Ecosystem Roles of Sanderlings and Dunlins: How They Impact Coastal Habitats?

Sanderlings and Dunlins, two small wading birds often found along coastlines and wetland habitats, share striking similarities in their appearances, behaviors, and habitats.

These avian cousins, belonging to the Calidris genus, can puzzle even experienced birdwatchers when they don their winter plumage. Yet, beneath the surface of their gray-and-white winter attire, distinct differences emerge.

From bill shapes to feeding strategies, migration patterns to vocalizations, and habitat preferences to breeding plumage, a closer look at these shorebirds reveals a rich tapestry of diversity.

In this exploration, we unravel the intricacies that set Sanderlings and Dunlins apart, shedding light on their unique characteristics and highlighting the captivating world of avian diversity.

Key Differences Between Sanderling and Dunlin

Here are some of the main differences between sanderling and dunlin:

Size

• Sanderling: Sanderlings are slightly larger wading birds, measuring approximately 7-8 inches (18-20 cm) in length. This size difference contributes to their relatively more substantial appearance compared to Dunlins.
• Dunlin: Dunlins, on the other hand, are smaller, with an average length of about 6.5-7.5 inches (16-19 cm). Their compact size distinguishes them from Sanderlings and is one of the key factors aiding in their differentiation.

Plumage (Winter)

• Sanderling: In winter, Sanderlings display a distinctive plumage characterized by grayish upperparts and white underparts. Their overall appearance is relatively clean and unmarked. This plumage adaptation serves as effective camouflage against the sandy beaches and shores they frequent.
• Dunlin: Dunlins, in their winter plumage, also sport grayish upperparts like the Sanderlings, making them appear remarkably similar at first glance. However, there is a noticeable difference when you inspect their breast and flanks.
  Dunlins tend to have more pronounced streaking on these areas, which can give them a slightly mottled appearance compared to the cleaner-looking Sanderlings.

Bill Shape

• Sanderling: One of the most significant differences between Sanderlings and Dunlins lies in the shape of their bills. Sanderlings have relatively short, straight, and black bills.
  This bill shape is well-suited for their feeding behavior, which involves probing the sand for tiny invertebrates. The short bill allows for quick and efficient foraging in the intertidal zones as they chase waves along the shoreline.
• Dunlin: In contrast, Dunlins possess longer bills that are distinctly down-curved. This down-curved bill is a prominent feature and a primary tool for their foraging strategy.
  The curvature helps them reach deeper into the substrate, such as mud or sand, to extract prey like small crustaceans and insects. It’s an adaptation that sets them apart from the Sanderlings and aids in their specialized feeding behavior.

Breast and Flanks

• Sanderling: Sanderlings, in their winter plumage, often look cleaner and whiter underneath. Their breast and flanks typically lack the pronounced streaking found in Dunlins.
  This cleaner appearance, combined with their short, straight bill, helps distinguish them from Dunlins when observing them in their shared coastal habitats.
• Dunlin: One of the notable characteristics of Dunlins in winter is the more defined streaking on their breast and flanks. These streaks create a slightly mottled or speckled appearance, which contrasts with the cleaner white underparts of Sanderlings.
  While the streaking is not as conspicuous as in some other shorebirds, it is a reliable field mark for identifying Dunlins.

Feeding Behavior

• Sanderling: Sanderlings are known for their unique feeding behavior of chasing waves on sandy beaches. They race along the shoreline, probing the sand for tiny invertebrates such as small crustaceans and insects. Their quick, darting movements and short bills allow them to efficiently capture prey in this dynamic environment.
• Dunlin: Dunlins have a different feeding behavior compared to Sanderlings. They are often seen wading in shallow water in various wetland habitats, including mudflats and estuaries. They use their long, down-curved bills to probe deeper into the substrate, seeking out prey beneath the surface.

Habitat Range

• Sanderling: Sanderlings primarily inhabit ocean shorelines, particularly sandy beaches. Their preferred habitat is the intertidal zone where they chase waves to forage for small invertebrates.
  These birds are often seen in the dynamic, open coastal environments where they can exploit the rich food resources brought by the tides.
• Dunlin: Dunlins exhibit a broader habitat range compared to Sanderlings. While they can also be found along coastlines, they are more versatile in terms of habitat selection.
  Dunlins are commonly observed in a variety of wetland habitats, including mudflats, estuaries, and salt marshes. Their adaptability allows them to thrive in both coastal and inland settings.

Bill Color

• Sanderling: Sanderlings have uniformly black bills, a distinct feature that contrasts with their predominantly white plumage.
  This black bill is relatively short and straight, ideal for their feeding behavior of probing the sand for prey along the shoreline. The bill’s dark coloration is a consistent and reliable characteristic for identifying Sanderlings.
• Dunlin: Similar to Sanderlings, Dunlins also possess black bills, but they can sometimes appear slightly darker or with a hint of dark gray.
  While this feature alone may not provide a clear differentiation, it complements other distinguishing characteristics like bill shape. The Dunlin’s bill, which is longer and down-curved, plays a crucial role in its foraging strategy in wetter habitats.

