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BARN SWALLOWS DO FEMALE BARN SWALLOWS CHOOSE LONG TAILS?

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Møller (1) found that experimental lengthening the tail of barn swallow males led to earlier mating and therefore an increase in offspring. Since he observed no significant differences in intensity of male-male aggressive encounters among males at the nesting sites he attributed the early mating solely to female choice. This released a flood of anthropomorphic speculations on what the female has in mind when she chooses a mate.

However, the earlier mating might be merely the result of use of the elongated tail as a status symbol in competition for foraging territories (100-500m from the nesting sites). Such use of display features would save energy otherwise used in physical fighting and competitive racing. The same could be said for the white spots on top of the tail as positively related to elongation of the tail. White spots are commonly displayed by birds in competition for food reserves.

Møller (2) does indeed carefully describe competitive flights of barn swallows in groups from which females are attracted to the nesting territories, though Møller does not consider any possible relationship between the area of such flights and reproductive resources. Such a relationship is clearly evident with the dragonfly, Perithemis tenera, in which groups of males perform competitive flights in areas from which females are later attracted (3). This resembles “trysting” behavior commonly observed among insects.

The male white-tailed skimmer dragonfliy, Plathemis lydia, displays the white upper surface of the abdomen toward other males competing for reproductive resources. Artificial blackening of the white surface diminishes territorial success of the males. This experimental elimination of the white feature results in greater expenditure of energy on the part of the blackened males (3). Observation would reveal the more successful in competition among these males (the white ones) would show less competitive intensity than the less successful (the black ones).

Among the barn swallows, optimal territory with plentiful food may influence the female in choice of a mate. Under natural conditions, Syrphidae flies form an important fraction of the food (2). These weak-flying yellowish flies that hover and perch on flowers may determine survival of the first brood of swallows in the cold spring weather. This may well account for the earlier mating and reproductive success of the males with the elongated tails. Regarding male features that attract females at the nesting sites, candidates might be the bright yellow gaping billl set off by the surrounding reddish plumage. The male displays these features toward the female at the nest site. The resplendency of the plumage may be conditioned by the adequate nutrition the competitively advantaged male has received in his foraging territory near the end of his prenuptial molt.

1. A.P. Møller (1992). Nature 357, 238-240,
2. A.P. Møller (1994). Sexual Selection and the Barn Swallow. Oxford University Press.
3. M.E. Jacobs (1955). Ecology 36, 566-586.

Add comment June 22nd, 2006

Hirundo rustica(barn swallow)

By Tanya Dewey
Information
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Aves
Order: Passeriformes
Family: Hirundinidae
Genus: Hirundo
Species: Hirun

Barn swallows are native in all the biogeographic regions except Australia and Antarctica. The breeding range of barn swallows includes North America, northern Europe, northcentral Asia, northern Africa, the Middle East, southern China, and Japan. They winter in South America, South Asia, Indonesia, and Micronesia. (Terres, 1980)
Biogeographic Regions:
nearctic (native ); palearctic (native ); oriental (native ); neotropical (native ).

Other Geographic Terms:
holarctic .
Reproduction
Barn swallows are socially monogamous. However, extra-pair copulations are common, making this species genetically polygamous. Breeding pairs form each spring after arrival on the breeding grounds. Pairs re-form each spring, though pairs that have nested together successfully may mate together for several years. Males try to attract females by spreading their tails to display them and singing.

Several studies have researched sexual selection in barn swallows. Moller (1994) documented female barn swallows selecting for symmetrical wings and tails in potential mates. Males exhibiting greater symmetry acquired mates more quickly than did asymmetric males. Asymmetry can result from genetic factors such as inbreeding or mutations as well as from environmental stress such as food deficiency, parasite infestation, or the presence of pathogens. Moller observed that individuals affected by these factors not only exhibited asymmetry, but also decreased strength and longevity. Therefor, females that selected symmetrical mates would presumably be selecting superior mates. In addition to selecting for symmetry, females also tend to select males with longer tail feathers. Moller observed a connection between the tail length of male barn swallows and their offspring’s vitality and longevity. Males with longer tail feathers exhibit traits of greater longevity which is passed on to their offspring. Females thus gain an indirect fitness benefit from this form of selection, as longer tail feathers indicate a genetically stronger individual who will produce offspring with enhanced vitality. Individuals with longer tails have also been observed to demonstrate greater disease resistance than their short-tailed counterparts. There is also evidence that males select female mates with long tails.

