Animal Diversity Web

Ge­o­graphic Range

Brown-headed cow­birds (Molothrus ater) in­habit the en­tire United States, north­ern Mex­ico and most of Canada. His­tor­i­cally, their core dis­tri­b­u­tion was lo­cated in the Great Plains of North Amer­ica, but dur­ing the 19th and 20th cen­turies they ex­panded from the plains in all di­rec­tions. Today, they are still much more abun­dant in the cen­tral parts of North Amer­ica, es­pe­cially from south­ern Canada to Ok­la­homa. The three rec­og­nized sub­species have vary­ing ranges, Molothrus ater ater is found in the east­ern United States, M. a. ob­scu­rus is found in the ex­treme south­west and M. a. artemisiae is found in the north­west. The sub­species may in­ter­breed near the bor­ders of their ranges, which has pro­duced in­di­vid­u­als with novel char­ac­ter­is­tics. (Or­tega, 1998; Pe­ter­john, et al., 2000; Roth­stein and Robin­son, 2000)

Brown-headed cow­birds are gen­er­ally mi­gra­tory, but the ex­tent of their mi­gra­tion de­pends on the in­di­vid­ual. Some brown-headed cow­birds mi­grate great dis­tances be­tween breed­ing and win­ter­ing sites, while oth­ers win­ter within their breed­ing grounds. Pop­u­la­tions of brown-headed cow­birds gen­er­ally do not travel to­gether from breed­ing to win­ter­ing grounds. In­stead, flocks in both breed­ing and win­ter­ing pop­u­la­tions dis­perse dur­ing each mi­gra­tion. While most cow­birds re­turn to the same areas to breed each breed­ing sea­son, there is far less fi­delity in win­ter­ing grounds and some birds mi­grate be­tween dif­fer­ent win­ter­ing grounds. (Or­tega, 1998)

• Biogeographic Regions
• nearctic
  • native

Habi­tat

The habi­tat of brown-headed cow­birds in­cludes for­est edges, ri­par­ian zones, thick­ets, prairies, fields, cat­tail marshes, pas­tures, or­chards and sub­ur­ban areas. They pre­fer eco­tonal habi­tats, which are close to both host nests and for­ag­ing areas. In the morn­ing, brown-headed cow­birds are found along the edges of closed, forested habi­tats. In the af­ter­noon, they are often found for­ag­ing in open habi­tats, such as prairies. (Lowther, 2003; Or­tega, 1998; Roth­stein, et al., 1986)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• savanna or grassland
• forest

• Other Habitat Features
• urban
• suburban
• agricultural

• Range elevation

  2,900 (high) m

  ft

Phys­i­cal De­scrip­tion

Brown-headed cow­birds are sex­u­ally di­mor­phic in body size and color pat­tern. Males are slightly larger than fe­males, with body lengths from 19 to 22 cm, an av­er­age wingspan of 36 cm and body masses of 42 to 50 g. They have a glossy, black body and a brown head, with a pointed gray beak. Fe­males have body lengths from 16 to 20 cm, wingspans from 32 to 38 cm and body masses of 38 to 45 g. They are dull brown and may have lightly col­ored streaks on their breast, with a pointed gray beak. The three sub­species in­clud­ing M. a. ater, M. a. artemisiae, and M. a. ob­scu­rus, are iden­ti­fied by beak mor­phol­ogy and wing cord. Male M. a. ater have a con­i­cal beak with a deeply curved upper mandible and their wing cord is be­tween 10.4 and 11.4 cm, male M. a. artemisiae have a straight upper mandible with a wing chord greater than 11.0 cm and male M. a. ob­scu­rus have a straight upper mandible with a wing chord less than 10.5 cm. Among fe­males, M. a. ater have a curved upper mandible and a wing chord from 9.6 to 10.1 cm, M. a. artemisiae have a straight upper mandible with a wing chord from 9.7 to 10.5 cm and fe­male M. a. ob­scu­rus have a straight upper mandible with a wing chord less than 9.1 cm. ("Brown-headed Cow­bird", 2013; Or­tega, 1998; Tacutu, et al., 2013; Tekiela, 2000)

