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Petrochelidon pyrrhonotacliff swallow

By Joshua Tulppo

Geographic Range

Cliff swallows (Petrochelidon pyrrhonota) occupy areas of North America and Central America based on whether it is breeding season or the migration season. The breeding range begins as far northwest as Alaska, and extends south down the western coast of the United States through California into central Mexico (Mexican plateau south to central Oaxaca). The breeding range extends eastward through the Rocky Mountains and midwest sections of Canada and the United States and stops in eastern Texas. This range includes parts of Tennessee, western North Carolina, Virginia, and West Virginia. The breeding range extends back northward through the northeastern states of the United States northward into Ontario and Quebec. The northern limit of the breeding range roughly ends where at the treeline's edge (around elevation 3050m), but colonies have been found further north.

The winter range extends south along the western coast of Mexico, to the boarder of Colombia and extends northward along the east coast of Mexico. The migration range also extends throughout the southeastern United States with colonies in Florida, Georgia, Alabama, Mississippi, Louisiana, eastern Texas. They are also found throughout parts of Tennessee, Kentucky, South Carolina, North Carolina, and parts of Virginia, West Virginia, and Ohio. Cliff swallows also migrate southward into Cuba, Puerto Rico and the Bahamas. There have also been multiple sightings of the birds migrating into South America, south through Paraguay, Argentina, and Bolivia mainly, but the definite range is unknown.

Vagrants of cliff swallows have also been found on Wrangel Island, Greenlad, Siberia, and the British Isles, but findings have been rare and few. (Brown and Brown, 1995; ; Brown and Brown, 2000a; Brown, 2010; Brown, et al., 2015a; BirdLife International, 2012; McNair, 2013; Sotherland, et al., 1980; Tumlison, 2009)

Habitat

Cliff swallow breeding habitat includes canyons, hills, valleys, and cliff faces. Man-made buildings and structures also provide shelter for nesting areas; any areas that have buildings or bridges serve as possible nesting sites, expanding their breeding areas to grasslands and towns. Any nesting areas with access to water/mud spots are beneficial, because of the availability of food and nesting materials. Nesting typically takes place from sea level to 2770m, but can be as high as 3200 m.

Habitats during the winter include coastlines and other inland bodies of water. Very little information is available on the habitat of cliff swallows during migration. Cliff swallows may target waterbodies while migrating, as a source of insect prey.

Very little is known about their habitat during the winter, but cliff swallows are known to use grasslands, agricultural areas, towns, and marshes. (Brown and Brown, 1995; Brown and Brown, 2000a)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • coastal
  • Range elevation
    0 to 3200 m
    0.00 to 10498.69 ft

Physical Description

Cliff swallows have square tails with an orange rump, and their throats have a chestnut hue. Adults have chins, throats, and sides of the neck that are tipped with a chestnut color. Their breasts are white or cream-colored. Some birds will have a cream or white triangular-shaped forehead patch, and a black or blue-ish crown. The birds' rumps can be pink. The bill of cliff swallows is black. The legs and feet are both brown in adults while juveniles are pink with a slight cinnamon hue.

The average mass of these birds ranges from 22.22 to 24.15 g. Length of cliff swallow ranges from 127 to 152.4 mm, and wingspans range from 279.4 to 299.72 mm. They exhibit little sexual dimorphism, as the only difference is a larger dark blue patch on the throat of males.

Plumage for juveniles is duller than the plumage of adults. The colors on their throats and foreheads vary considerably among individuals of this age. Nestlings have a slight bit of yellow, with brown irises.

Cliff swallows differ morphologically from other North American swallows in that their heads and necks are thicker. Color patterns also distinguish these cliff swallows. (Brown and Brown, 1995; ; Brown and Brown, 2000b; Brown and Brown, 2011)

  • Sexual Dimorphism
  • male more colorful
  • Range mass
    22.22 to 24.15 g
    0.78 to 0.85 oz
  • Range length
    127 to 152.4 mm
    5.00 to 6.00 in
  • Range wingspan
    279.4 to 299.72 mm
    11.00 to 11.80 in

Reproduction

Birds are socially monogamous and genetically polygamous. Cliff swallows will choose a mate with which to raise nestlings, but both the males and females will mate with other birds.