Leg Color

• Sanderling: Sanderlings have uniformly black legs, a feature that extends from their dark bills to their lower extremities. This uniformity in coloration is another consistent trait aiding in their identification.
• Dunlin: Dunlins typically exhibit black or dark gray legs. The leg coloration of Dunlins is another factor that aligns with their adaptability to various wetland environments. The variation in leg color can sometimes be subtle, but it is observable in close-range observations.

Tail Pattern

• Sanderling: Sanderlings in their winter plumage display tails with a distinctive pattern. Their tails are predominantly white but feature a thin dark line or band near the tail’s tip. This subtle tail pattern is an additional field mark for identifying Sanderlings when they are on the move along the shoreline.
• Dunlin: Dunlins also have white tails, but their tail pattern differs from that of Sanderlings. Instead of a thin dark line, Dunlins exhibit a more prominent dark tail band that extends across a larger portion of the tail. This contrasting tail pattern is a useful characteristic for separating Dunlins from Sanderlings.

Wing Stripe

• Sanderling: Sanderlings have a conspicuous white wing stripe on their upperwings. This white stripe contrasts with the grayish upperparts and is visible during flight. It is an important field mark for identifying Sanderlings in flight or when they are resting with their wings folded.
• Dunlin: Dunlins share the presence of a white wing stripe with Sanderlings. This stripe also contrasts with their grayish upperwings, making it a common feature between the two species.
  When observing the wing stripe alone, it may not provide a clear distinction between Sanderlings and Dunlins, but it can be a useful confirmation when combined with other characteristics.

Leg Length

• Sanderling: Sanderlings have moderately long legs that are adapted for their agile, fast-paced foraging behavior along sandy shorelines.
  These legs enable them to swiftly chase waves and probe the sand for small invertebrates. Their leg length is proportional to their body size and contributes to their distinctive running and feeding style.
• Dunlin: Dunlins also possess moderately long legs, similar to Sanderlings. These legs are well-suited for wading in shallow waters and probing mud or sand for prey. While both species have similar leg lengths, differences in bill shape and behavior help distinguish them in the field.

Migration Patterns

• Sanderling: Sanderlings are known for their long-distance migrations. They undertake extensive migrations between their breeding grounds in the Arctic and subarctic regions and their wintering grounds in warmer coastal areas.
  Their migration patterns are characterized by impressive journeys across continents, making them remarkable travelers among shorebirds.
• Dunlin: Dunlins also migrate, but their migration patterns may vary. Some Dunlins are migratory, following seasonal movements between breeding and wintering areas.
  However, some populations are more sedentary, with individuals residing in their breeding or wintering areas year-round. This variability in migration patterns adds complexity to the identification of Dunlin populations.

Breeding Range

• Sanderling: Sanderlings breed exclusively in the Arctic and subarctic regions. Their breeding range spans the northern parts of North America, Europe, and Asia. During the breeding season, they nest in tundra habitats, often near freshwater lakes and ponds.
• Dunlin: Dunlins have a broader breeding range compared to Sanderlings. They breed in Arctic and subarctic regions as well, but their range extends farther south into some temperate zones.
  Their breeding range includes a wide expanse of northern Eurasia and North America, making them more geographically diverse in their breeding distribution.

Breeding Plumage

• Sanderling: During the breeding season, Sanderlings undergo a striking transformation in their plumage. They acquire bright reddish-brown plumage on their head, neck, and upperparts, which is quite distinct from their winter appearance. This breeding plumage serves as a distinctive feature during the breeding season.
• Dunlin: Dunlins also undergo a change in their plumage during the breeding season, but it is characterized by a distinctive black belly patch.
  The black belly patch contrasts with its otherwise grayish appearance and is a prominent field mark during the breeding season. This feature helps separate them from Sanderlings and other shorebird species.

Voice

• Sanderling: Sanderlings are known for their high-pitched calls that can be heard during their foraging and interactions. These calls are typically brief and sharp, serving as a form of communication within flocks.
  While the vocalizations of Sanderlings may not be the primary means of identification, they can provide auditory cues in birdwatching.
• Dunlin: Dunlins are more vocal than Sanderlings and produce a variety of vocalizations. Their calls range from sharp and rhythmic to more melodious and trilling sounds.
  The diversity of vocalizations in Dunlins can be a useful tool for identifying them, especially when combined with other visual field marks.

Social Behavior

• Sanderling: Sanderlings are often observed in small flocks, and they exhibit social behavior primarily when foraging along shorelines. They chase waves and probe the sand for prey collectively, moving in unison as they navigate the dynamic coastal environment.
  Their flocking behavior is more pronounced during the non-breeding season when they gather in larger groups.
• Dunlin: Dunlins can be seen in both small and large flocks, and their social behavior varies with the context. During migration and winter, they often form larger flocks, sometimes comprising hundreds or even thousands of individuals. In breeding areas, they may be more territorial and less prone to large groupings.

