Dolichonyx oryzivorus - (Linnaeus, 1758)
Bobolink
Other English Common Names: bobolink
Other Common Names: Triste-Pia
Taxonomic Status: Accepted
Related ITIS Name(s): Dolichonyx oryzivorus (Linnaeus, 1758) (TSN 179032)
French Common Names: goglu des prés
Spanish Common Names: Tordo Arrocero, Charlatán
Unique Identifier: ELEMENT_GLOBAL.2.102736
Element Code: ABPBXA9010
Informal Taxonomy: Animals, Vertebrates - Birds - Perching Birds
Image 10701

© Dick Cannings

 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Passeriformes Icteridae Dolichonyx
Genus Size: A - Monotypic genus
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Concept Reference
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Concept Reference: American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.
Concept Reference Code: B98AOU01NAUS
Name Used in Concept Reference: Dolichonyx oryzivorus
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 07Apr2016
Global Status Last Changed: 04Dec1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Reasons: Large nesting range in North America; many subpopulations; nesting range expanded with historical anthropogenic habitat changes; large population size, but has declined over the past several decades, likely due to incompatible agricultural practices in the nesting range and probably also in the winter range.
Nation: United States
National Status: N5B (19Mar1997)
Nation: Canada
National Status: N5B,N4N5M (15Jan2018)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (SNRM), Arizona (S1), Arkansas (SNA), California (SNA), Colorado (S3B), Connecticut (S3B), Delaware (SU), District of Columbia (S3S4N), Florida (SNA), Georgia (SNRN), Idaho (S2B), Illinois (S4), Indiana (S4B), Iowa (S4B), Kansas (S1B), Kentucky (S2S3B), Louisiana (SNA), Maine (S4B), Maryland (S3S4B), Massachusetts (S3S4B), Michigan (S4), Minnesota (SNRB), Missouri (S3), Montana (S3B), Navajo Nation (SNA), Nebraska (S4), Nevada (S3B), New Hampshire (S4B), New Jersey (S2B,S3N), New Mexico (S1B,S3N), New York (S5B), North Carolina (S1B), North Dakota (SNRB), Ohio (S4), Oklahoma (S2N), Oregon (S2B), Pennsylvania (S4B), Rhode Island (S3B), South Carolina (SNA), South Dakota (S4B), Tennessee (SHB,S4N), Texas (S3), Utah (S2B), Vermont (S5B), Virginia (S1B), Washington (S2S3B), West Virginia (S3B), Wisconsin (S2S3B), Wyoming (S2)
Canada Alberta (S2B), British Columbia (S3B), Manitoba (S4B), New Brunswick (S3B,S3M), Newfoundland Island (S1B,SUM), Nova Scotia (S3S4B), Ontario (S4B), Prince Edward Island (S2B), Quebec (S3), Saskatchewan (S5B)

Other Statuses

Canadian Species at Risk Act (SARA) Schedule 1/Annexe 1 Status: T (02Nov2017)
Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Threatened (25Apr2010)
Comments on COSEWIC: Reason for designation: Over 25% of the global population of this grassland bird species breeds in Canada, which is the northern portion of its range. The species has suffered severe population declines since the late 1960's and the declines have continued over the last 10 years, particularly in the core of its range in Eastern Canada. The species is threatened by incidental mortality from agricultural operations, habitat loss and fragmentation, pesticide exposure and bird control at wintering roosts.

Status history: Designated Threatened in April 2010.

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: 200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Range Extent Comments: Breeding range extends from southern British Columbia across southern Canada to Nova Scotia and Newfoundland, south to central Washington, eastern Oregon, northern Utah, Kansas, Illinois, Ohio, southern Pennsylvania, and central New Jersey, locally to north-central Kentucky, western North Carolina, and western Maryland (AOU 1998). During the northern winter, the range is in central and southern South America, mainly from Peru, eastern Bolivia, and central Brazil to northern Argentina (Stiles and Skutch 1989, Martin and Gavin 1995, AOU 1998); mostly in the pampas of southwestern Brazil, Paraguay, and Argentina (Ridgely and Tudor 1989, Martin and Gavin 1995). Birdlife International estimate is 900,000 square kilometers.

Area of Occupancy: >12,500 4-km2 grid cells
Area of Occupancy Comments: With its large population size of 8,000,000, this species should easily occupty 20,000 square kilometers, which would be 400 birds per square kilometer.

Number of Occurrences: 81 to >300
Number of Occurrences Comments: This species is represented by a large number of occurrences (subpopulations), with an estimated global population of 8 million individuals (Partners in Flight, 2013) and a range encompassing the entire width of the northern half of the U.S. and southern portion of Canada (Birdlife International, 2014).