Cliff swallows will began pair formation when nest ownership and building starts. Males and females both contribute towards building the nest during the breeding period, but males may get a head-start and begin building before females arrive for the season. The nests are mud-based and have a domed shape, typically 1.5-10 above the ground or water's surface. It's not uncommon for nests from the previous year to be refurbished and reused by a new pair.

These birds generally have an informal courtship based on the twitter-squeak song to find mates. No visual displays or additional courtship efforts are part of courtship. Singing by males declines after eggs are laid and incubation starts.

Copulation can start in unfinished nests, as the pair works together to complete it. Males use the "churr" call to start copulation and attract the females to the back of the nests. Copulation may be attempted multiple times by the males. One brood per season is completed. (Brown and Brown, 1995; ; Brown and Brown, 2000b; Brown, et al., 2015b; Brown, et al., 2015a)

The breeding season lasts from mid-April until mid-June, and egg-laying may begin before nests are finished. Laying occurs in the mornings at or before 0800, and one egg per day is laid. The range per brood is 1-6 eggs, and the average is 4. The pairs need to guard the nests because conspecifics may invade and either brood parasitize (lay eggs for other pairs to raise) or forcefully remove eggs from the nest. If a nest completely fails, the pair may attempt a second, smaller brood of about 3 eggs, on average.

Incubation starts within three days after the first egg is laid and will continue until the last one is laid. The period of incubation varies depending on latitude (northern colonies take longer), but typically is 13.5 days (range 10-19 days).

Hatchlings will lack plumage at the time of hatching and will have a mass of 1.6 to 2.2 g (average 2.0 g). It takes the young typically 20-26 days (average 22 days) to fledge and become fully grown. The birds will become fully independent and began traveling at around 6 weeks old (range 5-8 weeks). Sexual maturity for females is reached in 42 to 50 days (average 45), 40 to 48 days in males (average 43). (Brown and Brown, 1995; Brown and Brown, 2000b; Brown, et al., 2015b; Brown, et al., 2015a; Weaver and Brown, 2004)

  • Breeding interval
    Cliff swallows will breed once per breeding season.
  • Breeding season
    Breeding occurs from mid-April to mid-June.
  • Range eggs per season
    1 to 6
  • Average eggs per season
    4
  • Range time to hatching
    10 to 19 days
  • Average time to hatching
    13.5 days
  • Range fledging age
    20 to 26 days
  • Average fledging age
    22 days
  • Range time to independence
    5 to 8 weeks
  • Average time to independence
    6 weeks
  • Range age at sexual or reproductive maturity (female)
    42 to 50 days
  • Average age at sexual or reproductive maturity (female)
    45 days
  • Range age at sexual or reproductive maturity (male)
    40 to 48 days
  • Average age at sexual or reproductive maturity (male)
    43 days

Parents are involved greatly before the eggs hatch and generally become less involved after fledging. Males and females both share the responsibilities of protecting eggs during incubation. They will incubate the eggs while the other sex is out of the nest. Nest-guarding is a necessary action, as other cliff swallows may attempt to add or remove eggs from neighboring nests,.

After hatching, both sexes will protect the young for 2-3 days. The parents generally continue to feed fledglings but start to lessen their investment in protecting them as fledging continues. (Brown and Brown, 1995; ; Brown, et al., 2015a; Weaver and Brown, 2004)

  • Parental Investment
  • pre-fertilization
    • protecting
      • male
      • female
  • pre-hatching/birth
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

The highest recorded lifespan for a cliff swallow was 11 years, as was observed from two birds in Nebraska. There is neither recorded average lifespan nor any information collected for cliff swallows in captivity. These birds typically are not kept in captivity.

The probability of survival of birds was recorded during their periods of growth. Cliff swallows have an annual probability of survival of 0.17 during their first year of growth, Brown and Brown (1995). This probability increases in the following years, up to 0.57 annually. There is no difference between male populations or female populations for survival. But, there is yearly variation in adult populations ranging from 0.47-0.64. (Brown and Brown, 1995; ; Brown, et al., 2008; Brown, et al., 2015b)

  • Range lifespan
    Status: wild
    11 (high) years

Behavior

Cliff swallows hold the largest colony sizes among all species of swallows. Colony size can range from 200-3700 total nests in the area (Brown and Brown 1995). Solitary nesting is rare, and typically occurs in close proximity to another large colony. These birds practice brood parasitism in their colony, laying eggs in the nests of neighbors. This lessens the reproductive effort for the layer and maximizes reproductive output. This has the opposite effect on the occupants of the nest. When defending nests, the birds will puff out feathers to appear larger. The white patches on cliff swallows' foreheads may be used as a display of ownership of a nest.

