Spotted sandpipers (Actitis macularius) are small shorebirds that breed across most of Canada and the northern United States. They are well known for their migratory habits, moving long distances between their summer breeding grounds and wintering areas. But why do spotted sandpipers undertake these long migrations?
To take advantage of seasonal resources
One of the main reasons spotted sandpipers migrate is to take advantage of seasonal peaks in food availability. Their breeding habitat consists of the shorelines of rivers, lakes, and wetlands, where they feed on aquatic insects, crustaceans, mollusks, and other invertebrates. However, these food resources decline during the winter in their northern breeding areas when inland waters freeze over.
By migrating south in the fall to warmer climates, spotted sandpipers can continue to feed along open shorelines all winter long. Their winter habitat includes coastlines, mudflats, marshes, and lake edges across the southern United States, Mexico, Central America, and the Caribbean. This allows them to find plentiful food through the winter to prepare for the breeding season.
To find suitable nesting habitat
Another reason spotted sandpipers migrate north in the spring is to reach appropriate nesting habitat for breeding. They nest in open, wetland areas with low, sparse vegetation near water. Their nests consist of small depressions scraped into the ground, usually lined with grasses and leaves.
These high quality nesting areas are more abundant across Canada and Alaska than farther south. The longer daylight hours of the northern summer also provide more favorable conditions to raise a clutch of young. So the migration allows spotted sandpipers to take advantage of the best opportunities for breeding success.
To avoid harsh winter weather
Migrating south also allows spotted sandpipers to avoid extremely cold temperatures and heavy snow cover, which could be challenging for a small shorebird to survive. Their winter habitat ranges from as far south as Panama up to the southern coasts of the United States. This warmer climate makes it easier for them to find sufficient food and avoid frigid or dangerous weather.
Remaining farther north through the winter would require more energy reserves to maintain body heat and locate unfrozen food sources. Migrating south reduces their risk of exposure and starvation during the lean winter months.
To find mating opportunities
Migration also brings a new influx of potential mates each breeding season. Spotted sandpipers exhibit a polyandrous mating system, where each female may mate with several males over the course of the breeding season.
The female lays up to four clutches of eggs with different mates, and the males provide all parental care of the young. By migrating north together, the population can remix and females can choose from new mate options while males compete for breeding opportunities.
Key events in the spotted sandpiper’s migration cycle
Spotted sandpipers follow a regular seasonal migration pattern that is timed to make the most of breeding and wintering conditions:
- February to April – Begin spring migration north to breeding grounds
- May to June – Arrive on breeding grounds, males establish territories
- June to July – Females lay eggs in multiple clutches with different mates
- July to August – Males incubate eggs and care for young after hatching
- August to September – Fall migration starts south to wintering habitat
- September to March – Winter along coasts from U.S. to Central America
This regular migration cycle takes advantage of the most favorable conditions and resources available throughout the year. Timed migration helps spotted sandpipers maximize their breeding opportunities and chances of survival.
How do spotted sandpipers navigate their migrations?
Spotted sandpipers manage to navigate thousands of miles between their breeding and wintering grounds each year. Researchers believe they use several strategies to accomplish these epic journeys:
- Orientation by the sun and stars: They are thought to use celestial cues from the sun and stars to orient themselves and maintain direction.
- Learned routes: Individuals may learn migration routes and key stopover sites from more experienced birds.
- Geomagnetic senses: They may orient by detecting the Earth’s magnetic fields.
- Landscape recognition: Visual landmarks like coastlines, rivers, and mountain ranges may help guide their navigation.
Spotted sandpipers migrate by night when celestial cues are available. Their ability to determine direction coupled with memory of routes and stopover sites enables them to make their long seasonal movements.
Unique breeding behavior adaptations
Spotted sandpipers exhibit some fascinating breeding adaptations that may be influenced or enabled by their migration:
- Females are larger and more aggressive than males, establishing a dominance hierarchy.
- Females develop ornamented tail feathers during breeding season to attract male mates.
- Females readily mate with multiple males per season.
- Males perform majority of parental care, incubating eggs and protecting young.
- Migration provides new potential mates each breeding season.
These unique aspects of spotted sandpiper breeding biology may help facilitate their mating opportunities and breeding success within the constraints of their migration cycle.
Conservation challenges
While spotted sandpiper populations remain relatively stable currently, they still face a variety of conservation threats, particularly during migration:
- Loss of stopover habitat along migration routes
- Disturbance from human recreation and activities
- Predation by cats, foxes, gulls, and other predators
- Pollution exposure at migratory stopover sites
Maintaining suitable habitats for feeding and resting along their migration paths will be key to preserving spotted sandpiper populations into the future. Research into their migratory patterns can help inform conservation efforts.
Conclusion
In summary, spotted sandpipers undertake seasonal migrations to take advantage of optimal breeding habitat and resources during the summer, while avoiding harsh winters and fueling up in milder climates during the winter. Their navigational abilities enable these long-distance migrations, which in turn have influenced their breeding behavior adaptations. Conservation of migratory stopover spots along their flyways will help ensure these unique shorebirds can continue their iconic migrations for generations to come.