Index of Species Information

WILDLIFE SPECIES:  Molothrus ater


WILDLIFE SPECIES: Molothrus ater
AUTHORSHIP AND CITATION : Sullivan, Janet. 1995. Molothrus ater. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].

ABBREVIATION : MOAT COMMON NAMES : brown-headed cowbird cowbird buffalo bird TAXONOMY : The currently accepted scientific name for brown-headed cowbird is Molothrus ater (Boddaert) [4,57]. It is a member of the family Emberizidae [35]. The three recognized subspecies are as follows: M. a. ssp. ater, brown-headed cowbird M. a. ssp. obscurus, dwarf cowbird M. a. ssp. artemisiae, western or sagebrush cowbird [3,4,35]. Introgression between western and dwarf cowbirds has been occurring since contact in the 1930's in the Sierra Nevada. The size of western cowbirds in the area of overlap has been decreasing [21]. ORDER : Passeriformes CLASS : Bird FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


WILDLIFE SPECIES: Molothrus ater
GENERAL DISTRIBUTION : Breeding Range: The range of brown-headed cowbird extends from southeastern Alaska, northern British Columbia, southern Mackenzie District, northern Alberta, and north-central Saskatchewan; east to southern Manitoba and southern Newfoundland; south to central Florida, the Gulf Coast, and southern Texas; and south in Mexico to Oaxaca and northern Baja California [57]. Winter Range: The brown-headed cowbird winters from northern California, central Arizona, the Great Lakes States, and New England south to Mexico, the Gulf Coast, and southern Florida [11]. Ranges of subspecies are as follows: Brown-headed cowbird - Midwest and eastern United States Western cowbird - western states including California Dwarf cowbird - Great Basin and California [35]. ECOSYSTEMS : FRES10 White-red-jack pine FRES11 Spruce-fir FRES12 Longleaf-slash pine FRES13 Loblolly-shortleaf pine FRES14 Oak-pine FRES15 Oak-hickory FRES16 Oak-gum-cypress FRES17 Elm-ash-cottonwood FRES18 Maple-beech-birch FRES19 Aspen-birch FRES20 Douglas-fir FRES21 Ponderosa pine FRES22 Western white pine FRES23 Fir-spruce FRES24 Hemlock-Sitka spruce FRES25 Larch FRES26 Lodgepole pine FRES27 Redwood FRES28 Western hardwoods FRES29 Sagebrush FRES30 Desert shrub FRES31 Shinnery FRES32 Texas savanna FRES33 Southwestern shrubsteppe FRES34 Chaparral-mountain shrub FRES35 Pinyon-juniper FRES36 Mountain grasslands FRES37 Mountain meadows FRES38 Plains grasslands FRES39 Prairie FRES40 Desert grasslands FRES41 Wet grasslands FRES42 Annual grasslands FRES44 Alpine STATES :


BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 3 Southern Pacific Border 4 Sierra Mountains 5 Columbia Plateau 6 Upper Basin and Range 7 Lower Basin and Range 8 Northern Rocky Mountains 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 14 Great Plains 15 Black Hills Uplift 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : The brown-headed cowbird occurs in all or nearly all Kuchler types. SAF COVER TYPES : The brown-headed cowbird occurs in all or nearly all SAF types. SRM (RANGELAND) COVER TYPES : The brown-headed cowbird occurs in all or nearly all SRM types. PLANT COMMUNITIES : In Maryland and the District of Columbia, brown-headed cowbirds inhabit agricultural areas and adjacent woodlands [64]. In the central and southeastern oak (Quercus spp.)-pine (Pinus spp.) region, brown-headed cowbirds are common to abundant in all successional stages of central hardwood forest. They are present to common in loblolly pine (P. taeda)-shortleaf pine (P. echinata) stands in early stages of succession, but not present in mature loblolly-shortleaf pine stands [13]. In Kansas a census of floodplain tallgrass prairie taken from 1974 to 1988 revealed 15.4 brown-headed cowbirds per square mile (6/sq km) in the prairie, but less than 2.6 per square mile (1/sq km) in adjacent wetlands. In southwestern South Dakota brown-headed cowbirds are present in Rocky Mountain juniper (Juniperus scopulorum) communities where fields or grasslands were interspersed with shrubs or trees. Brown-headed cowbirds use closed deciduous woodlands (riparian areas) for reproductive activities [58]. In Texas on the Rio Grande plain, brown-headed cowbirds are common in thorn forests dominated by blackbrush (Acacia rigidula), guajillo (A. berlandieri), Texas persimmon (Diospyros texana), and other thorny shrubs. They are also present in adjacent grasslands and areas cleared of shrubs for agriculture and cattle grazing [69]. On the lower Colorado River in Arizona, the brown-headed cowbird was one of a number of granivores that reached their highest densities in common reed (Phragmites