Unmated adults often associate with a breeding pair for up to an entire season. Though these “helpers” do not usually feed the young, they may help with nest defense, nest building, incubation and brooding. “Helpers” are predominantly male, and may succeed in mating with the resident female, leading to polygyny. (Bolzern, Moller, and Saino, 1997; Brown and Brown, 1999; De Lope and Moller, 1993; Moller, 1993; Moller, 1994a; Moller, 1994b)
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous .

In North America, both barn swallow parents incubate the eggs and feed the nestlings. However, females provide more parental care than do males. During the nestling period, barn swallow parents may feed their nestlings up to 400 times per day. Barn swallows feed their chicks insects compressed into a pellet, which is transported to the nest in the parent’s throat. Although all swallows are socially monogamous, barn swallows differ from most swallow species in the sharing of parental care. Juveniles from the first brood of the season have even been observed assisting their parents in feeding a second brood. (Perrins, 1989; Terres, 1980)
Parental investment:
altricial ; pre-fertilization (provisioning, protecting: female); pre-hatching/birth (protecting: male, female); pre-weaning/fledging (provisioning: male, female, protecting: male, female); pre-independence (provisioning: male, female, protecting: male, female); post-independence association with parents.
Lifespan/Longevity
The average lifespan of barn swallows is 4 years. Barn swallows of 8 years of age have been documented, but these are considered the exception. Survival prospects and longevity appear to increase with tail length and wing and tail symmetry. (Moller, 1994a; Moller, 1994b; Perrins, 1989; Terres, 1980)
Behavior
Barn swallows are diurnal and migratory. They have individual songs and often sing as a chorus.

Barn swallows are often seen in large social groups sitting on telephone wires or other elevated structures. They also nest colonially, probably as a result of the distribution of high quality nest sites. Within a colony, barn swallows defend a territory around their nest. In European barn swallows, these territories range in size from about 4 to 8 square meters. (Hebblethwaite and Shields, 1990; Moller, 1991)

A study in West Virginia found that barn swallows foraged within 1.2 km of their nests. In Europe, barn swallows foraged within 500 m of their nest. (Brown and Brown, 1999)

Key behaviors:
troglophilic; flies; diurnal ; motile ; migratory ; territorial ; colonial .

Communication and Perception

Barn swallows use vocalizations and body language (postures and movements) to communicate. Barn swallows sing, both individually and as a group. They have a wide variety of calls used in different situations, from predator alarm calls, to courtship calls, and calls of young in nests. Nestlings give off a faint chirp while begging for food. Barn swallows also make clicking noises, which they create by snapping their jaws together. (Brown and Brown, 1999)

Communicates with:
visual ; acoustic .

Other communication keywords:
choruses .

Perception channels:
visual ; tactile ; acoustic ; chemical .

Food Habits

Barn swallows are insectivores. Flies < >, grasshoppers, crickets, dragonflies, beetles, moths and other flying insects make up 99 % of their diet. They catch most of their prey while in flight, and are able to feed their young at the nest while flying.

Barn swallows forage opportunistically. They have been observed following tractors and plows, catching the insects that are disturbed by the machinery. They drink water by skimming the surface of a body of water while flying. (Brown and Brown, 1999; Perrins, 1989; Terres, 1980)

Primary Diet:
carnivore (insectivore ).

Animal Foods:
insects.
Predation
American kestrels and other hawks, such as sharp-shinned hawks and Cooper’s hawks, eastern screech owls, gulls, common grackles, boat-tailed grackles, rats, squirrels, weasels, raccoons, bobcats, domestic cats, snakes, bullfrogs, fish and fire ants are predators of barn swallows. Barn swallows usually give alarm calls when predators come near. Most predators of barn swallows attack the nestlings, but hawks, falcons, and owls tend to hunt adults.

Barn swallows mainly escape predators by being swift and agile in flight and by building their nests in places that are difficult for predators to reach. (Barker, Ewins, and Miller, 1994; Brown and Brown, 1999)
Ecosystem Roles
Although incidents of cowbirds parasitizing barn swallow nests are rare, they have been documented. A 1994 observation of 67 Barn Swallow nests found two of these nests to contain cowbird eggs, which were laid by the parent cowbird and left in the barn swallow nest in a parasitic fashion for the barn swallows to raise. Each of these nests contained 1 cowbird egg and both eggs were incubated by the barn swallows along with their own eggs. However, only one of the cowbird eggs hatched. The single cowbird hatchling fledged normally, thus demonstrating that barn swallows are capable of acting as cowbird hosts.

Barn swallows frequently engage in a symbiotic relationship with ospreys, coexisting in a single nesting area to the mutual benefit of both species. Barn swallows will nest either below a much larger osprey nest or in a portion of an abandoned osprey nest. By nesting near an osprey population, the barn swallows receive protection from birds of prey, which are driven away from the nests by the much larger ospreys. In return, ospreys are alerted to the presence of these predators by the barn swallows which give alarm calls when predators are nearby.