• Other Physical Features
• endothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• male more colorful

• Range mass

  38 to 50 g

  1.34 to 1.76 oz

• Range length

  16 to 22 cm

  6.30 to 8.66 in

• Range wingspan

  32 to 38 cm

  12.60 to 14.96 in

• Average basal metabolic rate

  0.6315 cm3.O2/g/hr

• Average basal metabolic rate

  0.6315 W

  AnAge

Re­pro­duc­tion

Mate se­lec­tion is con­trolled by fe­male brown-headed cow­birds. Males court fe­males through dis­plays and perched songs. Males give song-spread dis­plays in which they fluff their feath­ers, spread their wings and bow to the fe­male. Male se­lec­tion is based on the num­ber of dis­place­ments, song spreads and flight whis­tles in their reper­toire, the same char­ac­ter­is­tics used to de­ter­mine their so­cial hi­er­ar­chy. No sin­gle mat­ing sys­tem de­scribes all pop­u­la­tions, al­though most stud­ies imply a largely monog­a­mous mat­ing sys­tem. Al­most all pop­u­la­tions have more males than fe­males, so fe­males can be choosy. Males tend to be monog­a­mous through­out the breed­ing sea­son and try to main­tain their pair-bond by guard­ing their fe­male from other males. Fe­males, on the other hand, tend to be promis­cu­ous. There ap­pears to be no re­pro­duc­tive ad­van­tage to mat­ing with only one male as males do not pro­vide food, nest­ing re­sources, pro­tec­tion from pre­da­tion or parental care. Mat­ing with more than one male is ben­e­fi­cial to a fe­male's re­pro­duc­tive suc­cess, in­creas­ing the gene pool of her off­spring. Males that are not in a pair-bond may mate with un­guarded fe­males, often when the fe­male's mate is for­ag­ing. Ex­tra-pair cop­u­la­tions are more fre­quent in pop­u­la­tions where fe­males have larger home ranges than males. When the fe­male leaves her mate's home range she is no longer guarded and may there­fore be more likely to cop­u­late with an­other male. (Dar­ley, 1982; Or­tega, 1998)

• Mating System
• monogamous
• polygynandrous (promiscuous)

Brown-headed cow­birds are brood par­a­sites and lay their eggs in the nest of a host species. Be­cause their re­pro­duc­tion re­lies on hosts, their breed­ing sea­son varies and is adapted to co­in­cide with the breed­ing sea­sons of their hosts. The ear­li­est breed­ing sea­sons begin in early to mid-April and the lat­est sea­sons end in early Au­gust, but egg lay­ing nor­mally oc­curs from May to June. The num­ber of eggs per breed­ing sea­son varies, but brown-headed cow­birds have re­port­edly laid up to 77 eggs in one mat­ing sea­son. Be­cause they are brood par­a­sites, the num­ber of avail­able host nests prob­a­bly in­flu­ences the num­ber of eggs laid per breed­ing sea­son. To avoid de­tec­tion by the nest's host, fe­males have de­vel­oped rapid egg lay­ing. On av­er­age, brown-headed cow­birds lay eggs in 41 sec­onds, com­pared to 20.7 to 103 min­utes in other passer­ines. Their eggs hatch in 10 to 11.6 days. In many cases, this short in­cu­ba­tion time al­lows them to hatch be­fore host eggs and ob­tain food and begin grow­ing be­fore host hatch­lings. The hatch­lings of brown-headed cow­birds dis­play ex­ag­ger­ated beg­ging, which causes the host par­ents to feed cow­birds more than their own hatch­lings. Cow­birds out-com­pete host hatch­lings, re­sult­ing in the death of some, or all of the host's hatch­lings. Fledg­ling brown-headed cow­birds nor­mally leave the nest 10 to 11 days after hatch­ing and gain in­de­pen­dence from their fos­ter par­ents at 25 to 39 days old. At this point, they find and join a flock of other brown-headed cow­birds. (Or­tega, 1998; Roth­stein, 2004; Tacutu, et al., 2013)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• oviparous

• Breeding interval

  Brown-headed cowbirds mate many times during the breeding season.

• Breeding season

  The breeding season varies with the region, but egg laying occurs most often in May and June.

