Semipalmated and least sandpipers are two small shorebird species that are often confused with each other due to their similar size and coloring. However, there are some key differences between these two birds that can help birdwatchers identify them correctly.
In the opening paragraphs, we will provide quick answers to the key questions around comparing semipalmated and least sandpipers:
What are the main physical differences between semipalmated and least sandpipers?
The main physical differences are:
– Bill length – Semipalmated have slightly longer bills
– Leg color – Least sandpipers have yellowish legs, semipalmated have blackish legs
– Webbing on toes – Semipalmated sandpipers have partial webbing between their toes
Where are they found?
Both species breed in the arctic tundra regions and migrate south to coastal areas for winter. However, semipalmated sandpipers tend to be more common on the Atlantic coast, while least sandpipers are more numerous on the Pacific coast.
What are their habitat preferences?
They both prefer muddy, coastal wetland habitats like estuaries and mudflats. However, least sandpipers also readily use inland wetlands.
What differences are there in their behavior and feeding?
Their feeding behaviors are very similar, probing for invertebrates in mud or sand. However, semipalmated sandpipers tend to be more gregarious when feeding. Least sandpipers are aggressive and will chase other shorebirds from their feeding space.
Now we will go into more detail on each of these differences between the two species.
Physical Differences
While semipalmated and least sandpipers overlap somewhat in size, there are some subtle but consistent physical differences between the two species.
Bill Length
One of the most reliable ways to tell these birds apart is bill length. Semipalmated sandpipers have an average bill length of 20.5-22.5 mm, while least sandpipers have shorter bills averaging 16.5-19 mm long. This can be tricky to judge in the field, but alongside other features it can aid identification.
Leg Color
Leg color differs noticeably between these species. Least sandpipers have yellowish legs, whereas semipalmated sandpipers have blackish legs. The yellowish legs of the least sandpiper can appear duller in winter plumage.
Webbed Toes
As their name implies, semipalmated sandpipers have partially webbed toes on each foot. This webbing is most prominent between the middle and outer toes. Least sandpipers lack any webbing between their toes.
Body Plumage
In breeding plumage, these two species are somewhat easier to distinguish based on body plumage. Semipalmated sandpipers have bold black markings and rufous on the upperparts. Least sandpipers have more delicate streaking on the back and a brighter white underside.
However, in nonbreeding winter plumage this difference in plumage is much more subtle. Both appear grayish brown on the upperparts and white below. This makes distinguishing them more challenging.
Size and Shape
Semipalmated sandpipers measure 15–19 cm in length with a wingspan around 34 cm. Least sandpipers are very slightly smaller at 13–15 cm in length with a wingspan of 31 cm. Their body shape and proportions are essentially identical.
Plumage Differences Summary
Feature | Semipalmated Sandpiper | Least Sandpiper |
---|---|---|
Bill length | 20.5-22.5 mm | 16.5-19 mm |
Leg color | Blackish | Yellowish |
Toes | Partially webbed | No webbing |
Plumage | Bolder markings in breeding plumage | Delicate streaking in breeding plumage |
Size | 15-19 cm length | 13-15 cm length |
Range and Distribution
Semipalmated and least sandpipers breed in overlapping regions across the arctic tundra zones of North America and Eurasia. However, their wintering grounds and migration routes show some differences.
Breeding Range
The breeding ranges for both species cover arctic and subarctic tundra in Alaska, Canada, and eastern Siberia. They nest on the ground in open, treeless landscapes near water.
Wintering Range
In migration and winter, these two species show divergent patterns:
– Semipalmated sandpipers are more common along the Atlantic coast, concentrated from the Carolinas south to northern South America.
– Least sandpipers are more numerous along the Pacific coast, especially California and Mexico. They are also found along the Gulf Coast and south to Panama.
So while their nesting grounds overlap, semipalmated sandpipers predominantly use the Atlantic flyway, while least sandpipers migrate through the Pacific and Central flyways.