spp.) communities in fall, winter, and spring [1]. Brown-headed cowbirds are more numerous in riparian stands of Fremont cottonwood (Populus fremontii) than in nearby mesquite (Prosopis spp.) bosques or saltcedar (Tamarix ramosissima) stands [61]. In southern California brown-headed cowbirds sucessfully breed in chaparral communities [71]. In Washington shrub-steppe communities dominated by big sagebrush (Artemisia tridentata) and rubber rabbitbrush (Chrysothamnus nauseosus), brown-headed cowbirds occurred on 38.7 percent of transects. There was a positive correlation between observations of brown-headed cowbirds and big sagebrush cover. The presence of brown-headed cowbirds in this ecosystem is apparently recent. Shortly after settlement unbroken sagebrush and bunchgrass landscapes were rapidly degraded and fragmented by conversion to agriculture and cattle range, creating feeding habitat for brown-headed cowbirds [14]. REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Molothrus ater
TIMING OF MAJOR LIFE HISTORY EVENTS : Diurnal Activity: In the Sierra Nevada during the breeding season, brown-headed cowbirds spend the early morning hours in host-rich forests, then commute up to 2.7 miles (6.7 km) to prime feeding sites such as residential developments (especially where bird feeders are present) and horse corrals. Flocks of up to 30 brown-headed cowbirds may develop at feeding areas. Evening roosting behavior depends on locality. In the Sierra Nevada flocks of brown-headed cowbirds roost in willow (Salix spp.) thickets, away from both feeding and breeding areas. The flocks disperse to breeding areas in the early morning [51,70]. Spring Migration: The brown-headed cowbird is a short-distance migrant within North America. In the Northeast most brown-headed cowbirds travel 300 to 340 miles (800-850 km) between breeding season banding and winter recovery. Brown-headed cowbirds travel during the day, often as part of large mixed-species flocks with other blackbirds: red-winged blackbirds (Agelaius phoeniceus), common grackle (Quiscalus quiscula), European starling (Sturnus vulgaris), and, less frequently, Euphagus blackbirds and American robins (Turdus migratorius) [35]. In Maryland and the District of Columbia, spring movements of brown-headed cowbirds occur from February 5 to April 25, with a peak of activity from March 10 to April 10 [64]. Mating Systems and Pair Bonding: Brown-headed cowbird mating systems have been variously reported as monogamous, polygynous, and polygamous [35,51]. Rothstein and others [51] reviewed reports on mating systems and could come to no conclusion. Different mating systems may occur with different densities or sex ratios; males guard mates more frequently in low density populations. Pair bonding is difficult to assess due to the difficulty of defining a pair. Bonding may be brief or season-long [35]. Nesting: The brown-headed cowbird is a brood parasite; no nest is built and the eggs are laid in the nests of other birds (host species). In Maryland and the District of Columbia, brown-headed cowbirds lay eggs from late April to late July, with the peak from early May to early July. Extreme dates are April 24 and July 28 [64]. In Missouri brown-headed cowbirds eggs have been present in nests from mid-April until mid-July [35]. Nests: Female brown-headed cowbirds choose the nest, finding nests in one of three ways. They may perch in a hidden spot, watching for nest building activity in nearby open areas; walk on the ground watching for activity; or search noisily on short flights appearing to intentionally flush potential hosts from nests [35]. Preferred host nests have eggs present. Host eggs are usually of smaller volume than brown-headed cowbird eggs. Preferred nests are active; eggs are added on a daily basis by the host female. Large diameter (greater than 3 inches [7.6 cm]) closed nests are preferred over small diameter (less than 2 inches [5.1 cm]) open and closed nests. Large, open nests are least preferred. Clutch: Brown-headed cowbirds lay eggs in "sequences" of one to seven eggs (laid daily with pauses of 1 or more days between eggs) and rest periods of at least 2 days between sequences throughout the breeding season [54]. Incubation: Since incubation depends on host nesting activity it is difficult to assess; incubation may be as short as 10 days but is probably 11 to 12 days. Brown-headed cowbird eggs laid the same day as host eggs usually hatch first [35]. Development of Young: Brown-headed cowbird hatchlings are altricial and remain in the nest. Growth is rapid. Brown-headed cowbird