• Range eggs per season

  0 to 77

• Range time to hatching

  10 to 11.6 days

• Range fledging age

  8 to 13 days

• Average fledging age

  10-11 days

• Range time to independence

  25 to 39 days

• Average age at sexual or reproductive maturity (female)

  1 years

• Average age at sexual or reproductive maturity (female)
  Sex: female

  365 days

  AnAge

• Average age at sexual or reproductive maturity (male)

  1 years

• Average age at sexual or reproductive maturity (male)
  Sex: male

  365 days

  AnAge

The brood par­a­sitic re­pro­duc­tive strat­egy of brown-headed cow­birds is be­lieved to have evolved be­cause early cow­birds fol­lowed bison herds and could not stay in one place long enough to care for their young. While brown-headed cow­birds have been por­trayed as lazy or ne­glect­ful par­ents, re­cent ev­i­dence re­veals that cow­birds take an ac­tive in­ter­est in their young. They are care­ful in the place­ment of their eggs and may con­tinue to check on the nest. Fe­male brown-headed cow­birds search dili­gently through the for­est for host nests. Once a nest is found, the fe­male in­spects it and may even in­spect it sev­eral times dur­ing its con­struc­tion. Fe­males also watch the host for long pe­ri­ods of time be­fore lay­ing eggs in their nest. Once eggs are laid, fe­male cow­birds check the nest with some fre­quency. If a host re­jects a cow­birds' egg, the fe­male may re­tal­i­ate by de­stroy­ing the host's eggs or some­times their hatch­lings, this has been termed “mafia be­hav­ior”. De­stroy­ing eggs or hatch­lings may dis­cour­age fu­ture re­jec­tion be­hav­ior by the host, en­sur­ing that such be­hav­ior does not evolve. It may also stim­u­late the host to re-nest, al­low­ing cow­birds an­other op­por­tu­nity to par­a­sitize the host. While un­com­mon, some brown-headed cow­birds reg­u­larly feed their hatch­ling in the par­a­sitized nest, feed­ing only their own off­spring and peck­ing the host's nestlings on the head when they beg for food. (Hoover and Robin­son, 2007; Or­tega, 1998)

• Parental Investment
• female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female

Lifes­pan/Longevity

The longest known lifes­pan for a wild brown-headed cow­bird is 16.9 years. (Tacutu, et al., 2013)

• Range lifespan
  Status: wild

  16.9 (high) years

• Average lifespan
  Status: wild

  202 months

  Bird Banding Laboratory

Be­hav­ior

Brown-headed cow­birds are so­cial but tend to be more soli­tary in the morn­ings. It is dur­ing this time that mat­ing oc­curs, nor­mally away from other birds and in the pair's home range. Lone fe­males also look for host nests in the morn­ing. In the af­ter­noon, brown-headed cow­birds con­gre­gate in flocks to for­age. Dur­ing win­ter months, they con­gre­gate in very large flocks with other icterids and Eu­ro­pean star­lings. Roost­ing pop­u­la­tions may be as large as 38 mil­lion in­di­vid­u­als. In so­cial set­tings, a hi­er­ar­chy is es­tab­lished based on the num­ber of dis­place­ments, song spreads and flight whis­tles in a male's reper­toire. In order to de­ter­mine hi­er­ar­chy, brown-headed cow­birds en­gage in "tri­an­gle and quad­ran­gle cer­e­monies". In these ac­tiv­i­ties, male cow­birds stand in a cir­cle and give song spreads to one an­other to de­ter­mine so­cial sta­tus. After so­cial sta­tus has been es­tab­lished, it is nor­mally main­tained by non­ver­bal means. In flocks, singing is per­formed mostly by the dom­i­nant male. This may be en­forced by at­tack­ing in­fe­rior males that try to sing. (Dar­ley, 1982; Or­tega, 1998)

• Key Behaviors
• arboreal
• terricolous
• flies
• diurnal
• parasite
• motile
• migratory
• territorial
• social
• dominance hierarchies