Cliff swallows fight when selecting nesting areas. Many nests are existing ones from previous years, so repair and restoration is all that's needed. Birds use both their beaks and wings to attack one another and fights can last up to 15 minutes.

Not all cliff swallow interactions are negative. These birds may play while perched on high wires. Birds will attempt to knock one another off the wire and take their spots on the wire. This type of play will happen for a short period of time and then normal perching occurs again. Birds also will allopreen (clean one another) on high surfaces like powerlines close to the colonies, in large groups. The birds on the outer perimeter of preening groups will spend most of the time watching for predators. Preening generally happens in the mid-end of summer during periods of sunrise and sundown. Allopreening birds also will attack one another for unknown causes.

Birds also will chase one another in spring which could be part of their mating behaviors, because the twitter-squeak song is usually accompanying these chases.

Cliff swallows will sunbathe by rolling to one side and exposing the majority of their bodies to the sunlight. This mainly occurs when allopreening is taking place. They generally don't swim and actual bathing is uncommon.

Cliff swallows are speedy, efficient fliers. Flight altitudes range for birds from ground level to 60 m above ground. Flap speed will increase when making maneuvers or climbing in altitude. The tail is also outspread during turns. Cliff swallows will make these fast maneuvers when chasing their prey and flare tails after catching prey.

Migration takes place in late summer, and birds will migrate southward into South America along the coastlines. Cliff swallows will remain in large groups during the non-breeding seasons. Birds may also be nomadic during the winter times. Cliff swallows then migrate back into North America in early April. (Blake, 1948; ; Brown and Brown, 2002; Brown, 2010; Brown, et al., 2015b; Johnson and Freedberg, 2014; Withers, 1977)

  • Average territory size
    <1 m^2

Home Range

Colonies in the spring generally range from 2-15 km for males and 9-14km for females. Foraging generally happens in a 1.5 km radius around the colony. Foraging outside this area sometimes happens up to 6km outside the region.

Territories are restricted to the actual nest site that pairs will defend in the breeding season. These nests are mud domes, and pairs will attack neighbors who try to build nests within 8-12 cm from their nest opening. Therefore, territory sizes are negligible. (Brown and Brown, 1995; ; Brown and Brown, 2002; Brown, 2010; Brown, et al., 2015b; Johnson and Freedberg, 2014)

Communication and Perception

Vocalization is the main route of communication for cliff swallows. Nestlings can vocalize at 5-6 days old. These swallows' vocal range consists of five main vocal calls. These are: begging call, purr call (alarm), chur call (multiple uses), twitter-squeak song (courtship and nesting), and squeak call (foraging). Males most likely only make the twitter-squeak call, but both sexes make the other four. Each bird has a distinctive call that is distinguishable by 15-18 days old, and, for genetic reasons, siblings express similar calls. The begging call of youths becomes the "chur" call once adulthood is reached. Cliff swallows are also able to make their alarm call by week 6.

Vocalization also varies by seasons. Vocalization is at its lowest for these birds during the winter. There appears to be no effect on vocalization due to time of day. However, location is influential, as three of the calls (begging, chur, twitter-squeak) occur only inside the next.

The purr and chur calls are used during the nesting and breeding season. The twitter-squeak call is mainly used in spring and declines once mates are found, but is used again in late summer when defending nests. The squeak call is used during breeding in midsummer. The begging call is used primarily from youth to parents for food and recognition of the youth. Brown and Brown (1995) reported that cliff swallows in Washington will evict young that are not theirs from nests, while those in Nebraska do not. Adult birds distinguish which young is theirs based on the begging call. The purr call is used for when predators are threatening. Though directed at the predator, it may cause other colony members to come out of their nests in response. When the purr call is in the absence of predators, its goal may be to allow the caller to intrude upon others' nests. The chur call appears to have multiple uses between pairs, parents, offspring, or nearby nests.

