bss.sfsu.edu
San Francisco State University
Department of Geography
Geography 316: Biogeography
By Patrick O Connor, student in Geography 316, Fall 2000
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Hirundinidae
Genus: Riparia
Species: Riparia riparia
Description of Species:
The Bank Swallow (Riparia riparia) is the smallest bird in North America. They are also the least offensive, harmless, and entertaining tribe of birds ( Garrison 1990). The name riparia is indicative to where it lives. Riparia actually means bank (Jobling 1991). Although a riparian species they are not dependent on riparian vegetation. The Bank Swallow is a small bird. It averages 12cm in length. Each wing has a span between 89 – 111cm. As a result it only weighs from 10.2g –18.8g. The sexes are similar in appearance and their plumage does not vary throughout the year. There have been eight subspecies listed. The adult swallow has a grayish brown mantle, rump and wing coverts. The tail is entirely brown or brown with pale endings. The throat is white and contrasts nicely with the distinct brown breast band and grayish brown crown. There is no “sexual dimorphism”. “They are separated by brood patch or cloacal protuberance” (Garrison 1999).
Habitat:
The bank swallow has a unique distinguishing characteristic in that it is the only swallow that does not build a nest. Instead it forages holes. The bank swallow are considered to be “among the more basally branching (primitive) groups of swallows”, compared with those that build nests (Garrison 1999). The bank swallow arrives in high numbers to the same nesting areas they occupied the previous year. If that area is no longer present they will construct a new one. The male and female bank swallow help in the construction of the nest. Their nests can be found at the top of vertical caves and sand banks and in areas that have material that are conducive to foraging such as marshes and along river banks (Ellis 1982). They cling to the bank and peck, once inside they kick the dirt backwards. Their nests are from 1″-2″ wide and from 4ft-5ft in depth. The ephemeral nature of the nesting banks results in low levels of nesting fidelity. This is due to the fact that there is no evolutionary benefit to long-term connection to colony sites (Garrison 1990). Nests can also be found next to railroads and under highway embankments. Exotic species are no threat to the bank swallow. This is because of their unique nesting habitat requirements. However, starlings have been known to supplant bank swallows from their burrows at Fort Funston in San Francisco (Garrison 1990). Erosion and human interference, insect infestation and predators threaten the Bank swallows. Even though, erosion is sometimes necessary to create vertical cliffs necessary for building nests. Predators also are a threat. In California, Egrets, Herons, and Gopher snakes feed on nestling and adults in their burrows (Barrett 1999). Because they build on the bank of rivers, lakes and cliffs, they’ll nests are susceptible to all kind of weathering. Along cliff faces, coastal erosion threatens to destroy their homes. Along riverbanks, erosion control projects such as bank stabilization and flood control projects threaten their habitat. The Sacramento River in California has 70% to 80% of bank swallows nesting on the riverbanks with 50% of this number threatened by projects (Garrison, Humphrey, Laymon 1987).
Natural History:
Food
Bank swallows are not the largest of passerines and this is reflected in their diet. The swallows feed singly or in pairs in a flock. Parents bring back on average 60 prey items to the nest. They eat flying or jumping insects, which they find while flying over ponds and rivers, meadows and bogs. Insects constitute 99.8% of their diet; non-insects and plants make up the remainder; 33.5% ants, bees and wasps, 26.6% flies and 17.95 beetles (Garrison 1999). They are not known to store food. The bank swallow stays no further than 200m away from their young. They feed from dawn to dusk at an average height of 15m above the ground (Garrison 1999). They occasionally feed from the ground. They drink mostly in groups by skimming water and scooping up the water with their lower mandible (Garrison and Barrett 1999). It is also interesting to note that colonies do not transmit information about food. Colony size may influence information in large sites (Stutchbury 1988). Signature calls are uniquely recognizable to adults and is used to solicit food by the young (Garrison,Humphrey,Laymon 1987).
Bank swallows begin building their nests by aligning themselves against the bank, securing themselves with their claws. Their tail is spread to give support against the bank (Audubon 1995). The bill picks the soil until there is enough space for the body to fit inside. The feet and claws are also used (Audubon 1995). However, the ephemeral nature of the nesting banks results in relatively low levels of nesting fidelity. There is no evolutionary benefit to maintaining long-term ties to specific colony sites (Garrison, Humphrey, Laymon 1987). Nesting colonies can be up to 1500 pairs in size. The nesting area is defended early in the nesting period.
