Stilt sandpipers are small migratory shorebirds that breed in the arctic tundra and winter in coastal wetlands, mudflats, and agricultural fields across North and South America. Their diet consists primarily of invertebrates, with some plant material as well. Let’s take a closer look at the feeding habits and dietary composition of these interesting birds.
Invertebrates
Invertebrates make up the bulk of the stilt sandpiper’s diet. They use their long bills to probe into mud or shallow water and find small worms, insects, crustaceans, mollusks, and other invertebrates. Some of their common prey items include:
- Worms – Both marine worms like polychaetes and earthworms are eaten.
- Insects – Caterpillars, beetles, grasshoppers, craneflies, midges, and other insects are consumed.
- Shrimp and amphipods
- Crabs and isopods
- Snails, clams, and other small mollusks
The relative proportions of these different invertebrates in the diet varies depending on habitat and location. For example, stilt sandpipers feeding on tidal mudflats may eat more marine worms and mollusks, while those in grasslands consume more insects. But across all habitats, invertebrates make up 60-95% of the food items eaten.
Methods of Hunting Invertebrates
Stilt sandpipers use several different techniques to find and capture invertebrate prey:
- Probing – Inserting their long bills into mud or soft soil to catch buried worms, larvae, and mollusks.
- Pecking – Quickly jabbing their bills to pick up insects and crustaceans on the surface of mud or shallow water.
- Sewage treatment – Moving bills from side to side through water to stir up prey.
- Spot pursuits – Chasing after specific visible prey on the move.
Their bill morphology, with sensitive tip organs, assists them in locating prey hidden in sediment or vegetation. The ability to rapidly switch between various feeding techniques allows stilt sandpipers to take advantage of different prey availability across habitats.
Plant Material
While not the main component, plant material does make up a small part of the stilt sandpiper’s diet. They are considered omnivorous as they consume some vegetable matter in addition to animal prey. Some plant foods eaten include:
- Seeds of grasses, sedges, and other plants
- Aquatic vegetation
- Algae
Seeds and aquatic plants are obtained by surface pecking or probing in shallows. The proportion of plant material in the diet ranges from around 5-40% and seems to increase during migration and wintering periods when fewer invertebrates may be available.
Drinking and Excreting
In addition to prey items, stilt sandpipers get much of their water intake directly by drinking from freshwater habitats, tidal pools, rainwater, and even dew. Excess water is excreted through their kidneys and out the cloaca as a wet white paste along with solid uric acid waste. They do not have separate ureters for uric waste like mammals.
Feeding Habits and Behaviors
Stilt sandpipers exhibit a variety of feeding behaviors and adaptations that allow them to take advantage of different food resources:
- They mainly feed during daytime, especially early morning and evening.
- Feeding is done solitarily, in pairs, or in small flocks.
- They are somewhat territorial on feeding grounds and chase others from preferred spots.
- Sometimes they probe synchronously in groups to flush out more prey.
- They walk steadily and slowly when feeding but can move rapidly to catch prey or chase others.
- Wings are flicked open for balance when running quickly or lunging.
- They are highly vigilant when feeding, pausing between strikes to scan for danger.
These feeding habits allow them to meet their high energy demands while migrating and accumulating fat reserves. Their wide variety of prey capture methods provides flexibility across different habitats as well.
Diet Differences by Location
The specific composition of a stilt sandpiper’s diet differs across their broad geographic range due to habitat variability and prey availability. Here are some key differences by location:
Arctic Breeding Grounds
- Mostly terrestrial insects like crane flies, mosquitos, beetles.
- Some earthworms and soil-dwelling larvae.
- Few marine invertebrates due to inland habitat.
- Higher proportion of seeds from tundra plants.
Migration Stopovers
- Greater consumption of brine shrimp, marine worms, amphipods at coastal wetlands.
- Agricultural fields provide grasshoppers, caterpillars, craneflies.
- More emphasis on high-calorie prey to quickly rebuild energy.
Wintering Grounds
- Intertidal marine invertebrates dominate at coastal sites.
- Inland sites have more earthworms, terrestrial insects.
- Rice fields provide grass seeds and insects.
- Competition from other migratory shorebirds may limit prey availability.
This highlights the adaptability of stilt sandpipers to take advantage of different food resources across a variety of habitats on their migratory journey.