Home Range

Brown-headed cow­birds have large home ranges be­cause they may travel be­tween nest­ing and feed­ing sites each day. Their home range size de­pends on their spe­cific habi­tat, fe­males use 4.5 ha and males use 6.6 ha in On­tario, whereas they may use 68 ha^3 in the Sierra Nevada Moun­tains, where they oc­cupy an el­e­va­tional gra­di­ent. Some brown-headed cow­birds re­port­edly travel 7 km from nest­ing to feed­ing sites each day, while oth­ers stay within the same area to nest and for­age. The re­pro­duc­tive strat­egy of brown-headed cow­birds may play a role in this be­hav­ior. Due to their brood par­a­sitic ten­dency, they do not need to care for their young. Free­dom from parental care al­lows them to travel to sites with more abun­dant food sources. This hy­poth­e­sis is sup­ported by ev­i­dence that red-winged black­birds, a non-par­a­sitic species from fam­ily Icteri­dae, travel be­tween nest­ing and for­ag­ing areas early in the breed­ing sea­son, be­fore they lay eggs. (Ori­ans, 1961; Roth­stein, et al., 1984; Ori­ans, 1961; Or­tega, 1998; Roth­stein, et al., 1984)

Male brown-headed cow­birds are not known to be ter­ri­to­r­ial. Rather than guard a ter­ri­tory, they tend to guard mates. Fe­males, on the other hand, tend to be more ter­ri­to­r­ial, al­though de­grees of ter­ri­to­ri­al­ity de­pend on their re­gion and the den­sity of host nests. In re­gions with higher den­si­ties of host nests, such as the north­east­ern United States, fe­males are more ter­ri­to­r­ial. Due to higher den­si­ties of nests, cow­birds are able to find many nests in a smaller home range and this is eas­ier to de­fend from oth­ers. In prairie re­gions, such as Kansas, there is a lower den­sity of host nests. It is not pos­si­ble to ob­tain a home range that can be de­fended with the num­ber of nests needed by fe­males; there­fore, fe­males in these re­gions show lit­tle to no ter­ri­to­ri­al­ity. (Or­tega, 1998)

Com­mu­ni­ca­tion and Per­cep­tion

Brown-headed cow­birds have a va­ri­ety of vo­cal­iza­tions, in­clud­ing flight whis­tles, sin­gle-syl­la­ble calls, perched songs, keks or chucks and chat­ter. These func­tion in courtship, species and in­di­vid­ual iden­ti­fi­ca­tion, ag­gres­sion and alerts to threats. Songs are in­nate, at least in part. In the wild, fledg­lings never learn the songs of their hosts and in­stead learn con­spe­cific vo­cal­iza­tions de­spite host up­bring­ing. Males can learn perched songs even in acoustic iso­la­tion, which im­plies an in­nate com­po­nent of this song. This abil­ity is unique; the songs of most other song­birds must be learned. How­ever, at the same time, brown-headed cow­birds are known to vary perched songs in re­sponse to the songs of other males, male ag­gres­sion in re­sponse to songs and non-vo­cal com­mu­ni­ca­tion of fe­males. (Or­tega, 1998; Roth­stein, et al., 2000)

Flight whis­tles are a form of long dis­tance com­mu­ni­ca­tion given ex­clu­sively by males and con­sist of pure tones, be­tween 3 and 9 kHz. Flight whis­tles vary and may in­clude trills, they are often given be­fore or dur­ing flight and within 5 sec­onds of cop­u­la­tion, they also func­tion as an alarm call. Sin­gle-syl­la­ble calls are given by males and con­sist of a sin­gle pure tone, with a fun­da­men­tal fre­quency be­tween 2 and 8 kHz. Males gen­er­ally have 1 or 2 in their reper­toire, their func­tions are sim­i­lar to flight whis­tles, but they are given more often when con­specifics are nearby. Perched songs are used ex­clu­sively by males and have a fre­quency range of 0.5 to 12 kHz, which is the widest fre­quency range of any bird song. Males have a reper­toire of 1 to 8 dif­fer­ent perched songs. When used in courtship, these songs are ac­com­pa­nied by a song-spread dis­play. They also func­tion in male to male ag­gres­sion, iden­ti­fi­ca­tion and es­tab­lish­ment of so­cial hi­er­ar­chies. Keks or chucks are short notes given by males and fe­males. They are not de­tectable be­yond 5 m of the bird, so rel­a­tively lit­tle is known about this vo­cal­iza­tion. Chat­ter is given pri­mar­ily by fe­males and may be used in re­sponse to other vo­cal­iza­tions. It con­sists of sev­eral el­e­ments with fre­quen­cies from 2 to 6 kHz. There is lit­tle or no vari­a­tion be­tween sub­species or dif­fer­ent pop­u­la­tions, how­ever, there are dif­fer­ences be­tween in­di­vid­u­als, this may imply that sounds are used in iden­ti­fi­ca­tion. (Or­tega, 1998; Roth­stein, et al., 2000; West, et al., 1979)