Population Size: >1,000,000 individuals
Population Size Comments: Total adult population size is unknown but certainly exceeds 1,000,000. Rich et al. (2004) estimated population size at 11,000,000. Concentrations of ~140,000 bobolinks have been observed in Bolivia (Renfrew and Saavedra 2007). The latest Partners in Flight (2013) estimate is 8 million individuals.

Number of Occurrences with Good Viability/Integrity: Many to very many (41 to >125)
Viability/Integrity Comments: The number of occurrences with at least good estimated viability is uncertain but likely exceeds 40.

Overall Threat Impact: High
Overall Threat Impact Comments: Primary threat in the breeding range is habitat loss (Herkert 1997). Declines in some areas have been attributed to decrease in hayfield area, earlier and more frequent hay-cropping, and shift from timothy and clover to alfalfa; earlier, agricultural practices that converted wooded land to open land resulted in an increase in range (Bollinger et al. 1990, Bollinger and Gavin 1992).

Hay-cropping destroyed 16-23% of the yearly production of fledglings in upstate New York, with up to 29-45% in an area with intensive dairy farming (Bollinger et al. 1990; Bollinger, pers. comm.).

Bobolinks generally are considered to be an uncommon (Friedmann 1963, Martin and Gavin 1995) or rare (Martin 1967) host of the brown-headed cowbird.

Scope and severity of threats in the winter range are not well documented (Martin and Gavin 1995), but habitat loss is a significant concern in Argentina (Di Giacomo et al. 2005). Bobolink populations in winter in Bolivia face conservation threats because of the degree to which they concentrate in rice production regions, their status as a pest, and the pesticides currently used on rice (Renfrew and Saavedra 2007).

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: Breeding Bird Survey (BBS) data for 1980-2007 indicate a significant decline averaging 3.0% per year; this rate of decline amounts to a 26% decline over 10 years. Three generations probably is roughly 15 years; a 3% annual decline over 15 years amounts to a 37% decline over an estimated three generations. However, BBS counts have been highly variable over the past 15 years, and the trend for that period appears to be a very small decline. Abundance declined much more steeply in the 1980s. The latest BBS data has a 1.32% annual decline from 2002 - 2013, which translates to an decline of slightly less than 15% (Sauer, et. al. 2014).

Long-term Trend: Decline of 50-70%
Long-term Trend Comments: Long-term trend (past 200 years) in unknown. Much habitat appears to have been lost in some areas due to intensive agriculture, but on the other hand the species likely increased its range with historical deforestation and agricultural development in eastern North America and with development and expansion of irrigated agriculture in the west (Martin and Gavin 1995).

Winter range in Argentina has decreased by at least 25% (Di Giacomo et al. 2005).

Breeding Bird Survey (BBS) data for 1966-2007 indicate a significant decline averaging 1.8 percent per year; this amounts to a 53% decline for the time period. BBS abundance (average number of birds per route) reclined from around 6 in the late 1960s and early 1970s to 3-4 in 2000-2007.

BBS data for 1966-2003 indicates widepsread declines throughout most of the range, with increasing trends that are much more geographaically restricted and mostly in the north-central United States. The latest BBS data (Sauer, et. al. 2014) shows a 2.17% annual decline from 1996 - 2012, which translates to a 63% decline.

Intrinsic Vulnerability: Moderately vulnerable to not intrinsically vulnerable.
Intrinsic Vulnerability Comments: Not usually vulnerable but its flocking behavior may concentrate birds which could lead to rapid popuolation declines if efficient methods of removing this bird from areas are developed (Martin and Gavin, 1995).

Environmental Specificity: Broad. Generalist or community with all key requirements common.
Environmental Specificity Comments: This bird has shown an ability to changing environmental conditions brought about my humans (Martin and Gavin, 1995).

Other NatureServe Conservation Status Information

Inventory Needs: Not needed at this time

Protection Needs: A probable factor on wintering grounds in South America, where species is considered a pest of agricultural crops and where males are sold in local pet trade (Martin and Gavin, 1995).

Distribution
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Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) Breeding range extends from southern British Columbia across southern Canada to Nova Scotia and Newfoundland, south to central Washington, eastern Oregon, northern Utah, Kansas, Illinois, Ohio, southern Pennsylvania, and central New Jersey, locally to north-central Kentucky, western North Carolina, and western Maryland (AOU 1998). During the northern winter, the range is in central and southern South America, mainly from Peru, eastern Bolivia, and central Brazil to northern Argentina (Stiles and Skutch 1989, Martin and Gavin 1995, AOU 1998); mostly in the pampas of southwestern Brazil, Paraguay, and Argentina (Ridgely and Tudor 1989, Martin and Gavin 1995). Birdlife International estimate is 900,000 square kilometers.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The maps for birds represent the breeding status by state and province. In some jurisdictions, the subnational statuses for common species have not been assessed and the status is shown as not-assessed (SNR). In some jurisdictions, the subnational status refers to the status as a non-breeder; these errors will be corrected in future versions of these maps. A species is not shown in a jurisdiction if it is not known to breed in the jurisdiction or if it occurs only accidentally or casually in the jurisdiction. Thus, the species may occur in a jurisdiction as a seasonal non-breeding resident or as a migratory transient but this will not be indicated on these maps. See other maps on this web site that depict the Western Hemisphere ranges of these species at all seasons of the year.
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MT, NC, ND, NE, NH, NJ, NM, NN, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY
Canada AB, BC, MB, NB, NF, NS, ON, PE, QC, SK