nestlings emerge from the nest onto nearby branches at 8 to 13 days. Short flights are attempted at 11 days. Fledglings continue to be fed by host parents until 16 to 28 days after leaving the nest [35]. Territoriality: In the eastern Sierra Nevada, where both hosts and brown-headed cowbirds are widely dispersed on the breeding areas, there is no apparent territoriality. Elsewhere, such as in the eastern states where brown-headed cowbirds are moderately abundant and competition for host nests is higher, territorial defense is typical. At very high brown-headed cowbird densities, territoriality is apparently not cost effective and is rarely observed [51]. Resistant Hosts: Vireos (Vireo spp.) and some warblers (i.e., yellow warbler [Dendroica petechia]) cover brown-headed cowbird eggs with a new floor and lay their own eggs on top of it. Yellow-breasted chats (Icteria virens) abandon nests with foreign eggs [36]. American robins and gray catbirds (Dumetella carolinensis) usually eject foreign eggs from the nest. Instances of brown-headed cowbird nest parasitism in gray catbird nests apparently occur when the brown-headed cowbird egg is laid before a gray catbird has laid any of its own eggs and has learned to recognize its own eggs [34,36]. Fall Migration: On western slopes of the Sierra Nevada, juvenile brown-headed cowbirds began to form flocks as independence was achieved. The first independent juveniles appeared on July 14. In the same area all adult brown-headed cowbirds left between July 17 and July 21. In Maryland and the District of Columbia, fall movements occur from August 15 to December 10, with peak activity from September 25 to November 1 [64]. Roosting Behavior: In the nonbreeding season, brown-headed cowbirds spend the night in large mixed-species roosts with other blackbirds [40]. Mixed-species roosts in Kentucky may be as large as 5 million birds, 2 to 5 percent of which are usually brown-headed cowbirds. Oklahoma roost numbers peak in November with 250 to 900 thousand birds [35]. Demography: Males are sexually mature at 1 year but rarely copulate until they are 2 years old. Females breed at 1 year [35]. Female brown-headed cowbirds may lay up to 40 eggs in a season [52]. Stable populations of brown-headed cowbirds would be maintained by 2.5 percent survival rate and lifetime fecundity of 80 eggs per female. Annual adult survivorship is 48.5 percent for males and 40.4 percent for females. The longevity record is 15 years, 10 months for a banded male [35]. Mortality Factors: Lowther [35] reviewed reports of ectoparasites, helminth parasites, and infectious bacteria in brown-headed cowbirds. PREFERRED HABITAT : Brown-headed cowbirds prefer open habitats of low or scattered trees interspersed with grasslands; they usually avoid unbroken forest. They prefer, and may require, areas of short grass or bare ground for foraging [50]. Open coniferous and deciduous woodlands, forest edges, brushy thickets, agricultural land, and suburban areas are all acceptable brown-headed cowbird habitat [11,24]. In the Sierra Nevada brown-headed cowbirds are largely or completely absent from extensive stands of old-growth forest. They are rare in meadow and riparian areas more than 16 miles (10 km) from centers of human activities. In areas close to human activities, brown-headed cowbirds were observed in meadow-edge communities more often than in clearcuts, partially logged forests, or uncut forests [70]. In Saskatchewan aspen (Populus spp.) parklands, brown-headed cowbird abundance increased with increasing grove size; however, brown-headed cowbirds occupied even very small groves [29]. In the western states the brown-headed cowbird is more abundant in second-growth than in old-growth forests, and more abundant in stands surrounded by a large amount of open land [25]. In North Dakota mixed-grass prairie, brown-headed cowbird density was higher on plots with shrubs present than on shrubless plots [5]. In Texas loblolly pine plantations less than 10 years old, brown-headed cowbirds were more abundant on plots with snags than on snagless plots [12]. In Pennsylvania a mosaic of even-aged aspen stands (various ages) and mixed-oak stands (either mature or early successional) was assessed for use of edges by birds. In mature aspen stands, there was no difference between brown-headed cowbird use of edge and interior. In stands that were cut less than 10 years prior to the survey, brown-headed cowbirds only occupied edges, and they were not present in recently cut (less than 2 years) stands. In mature oak stands, brown-headed cowbird use