• Communication Channels
• visual
• acoustic

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Brown-headed cow­birds mainly for­age for food on the ground in open habi­tats such as grass­lands. They fre­quently for­age near herds of an­i­mals, such as cows, that stir up in­sects from the grass as they walk. Sev­enty-five per­cent of their diet con­sists of plant mat­ter in­clud­ing fruits and seeds. They also feed on spi­ders and arthro­pods, such as grasshop­pers, leafhop­pers and bee­tles. Dur­ing the breed­ing sea­son, fe­males eat mol­lusk shells to in­crease their cal­cium lev­els, which aids in egg pro­duc­tion. Al­though both sexes eat eggs, fe­males may do so to in­gest more cal­cium. Dur­ing the win­ter, their diet con­sists mainly of grains. ("Brown-headed Cow­bird", 2013; Or­tega, 1998; Reilly, Jr (ed.) and Pet­tingill, Jr (ed.), 1968)

• Primary Diet
• herbivore
  • frugivore
  • granivore

• Animal Foods
• eggs
• insects
• terrestrial non-insect arthropods
• mollusks

• Plant Foods
• seeds, grains, and nuts
• fruit

Pre­da­tion

Blue Jays are com­mon egg preda­tors, but red squir­rels, north­ern fly­ing squir­rels and yel­low-bel­lied sap­suck­ers also at­tack brown-headed cow­birds dur­ing in­cu­ba­tion. Broad-winged hawks and barred owls are com­mon preda­tors of nestlings, as well as north­ern goshawks, Cooper's hawks, sharp-shinned hawks, north­ern saw-whet owls, blue jays and north­ern fly­ing squir­rels. (Cox, et al., 2012; Han­non, et al., 2009)

• Known Predators

  • broad-winged Hawks (Buteo platypterus)
  • barred Owls (Strix asio)
  • blue jays (Cyanocitta cristata)
  • red squirrels (Tamiasciurus hudsonicus)
  • northern flying squirrels (Glaucomys sabrinus)
  • yellow-bellied sapsucker (Sphyrapicus varius)
  • northern goshawk (Accipiter gentilis)
  • Cooper’s hawks (Accipiter cooperii)
  • sharp-shinned hawks (Accipiter striatus)
  • northern saw-whet owl (Aegolius acadicus)

Ecosys­tem Roles

Due to their ob­lig­ate brood par­a­sitic re­pro­duc­tive strat­egy, the re­pro­duc­tive ac­tiv­ity of brown-headed cow­birds af­fects many pop­u­la­tions of birds. Brown-headed cow­birds have 226 host species of all dif­fer­ent sizes, from war­blers that weigh 8 to 15 g, to black­birds that weigh over 100 g. How­ever, they reg­u­larly par­a­sitize only 132 species. The most com­monly uti­lized hosts in­clude yel­low war­blers, red-eyed vireos, song spar­rows, wood thrushes and com­mon yel­low throats. The re­pro­duc­tive suc­cess of these pop­u­la­tions can be se­verely af­fected be­cause par­a­sitized nests yield re­duced num­bers of host off­spring. This is caused by sev­eral cow­bird be­hav­iors in­clud­ing egg re­moval, egg punc­tur­ing and out-com­pet­ing host hatch­lings, in ad­di­tion to aban­don­ment of par­a­sitized nests by the host. (Or­tega, 1998; Roth­stein, 2004; Smith, et al., 2000)