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at www.natureserve.org/conservation-tools/data-maps-tools.

Range Map Compilers: NatureServe, 2002; WILDSPACE 2002


U.S. Distribution by County Help
State County Name (FIPS Code)
AZ Apache (04001), Gila (04007)
CT Fairfield (09001), Hartford (09003), Litchfield (09005), Middlesex (09007), New Haven (09009), New London (09011), Tolland (09013), Windham (09015)
DE New Castle (10003)
ID Oneida (16071)
KS Atchison (20005), Barton (20009), Cowley (20035), Jefferson (20087), Lyon (20111), Riley (20161), Stafford (20185)
KY Bourbon (21017), Boyle (21021), Clark (21049), Fayette (21067), Henry (21103), Jessamine (21113), Mercer (21167), Oldham (21185), Shelby (21211), Woodford (21239)
MI Mecosta (26107)
MO Harrison (29081), Johnson (29101), Mercer (29129)
MT Beaverhead (30001), Big Horn (30003), Blaine (30005), Broadwater (30007), Carbon (30009), Carter (30011), Cascade (30013), Chouteau (30015), Custer (30017), Daniels (30019), Dawson (30021), Fallon (30025), Fergus (30027), Flathead (30029), Gallatin (30031), Granite (30039), Jefferson (30043), Judith Basin (30045), Lake (30047), Lewis and Clark (30049), Liberty (30051), Madison (30057), Meagher (30059), Missoula (30063), Park (30067), Petroleum (30069), Phillips (30071), Powell (30077), Ravalli (30081), Richland (30083), Roosevelt (30085), Sanders (30089), Sheridan (30091), Stillwater (30095), Sweet Grass (30097), Teton (30099), Valley (30105), Wibaux (30109), Yellowstone (30111)
NC Ashe (37009), Haywood (37087), Henderson (37089), Transylvania (37175), Watauga (37189)
NJ Bergen (34003), Burlington (34005), Cape May (34009), Cumberland (34011), Gloucester (34015), Hudson (34017), Hunterdon (34019), Mercer (34021), Middlesex (34023), Monmouth (34025), Morris (34027), Salem (34033), Somerset (34035), Sussex (34037), Warren (34041)
OH Harrison (39067), Lake (39085), Portage (39133), Trumbull (39155), Wayne (39169)
OR Baker (41001)*, Grant (41023)*, Harney (41025), Lake (41037)*, Malheur (41045)*, Union (41061)*
UT Box Elder (49003), Cache (49005), Davis (49011), Morgan (49029), Rich (49033), Salt Lake (49035), San Juan (49037)*, Summit (49043), Tooele (49045)*, Uintah (49047)*, Utah (49049), Wasatch (49051), Weber (49057)
VA Highland (51091), Loudoun (51107), Pulaski (51155), Roanoke (51161), Russell (51167), Tazewell (51185), Warren (51187)
WA Pend Oreille (53051)+, Stevens (53065)+
WV Grant (54023), Monongalia (54061), Ohio (54069), Pendleton (54071), Preston (54077), Tucker (54093)
WY Campbell (56005), Carbon (56007)*, Crook (56011), Fremont (56013)*, Johnson (56019), Natrona (56025)*, Park (56029)*, Sheridan (56033), Sublette (56035), Sweetwater (56037)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
01 Lower Connecticut (01080205)+, Farmington (01080207)+, Quinebaug (01100001)+, Shetucket (01100002)+, Thames (01100003)+, Quinnipiac (01100004)+, Housatonic (01100005)+, Saugatuck (01100006)+
02 Rondout (02020007)+, Hackensack-Passaic (02030103)+, Sandy Hook-Staten Island (02030104)+, Raritan (02030105)+, Middle Delaware-Mongaup-Brodhead (02040104)+, Middle Delaware-Musconetcong (02040105)+, Crosswicks-Neshaminy (02040201)+, Lower Delaware (02040202)+, Brandywine-Christina (02040205)+, Cohansey-Maurice (02040206)+, Great Egg Harbor (02040302)+, South Branch Potomac (02070001)+, North Branch Potomac (02070002)+, Shenandoah (02070007)+, Middle Potomac-Catoctin (02070008)+, Upper James (02080201)+
03 Upper Roanoke (03010101)+
04 Muskegon (04060102)+, Ashtabula-Chagrin (04110003)+
05 Upper Monongahela (05020003)+, Cheat (05020004)+, Mahoning (05030103)+, Upper Ohio-Wheeling (05030106)+, Tuscarawas (05040001)+, Walhonding (05040003)+, Upper New (05050001)+, Middle New (05050002)+*, South Fork Licking (05100102)+, Lower Kentucky (05100205)+, Silver-Little Kentucky (05140101)+, Salt (05140102)+
06 North Fork Holston (06010101)+*, Watauga (06010103)+, Upper French Broad (06010105)+, Pigeon (06010106)+, Upper Clinch (06010205)+
