles.
Chaetognaths – Arrow worms or chaetognaths are predatory zooplankton eaten by some birds like shearwaters.
Polychaetes – Marine bristle worms known as polychaetes sometimes appear in seabird diets.
Targeting these high density zooplankton hotspots and aggregations can serve as a profitable nutritional strategy for efficient marine predators like seabirds.
Impacts of Zooplankton Loss on Seabirds
Declines in zooplankton abundance and availability due to climate change or human activities could have detrimental impacts on birds that rely on these prey sources:
- Starvation – Less zooplankton availability means less food for dependent seabirds.
- Lower breeding success – Parents have trouble provisioning chicks without sufficient prey.
- Population declines – Loss of an important seasonal food supply can lead to less reproductive success and higher mortality.
- Range shifts – Birds may have to travel farther or change foraging grounds to find zooplankton prey if populations contract.
- Phenology mismatch – Shifts in timing between zooplankton blooms and breeding seasons makes prey unavailable when needed.
Zooplankton are key nutrient-rich resources that some seabirds rely heavily upon at vulnerable parts of their life cycle. Substantial zooplankton losses could ripple through marine food webs with broad ecological impacts.
Future Research
Further research questions on birds and zooplankton include:
– How will seabird foraging, diving behavior, and energetics be affected by declining zooplankton abundance from climate change?
– What mechanisms allow certain seabird species to locate and exploit ephemeral zooplankton patches and hotspots?
– How flexible and adaptable are different seabird species to switching between zooplankton prey and alternate food sources?
– How can fisheries be managed to prevent competition and overexploitation of zooplankton that seabirds depend on?
– How does parental provisioning of chicks with zooplankton impact development, growth rates, and survival?
– Can supplemental feeding of breeding seabirds mitigate impacts from zooplankton losses?
More research is needed to elucidate the implications of zooplankton declines on seabird populations around the world. Monitoring zooplankton-seabird interactions in the context of climate change and human activity will be important going forward.
Conclusion
In summary, some groups of seabirds and waterbirds are significant zooplankton consumers. These include penguins, alcids, tubenoses, gulls, terns, and other marine bird species. Zooplankton like krill and copepods provide an abundant, nutritious food source for these pursuit diving and filter feeding birds. However, land birds do not directly eat zooplankton. Declining zooplankton populations from threats like overfishing and climate change could have negative cascading impacts on seabirds that rely on these prey. More research is needed to fully understand the implications of changes in zooplankton abundance for seabirds around the globe. Careful monitoring and management of marine food webs will be important going forward to maintain healthy seabird-zooplankton linkages.