Vision and tactile senses are important in the colonial group, and they allopreen, fly to avoid one another, and play pecking games on highwires. Their sense of hearing also is important, especially for parents to recognize the calls of their young. (Brown and Brown, 1995; ; Johnson and Freedberg, 2014; Weaver and Brown, 2004)

Food Habits

Cliff swallows' main source of food is flying insects. It appears that insects are taken opportunistically, without preference for certain orders or families. However, cliff swallows' diets may include more swarming species than not, do to the nature of efficiently consuming large volumes of insects.

Occasional ingestion of seeds and gravel has been reported, as these could help break up food during digestion. During foraging, cliff swallows feed from 50m and above from ground level. General foraging areas are grassy areas, but lakes, ponds, and rivers are also sources of food when the insect population is low in the area. Some populations have individuals that will forage on the ground, consuming terrestrial invertebrates, like ants.

Cliff swallows are diurnal foragers and feed in groups of 2-1000 birds at times. They use the presence of other insect eaters as a signal of where to feed, then swarm the feeding area for insects. Thermals (upward wind currents) also are locations where insects concentrate, so the birds often target these. Feeding is generally intense before the nesting season and lasts all day long during the nesting season. The birds will travel out of the colonies to feed in shorter but more frequent bursts during the nesting season. (Brown and Brown, 1995; ; Brown and Brown, 2002)

  • Animal Foods
  • insects
  • Plant Foods
  • seeds, grains, and nuts

Predation

Birds and snakes are the major predators of cliff swallows. The birds and that are predators of cliff swallows are sharp-shinned hawks (Accipiter striatus), American kestrels (Falco sparverius), barn owls (Tyto alba), great horned owls (Bubo virginianus), black-billed magpies (Pica pica), loggerhead shrikes (Lanius ludovicianus), common grackles (Quisalus quiscula), peregrine falcons (Falco peregrinus), prairie falcons (Falco mexicanus), and Mississippi kites (Ictinia mississippiensis). The snakes that are predators are bull snakes (Pituophis catenifer) and rattlesnakes (Crotalus).

American minks (Neovison vison) and red imported fire ants (Solenopsis invicta) also can be predators of these birds.

House sparrows (Passer domesticus), acorn woodpeckers (Melanerpes formicivorus), red-headed woodpeckers (Melanerpes erythrocephalus), and deer mice (Peromyscus maniculatus) will prey on eggs of cliff swallows.

The cliff swallows response to predators is warning other birds in the colony with the purr call. They will exit the colony, when falcons or hawks attack, in a mass flock to evade them. Predators understand that they are detected when this occurs and will leave. Cliff swallows use the purr call for ground predators as well.

Large colonies are a benefit to cliff swallows because, with the larger size comes the benefit of detectability. More nests and colony size makes it easier for the birds to detect incoming predators from the outside. (Brown and Brown, 1995; Fajer, et al., 1987; Jones, 1883; Tumlison, 2009)

Ecosystem Roles

Cliff swallows may spread plant seeds during nesting and migration. Birds will compete for nests with barn swallows (Hirundo rustica) and convert them to the cliff swallow style nest. Cliff swallows are also brood parasites within their colonies.

A study by Brown and Sethi (2002) also found that mosquito abundance was positively related to colony size. The authors could find no weather connections or Julian date issues to influence this trend, and hypothesized that mosquito species were drawn to the large mud colonies in some way.

The parasites that affect cliff swallows range from cimicid bugs Oeciacus vicarius, ticks, fleas, dipterans, dermestid beetles, lice, mites, nematodes, cestodes, trematodes, acanthocephalans, and protozoans.