10 Beaverhead (10020002)+, Ruby (10020003)+, Big Hole (10020004)+, Jefferson (10020005)+, Madison (10020007)+, Gallatin (10020008)+, Upper Missouri (10030101)+, Upper Missouri-Dearborn (10030102)+, Smith (10030103)+, Sun (10030104)+, Belt (10030105)+, Marias (10030203)+, Willow (10030204)+, Teton (10030205)+, Bullwhacker-Dog (10040101)+, Arrow (10040102)+, Judith (10040103)+, Fort Peck Reservoir (10040104)+, Upper Musselshell (10040201)+, Flatwillow (10040203)+, Box Elder (10040204)+, Middle Milk (10050004)+, Big Sandy (10050005)+, Sage (10050006)+, Cottonwood (10050010)+, Whitewater (10050011)+, Lower Milk (10050012)+, Rock (10050015)+, Porcupine (10050016)+, West Fork Poplar (10060004)+, Charlie-Little Muddy (10060005)+, Big Muddy (10060006)+, Brush Lake closed basin (10060007)+, Yellowstone Headwaters (10070001)+, Upper Yellowstone (10070002)+, Shields (10070003)+, Stillwater (10070005)+, Clarks Fork Yellowstone (10070006)+, Upper Yellowstone-Pompeys Pillar (10070007)+, Pryor (10070008)+, Lower Wind (10080005)+*, Badwater (10080006)+*, Greybull (10080009)+*, South Fork Shoshone (10080013)+*, Shoshone (10080014)+, Upper Tongue (10090101)+, Upper Powder (10090202)+, Clear (10090206)+, Lower Yellowstone (10100004)+, O'fallon (10100005)+, Upper Little Missouri (10110201)+, Beaver (10110204)+, Upper Belle Fourche (10120201)+, Lower Belle Fourche (10120202)+, Redwater (10120203)+, Upper North Platte (10180002)+*, Medicine Bow (10180004)+*, Sweetwater (10180006)+*, Middle North Platte-Casper (10180007)+*, Upper Kansas (10270101)+, Middle Kansas (10270102)+, Delaware (10270103)+, Lower Kansas (10270104)+, Upper Grand (10280101)+, Thompson (10280102)+, Blackwater (10300104)+
11 Rattlesnake (11030009)+, Cow (11030011)+, Kaw Lake (11060001)+, Neosho headwaters (11070201)+
14 Upper Green-Slate (14040103)+, Big Sandy (14040104)+, Lower Green-Diamond (14060001)+*, Ashley-Brush (14060002)+*, Lower San Juan-Four Corners (14080201)+*
15 Little Colorado headwaters (15020001)+, Lower Verde (15060203)+
16 Upper Bear (16010101)+, Bear Lake (16010201)+, Middle Bear (16010202)+, Little Bear-Logan (16010203)+, Lower Bear-Malad (16010204)+, Upper Weber (16020101)+, Lower Weber (16020102)+, Utah Lake (16020201)+, Spanish Fork (16020202)+, Provo (16020203)+, Jordan (16020204)+, Southern Great Salt Lake Desert (16020306)+*, Great Salt Lake (16020310)+
17 Upper Clark Fork (17010201)+, Flint-Rock (17010202)+, Blackfoot (17010203)+, Middle Clark Fork (17010204)+, Bitterroot (17010205)+, Flathead Lake (17010208)+, Stillwater (17010210)+, Lower Flathead (17010212)+, Lower Clark Fork (17010213)+, Pend Oreille (17010216), Little Spokane (17010308), Colville (17020003), Upper Malheur (17050116)+*, Powder (17050203)+*, Upper Grande Ronde (17060104)+*, Upper John Day (17070201)+*, Donner Und Blitzen (17120003)+, Warner Lakes (17120007)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A small bird.
General Description: A 18-cm-long bird with a stout, relatively short, pointed bill and sharply pointed tail feathers; breeding male is black below, with a buff to whitish hind-neck, white scapulars, and white rump; early spring male has pale feather edgings; breeding female is buffy with dark streaks on the back, rump, sides, and head; juvenile resembles breeding female but lacks streaks below; fall adults and immatures resemble breeding female but are darker above and richer buff below (NGS 1983). Strongly sexually and seasonally dimorphic with respect to body mass; mean body weights: breeding females, 29.1 g; breeding males, 33.9 g; migrating females, 39.9 g; migrating males, 51. g (Martin and Gavin 1995).
Reproduction Comments: Clutch size is four to seven (usually five to six). Incubation, by female, lasts 11-13 days. Young are tended by both parents, leave nest at 10-14 days (still unable to fly). In some areas, individual females very rarely may produce a second clutch (unsuccessful) after the first brood fledges (Gavin 1984).
Ecology Comments: Bobolinks often are in large flocks during northward migration.
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: Y
Mobility and Migration Comments: Bobolinks arrive in northern nesting areas late April-early May; males arrive a few days to a week before females (Terres 1980). Bobolinks are uncommon migrants in fall in Puerto Rico and the Virgin Islands, rare in spring (Raffaele 1983). Migration occurs mostly via the West Indies; small numbers reach Middle America (Ridgely and Gwynne 1989). Bobolinks are rare fall migrants in Costa Rica, mid-September to October, and are basically absent in spring (Stiles and Skutch 1989). They are transient in Colombia, mainly early September-late November and early March to mid-May (Hilty and Brown 1986).
Palustrine Habitat(s): HERBACEOUS WETLAND
Terrestrial Habitat(s): Cropland/hedgerow, Grassland/herbaceous
Habitat Comments: Breeding habitat includes tall grass areas, flooded meadows, prairie, deep cultivated grains, and hayfields (AOU 1998). In New York, old hayfields, at least 8 years since planting and including a minimum of alfalfa, were important nesting habitat (Bollinger and Gavin 1992). Nests are on the ground in small hollows in areas of concealing herbaceous vegetation. Individuals tend to return to breed in the same area in successive years, especially if that site has had good bobolink productivity (Bollinger and Gavin 1989).

