Sanderlings are small shorebirds that are known for their behavior of running along sandy beaches away from incoming waves. As the foam from the wave recedes, the sanderlings will chase after it to pick up food from the sand that has been churned up by the wave. This gives them the appearance of constantly running from the water. There are several reasons why sanderlings exhibit this behavior:
Foraging strategy
The primary reason sanderlings run from the water is because it is an effective foraging strategy. Sanderlings eat small invertebrates that live burrowed in the wet sand, such as crustaceans, worms, and mollusks. When a wave washes over the beach, it disturbs these invertebrates, bringing some to the surface and forcing others deeper into the sand. By running down to the water line as the wave recedes, sanderlings can pick out exposed invertebrates before the sand compacts again. The retreating wave also leaves behind puddles and saturated sand where it is easier for the birds to probe for food.
Avoid getting wet
Sanderlings have dense, insulating plumage to help conserve heat. However, their feathers are not waterproof. Getting wet would risk the birds getting chilled, especially in cold weather. Running away from incoming waves minimizes the risk of their feathers getting soaked and allows them to stay dry and warm. Staying dry also reduces the amount of energy a sanderling would need to expend on thermoregulation.
Scan for predators
As sanderlings run down the beach with the receding wave, they are able to scan the newly exposed sand for potential predators. The saturated sand left behind by the wave often disguises scent cues that could reveal lurking predators. Visually scanning freshly exposed terrain may allow sanderlings to detect threats before getting ambushed. Running down the beach also disturbs hidden predators and could flush them out of hiding.
Sanderling Physiology
Sanderlings have several physiological and morphological adaptations that allow them to chase after waves so effectively:
Long legs
Sanderlings have legs that appear disproportionately long compared to their body size. Their legs make up around 30% of their total body length. This gives them a high running speed and long stride length to rapidly chase waves.
Sanderling feature | Length (cm) |
---|---|
Total body length | 18-20 |
Tarsus (lower leg) length | 2.4-3.1 |
Low wing loading
Wing loading refers to the ratio of a bird’s body weight to its wing area. Sanderlings have broad wings relative to their body weight, giving them a low wing loading. This allows them to run and take off quickly when chasing waves. Their short, rounded wings are optimized for speed and maneuverability on the ground rather than soaring flight.
Sanderling wing characteristics | Measurement |
---|---|
Wingspan | 32-36 cm |
Wing area | 121-135 cm2 |
Body mass | 42-64 g |
Wing loading | 0.35 g/cm2 |
Rapid digestion
Sanderlings need to consume a lot of small invertebrate prey to meet their high energy demands. They have a rapid digestion rate that likely enables them to quickly process food to fuel their running and flying. Their digestive tract is only about three times the length of their body. This short gut passage time means they can eat frequently throughout the day while chasing waves.
Ecology and Behavior
Sanderlings are found on sandy beaches on every continent except Antarctica. Here are some key facts about their ecology and behavior:
Breeding
- Nest on high arctic tundra near coasts and inland lakes
- Lay 4 eggs in shallow ground scrape
- Both parents incubate eggs for 22-24 days
- Precocial chicks can feed themselves immediately after hatching
Migration
- Long-distance migrants, traveling from arctic breeding areas to southern coastlines
- Some populations migrate over 18,000 km between nesting and wintering grounds
- Use coastal stopover sites to rest and feed during migration
- Fly nonstop for 2,000-4,000 km at a time over oceans
Wintering and habitat
- Found on sandy marine coasts worldwide
- Prefer beaches with wet, soft sand and abundant tidal debris
- Small tidal pools and film of water left by receding waves creates good foraging habitat
- World population estimated at 1.5-2 million birds
Social behavior
- Outside of breeding season, found in large mixed-species shorebird flocks
- Aggressively defend small territories against conspecifics when feeding
- Rely on cryptic plumage patterns to avoid predation when nesting and roosting
- Use distraction displays and mobbing to deter aerial predators
Threats and Conservation Status
Although a widespread and abundant species, sanderlings face a variety of threats on their breeding and wintering grounds:
Predators
- Foxes, gulls, jaegers, raptors prey on eggs and chicks in the arctic breeding grounds
- Various birds of prey and mammal species hunt adults and juveniles at coastal wintering sites
Habitat loss
- Expanding human development destroys coastal wetland habitat important for migration stopovers
- Increasing disturbance on beaches from recreation, vehicles, and unleashed pets
Pollution
- Oil spills foul shoreline habitats and coat feathers
- Plastic debris and garbage patch buildups in oceans
Conservation status | Classification |
---|---|
IUCN Red List | Least Concern |
US Endangered Species Act | Not listed |
CITES | Not listed |
Research and Study Techniques
Sanderlings are well-studied shorebird species around the world. Scientists use various techniques to research and monitor sanderling populations:
Surveys and censusing
- Conduct population surveys at known breeding sites, wintering grounds, and migratory stopovers
- Resight color-marked individuals to estimate population sizes and survival rates
- International shorebird surveys performed to monitor trends
Tracking migration
- Attach small radio transmitters or leg flags to track migration routes and distances
- Use stable isotope analysis of feathers to determine breeding origins
- Observe color-marked individuals to determine migratory connectivity
Measuring energetics
- Analyze prey capture rates when running on beaches
- Use doubly-labeled water technique to measure metabolic rates
- Collect time-activity budgets via direct observation
Habitat and diet analyses
- Record behavior and habitat variables at wintering and breeding sites
- Characterize invertebrate prey populations through sediment sampling
- Collect and examine fecal samples for prey fragments
Conclusion
In summary, sanderlings exhibit a unique behavioral adaptation of running along sandy beaches to take advantage of the foraging opportunities presented by the ebbing and flowing tides. Their elongated legs, shorebird physiology, and coastal habitats enable this characteristic feeding strategy. While widespread, sanderlings face growing threats from human disturbance, habitat destruction, and environmental contamination across their global range. Targeted research and monitoring efforts are needed to ensure the continued survival of these energetic little shorebirds into the future.