Stopover Habitats
During migration, semipalmated sandpipers stopover in huge numbers at key staging areas like the Bay of Fundy and Delaware Bay. Least sandpipers use inland wetlands and agricultural fields more regularly as stopovers.
Behavioral Differences
Semipalmated and least sandpipers share very similar behaviors, as they occupy comparable ecological niches. However, there are some subtle differences between the species:
Feeding
Both species typically probe into mud or sandy substrates to find small invertebrate prey. Their diets are varied but largely consist of insects, marine worms, mollusks and crustaceans.
Semipalmated sandpipers often forage in dense flocks, especially during migration. Least sandpipers are more aggressive and will chase other shorebirds away from prime feeding areas.
Migration
These sandpipers migrate long distances between their arctic breeding sites and wintering grounds. Semipalmated sandpipers travel huge distances across ocean and tend to migrate slightly later in fall than least sandpipers.
During migration, semipalmated sandpipers form enormous dense flocks at staging areas. Least sandpipers gather in smaller, looser flocks.
Nesting
Both species nest on the ground in open tundra habitats, usually in dry ridges or hummocks. The nests are simple scrapes lined with grasses and lichens. Males perform aerial displays during courtship.
Least sandpipers are more likely to nest solitarily, while semipalmated sandpipers occasionally nest in loose colonies. Family groups forage together until southward migration.
Vocalizations
The calls and alarm sounds of these species are very similar – high, weak whistles. Semipalmated sandpipers have a distinctive trilled display flight, but otherwise vocalizations do not reliably separate these species.
Habitat Preferences
Semipalmated and least sandpipers occupy generally comparable habitats, with some key differences:
Breeding Habitat
During the breeding season, both species inhabit open, treeless landscapes in the arctic tundra zones:
– Wet sedge meadows
– Drier heath vegetation
– Ponds, lakeshores and river banks
They nest on the ground in elevated dry sites with good visibility all around. Habitat use during breeding is very similar between the two sandpipers.
Migration Stopovers
On migration, semipalmated sandpipers are strongly tied to coastal tidal habitats:
– Estuaries
– Mudflats
– Salt marshes
– Sandy beaches
Least sandpipers also use those coastal habitats regularly on migration, but additionally stopover in:
– Freshwater wetlands
– Flooded fields
– Wet grasslands
– River shorelines
So semipalmated sandpipers concentrate along coasts, while least sandpipers use a broader range of inland wetland habitats.
Winter Habitats
In their wintering grounds, these sandpipers settle into similar coastal wetland environments:
– Estuaries
– Tidal mudflats
– Lagoons
– Saltpans
– Mangrove forests
Winter habitat preferences are essentially identical between the two species – coastal areas with muddy or sandy substrates.
Conservation Status
Both semipalmated and least sandpipers remain widespread and abundant species. They are categorized as Least Concern by the IUCN Red List.
However, both sandpipers face a variety of threats particularly during migration when they concentrate in huge numbers at stopover sites:
– Habitat loss of coastal wetlands
– Human disturbance
– Pollution
– Collision risks with buildings and vehicles
Ongoing monitoring is important for these species that rely so heavily on diminishing stopover habitats along their migration routes. Maintaining the quality of tidal flats, estuaries, and inland wetlands enables these long-distance migrants to successfully complete their annual journeys.
Conclusion
In summary, semipalmated and least sandpipers exhibit many similarities but can be reliably distinguished by a few key differences:
– Bill length – semipalmated have slightly longer bills
– Leg color – least sandpipers have yellowish legs
– Webbing – only semipalmated have partially webbed toes
– Plumage – breeding plumage shows subtle differences
– Range – winter distributions concentrated on opposite coasts
– Behavior – semipalmated feed in denser flocks
– Habitat – least readily use inland wetlands in migration
Being able to distinguish these abundant but declining shorebirds enables us to better understand the status of each species and conserve their habitats accordingly. Careful attention to details of bill length, leg color, webbing, and distribution will help anyone identify semipalmated and least sandpipers accurately.