This species generally selects habitat with moderate to tall vegetation, moderate to dense vegetation, and moderately deep litter (Tester and Marshall 1961, Bent 1958, Harrison 1974, Bollinger 1995), lacking oody vegetation (Sample 1989, Bollinger and Gavin 1992). It is found in native and tame grasslands, haylands, lightly to moderately grazed pastures, no-till cropland, small-grain fields, oldfields, wet meadows, and planted cover (e.g., Conservation Reserve Program [CRP] fields, Permanent Cover Program [PCP] fields, and Dense Nesting Cover [DNC]) (Bent 1958; Speirs and Orenstein 1967; Birkenholz 1973; Harrison 1974; Skinner 1974, 1975; Stewart 1975; Joyner 1978; Johnsgard 1979, 1980; Faanes 1981; Kantrud 1981; Kantrud and Kologiski 1982; Renken 1983; Huber and Steuter 1984; Basore et al. 1986; Renken and Dinsmore 1987; Bollinger 1988, 1991, 1995; Sample 1989; Bollinger et al. 1990; Messmer 1990; Herkert 1991a, 1994a,1997; Bollinger and Gavin 1992; Bock et al. 1993; Johnson and Schwartz 1993; Dhol et al. 1994; Hartley 1994; Jones 1994; King and Savidge 1995; Madden 1996; Patterson and Best 1996; Prescott and Murphy 1996; Best et al. 1997; Dale et al. 1997; Delisle and Savidge 1997; McMaster and Davis 1998; Schneider 1998). Commonly it occurs in areas with high percent grass cover and moderate percent forb cover (Wiens 1969, Skinner 1974, Renken 1983, Renken and Dinsmore 1987, Sample 1989, Herkert 1994a, Madden 1996). Bollinger (1988, 1995) noted preference for haylands with high grass-to-forb ratios and avoidance of haylands with high legume-to-grass ratios; however, a forb component was beneficial for nesting cover.

Within mixed-grass pastures in North Dakota, abundance was positively associated with percent grass cover, litter depth, density of low-growing shrubs (western snowberry, Symphoricarpos occidentalis; silverberry, Elaeagnus commutata), vegetation density, and plant communities dominated by Kentucky bluegrass (Poa pratensis) and native grasses (Stipa, Bouteloua, Koeleria, and Schizachyrium) (Schneider 1998). Abundance was negatively associated with percent clubmoss (Selaginella densa) cover, bare ground, and plant communities dominated solely by native grass. Strongest vegetational predictors of the presence of bobolinks were decreasing bare ground, increasing litter, and increasing vegetation density. Madden (1996) found that the best predictors of occurrence in North Dakota mixed-grass prairie were increasing amounts of forb and grass cover, decreasing amounts of shrub cover, and decreasing frequency of native grasses.