was confined largely to edges; in stands cut less than 10 years prior to the survey a few brown-headed cowbirds were observed in the interior and none on the edges [72]. COVER REQUIREMENTS : Female brown-headed cowbirds use perches to spot potential host nests; areas with hidden perches are preferred (i.e., shrubs in grass-dominated communities) [35]. In Ohio autumn roosts were usually in dense stands of deciduous trees on moist soils; tree crowns were generally narrow, vertical, and dense [40]. In the Southeast brown-headed cowbirds commonly roost in thickets [24]. FOOD HABITS : The brown-headed cowbird is a ground gleaner, consuming weed seeds, grass seeds, waste grain, and insects. Historically it may have depended on grazing by large ungulates to create suitable feeding conditions. A common foraging technique is to follow large grazing animals, gleaning seeds and the insects stirred up by the feet of the grazer [11,39,35]. Brown-headed cowbirds also feed on insects present on large ungulates; they have been observed walking on resting bison (Bison bison), picking insects from the hide [39]. In the northeastern United States plant foods common in brown-headed cowbird diets include seeds of bristle grasses (Setaria spp.), ragweeds (Ambrosia spp.), oats (Avena spp.), corn (Zea mays), crab grasses (Digitaria spp.), knotweeds and smartweeds (Polygonum spp.), paspalums (Paspalum spp.), and sheepsorrel (Rumex spp.). In the Southeast plant foods include seeds of bristle grasses, panic grasses (Panicum spp.), ragweeds, oats, wheat (Triticum spp.), doveweeds (Croton spp.), corn, and paspalums [36]. A summary of several dietary studies reveals that approximately 75 percent of the brown-headed cowbird diet is weed seeds; grasshoppers and beetles form the larger part of the remaining 25 percent of the diet [35]. PREDATORS : In northeastern Arkansas short-eared owl (Asio flammeus) pellets contained brown-headed cowbird remains [60]. Predators on fledglings include black racer (Coluber constictor), black rat snake (Elaphe obsoleta), and blue jay (Cyanocitta cristata). Brown-headed cowbirds join in mobbing great horned owls (Bubo virginianus), a potential predator of both adults and young [35]. MANAGEMENT CONSIDERATIONS : Range Expansion: Historically brown-headed cowbirds were largely confined to the mid-continental prairies where they presumably followed herds of nomadic bison, and perhaps pronghorn (Antilocapra americana) and elk (Cervus canadensis) as well [46]. The brown-headed cowbird underwent a rapid range expansion with habitat alterations due to forest clearing, domestic cattle grazing, urbanization, and conversion of forested habitats to agricultural land [46]. It invaded the Great Lakes States and the Northeast during the nineteenth century [44]. Root and Weckstein [49] reported that brown-headed cowbird winter range has recently expanded into Maine and Nova but has contracted elsewhere, particularly Pennsylvania, Michigan, Wisconsin, Iowa, Montana, and Washington. He speculated that the trapping of brown-headed cowbirds in Michigan (for preservation of the Kirtland's warbler [Dendroica kirtlandii]) that removed more than 40,000 brown-headed cowbirds was partly responsible for this unexpected phenomenon. Breeding Bird Survey (BBS) data from 1965 to 1979 indicate that brown-headed cowbirds have been increasing in the Southeast, including the Carolinas and southern Georgia [44]. Colonization of the Sierra Nevada by brown-headed cowbirds has taken place in the last 50 years [51]. Expansion into the western states is due largely to rapid colonization by dwarf cowbirds [32,50]. Rothstein [50] stated that the separation of breeding and feeding areas has allowed much of this range expansion. Since brown-headed cowbirds can commute up to 3 miles (7 km) between breeding areas and feeding areas, creation of feeding habitat (i.e., pack stations, horse corrals, suburban developments, and bird feeders) within formerly continuous forest has opened new areas for brown-headed cowbird breeding [50]. In the Sierra Nevada brown-headed cowbird numbers dropped sharply with distance from pack stations; they were always present when horses were present [70]. Population Status: Estimates of the North American population of brown-headed cowbirds range from 20 to 40 million individuals [63]. Graber and Graber [76] estimated the 1957 brown-headed cowbird population of Illinois as 1.1 million. The estimated brown-headed cowbird population in North Dakota in 1972 was approximately 1 million, with a maximum density of 15.2 pairs per square mile (5.9 