The ectoparasitic ticks observed are: Ixodes baergi, Ixodes howelli, Argas cooleyi, Carios concanensis, Ornithodoros turicata. Ectoparastic fleas observed are: Ceratophyllus celsus, Ceratophyllus petrochelidoni, Ceratophyllus arcuegens, Ceratophyllus calderwoodi, Ceratophyllus coahuilensis, Ceratophyllus idius, Ceratophyllus scopulorum, and Hectopsylla psittaci. Dipterans, specifically blowflies, observed are: Protocalliphora hirundo, Protocalliphora asiovora, Protocalliphora braueri, and Protocalliphora sialia. Dermestid beetles were observed affecting cliff swallows, but no specific genius or species has been listed. Feather lice observed are: Machaerilaemus malleus, Brueelia longa, Philopterus excisus, and Mysidea dissimilis. Mites observed are: Dermanyssus gallinae, Dermanyssus hirundinis, Dermanyssus triscutatus, Cheyletus, Ornithocheyla, Hirstiosoma, Eutromibcula alfredugesia, Dermatophagoides evansi, Proctophyllodes, and Ptilonyssus echinatus. Nematodes observed are: Hadjelia pyrrhonota, Acuaria, Microtetrameres inermis, Splendidofilaria, and Diplotriaena. Cestodes observed are: Angularella audubonensis, Angularella beema, Anonchotaenia globata, Vitta magniuncinata, Vitta parvirostris, Vitta riparia, and Mayhewia ababili. Trematodes seen are: Collyriclum faba, Concinnum minor, Brachylecithum marinholutzi, Plagiorchis maculosus, and Stomylotrema gratiosus. Acanthocephalans include: Mediorhynchus grandis and Mediorhynchus papillosus. Protozoan blood parasites that were also spotted include: Hepatozoon, Trypanosoma, Haemoproteus, Leucocytozoon, and Isospara petrochelidon. (Brown and Brown, 1995)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Like many other songbirds and other migratory birds, cliff swallows contribute towards bird-watching in many regions. (Brown and Brown, 1995; ; Brown and Sethi, 2002)

Economic Importance for Humans: Negative

There are no reported negative effects of cliff swallows on humans.

Conservation Status

Cliff swallows are listed as species of "Least Concern" under The IUCN Red List and are protected under the US Migratory Bird Act. The US Migratory Bird Act prohibits any hunting of cliff swallows. This species, because it's the edge of its range, is listed as "Threatened" in Pennsylvania and New Jersey. They are not listed on the CITES appendices or on the US Federal List.

Cliff swallows contract the Fort Morgan Virus, but it appears to have no adverse effects during the fledging process. Another unknown virus also affected multiple birds in Oklahoma that also has no witnessed effects on birds.

As a species that can benefit from human interaction, cliff swallow populations have been reportedly increasing. Habitats for cliff swallows are enhanced by man-made structures such as bridges and buildings as possible nesting sites. Because the birds are very tolerant of human disturbance, human expansion does not negatively impact cliff swallows.

There are state- and locality-based conservation efforts that have attempted to increase the population of cliff swallows in certain areas. Efforts include man-made nests being put up to attract cliff swallows to colonize in certain areas and help increase the cliff swallow populations in localities. Control or elimination of competing, invasive house sparrows Passer domesticus also has shown to have positive impacts on cliff swallows. (Brown and Brown, 1995; ; BirdLife International, 2012)

Contributors

Joshua Tulppo (author), Radford University, Alex Atwood (editor), Radford University, Marisa Dameron (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

crepuscular

active at dawn and dusk

diurnal
  1. active during the day, 2. lasting for one day.
ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Bent, I. 1942. A managed cliff swallow colony in southern Wisconsin. Wilson Bulletin, 54: 153-161.

BirdLife International, 2012. "Petrochelidon pyrrhonota" (On-line). The IUCN Red List of Threatened Species 2012: e.T22712427A38672463. Accessed September 15, 2016 at http://dx.doi.org/10.2305/IUCN.UK.2012-1.RLTS.T22712427A38672463.en.

Blake, C. 1948. The flight of swallows. Auk, 65: 54-62.

Brown, C., M. Brown. 1996. Coloniality in the Cliff Swallow: The Effect of Group Size on Social Behavior. Chicago, Illinois: University of Chicago Press.

Brown, C., M. Brown. 2000. Weather-mediated natural selection on arrival time in cliff swallows (Petrochelidon pyrrhonota). Behavioral Ecology and Sociobiology, 47/5: 339-345.

Brown, C. 2010. How cliff swallows choose where to live. Phi Kappa Phi Forum, 90/1: 4-7.

Brown, C., M. Brown. 2002. Does intercolony competition for food affect colony choice in cliff swallows?. The Condor, 104/1: 117-128.