In Illinois tallgrass prairie fragments, the best predictors of occurrence were mean number of live forb contacts, mean vegetation height, and mean grass height (Herkert 1994a). In another Illinois study, occurred only in patches of Kentucky bluegrass and were absent from tallgrass prairie (Birkenholz 1973).

In Nebraska, abundance in CRP planted to cool-season grasses was significantly and positively correlated with percent litter cover and negatively correlated with vertical density of vegetation (measured using a Robel pole) (Delisle and Savidge 1997). In tame CRP grasslands in Iowa, abundance was positively correlated with litter cover and grass canopy cover and negatively correlated with forb cover and the horizontal patchiness of vegetation (Patterson and Best 1996). Abundance in Wisconsin was highest in cool-season grasses, followed by wet pastures, bluegrass (Poa)/quackgrass (Agropyron repens) communities, and alfalfa (Medicago sativa/grass hayfields (Sample 1989). In New York tame hayfields, increased in abundance as the hayfields aged (Bollinger 1988, 1995). Older hayfields (more than 3 years old) were characterized by sparse, patchy, grass-dominated vegetation and high litter cover.

In Nebraska, boblinks nested in wet prairie, alfalfa, upland native prairie, domestic hayland, and wheat (Faanes and Lingle 1995). In Iowa they nested under or near native bluestem (Andropogon or Schizachyrium not specified) or Kentucky bluegrass (Kendeigh 1941). In Wisconsin boblinks nested at the bases of large forbs (Martin 1971). In Montana, nested in a wet-meadow pasture (Silloway 1904). In Ontario, they nested in a weedy meadow near a wetland; nests were built in the litter layer, had a canopy of dead grasses, and were surrounded by living vegetation 33-41 centimeters tall (Boyer and Devitt 1961, Joyner 1978). Boblinks have been found nesting in CRP fields in Iowa and Michigan (Best et al. 1997).

Boblinks occasionally nest in cropland. In Iowa, they nested at low densities in untilled fields of corn that were idle in the fall and spring and contained year-round crop residue, rather than in tilled fields or strip cover (Basore et al. 1986). In Wisconsin, a few were found in small-grain fields, but none were found in rowcrops (Sample 1989). Graber and Graber (1963) reported fairly heavy use of small grain fields in Illinois. The species was absent from cropland in Saskatchewan and Manitoba (Hartley 1994, Jones 1994).

During the nonbreeding season, boblinks also occur in rice fields, marshes, and open woody areas (AOU 1983).
In Argentina, bobolinks primarily use natural wet grassland habitats associated with main rivers and huge marshes (Di Giacomo et al. 2005).

Adult Food Habits: Granivore, Invertivore
Immature Food Habits: Granivore, Invertivore
Food Comments: Diet includes insects, seeds, grain (Terres 1980); mainly seeds (Stiles and Skutch 1989).
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Length: 18 centimeters
Weight: 47 grams
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Keys to management are providing large areas of suitable habitat (native and tame grasslands of moderate height and density, with adequate litter), controlling succession, and protecting nesting habitat from disturbance during the breeding season. Regardless of geographic location, avoid disturbing (e.g., haying, burning, moderately or heavily grazing) nesting habitat during the breeding season, approximately early May to mid-July (Bollinger 1991). Treatments can be done in early spring (several weeks prior to the arrival of adults on the breeding grounds) or in the fall after the breeding season (Martin and Gavin 1995).

GREAT PLAINS: Create large patches of habitat and minimize woody edges whenever possible to increase densities (Johnson and Temple 1990, Helzer 1996). In Nebraska, minimum patch size requirement for wet meadows was greater than 40 hectares, and abundance was lower near woody edges (less than 100 meters) than far (greater then 100 meters) from woody edges (Helzer 1996). Burn habitat once every 2-4 years to prevent encroachment of woody vegetation and remove deep litter (Johnson and Temple 1990, Madden 1996, Johnson 1997). Conduct controlled burns on Conservation Reserve Program (CRP) fields every 3-5 years to reduce dense vegetation (King and Savidge 1995). In Nebraska, Bobolink abundance was negatively correlated with vertical density of vegetation (Delisle and Savidge 1997). Burn large areas on a rotational basis, burning portions of the total area each year (Johnson 1997). Burn small areas periodically. Ensure that adjacent areas are burned in different years to create a variety of successional stages. Provide hayland areas, and mow as late as possible. In Nebraska, occurred more frequently in native hayland than pastures (Helzer 1996). Kantrud (1981) found densities to be highest in hayland mowed the previous year, with lightly grazed areas containing the second highest density. Dale et al. (1997) found that abundance in Saskatchewan was higher in annually or periodically mowed tame hayland than in native grassland. Delay mowing until after 15 July, by which time at least 70 percent of nestlings will have fledged in years of normal breeding phenology (Dale et al. 1997). To maintain dense cover in idle haylands, mow some fields in alternate years while leaving others idle for at least 3 years. Divide large fields in half, with each half being mowed in alternate years, thus ensuring productivity of hay and of birds. Lightly graze areas where Bobolinks have exhibited positive responses to this treatment; heavy or moderate grazing may have negative impact on populations (Kantrud 1981).