Brown-headed cow­birds pose a threat to some en­dan­gered species. This has led to the de­vel­op­ment of pro­grams to con­trol their pop­u­la­tions. These pro­grams kill thou­sands of cow­birds an­nu­ally in an at­tempt to in­crease host pop­u­la­tions. Con­trol pro­grams have been uti­lized to pro­tect Kirt­land's war­blers, least bell's vireos, black-capped vireos and south­west­ern wil­low fly­catch­ers. While cow­birds have some part in re­duc­ing the pop­u­la­tions of en­dan­gered species, their ac­tual role is prob­a­bly not as large as it is por­trayed. Roth­stein (2004) sug­gests that cow­birds func­tion as a scape­goat be­cause en­dan­gered species pop­u­la­tions are most af­fected by the dis­ap­pear­ance of their nat­ural habi­tat due to ur­ban­iza­tion rather than by nest par­a­sitism. (Roth­stein, 2004)

• Ecosystem Impact
• disperses seeds
• parasite

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Brown-headed cow­birds help con­trol in­sect pop­u­la­tions that may be pests to hu­mans.

• Positive Impacts
• controls pest population

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Con­trol pro­grams ini­ti­ated to pro­tect en­dan­gered bird species from brown-headed cow­birds are costly. These con­trol pro­grams cost tax­pay­ers about one mil­lion dol­lars every year. (Roth­stein, 2004)

Con­ser­va­tion Sta­tus

There are large num­bers of brown-headed cow­birds across North Amer­ica. This is due to their suc­cess in the use of a brood par­a­sitic re­pro­duc­tive strat­egy and the ex­pan­sion of their habi­tats through farm­ing, de­for­esta­tion and ur­ban­iza­tion. (Or­tega, 1998)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Migratory Bird Act

  No special status

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

Brit­tany By­er­ley (au­thor), In­di­ana Uni­ver­sity-Pur­due Uni­ver­sity Fort Wayne, Mark Jor­dan (ed­i­tor), In­di­ana Uni­ver­sity-Pur­due Uni­ver­sity Fort Wayne, Leila Si­cil­iano Mar­tina (ed­i­tor), An­i­mal Di­ver­sity Web Staff.

Ref­er­ences

Cor­nell Uni­ver­sity. 2013. "Brown-headed Cow­bird" (On-line). The Cor­nell Lab of Or­nithol­ogy: All About Birds. Ac­cessed March 21, 2013 at http://​www.​allaboutbirds.​org/​guide/​Brown-headed_​Cowbird/​lifehistory.

Cox, W., F. Thomp­son, B. Root, J. Faaborg. 2012. De­clin­ing Brown-Headed Cow­bird (Molothrus ater) Pop­u­la­tions Are As­so­ci­ated with Land­scape-Spe­cific Re­duc­tions in Brood Par­a­sitism and In­creases in Song­bird Pro­duc­tiv­ity. PLoS ONE, 7/10: e47591. Ac­cessed May 17, 2013 at http://​www.​plosone.​org/​article/​info%3Adoi%2F10.​1371%2Fjournal.​pone.​0047591#​s1.

Dar­ley, J. 1982. Ter­ri­to­ri­al­ity and Mat­ing Be­hav­ior of the Male Brown-headed Cow­bird. The Con­dor, 84/1: 15-21.

Han­non, S., S. Wil­son, C. Mc­Cal­lum. 2009. Does cow­bird par­a­sitism in­crease pre­da­tion risk to Amer­i­can red­start nests?. Oikos, 118/7: 1035-1043.

Hoover, J., S. Robin­son. 2007. Re­tal­ia­tory Mafia Be­hav­ior by a Par­a­sitic Cow­bird Fa­vors Host Ac­cep­tance of Par­a­sitic Eggs. PNAS, 104/11: 4479-4483.

Lowther, P. 2003. "Brown-headed cow­bird (Molothrus ater)" (On-line). The Birds of North Amer­ica On­line. Ac­cessed March 20, 2013 at http://​bna.​birds.​cornell.​edu/​bna/​species/​047.