Brown, C., M. Brown. 2000. Heritable basis for choice of group size in a colonial bird. Proceedings of the National Academy of Sciences, 97/26: 14825–14830.

Brown, C., M. Brown, K. Brazeal. 2008. Familiarity with breeding habitat improves daily survival in colonial cliff swallows. Animal Behaviour, 76/4: 1201-1210.

Brown, C., m. Brown, M. Shaffer. 1991. Food-sharing signals among socially foraging cliff swallows. Animal Behaviour, 42/4: 551-564.

Brown, C., M. Brown. 1995. Cliff swallow (Petrochelidon pyrrhonota). Pp. None in P Rodewald, ed. Birds of North America, Vol. None. Ithaca, New York: Cornell Lab of Ornithology. Accessed November 27, 2016 at https://birdsna.org/Species-Account/bna/species/cliswa.

Brown, C., E. Roche, M. Brown. 2015. Parent-offspring resemblance in colony-specific adult survival of cliff swallows. Evolutionary Ecology, 29/4: 537-550.

Brown, C., E. Roche, V. O'Brien. 2015. Costs and benefits of late nesting in cliff swallows. Oeocologia, 177/2: 413-421.

Brown, C., R. Sethi. 2002. Mosquito abundance is correlated with cliff swallow (Petrochelidon pyrrhonota) colony size. Journal of Medical Entomology, 39/1: 115-120.

Brown, M., C. Brown. 2011. Intense natural selection on morphology of cliff swallows (Petrochelidon pyrrhonota) a decade later: Did the population move between adaptive peaks?. The Auk, 128/1: 69-77.

Bullard, R. 1963. Banding notes on the Nickajack cliff swallows (Petrochelidon pyrrhonota). Eastern Bird-Banding Association News, 26: 191-203.

Byard, M., R. Freeman, G. Pester. 1979. Peregrine falcons sighted in Texas County, Oklahoma. Bulletin of the Oklahoma Ornithological Society, 12/2: 13-14.

Dugas, M. 2010. Nestling birds put their best flange forward. Journal of Avian Biology, 41/3: 336-341.

Fajer, E., K. Schmidt, J. Eschler. 1987. Acorn woodpecker predation on cliff swallow nests. Condor, 89: 177-178.

Johnson, A., S. Freedberg. 2014. Variable facial plumage in juvenile cliff swallows: A potential offspring recognition cue?. The Auk, 131/2: 121-128.

Jones, H. 1883. An unrecorded habit of the Red-headed Woodpecker. Ornithologist and Oologist, 8: 56.

Kirby, R. 1978. Roosting of passerines over open water at night.. North American Bird Bander, 3: 104-105.

McNair, D. 2013. Cliff swallow breeding range expansion along the Great Pee Dee River corridor in the Carolinas. Southeastern Naturalist, 12/3: 500-513.

Oliver, G. 1970. Black ratsnake predation upon nesting Barn and Cliff swallows. Oklahoma Ornithological Society, 3: 17-20.

Sikes, P., K. Arnold. 1986. Red imported fire ant (Solenopsis invicta) predation on cliff swallow (Hirundo pyrrhonota) nestlings in east-central Texas. Southwestern Naturalist, 31: 105-106.

Sotherland, P., G. Packard, T. Taigen, T. Boardman. 1980. An altitudinal cline in conductance of cliff swallow (Petrochelidon pyrrhonota) eggs to water vapor. The Auk, 971: 177-185.

Thompson, B., C. Turner. 1980. Bull snake predation at a cliff swallow nest. Murrelet, 61: 35-36.

Tumlison, R. 2009. Breeding by cliff swallows (Petrochelidon pyrrhonota) in southern Arkansas. Southwestern Naturalist, 54/2: 208-210.

Weaver, H., C. Brown. 2004. Brood parasitism and egg transfer in cave swallows (Petrochelidon fulva) and cliff swallows (Petrochelidon pyrrhonota) in south Texas. The Auk, 121/4: 1122-1129.

Wilkinson, G., G. English-Loeb. 1982. Predation and coloniality in cliff swallows (Petrochelidon pyrrhonota). Auk, 99: 459-467.

Withers, P. 1977. Energetic aspects of reproduction by the cliff swallow. Auk, 94: 718-725.

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