EAST AND MIDWEST: Delay treatments until late July or August to protect fledglings and late-nesting females (Bollinger 1991). Create large habitat patches (greater then 10-30 hectares) and minimize woody edges whenever possible (Bollinger and Gavin 1992). Use a rotating treatment schedule on several nearby prairie fragments to make a variety of successional stages available (Herkert 1994b). Adjacent patches of alternative habitat provide refuge for fledglings to escape from mowed areas and for late-nesting females (Bollinger et al. 1990). Create or maintain patches of relatively sparse, grass-dominated vegetation resembling old (more then 8 years since planted) hayfields (Bollinger and Gavin 1992). Scattered forbs (e.g., clover [TRIFOLIUM SPP.]) should be encouraged for nest-site cover. Bollinger (1988, 1995) found that a minimal forb component for nesting cover was beneficial, but Bobolinks preferred haylands with high grass-to-forb ratios and avoided haylands with high legume-to-grass ratios. Burn large areas (greater then 80 hectares) using a rotational system. Subunits of more than 30 hectares in area, or about 20-30 percent of the total area, should be treated in a year (Herkert 1994b). Johnson and Temple (1990) found lower rates of nest depredation of nests in recently burned (less then 3 years ago) areas in Minnesota. In small, isolated prairie fragments, burn more 50-60 percent of the total area at a time (Herkert 1994b). Mow or burn patches every 2-3 years to prevent excessive encroachment of woody vegetation (Bollinger and Gavin 1992, Herkert 1994a). In most years, delaying mowing until the end of June may allow young Bobolinks time to fledge (Harrison 1974). Graze at moderate levels to provide diverse grass heights and densities in areas where the average height of vegetation is 20-30 centimeters (Skinner 1974, 1975). Graze using a rotational system of two or more grazing units (Skinner 1974). This will increase the variation in grass heights and densities within and between units. To maintain plant vigor, do not graze warm-season grasses in tallgrass prairie to a height of less than 25 centimeters during the growing season (Skinner 1975).

Restoration Potential: Plant late maturing hay species rather than legumes, ideally with no-till seeding (Jones and Vickery 1997).
Preserve Selection & Design Considerations: Minimum grassland size two to four hectares (Jones and Vickery 1997). Territories include both foraging and nesting areas (Martin 1967). Average territory size ranged from 0.45 to 0.69 hectares in a mixed hayland on a floodplain in Wisconsin (Martin 1967, 1971), 0.49 hectares at six tame hayfields in New York (Bollinger 1988), 1.4 hectares in a tame hayfield in Michigan (Raim 1975), and 2.6 hectares in a dry, sparsely vegetated pasture in Wisconsin (Wiens 1969). Appear to be area sensitive, preferring large grassland areas over small (Herkert et al. 1993). Herkert (1991b) reported that the minimum area on which Bobolinks were found was 10-30 hectares in Illinois tallgrass prairie fragments. The minimum patch size requirement in wet meadows in Nebraska was more than 40 hectares (Helzer 1996). Abundance in tallgrass prairie fragments was positively related to area (Herkert 1994b). Abundance also was positively correlated with fragment size in New York and Maine (Bollinger and Gavin 1992, Vickery et al. 1994).

In Minnesota tallgrass prairie, nest depredation and Brown-headed Cowbird (MOLOTHRUS ATER) brood parasitism decreased farther from woody edges, and nest depredation rates were lower on large (130-486 hectares) than on small (16-32 hectares) grasslands (Johnson and Temple 1990). Nest productivity in Minnestoa was highest for nests in habitats far (more than 45 meters) from a forest edge (Johnson and Temple 1986). In Nebraska, abundance was lower near woody edges (less than 100 meters) than far (more than 100 meters) from woody edges (Helzer 1996).