Foraging Behavior

• Sanderling: Sanderlings are renowned for their distinctive foraging behavior of chasing waves along sandy beaches. They run rapidly, probing the sand with their bills to capture small invertebrates, such as sand fleas and beach hoppers, exposed by the receding waves. Their quick and agile movements are a key feature of their foraging strategy.
• Dunlin: Dunlins exhibit diverse foraging behaviors depending on their habitat and the availability of food. While they can also probe the substrate for invertebrates, including crustaceans and insects, their foraging behavior may vary.
  In wetland habitats, they wade in shallow waters, sometimes stirring up prey by repeatedly pecking at the substrate.

Bill Length Relative to Head

• Sanderling: Sanderlings have relatively short bills compared to the size of their heads. The bill’s length is proportional to their head size, and it is adapted for their specific feeding strategy of probing shallow sand and chasing prey along the shoreline.
• Dunlin: Dunlins have bills that are longer relative to the size of their heads, especially when compared to Sanderlings. This longer bill is essential for their foraging behavior in a variety of wetland substrates, allowing them to reach deeper and extract prey from mud, sand, and water.

Tail Shape

• Sanderling: Sanderlings typically have pointed tails, which contribute to their streamlined appearance when in flight or running along the shoreline. The pointed tail is an adaptation for their agile and rapid movements.
• Dunlin: Dunlins generally have slightly rounded tails. While the difference in tail shape may not be as prominent or reliable for field identification as other characteristics, it can still be observed during close-range observations.

Migration Timing

• Sanderling: Sanderlings have well-defined migration patterns, with distinct timing for their movements between breeding and wintering grounds. They are known for their long-distance migrations, with specific schedules for departing and returning to their respective habitats.
• Dunlin: Dunlin migration patterns can vary depending on the population. While many Dunlins undertake migrations, some populations may have more variable or localized movements, including sedentary individuals that remain in the same areas year-round.
  The timing of their migrations can be influenced by factors such as food availability and environmental conditions.

Range

• Sanderling: Sanderlings are commonly found along ocean shorelines, particularly on sandy beaches and intertidal zones. Their range includes coastal areas of North America, Europe, Asia, and other continents, with specific regions serving as important stopover points during migration.
• Dunlin: Dunlins have a broader range compared to Sanderlings, encompassing a wide variety of wetland habitats. They can be found along coastlines, mudflats, estuaries, salt marshes, and even inland lakes and ponds. Their adaptability to different environments contributes to their broader distribution.

Sanderling Vs Dunlin: Comparison Table

Feature	Sanderling	Dunlin
Size	Slightly larger (7-8 inches or 18-20 cm)	Smaller (6.5-7.5 inches or 16-19 cm)
Plumage (Winter)	Grayish upperparts, white underparts	Grayish upperparts, white underparts, streaked
Bill Shape	Short, straight, black bill	Long, down-curved bill
Breast and Flanks	Less streaking, cleaner appearance	More pronounced streaking
Feeding Behavior	Chases waves on sandy beaches	Wades in wetland habitats
Habitat Range	Mainly ocean shorelines	Broader range, including mudflats and estuaries
Bill Color	Black	Black
Leg Color	Black	Black or dark gray
Tail Pattern	White with a thin dark line	White with a dark tail band
Wing Stripe	White wing stripe on upperwing	White wing stripe on upperwing
Leg Length	Moderately long legs	Moderately long legs
Migration Patterns	Long-distance migrants	Migrate, but some may be year-round residents
Breeding Range	Arctic tundra	Arctic and subarctic regions
Breeding Plumage	Bright reddish-brown plumage (breeding)	Distinctive black belly patch (breeding)
Voice	High-pitched calls	Varied vocalizations
Social Behavior	Often seen in small flocks	Can be seen in larger flocks
Foraging Behavior	Probes sand for invertebrates	Wades and forages in various substrates
Bill Length Relative to Head	Shorter relative to head size	Longer relative to head size
Tail Shape	Pointed tail	Slightly rounded tail
Migration Timing	Spring and fall migrations	Migrations coincide with seasons
Range	Mainly along ocean shorelines	Coastal and inland wetland habitats

Frequently Asked Questions

To Recap

In the intricate world of shorebirds, Sanderlings and Dunlins stand as remarkable examples of nature’s diversity. While their winter plumage may cloak them in apparent uniformity, a deeper understanding reveals distinct identities.

From bill shape to habitat preferences, these birds embody adaptations that allow them to thrive in different niches, from wave-chasing along sandy shores to probing muddy wetlands.

Beyond their physical attributes, their migratory journeys and vocal expressions reflect nuanced survival strategies.

Observing Sanderlings and Dunlins not only enriches our understanding of avian ecology but also underscores the importance of preserving the diverse habitats they depend on.

In the vast and vibrant world of birds, these two species serve as living testaments to the marvels of adaptation and coexistence.