Energy Requirements
The small size of stilt sandpipers, about 15-28 cm (6-11 in) long and weighing 26-63 g (0.9-2.2 oz), means they have high metabolic rates and must consume large quantities of prey. Their estimated daily energy expenditure is around 95 kcal/day for an adult sandpiper. To meet these needs, they require about 40% of their body mass in prey intake each day while feeding.
During migration, energy demands increase further when fueling long flights. Sandpipers nearly double their body mass by storing fat before migration flights of 4,000 km or more. The prolific availability of prey at key migratory stopover sites like the Copper River Delta in Alaska allows them to rapidly gain weight for these journeys.
Dietary Adaptations
Stilt sandpipers exhibit excellent anatomical and behavioral adaptations for their dietary lifestyle:
- Specialized bill shape – Thin and tapered bill allows probing deeply in mud or water. Sensitive bill tip helps locate prey.
- Large eyes – Provide keen eyesight to spot prey items while scanning constantly.
- Cryptic plumage – Browns, grays, and white mimic substrates and avoid startling prey.
- Rapid pecking – Bill muscles allow lightning strikes to grab fast-moving insects and crustaceans.
- Flexible feeding methods – Switching between probing, pecking, sewing, and running gives dietary flexibility.
Additionally, their migratory habits take advantage of seasonally abundant food resources across a variety of biomes and habitats throughout the year.
Predation and Defense
While feeding, stilt sandpipers must also watch out for their own predators. Their small size makes them vulnerable to many larger predators. Some key natural predators they must detect and evade include:
- Falcons – Such as peregrine falcons and merlins.
- Hawks – Sharp-shinned hawks, Cooper’s hawks, and others.
- Gulls – Species like herring gulls.
- Owls – Short-eared owls and snowy owls.
- Foxes – Especially in the Arctic tundra.
Stilt sandpipers rely on crypsis and vigilance to detect approaching predators during feeding. At the first sign of danger, they take flight rapidly and may form tight flocks to confuse predators. They also may regurgitate food to reduce weight during escape flight. Nesting Arctic terns provide helpful “escort services” to migrating sandpipers, driving away predators that get too close.
Role in the Food Chain
As consumers of a wide range of invertebrate species, stilt sandpipers play an important role in aquatic and terrestrial food chains. They help regulate prey populations, including consuming pest insect species. Their eggs, chicks, and even adults also provide food for their predators higher up the food chain. Their migrations redistribute nutrients between northern breeding areas and southern wintering grounds.
Some key interactions include:
- Consuming worms, mollusks, and insects, providing prey population control.
- Compete with other migratory shorebirds for invertebrate prey.
- Eggs and young eaten by foxes, bears, gulls, and other predators.
- Adults eaten by falcons, accipiters, owls, providing food higher up food chain.
- Guano fertilizes aquatic ecosystems.
- Redistribute nutrients through seasonal migrations across continents.
Population Threats
With an estimated global population of 500,000, stilt sandpipers are considered a species of Least Concern by the IUCN Red List. However, they do face a variety of threats especially related to habitat loss and degradation:
- Draining or pollution of wetlands reduces food availability and stopover habitats.
- Coastal development destroys estuarine feeding areas.
- Climate change affects Arctic breeding grounds and migration timing.
- Agricultural intensification reduces prey abundance.
- Disturbance from roads or recreation disrupts feeding.
Conservation initiatives like preserving wetlands through easements, managing water levels, and limiting development are important for protecting stilt sandpiper populations into the future.
Key Facts About Stilt Sandpiper Diet
- Primarily carnivorous, eating a variety of invertebrates like insects, worms, crustaceans.
- Use several feeding techniques: probing, pecking, sewing, spot pursuit.
- May eat some plant material like seeds, aquatic vegetation.
- High daily energy expenditure requires large amount of prey consumption.
- Diet composition varies across breeding, migration, and wintering habitats.
- Specialized bill, eyes, cryptic plumage aid feeding ability.
- Play important role in aquatic and terrestrial food chains.
Conclusion
Stilt sandpipers are fascinating migratory shorebirds with a diverse invertebrate-rich diet. Their specialized feeding adaptations allow them to thrive across a range of global habitats during their annual cycle. Careful conservation is needed to preserve wetland ecosystems and help maintain healthy stilt sandpiper populations into the future.