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bank swallow
Riparia riparia

STATUS

California Threatened

LIFE HISTORY

The bank swallow is a migrant of California and utilizes the state's sand banks and vertical embankments for nesting purposes. It is a colonial nester that selects sand or gravel banks and railroad and highway embankments for colony sites. The banks must be at least one meter in height to prohibit predators from entering the colony and the soils around the embankment must be friable to allow the small swallows to excavate their burrows. Vegetation surrounding the colonies is extremely variable and does not appear to influence nest selection. Soil type, height and slope of the embankment seem to have more relevance when choosing nesting locations. The bank swallow forages mostly on flying insects such as termites, treehoppers, leafhoppers, beetles, moths and flies which it captures on the wing. Although the bank swallow rarely feeds on the ground, it will occasionally prey upon spiders or ants if there is a scarcity of aerial prey. Foraging occurs throughout the daylight hours singly or in flocks. It is hypothesized that some colonies enhance their foraging opportunities by acting as information centers. Successful foragers will "transmit" information of food locations to other individuals in the colony. This altruistic behavior has been observed within certain colonies, but is not believed to be a standard practice for all. Both sexes participate in the excavation of a burrow with each alternately clinging to the face of the bank and digging with their bills. Once inside, they kick dirt backwards out of the hole with their feet. The nesting burrows are near the top of the vertical bank and are dug straight into the bank or slightly upward and range from a length of 20-100 cm. The nest of the bank swallow lies at the end of this burrow and is a flat platform of dried vegetation, feathers, pieces of wool, etc. Females lay an average of 4-5 eggs and are responsible for much of the incubation. Incubation lasts from 13-15 days. The young fledge the nest after approximately 20 days, but will return to the burrow frequently for several days after fledging.

Distribution

The historical distribution of the bank swallow included scattered coastal areas and riparian areas in central and southern California. It is not clear whether there were historic breeding colonies in northern California due to insufficient historical records for that region. Current distribution ranges from central to northern California wherever suitable nesting habitat exists.  Most major breeding colonies are found along the Sacramento and Feather rivers. The colony locations are extremely ephemeral because the areas favored for nesting are prone to erosion.  Therefore, new burrows are usually dug each year and colony sites will vary from year to year. Flood control projects and bank protection projects can negatively impact the nesting habitat of bank swallows by stabilizing the eroding banks. A certain amount of erosive action is required to maintain a vertical slope on banks, but since many of these projects are engineered to prevent erosion, the banks become unsuitable for bank swallow nesting.

CLASSIFICATION

Order PASSERIFORMES, Family HIRUNDINIDAE, Genus Riparia, Species riparia

SUBSPECIES

None

RECENT SYNONYMS

None

OTHER COMMON NAMES

sand martin, sand swallow, bank martin

REFERENCES

Garrison, B. Bank swallow. California Partners in Flight Riparian Bird Conservation Plan.   Point Reyes Bird Observatory. http://www.prbo/CPIF/Riparian/Bans.html (4 Dec. 2000); Peterson, R.T. 1990. A field guide to western birds. Houghton-Mifflin. Boston, Massachusetts. 432 pp.; Terres, J.K. 1996. The Audubon Society Encyclopedia of North American Birds. Wings Books. New York, New York. 1109 pp.

SIZE

Total length: 12-13 cm
Weight: 13-16 g

IDENTIFICATION

The bank swallow is the smallest North American swallow. Its distinguishing characteristics are a brown band across its white breast, white underparts and a brown back. As with most members of the swallow family, the bank swallow has a streamlined appearance with a short neck, long pointed wings, a short, flat bill and a tail that is slightly forked. The fork in the tail is believed to help with maneuverability in flight and allows the bank swallow to twist and turn in the erratic, zigzag pattern characteristic of its species.

AUTHOR OF PROFILE

K. E. Kreitinger

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