Cassin’s Auklet is a small seabird found along the Pacific coast of North America. They are known for their unique diet, feeding primarily on plankton and small crustaceans. In this article, we will explore what Cassin’s Auklet eats and how their diet helps them survive in their marine environment.
Zooplankton
The main component of a Cassin’s Auklet’s diet is zooplankton. Zooplankton are tiny marine animals that drift along ocean currents. Some common zooplankton that Cassin’s Auklets eat include:
- Krill – shrimp-like crustaceans
- Copepods – small floating crustaceans
- Amphipods – small shrimp-like crustaceans
- Pteropods – swimming snails
- Larvaceans – gelatinous zooplankton that filter feed
Cassin’s Auklets have specialized bills to help them catch and eat zooplankton. Their bills have thin, forward-pointing hooks that allow them to efficiently scoop up these tiny prey items as they swim along the ocean’s surface. Zooplankton provides Cassin’s Auklets with protein and nutrients to sustain their high-energy lifestyle.
Small Fish
In addition to zooplankton, Cassin’s Auklets will occasionally feed on small fish such as:
- Anchovies
- Smelts
- Lanternfish
These fish provide an extra boost of calories and fat for developing chicks during breeding season. The adult birds will capture the fish and return to their nesting burrows to regurgitate the intact fish for their young to eat. This supplemental diet helps ensure chicks grow large and healthy before fledging out to sea.
Crustaceans
Cassin’s Auklets also feed on small crustaceans to supplement their plankton diet. Some of their favorite crustacean prey includes:
- Mysid shrimp
- Barnacle larvae
- Crab larvae
- Sand lice
These small swimming crustaceans provide essential nutrients and are easy for Cassin’s Auklets to scoop up as they swim along the water’s surface. The diversity of crustaceans in their diet helps ensure Cassin’s Auklets get the complete nutrition they need.
Seasonal Variation
The diet of Cassin’s Auklet can vary somewhat depending on the time of year. Some key seasonal shifts include:
- Breeding season – More small fish are eaten to feed growing chicks.
- Winter – Their plankton diet includes more large copepods that are abundant in winter.
- Summer – The plankton diet includes more larvaceans and pteropods which thrive in summer.
Cassin’s Auklets are nimble foragers that can shift their diet to take advantage of the most abundant seasonal food sources. This adaptability allows them to flourish year-round in the dynamic marine ecosystem.
Foraging Behavior
Cassin’s Auklets have a very unique foraging strategy to target zooplankton and small crustaceans. Here are some key behaviors they use:
- Surface diving – They dive from the surface and swim underwater to catch prey items.
- Nocturnal feeding – They primarily feed at night when zooplankton migrate up towards the surface.
- Fluttering flight – They use a fluttering flight pattern close to the water to scoop up food.
- Underwing feeding – They will cup their wings under the water to trap prey.
These specialized foraging techniques allow Cassin’s Auklets to exploit the abundant zooplankton and crustaceans they depend on. Their unique bill and nimble flying ability are perfectly adapted to this feeding strategy.
Geography and Habitat
Cassin’s Auklets are found along the entire Pacific coast of North America. Their diet can vary somewhat depending on local marine conditions:
- Northern range – More krill and large copepods in colder subarctic waters.
- Central California – Areas with coastal upwelling have more larvaceans.
- Southern range – Warmer equatorial waters have more diversity of small crustaceans.
No matter where they are found, Cassin’s Auklets can adapt their diet to take advantage of the abundant plankton and small crustaceans provided by highly productive coastal upwelling zones.
Unique Digestive System
Cassin’s Auklets have special digestive adaptations to process their unique zooplankton diet:
- A long coiled intestine allows them to digest chitin-rich crustacean prey.
- A muscular gizzard helps crush the hard exoskeletons of zooplankton.
- A short intestine section aids rapid digestion of small soft-bodied prey.
Their digestive system is also designed to hold a large food load. This allows Cassin’s Auklets to efficiently process the abundant food they gulps while out foraging on the water. These adaptations give them tremendous digestive flexibility to capitalize on zooplankton prey.
Diving Ability
Cassin’s Auklets have high underwater diving capabilities that aid their specialized foraging strategy:
- They can dive over 60 meters deep when searching for prey patches.
- Their wings are optimized for swimming with short broad shapes.
- Dense plumage resists water penetration when diving.
- Nostril valves seal to prevent water entry when submerged.
This allows Cassin’s Auklets to dive deep and pursue prey far below the ocean’s surface. Their diving skills let them fully utilize the rich zooplankton resources available in their coastal habitat.
Breeding Diet
Cassin’s Auklets have an unusual breeding diet driven by the need to feed their chicks:
- Adults eat small fish and crustaceans out at sea.
- They return to land each night to regurgitate food for the chick.
- Chicks are fed up to 20 whole fish per night.
- This continues for over 40 days until the chick fledges.
This lets the chicks get adequate nutrition without the adults having to carry heavy loads of small zooplankton. The delivery of whole intact fish is essential to support the chick’s rapid growth.
Population Threats
Several factors can threaten Cassin’s Auklet populations and disrupt their plankton diet:
- Climate change – Ocean warming may alter zooplankton abundance and distribution.
- Overfishing – Removal of forage fish species can reduce food resources.
- Pollution – Oil spills and plastic debris can be ingested.
- Predators – Increased predation limits adult survival and breeding success.
Protecting key breeding sites and maintaining healthy ocean habitat is crucial to ensure Cassin’s Auklets can continue to thrive on their specialized plankton and small crustacean diet.
Conclusion
In summary, Cassin’s Auklet has a very specialized diet consisting mainly of zooplankton, small crustaceans and fish. Their unique bill shape, foraging style, diving ability, and digestive system allow them to specialize on these small aquatic prey. While the exact composition of their diet varies geographically and seasonally, Cassin’s Auklets remain dependent on the availability of plankton and other micronekton throughout their range. Protecting the productivity of coastal waters will be key to preserving food resources for this unusual seabird into the future.