pairs/sq km) [63]. Brown-headed cowbird populations have increased throughout the twentieth century in most sections of the United States. In the Northeast, brown-headed cowbirds have experienced a statistically significant population decrease [59]. A ranking system for neotropical migrants (including brown-headed cowbird) listed the population trend for brown-headed cowbird in Alaska as unknown (no data), decreasing in Arizona (uncertain due to small size of the BBS), slightly increasing in Idaho (also uncertain due to small BBS sample), and sharply increasing in Montana [75]. In Oregon brown-headed cowbird populations increased in juniper woodlands between 1899 and 1983, although they decreased significantly statewide [35,55]. In the Sierra Nevada brown-headed cowbird populations increased between 1966 and 1985 [43]. Breeding Bird Survey data for the Midwest suggest a decrease in brown-headed cowbird populations for the period 1966 to 1981, but an increase from 1982 to 1991 [66]. Significant population increases (BBS data 1966-1987) occurred in Georgia, North Carolina, Iowa, North Dakota, Utah, and Colorado. Significant decreases occurred in Minnesota, Michigan, Wisconsin, New York, Rhode Island, Ohio, Ontario, West Virginia, Tennessee, New Brunswick, Oklahoma, and Texas [35]. Another interpretation of BBS data indicates a generally negative trend for the United States but a sharply increasing trend for Illinois during the period 1966 to 1991 [26]. Host Species: Because of range expansion the brown-headed cowbird has come into recent contact with many new potential host species, most of which lack defenses against nest parasitism. Numbers of parasitized species have increased in the last half century; new parasitism records for species continue to be reported making estimation of the number of parasitized species difficult. Stewart and Robbins [64] listed 223 parasitized species in the United States. In their area (Maryland and the District of Columbia), the species most heavily parasitized were red-eyed vireo (Vireo olivaceous), song sparrow (Melospiza melodia), and chipping sparrow (Spizella passerina) [64]. In 1985, Friedmann and Kiff [73] listed 240 species known to be parasitized, the majority of which are neotropical migrant songbirds. Lowther [35] reported that 144 species have actually reared brown-headed cowbird young. Over the entire United States the top 17 species with over 100 records of fledged brown-headed cowbirds are yellow warbler, song sparrow, red-eyed vireo, chipping sparrow, eastern phoebe (Sayornis phoebe), rufous-sided towhee (Pipilo erythrophthalmus), ovenbird (Seiurus aurocappilus), common yellowthroat (Geothylpis trichas), American redstart (Setophaga ruticilla), indigo bunting (Passerina cyanea), yellow-breasted chat, red-winged blackbird, Kentucky warbler (Oporomis formosis), willow flycatcher (Empidonax traillii), Bell's vireo (Vireo bellii), yellow-throated vireo (V. flavescens), and field sparrow (Spizella pusilla) [35] Brown-headed cowbirds reduce host productivity because 1) females remove one egg from 33 to 90 percent of host nests, 2) brown-headed cowbird eggs are thick-shelled, often causing breakage of host eggs, 3) brown-headed cowbird eggs have a shorter incubation period than those of host species, 4) host nestlings are usually smaller and less aggressive than brown-headed cowbird nestlings, and 5) brown-headed cowbird nestlings grow more rapidly, beg louder, and have larger gapes (bigger mouths) than host nestlings [46]. Threats to Endangered Species: Brown-headed cowbird parasitism is one of the variables used in a scoring method to determined species prioritization for songbird conservation [28]. Several neotropical migrant songbirds with restricted ranges are endangered at least partly as a result of brown-headed cowbird nest parasitism, including Kirtland's warbler [37,48], Bell's vireo [42,48], golden-cheeked warbler (Dendroica chrysoparia) [48], black-capped vireo (V. atricapillus), and willow flycatcher [46,48,53]. The precise effect of nest parasitism on willow flycatcher has not been clearly established, however. For willow flycatcher and most of the other endangered species affected by brown-headed cowbird parasitism, there is a complex interaction between direct effects due to habitat loss and indirect effects related to nest parasitism [50]. Threat to Other Species: Brown-headed cowbirds pose a potential threat to many neotropical migrant songbirds. Brown-headed cowbirds feed mostly in short grass communities including shortgrass prairie, pastures, and lawns; and on bare