Breeding
The nesting area is defended early in the nesting period. The males are usually the first to arrive at the nesting site, passing the females on the way. This is an attempt by the male to be in a position to attract a female upon arrival (Barrett 1999). However, if paired before the arrival, the female will keep watch at the site entrance while the male continues digging.
While finishing up the nest, the male puts on a show for the females. The male begins to sing and ruffle his head and throat feathers until he gets what he wants (males are very protective of the females). Bank swallows are socially monogamous. Males are attracted to heavier females. It is a sign that they are fertile( Barrett 1999).
The clutch size averages between 2 to 7 eggs, with only one brood per year. Both sexes feed the young however; females do the majority of incubating. Males take over when females leave the nest. Incubation periods range from 13 to 15 days. There is rapid growth in the first 6 to 8 days, escpeially with the tarsi. The tarsal development enables them to stand straight. The young leave the nest between 8 to 22 days. The adults reduce their feeding and use vocalization to encourage the young to leave. Occasionally they will return to feed within the first 5 days (Barrett 1999). At day 28 the young have taken over abandoned nests and after about the 30th day they are independent. The juveniles begin fall migration the earliest and continue later than the adults. The adults also vacate the breeding ground as soon as the young disperse. The bank swallows begin breeding after the first summer they are born.
Evolution:
The order passeriformes or passerines alludes to the fact that these types of birds are perching birds and possess arboreal habits. Just as their order suggests swallows like to sing loudly and are referred to as oscines which means singing bird (Chatterjee 1997). They have evolved to become the dominant avian group on Earth today (Encyclopedia Britannica 1998). Passerines are the most highly evolved of all birds, and are highly adaptive to terrestrial terrain. They are found all over the world, except Antarctica. The order Passerine has the largest number of bird species, with over 5,100 different kind. All other birds have just 3,500 types (Encyclopedia Britannica 1998). Passerinerines are small land birds with fragile bones. As a result they are rarely fossilized, giving few clues to their evolution. The Hirundinidae family, is the family name the Swallows belongs to, and is also part of the Passerines order. Swallows have evolved to become areal feeders, which sets them apart from all other oscines (Chatterjee 1997). Even though nothing is known for sure about the type or types of birds from which the Passerines arose, it is believed they are of polyphyletic origin (Sibley and Ahlquist 1990). What is known is that the Cretaceous period (144-65 million years ago) marks the first global radiation of birds. It was in this period that Laurasia and Gondwanaland fragmented. Pterodactyls and other small birds diversified at a fast pace during this time. Archaeopteryx is the most primitive taxon. It is further hypothesized that the origin of birds is often associated with the origin of Archaeopteryx (Chatterjee 1997).
The morphological evolution of the oscines is of a complex nature. Identification of this avian class of birds was difficult to determine. It was later discovered that the Passeriformes are divided into two groups, Tyranni for the sub oscines and Passeri for the oscines. The Passeriformes diverged from the non-passerine clad composed of the Columbiformes (doves), Gruiformes (Rail) and the Ciconiformes (warbler) (Sibley and Alquist 1990). The areal adaptation and the structures of their tarsi (ankle joints and muscles) and syringes (vocal chords) are unique. This evolutionary quality has been the basis for setting them apart as a family of the Passeri ( Sibley and Alquist 1990). It was also discovered using DNA hybridization that the swallows are members of the Sylvioidea and that their lineage branched from other Sylvioids (Sibley and Alquist 1990).
Distribution
The Bank Swallow is one of seventy-four species of swallows representing the Hirundinidae Family. The species includes both the swallow and the martin families and are found worldwide, except above the Arctic Circle, Antarctica and some remote islands. The swallow is a social land bird with a Holarctic breeding distribution (Garrison, Humphrey and Layman 1987 ). The cosmopolitan nature of the bank swallow enables it to adapt to many different living conditions from sea level to high mountains (Ellis 1982).
The Neotropical trait of the bank swallow is a good indication that spring has arrived. The earliest (recorded) they have arrived is April and the latest is early May. In North America they migrate, following the rivers and coasts to the high latitude regions of Alaska, east across America and Canada and south to Florida. In California they are found along the Sacramento River. Their migration north is typically mixed with other species of Swallow. Intraseasonal movement is not known.
