Willets are medium-sized shorebirds that are found along coastlines, mudflats, and beaches across North America. They have long legs and long, tapered bills that they use to probe into sand or mud to find food. Willets feed primarily on invertebrates such as insects, crustaceans, mollusks, and marine worms. Their specialized bill allows them to feel and catch food hidden below the substrate. Willets have a varied diet and employ a range of foraging techniques to catch different types of prey.
What do willets eat?
Willets are opportunistic feeders and will eat a wide variety of invertebrate prey. Some of their common food sources include:
- Insects: such as beetles, flies, grasshoppers, caterpillars, and larvae
- Marine worms: such as lugworms, earthworms, and polychaete worms
- Mollusks: including snails, limpets, mussels, and clams
- Crustaceans: like crabs, shrimp, isopods, and amphipods
- Other invertebrates: including spiders and echinoderms
The specific composition of a willet’s diet varies depending on location, season, and food availability. But they consistently target small invertebrate prey that live on sandy or muddy substrates. Their long bills allow them to hunt for buried and hidden food sources.
How do willets hunt?
Willets employ a variety of hunting techniques to catch different types of prey:
Probing
Their most common hunting method is to probe into the mud or sand in search of hidden prey. They will walk along slowly, inserting their bills into the substrate looking for food. Their bills are equipped with thousands of sensory receptors that can detect prey items buried under several inches of sand or mud. When they detect something, they will quickly plunge their bill down, grasp the item, and pull it out.
Visual hunting
Willets also employ visual hunting techniques. They will scan the substrate looking for signs of movement that gives away buried prey. When they see a crab scurry or worm peeking out, they will run over and catch it before it disappears. They also visually hunt for insects and other prey on the surface of mudflats and beaches.
Tapping and vibrations
Willets sometimes use tapping and vibration techniques to bring worms and burrowed prey to the surface. They will stomp their feet on the ground, creating vibrations that irritate worms and invertebrates, causing them to come up out of their burrows where they can be caught.
Excavating
When hunting for deeper buried prey like clams or crabs, willets will excavate into the sand or mud using their bill. They will dig into the substrate, flinging it out behind them until the prey item is uncovered and can be eaten.
Where do willets forage for food?
Willets exploit a variety of intertidal habitats while foraging:
- Mudflats: They commonly feed on mudflats rich in marine worms, mollusks, and crustaceans. The wet mud provides great probing opportunities.
- Sand beaches: Beach environments also harbor many prey items. Willets probe into the sand searching for crabs, coquina clams, insects, and more.
- Tidal marshes: Coastal marshes contain worms, fiddler crabs, and other prey that willets can easily access when foraging.
- Tidal wracks: Piles of organic debris and seaweed deposited on beaches contain large amounts of insects and invertebrates that willets consume.
Willets patrol these intertidal areas during low tide, when receding water exposes their feeding grounds. The rising and falling tides dictate their foraging patterns.
How do morphological adaptations aid feeding?
Willets have several key adaptations that allow them to effectively probe into substrates and catch buried prey:
Long bills
Their long, tapered bills can penetrate several inches into mud and sand. This allows them to reach buried prey not accessible to shorter-billed species. The bills also have slight upward curvature at the tip which is useful for probing deeply.
Sensory pits
Their bill tips contain a concentration of mechanoreceptors called Herbst corpuscles. These sensory pits allow willets to feel for movements and vibrations made by buried prey items. This helps them pinpoint food hidden under the substrate.
Serrated edges
The inside edges of their bills feature small serrations or ridges. This helps them effectively grasp and hold onto slippery prey like worms, clams, and crabs as they pull them out of mud or sand.
How does diet change seasonally?
The diet of willets can shift over the course of the year as different food sources become more available:
- Spring: They eat protein-rich foods needed for breeding like worms, crabs, and clams.
- Summer: With insect hatches, they eat more terrestrial insects and larvae.
- Fall: They shift back to marine invertebrates to build up fat for migration.
- Winter: On coastal wintering grounds, they focus on crabs, shrimp, and marine worms.
The abundance of their specialized intertidal prey dictates seasonal shifts in diet. But willets maintain the probing and excavating skills needed to exploit these ever-changing food resources throughout the year.
How do willets behave when feeding?
Willets exhibit particular behaviors and patterns while foraging:
- Daytime feeding: They are active daytime feeders, taking advantage of low tides when prey is most accessible.
- Night roosting: They roost communally at night in coastal areas and feed again during the day.
- Territoriality: They often defend prime feeding territories from conspecifics and other shorebirds.
- Feeding frenzies: When prey is abundant, they will engage in feeding frenzies, gorging themselves as quickly as possible.
- Tide following: They follow the ebb and flow of tides to access the best newly exposed mudflats and sandbars.
Understanding these daily and seasonal movements and behaviors helps shed light on their feeding ecology.
Do willets exhibit feeding specializations?
Willets do show some degrees of individual feeding specialization:
- Prey preferences: Individual birds may become proficient at catching certain prey types, like crabs or clams.