ground. Feeding areas are enhanced by human activities [46]. At least 10 species of songbirds have declined since brown-headed cowbirds have expanded their range into California, possibly due to brown-headed cowbird nest parasitism [50]. On the western slopes of the Sierra Nevada, no host species is immediately threatened, but increased human use of backcountry areas and increased fragmentation of dense forests will increase potential feeding areas for brown-headed cowbirds [70]. Low intensity monitoring for neotropical migrant conservation may include checks for cowbird parasitism every 3 years in management areas; monitoring is recommended for the western Sierra Nevada [15,70]. Airola [2] recommended that any development activities should be far from the highest densities of potential host species. Parasitism Rates and Habitat Parameters: Brown-headed cowbird nest parasitism has been enhanced by shifts in agricultural practice and farmland structure in this century. There is a higher rate of brown-headed cowbird parasitism near field edges with elevated perches than away from field edges and perches [48]. Brown-headed cowbirds are often more abundant on edges than in interior. Parasitism rates are higher near forest edges and edges of prairie fragments [19]. In the eastern deciduous forest, numbers of brown-headed cowbirds and rates of parasitism decrease with distance from forest edges [9]. According to Brittingham and Temple [9] forest fragmentation leads to higher levels of nest parasitism by increasing the ratio of forest edge to forest interior (defined as area more than 990 feet [300 m] from an edge). In the Midwest brown-headed cowbird parasitism is negatively correlated with forest cover [47]. Nest parasitism is low (less than 10% of all potential host nests) in extensively forested sections of Mark Twain and Hoosier National Forests (Missouri and Indiana, respectively) [46]. However, Robinson and others [47] reported that in a highly fragmented landscape with a long history of brown-headed cowbird presence, there was no appreciable decline in nest parasitism even more than 2,310 feet (700 m) from the nearest edge. They speculated that in this area, brown-headed cowbirds have saturated all available host nests because brown-headed cowbird populations are high and host populations are minimal. In addition, brown-headed cowbird populations in the most highly fragmented areas may be more limited by host availability than feeding sites or forest density [47]. In western states and particularly in the Sierra Nevada, availability of local feeding areas such as livestock corrals and pack stations is associated with increased levels of brown-headed cowbird nest parasitism [46]. Bock and others [8] listed the brown-headed cowbird as either unresponsive or showing mixed or uncertain response to grazing in grasslands in the western states but showed a positive response to domestic cattle grazing in shrub-steppe communities. Robinson and others [46] concluded the magnitude of edge effect on brown-headed cowbird parasitism rates varies within and among regions in relation to landscape level variation in fragmentation and brown-headed cowbird abundance. Management Recommendations/Cowbird Control: Methods for removal of brown-headed cowbirds from critical breeding habitat for neotropical migrants include trapping and shooting individuals, and roost kills. The use of baited decoy traps to capture and kill female brown-headed cowbirds has reduced the rate of nest parasitism and increased nesting success for a few species. It is thought that this action was the key element in stabilizing populations of Kirtland's warbler [38,46]. In 1971 Mayfield [37] predicted that the Kirtland's warbler would be extinct by 1980 if brown-headed cowbirds were not controlled. An extensive program of trapping and shooting of brown-headed cowbirds was initiated in 1972. The Kirtland's warbler population did not rebound, but remained stabilized (with very low levels of nest parasitism) until there was a slight population increase in 1991 and 1992 [38]. In other cases use of decoys and shooting of female brown-headed cowbirds has effectively reduced nest parasitism rates [32,46]. Removal of brown-headed cowbirds from riparian habitats occupied by Bell's vireos has resulted in increased Bell's vireo productivity [22]. It is not clear whether brown-headed cowbird trapping at the landscape level would reduce nest parasitism in extensively fragmented landscapes such as the Midwest. Large-scale elimination of brown-headed cowbirds at winter roosts may reduce overall