Ori­ans, G. 1961. The Ecol­ogy of Black­bird (Age­laius) So­cial Sys­tems. Eco­log­i­cal Mono­graphs, 31/3: 285-312.

Or­tega, C. 1998. Cow­birds and Other Brood Par­a­sites. USA: The Uni­ver­sity of Ari­zona Press.

Pe­ter­john, B., J. Sauer, S. Schwarz. 2000. Tem­po­ral and Ge­o­graphic Pat­terns in Pop­u­la­tion Trends of Brown-headed Cow­birds. Pp. 21-34 in J Smith, T Cook, S Roth­stein, S Robin­son, S Sealy, eds. Ecol­ogy and Man­age­ment of Cow­birds and Their Hosts. Austin: Uni­ver­sity of Texas Press.

Reilly, Jr (ed.), E., O. Pet­tingill, Jr (ed.). 1968. The Audubon Il­lus­trated Hand­book of Amer­i­can Birds. USA: Mc­Graw-Hill Book Com­pany.

Roth­stein, S. 2004. Brown-headed Cow­bird: Vil­lain or Scape­goat. Bird­ing, 36: 374-384.

Roth­stein, S., C. Farmer, J. Verner. 2000. The Struc­ture and Func­tion of Cow­bird Vo­cal­iza­tions and the Use of Play­backs to En­hance Cow­bird De­tectabil­ity: Re­la­tions to Po­ten­tial Cen­sus­ing Bi­ases. Pp. 69-80 in J Smith, T Cook, S Roth­stein, S Robin­son, S Sealy, eds. Ecol­ogy and Man­age­ment of Cow­birds and Their Hosts. Austin: Uni­ver­sity of Texas Press.

Roth­stein, S., S. Robin­son. 2000. Part I In­tro­duc­tion: Pop­u­la­tion Trends of Cow­birds and Hosts and Rel­e­vant Method­ol­ogy. Pp. 13-20 in J Smith, T Cook, S Roth­stein, S Robin­son, S Sealy, eds. Ecol­ogy and Man­age­ment of Cow­birds and Their Hosts. Austin: Uni­ver­sity of Texas Press.

Roth­stein, S., J. Verner, E. Steven. 1984. Ra­dio-Track­ing Con­firms a Unique Di­ur­nal Pat­tern of Spa­tial Oc­cur­rence in the Par­a­sitic Brown-headed Cow­bird. Ecol­ogy, 65/1: 77-88.

Roth­stein, S., D. Yokel, R. Fleis­cher. 1986. So­cial Dom­i­nance, Mat­ing and Spac­ing Sys­tems, Fe­male Fe­cun­dity, and Vocal Di­alects in Cap­tive and Free-Rang­ing Brown-headed Cow­birds. Cur­rent Or­nithol­ogy, 3: 127-185.

Smith, J., S. Sealy, T. Cook. 2000. Part II In­tro­duc­tion: Cow­bird Spac­ing Be­hav­ior, Host Se­lec­tion, and Neg­a­tive Con­se­quences of Par­a­sitism for Com­monly Used Hosts. Pp. 83-86 in J Smith, T Cook, S Roth­stein, S Robin­son, S Sealy, eds. Ecol­ogy and Man­age­ment of Cow­birds and Their Hosts. Austin: Uni­ver­sity of Texas Press.

Tacutu, R., T. Craig, A. Bu­dovsky, D. Wut­tke, G. Lehmann, D. Taranukha, J. Costa, V. Fraifeld, J. de Ma­g­a­l­haes. 2013. "AnAge entry for Molothrus ater" (On-line). AnAge: The An­i­mal Age­ing and Longevity Data­base. Ac­cessed March 21, 2013 at http://​genomics.​senescence.​info/​species/​entry.​php?​species=Molothrus_​ater.

Tekiela, S. 2000. Birds of In­di­ana Field Guide. Cam­bridge, Min­nesota: Ad­ven­ture Pub­li­ca­tions.

West, M., A. King, D. East­zer, J. Stad­don. 1979. A Bioas­say of Iso­late Cow­bird Song. Jour­nal of Com­par­a­tive and Phys­i­o­log­i­cal Psy­chol­ogy, 93/1: 124-133.