The bank swallow is now on the endangered species list in California and is also listed under the migratory Bird Treaty Act for the past ten years (O’ Neill 2000). At Fort Funston in San Francisco, California, the National Park Service (NPS) has taken action to protect the bank swallow ;under the recommendation from the California historic current status of the bank swallow report in 1988, they recommended that the species be protected against human disturbance. The report showed that numbers have been declining. From 1993 to 1996 the numbers decreased from 500 to 140. Fort Funston supports two of the last remaining cliff dwelling colonies in California for the bank swallow. The other site is at Ano Nuevo State Park in San Cruz County. At this park the sites are blocked off to public access (O’Neill 2000). The bank swallow have been nesting here for the last one hundred years. Bank swallows are susceptible to habitat loss, colonies vary due to predation and wintering ground weather. The National Park Service have responded by denying access of 12 acres to the public in an effort to restore population numbers. The area concerned had been inundated with public use (O’Neill 2000). Dogs and humans have for a long time used the area for recreational purposes. People were unaware of the damage they were doing to the bank swallow habitat. Because, bank swallows forage their nest near cliff tops they are often fragile and are susceptible to damage as people pass over head. Even the shadows cast by passing dogs and humans are perceived by the birds as predators. Graffiti writing on the cliff face has also been a problem in the past. These are some of the challenges that the bank swallow faces in their day to day lives. Presently, fencing and signs (figures above) has been put in place to block access to the area and also to educate the public (O’Neill 2000).
Bibliography
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“Birds” the new Encyclopedia Britannica: macropedia. 15th edition. Chicago, Illinois. Encyclopedia Britannica, inc.
Barrett, A Garrison.1999. California partners in flight bird conservation plan. [on-line] http://www.prbo.org/CPIF/Riparian/Bans.html-101K-
Chatterjee, Sankar. 1997. THE RISE OF BIRDS. Baltimore, Maryland. The John Hopkins University Press.
Ellis, J. H. 1982. “Condor”. Pg 441-443. The thermal nest environment and parental behaviour of a burrowing bird, the bank swallow. Lawrence, Kansas. Cooper Ornithological Society.
Farrand, John jr. 1985. THE AUDOBON SOCIETY MASTER GUIDE TO BIRDING. Garrison, B.A. 1999. Bank Swallow (RIPARIA riparia). In the Birds of North America, No.414 (A. Poole and F. Gill, eds) The Birds of North America, Inc., Philadelphia, PA.
Garrison, Barrett. 1990. “Birds of North America 414”, pg 1-27. Bank swallow Riparia riparia.
Garrison, B.A., Humphrey, J.M. and Layman, S.A. 1987. “Western birds”. Pg 71-76. Bank swallow distribution and nesting ecology on the Sacramento River, California. Berkley, California. Western Fields Ornithologists.
Gough,GA., Sauer,JR.,Iliff,M. Pauxtend Bird identification infocenter. 1998 Version 97.1. Pauxtent wildlife research center, Laurel MD. [On-line] http://www.mbr-pwrc.usgs.gov/Infocenter/Glossary/glossary.html
Haas,GE. 1980.“Nesting science”. Pg 210-215. Flees from nests and burrows of the bank swallow (Riparia riparia) in Alaska. Washington. Washington State University Press
Hjertaas,DG. , Hjertaas,P., Mahler,WJ. 1988. “Canadian field naturalist”. Pg 465-470. Colony size and reproductive biology of the bank swallow, RIPARIA riparia, in saskatchewan. Ottowa, Canada. The Ottawa Fields Naturalists Club.
Jobling, James A 1991. A DICTIONARY OF SCIENTIFIC BIRD NAMES. Oxford, England. Oxford University Press.
O’ Connor, Patrick. 2000. Distribution and notices photos. Dept. of Geography, San Francisco State University.
O’ Neil, Brian. 2000. Golden Gate National Recreation Area. “Notice of proposed year round closure at Fort Funston and request for correction for comments”. [on-line] http://www.fortfunstonforum.com/proposal.htm
Sibley, Charles, G., Ahlquist, Jon. E. 1990. PHYLOGENY AND CLASSIFICATION OF BIRDS. The New Haven University Press c1990.
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