numbers of brown-headed cowbirds, but this approach may not affect target songbird populations in breeding habitats. Winter banding programs are needed to determine movements of brown-headed cowbirds and the feasibility of winter trapping for population reduction in critical areas [32]. The ethical implications of large-scale eradication of the brown-headed cowbird, a native songbird, need to be considered [46]. The brown-headed cowbird is protected under the Migratory Bird Treaty Act [68]. Trapping and killing female brown-headed cowbirds is at best a temporary solution to excessive nest parasitism. The most complete solution is landscape level management including consolidation of ownership to preserve large tracts of forest, reduction or elimination of brown-headed cowbird feeding areas within large tracts, and minimization of edge [47]. Shape of forest tracts influences the ratio of edge to interior. Long narrow areas like riparian woodlands have very little interior area. Forest tracts in simple square or circle shapes have the greatest interior to edge ratios [19]. Riparian corridors need to be wide [46]. In the case of willow flycatcher in California, protection of high-elevation riparian areas and meadows from grazing and/or pack animals is recommended to reduce the threat of brown-headed cowbird parasitism [53]. Laymon [32] recommended elimination of grazing near riparian areas and removal of feedlots, stables, and dairies in critical areas, and reforestation of riparian areas. Robbins and others [45] suggested that in the mid-Atlandtic States, 7,410 acres (3,000 ha) of contiguous forest is the minimum required for population maintenance of other songbirds in the presence of brown-headed cowbird parasitism. Data from moderately fragmented areas of the Midwest suggest that 49 thousand to 1.2 million acres (20,000-50,000 ha) may be necessary. In Texas the Biological Advisory Team [74] suggested that 4,940 to 12,700 acres (2,000-5,000 ha) are needed to minimize the effects of brown-headed cowbird parasitism on the golden-cheeked warbler [46]. REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Molothrus ater
DIRECT FIRE EFFECTS ON ANIMALS : There were no references in the literature concening direct or indirect mortality of brown-headed cowbirds due to fire. Adults could easily escape fire. Nests and young are vulnerable to fire but unlikely to be exposed to fire because in most areas fire seasons are not coincident with early nesting seasons. Literature references are mostly on the topic of bird use of recently burned versus unburned plots. Brown-headed cowbird use of burns is likely to be related to food availability and availability of perches. It is also likely to be related to the presence of host species nests. In Connecticut a 1982 census revealed that brown-headed cowbirds were more abundant on old fields that had been burned in spring of 1981 than on unburned fields. Vegetation in these plots consisted of shrubs and saplings (mostly red maple [Acer rubrum]) [17]. In Kansas a survey of birds was made on successional (i.e., undisturbed) plots dominated by shrubs and prairie plots dominated by grasses that had been mowed and burned. Brown-headed cowbirds occurred only on the shrub plots; none were observed on the mowed and burned plots. There was an extreme drop in the numbers of other bird species on the mowed and burned plots as well [10]. On the Curtis Prairie, Wisconsin, there was little difference between brown-headed cowbird recapture rates on unburned plots and on recently burned plots [33]. In South Dakota a prescribed fire was conducted in mixed-grass prairie in May 1983. A bird census was conducted on the burned area and on an adjacent unburned area in June and July of the same year. Brown-headed cowbirds were observed on both burned and unburned areas with no significant differences in numbers of observations [27]. In Arizona an October 1973 census of nonbreeding birds in ponderosa pine (Pinus ponderosa) stands showed brown-headed cowbirds with a slightly higher prominence value (product of number of individuals and frequency of occurrence) on unburned plots than on plots that had been burned by wildfire in May 1972 [7]. HABITAT RELATED FIRE EFFECTS : Effects of Fire Exclusion: Fire exclusion in mixed-grass prairie has allowed shrubs to invade grasslands. In North Dakota brown-headed cowbird density was higher on shrubby plots than on shrubless plots [5]. FIRE USE : NO-ENTRY REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Molothrus ater
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