Barn swallows eat an enormous amount of insects and are very important in the control of their populations. Barn swallows are also a useful food source for many predators. (Barker, Ewins, and Miller, 1994; Brown and Brown, 1999; Wolfe, 1994)
Species (or larger taxonomic groups) that are mutualists with this species
• Ospreys

Economic Importance for Humans: Negative

Some humans feel that barn swallow nests are a nuisance, and are unsightly when they are attached to buildings and other man-made structures. Large colonies in urban areas can also create detrimental cleanliness and health issues for humans. Finally, salmonella can be transmitted through their feces, posing a threat to livestock that live in close proximity to barn swallow colonies. (Brown and Brown, 1999; Perrins, 1989)

Ways that these animals might be a problem for humans:
causes or carries domestic animal disease .

Economic Importance for Humans: Positive

Barn swallows are quite effective in reducing insect pest populations. They also can serve as an indicator or trigger organism, indicating possible environmental trouble, as declines in their relatively abundant numbers may precede other more obvious effects of environmental stress. (Moore, 2001; Perrins, 1989)

Ways that people benefit from these animals:
controls pest population.
Conservation Status
Barn swallow populations are generally considered to be stable and sufficiently extensive. However, declines in the amount of acreage devoted to agriculture in recent years have resulted in reduced barn swallow numbers. This can be attributed to a reduction in habitat as the barns and outbuildings which once housed barn swallows, give way to more urban settings. Another contributing factor is the reduction in food supply. Insects attracted by the presence of livestock and the ideal surrounding habitat are the primary food source for barn swallows living in agricultural areas. Locations where farming has ceased exhibit a 50% reduction in insect populations.

Barn swallows continue to be widespread and common throughout their range. There are an estimated 190,000,000 individuals worldwide. (Brown and Brown, 1999; Moore, 2001)

Contributors

Tanya Dewey (author), Animal Diversity Web, University of Michigan Museum of Zoology.

Chava Roth (author), Western Maryland College.
Randall L. Morrison (editor), Western Maryland College.

Kari Kirschbaum (editor), Animal Diversity Web Staff.

References

Barker, E., P. Ewins, J. Miller. 1994. Birds breeding in or beneath Osprey nests. Wilson Bulletin, 106: 743-750.

Beecher, M., M. Medvin, P. Stoddard. 1993. Signals for parent-offspring recognition: a comparative analysis of the begging calls of Cliff Swallows and Barn Swallows. Animal Behavior, 45: 841-850.

Bolzern, A., A. Moller, N. Saino. 1997. Immunocompetence, ornamentation, and viability of male Barn Swallows. Proceedings of the National Academy of Sciences, 94: 54-552.

Brown, C., B. Brown. 1999. Barn swallow (Hirundo rustica). Pp. 1-32 in A. Poole, F. Gill, eds. The Birds of North America, Vol. 452. Philadelphia, PA: The Birds of North America.

De Lope, F., A. Moller. 1993. Female reproductive effort depends on the degree of ornamentation. Evolution, 47: 1152-1161.

Hebblethwaite, M., W. Shields. 1990. Social influences on Barn Swallow foraging in the Adirondacks: a test of competing hypotheses. Animal Behavior, 39: 97-104.

McWilliams, G. 2000. The Birds of Pennsylvania. New York: Cornell University Press.

Moller, A. 1991. The preening activity of swallows, *Hirundo rustica*, in relation to experementally manipulated loads of haematophagous mites. Animal Behavior, 42: 251-260.

Moller, A. 1993. Sexual selection in the Barn Swallow *Hirundo rustica*: female tail ornaments. Evolution, 47: 417-432.

Moller, A. 1994. Male ornament size as a reliable cue to enhanced offspring viability. Proceedings of the National Academy of Sciences, 91: 6929-6932.

Moller, A. 1994. Patterns of fluctuating asymmetry and selection against asymmetry. Evolution, 48: 658-671.

Moore, P. 2001. Dairy declines hard to swallow. Nature, 411: 904-905.

Perrins, C. 1989. Encyclopedia of Birds. England: Equinox Ltd..

Terres, J. 1980. The Audubon Society Encyclopedia of North American Birds. New York: Alfred A. Knopf, Inc.

Wolfe, D. 1994. Brown-headed Cowbirds fledged from Barn Swallow and American Robin nests. Wilson Bulletin, 106: 764-767.

Add comment June 22nd, 2006