- Habitat preferences: Some individuals prefer feeding on open beaches, while others utilize marsh habitats.
- Feeding techniques: Each willet develops its own style of feeding based on factors like bill morphology and learned behaviors.
- Dominance hierarchies: Dominant, territorial individuals get first access to the most profitable feeding areas.
Their flexible, opportunistic feeding strategy allows for individual variability. Specializations enhance the survival of certain birds in particular habitats and conditions.
How do willets find and catch prey?
Here is a simple overview of how willets locate, capture, and consume different types of prey:
Insects and larvae
- Visual detection as they walk along scanning the mudflat.
- Rapid pecking or lunging movements to catch insects before they take off.
- Swallowing prey whole, crushing with muscular gizzard.
Worms
- Vibrations and probing to detect worms under the surface.
- Rapid plunging of bill to grab and extract worms.
- Using serrated bill edges to hold slippery worms.
- Swallowing worms whole while holding both ends.
Crabs
- Visually seeing crabs scurry across the surface.
- Quickly predating upon exposed crabs before they can burrow.
- Subduing larger crabs by shaking or pounding them against the ground.
- Using bill tip to pry apart and consume crab armor.
Bivalves
- Probing bill into sand or mud to feel buried clams and mussels.
- Excavating with bill to fully expose bivalves.
- Inserting bill tip into shell to cut muscles and pry open.
- Discarding crushed shells and consuming soft inner parts only.
Willets have an impressive range of tactics for locating and consuming different prey types. Their versatile bill allows them to take advantage of a wide array of food resources.
How much do willets eat daily?
The exact daily food intake of willets likely varies considerably based on factors like season, tidal cycle, prey availability, and individual energy requirements. However some observations indicate that willets consume a substantial amount of food daily:
- Up to 92 grams of food per day based on observational studies.
- Hundreds of individual prey items per day including crabs, snails, clams.
- Nearly continuous daytime foraging activity.
- Frenzied feeding when prey is abundant.
- Crops filled to capacity before roosting overnight.
Their active foraging strategy and opportunistic diet allow willets to meet their high energy demands. During times of plenty, they will voraciously consume as much as they can find.
What affects feeding success?
Several biotic and abiotic factors influence the feeding success and energy intake rates of willets:
- Prey availability – Abundance and accessibility of key prey types dictates intake rates.
- Tidal cycles – Low tides expose more feeding habitat and food resources.
- Climate – Severe storms and cold weather can reduce prey abundance and availability.
- Habitat quality – Intertidal areas with high biomass support more prey.
- Competition – Other shorebirds competing for resources can exclude willets.
- Predation risk – Time spent avoiding predators reduces feeding.
- Human disturbance – Human activities that disrupt feeding reduce intake.
When conditions are optimal, willets can feed efficiently and meet energy needs. But various biotic and abiotic factors often create challenges.
How do willets swallow their prey whole?
Willets are able to swallow large prey items whole due to several key adaptations:
- Distensible esophagus – Their flexible throat allows very large items to be swallowed.
- Muscular gizzard – The gizzard crushes and grinds food items after swallowing.
- Large egg size – Shorebirds that swallow whole food produce relatively large eggs to accommodate big chicks.
- Rapid chick growth – Chicks grow very quickly and develop the ability to swallow whole prey early on.
Additionally, willets employ some tactics and behaviors to help get prey down:
- Tilting bill up – This straightens the throat and aligns it for swallowing.
- Raising head – Raising the head uses gravity to help draw food down.
- Bill shaking – Rapidly shaking the bill helps work prey further down the throat.
- Neck extending – Fully extending the neck opens the esophagus more.
So through anatomical adaptations and specialized behaviors, willets are able to swallow even very large prey items. This allows them to take advantage of the abundant food on intertidal habitats.
Do willets ever store food?
Willets do not typically store or cache food for later use. However, there are a few observations of food storage behaviors in willets:
- Crops – Willets may fill up their esophageal crop with food before roosting overnight.
- Regurgitation – Rarely, they have been seen regurgitating food for mate or young.
- Gravel ingestion – They ingest some rocks and gravel which may help grind up food.
- Caching – There is anecdotal evidence of willets wedging prey in mud or vegetation, but this is atypical.
Overall though, willets are adapted to opportunistically feeding on abundant food that is best consumed immediately. They have not developed adaptations for hoarding or caching food for extended periods. Their digestive system is geared towards maximum intake rates and rapid digestion of prey. So while they may store some food in their crop short-term, prolonged food storage is uncommon.
Conclusion
In summary, willets are remarkably well-adapted shorebirds that utilize a range of specialized skills and behaviors to feed on intertidal invertebrate prey. Their versatile bills allow them to probe deeply into mud and sand, feel for buried prey, excavate large food items, and swallow everything whole. Willets move between favored coastal habitats as tides fluctuate, consuming as much energy-rich food as possible during daytime low tides. Their particular adaptations and dependence on transient intertidal resources make willets a fascinating species to observe in their coastal realm.