Bank swallows (Riparia riparia) are small, migratory songbirds that breed in North America during the summer months and migrate to Central and South America for the winter. While they are still common and widespread overall, there are some indications that bank swallow populations may be declining in parts of their range.
Quick Facts on Bank Swallows
Here are some key facts about bank swallows:
- Scientific name: Riparia riparia
- Other common names: sand martin, sand cliff swallow
- Size: 5-6 inches long with a wingspan around 12 inches
- Identifying marks: Brown back, white underside, brown breastband
- Habitat: Open areas near rivers, lakes, ocean cliffs
- Diet: Flying insects like flies, bees, beetles
- Migration: Winters in Central and South America, summers across North America
- Nesting: Colonies in burrows dug into vertical banks, cliffs, bluffs
- Conservation status: Least concern but with decreasing populations in parts of range
Population and Distribution
Bank swallows have an extremely large geographic range, breeding across nearly all of North America except for the far north. They winter from Mexico south to Peru and Brazil. Overall population estimates indicate there are likely 15-30 million breeding pairs in North America.
However, Breeding Bird Survey (BBS) data shows bank swallow populations declined by about 45% between 1970 and 2014. The declines have been most severe in the northeastern United States and southern Canada. Possible reasons for declines include:
- Loss of suitable nesting sites
- Reduced availability of aerial insects due to pesticides
- Extreme weather events on wintering grounds
- Competition with invasive bird species for nest sites
Despite the declines, bank swallows remain common across large areas of their breeding range. Partners in Flight estimates their global breeding population at 28 million, and they have a large range of over 4 million square kilometers. Their overall conservation status is Least Concern.
Habitat and Nesting
Bank swallows need open habitat near sources of insects where they can dig nesting colonies. They are almost always found near water – rivers, lakes, oceans – where they nest in burrows dug into vertical banks, cliffs, and bluffs. Favorite nesting sites include:
- Riverbanks
- Roadcuts
- Gravel pits
- Sand and clay quarries
- Ocean cliffs
Nest burrows are dug horizontally, typically in near-vertical banks at least 1 meter tall. Colonies can range from just a few pairs to over 3,000 pairs, with an average of 287 pairs. The nest is a chamber at the end of the burrow lined with grasses and feathers.
Migration and Wintering
Bank swallows migrate long distances, wintering in South and Central America. Fall migration begins in late summer, with most bank swallows arriving on the wintering grounds by October and November. They generally migrate in flocks, sometimes joining other swallows like barn and cliff swallows.
Their wintering range extends from Mexico south to Peru and central Brazil in South America. They are found in a variety of open and semi-open habitats, often near water. Coastal mangroves and savanna seem to be preferred wintering areas.
Spring migration starts in March and April as the birds move back north to their breeding areas. Most will arrive back on the breeding grounds by late April or early May. Migration allows them to take advantage of abundant insects in the north during summer.
Diet and Feeding
Bank swallows are aerial insectivores, catching insects exclusively on the wing. They eat a wide variety of flying insects including:
- Flies
- Bees
- Wasps
- Ants
- Beetles
- Mayflies
- Dragonflies
- Damselflies
They will congregate in large feeding flocks over water, fields, or woodland clearings where flying insects tend to converge. Bank swallows drink by skimming along the surface of lakes and rivers.
Threats and Conservation Status
The bank swallow population has declined by 45% in the last 44 years across much of its range according to the Breeding Bird Survey. However, it remains common and widespread overall. The main threats and conservation concerns include:
- Habitat loss: Riverbank stabilization, gravel pit reclamation, and loss of suitable cliff nesting sites reduces available habitat.
- Declining prey: Widespread pesticide use may reduce insect prey populations.
- Extreme weather: Drought or storms on wintering grounds may kill many birds.
- Competition: Invasive house sparrows compete for nest sites.
Protecting existing colony sites, allowing rivers to erode banks naturally, and ensuring adequate insect prey by reducing pesticide use will benefit bank swallow populations. Their status will require continued monitoring.
Fun Facts About Bank Swallows
- Bank swallows are colonial nesters, with up to thousands of pairs nesting together in a colony.
- The nest burrows they dig can be up to 3 feet deep into a bank or sand cliff.
- They breed the furthest north of any swallow species in North America.
- They sometimes reuse nesting sites for many years in a row.
- They fly on their long migrations day and night, eating and drinking on the wing.
- They winter the furthest south of the regularly occurring North American swallows.
- They are very social at all times of the year, often gathering in huge flocks.
- They will sometimes nest alongside other hole-nesting bird species.
- They are excellent fliers and highly maneuverable in the air.
- Their scientific name “riparia” means “of the riverbank” in Latin.
Summary and Conclusion
Here is a summary of the key points:
- Bank swallows are widespread songbirds that nest colonially in burrows and migrate to Central and South America.
- They have declined significantly in parts of their range but remain common overall.
- Major threats include habitat loss, lack of insect prey, extreme weather, and competition.
- Conserving existing colony sites and reducing pesticide use can help populations.
- They are aerial insectivores, eating only flying insects caught on the wing.
- Bank swallows are very social and congregate in huge migratory flocks.
- More monitoring is needed to track populations over time.
In conclusion, bank swallows are still abundant across much of their breeding range but may be declining in parts of eastern North America. Protecting nesting habitat, controlling invasive species, and providing adequate insect food sources will be important conservation measures going forward. Their colonial nesting behavior makes them vulnerable to habitat loss and degradation. Careful monitoring of populations should continue to detect any concerning trends. With appropriate conservation action, magnificent flocks of migrating bank swallows will hopefully continue gracing North American skies for years to come.