Management Requirements: Prairie management to maximize nest productivity should provide large (more then 130 hectares), regularly burned prairies with no nearby wooded edges (Johnson and Temple 1990). Bollinger and Gavin (1992) recommended that, in an agricultural landscape, habitat patches be larger than 10-15 hectares. Timing of hay-cropping has large effects on reproductive success; Bollinger et al. (1990) recommended that conservation lands be hayed every 2-3 years, with cutting not to begin before mid-July. Hay should be removed to prevent thatch build-up. Will tolerate light, but not heavy, grazing, with grass heights of 8-12 inches. Burns should be conducted every 2-5 years, but do not burn all of one unit in one year (Jones and Vickery 1997).

BURNING: If habitat is not maintained, use declines significantly, possibly due to the accumulation of litter and encroachment of woody vegetation (Johnson 1997). Respond positively to properly timed burning or mowing treatments (Herkert 1991a, 1994b; Bollinger and Gavin 1992; Madden 1996; Johnson 1997). In Wisconsin, a field that was burned in April each year was occupied in early June; the year it was not burned, the field was occupied by mid-May (Martin 1971). Absent in Minnesota tallgrass prairie 1 year postburn but established territories 2 years postburn (Tester and Marshall 1961). Nest productivity in Minnesota was highest 1 year postburn, and the probability of encountering Bobolinks was highest on areas 1 year postburn (Johnson and Temple 1986). In Illinois tallgrass prairie fragments, preferred recently burned or mowed (burned or mowed 1-4 months prior to the breeding season) sites over areas burned more then 1 year previous or to unmowed areas (Herkert 1991a, 1994b). In North Dakota, abundance peaked 1-3 years postburn (Madden 1996, Johnson 1997), but declined 5 years postburn (Johnson 1997). Abundance in Maine declined in the burn year, but peaked 1-2 years postburn (Vickery 1993).

HAYLAND: In Nebraska, occurred more frequently in tallgrass hayland than tallgrass pasture (Helzer 1996). In North Dakota, Kantrud (1981) found the highest densities in hayland mowed the previous year, with lightly grazed areas containing the second highest densities. In Michigan and Wisconsin, were common in hayfields before mowing, but deserted these fields after the fields were mowed (Harrison 1974, Sample 1989). In Missouri, however, found in hayfields before and after mowing (Skinner 1974). In Illinois, a decline in abundance was significantly correlated to declines in the number of hectares of alfalfa, oats, and pasture in the northern one-third of the state from 1952 to 1992 (Herkert 1997). In Saskatchewan, were more abundant in emergency-mowed (mowed during drought years) tame hayfields than in native grassland, tame grassland, or annually mowed tame haylands (Dale 1992). Dale et al. (1997) found that abundance in Saskatchewan was higher in annually or periodically (idle for 4-8 years) mowed tame hayland than in idle native grassland.

GRAZING: In the Great Plains, measures of abundance indicated positive responses to moderate grazing in tallgrass, but negative responses to heavy grazing in shortgrass (Bock et al. 1993). In southeastern North Dakota, occurred in grazed areas that had few shrubs and moderate to deep litter (Messmer 1990). Higher densities were found in areas under a short-duration grazing treatment (involved a system of pastures rotated through a grazing schedule of about 1 week grazed and 1 month ungrazed) than in idle areas. In South Dakota, preferred lightly grazed (grazed by American bison [BISON BISON]) areas over spring-burned areas (Huber and Steuter 1984). In southeastern South Dakota, preferred lightly grazed areas on typic ustoll soils (Kantrud and Kologiski 1982). In Missouri, were most abundant in lightly to moderately grazed tallgrass prairie and were not present in idle prairie (Skinner 1974, 1975). In Alberta, were found in tame pastures but not in native pastures (Prescott and Murphy 1996).

CONSERVATION RESERVE PROGRAM (CRP): Nested or were found in CRP fields in Illinois, Iowa, Michigan, Minnesota, Montana, Nebraska, North Dakota, and South Dakota (Johnson and Schwartz 1993, Patterson and Best 1996, Best et al. 1997, Delisle and Savidge 1997, Davison 1998). In North Dakota, higher densities were found in Dense Nesting Cover (DNC) planted to alfalfa and wheatgrass (AGROPYRON spp.) than in idle mixed-grass prairie (Renken 1983, Renken and Dinsmore 1987). In CRP fields in Nebraska, abundance was significantly higher in cool-season grasses than in warm-season grasses, possibly because of shorter vegetation in cool-season grasses (Delisle and Savidge 1997). King and Savidge (1995) found Bobolinks in tallgrass prairie and CRP planted to cool-season grasses but did not find them in CRP planted to warm-season grasses. In Manitoba and Saskatchewan, were found in native and tame DNC and in idle native grassland (Dhol et al. 1994, Hartley 1994); wheat fields were avoided (Hartley 1994). Also were found in Permanent Cover Program (PCP) lands in Canada (McMaster and Davis 1998). PCP is a Canadian program that pays farmers to seed highly erodible land to perennial grassland cover; it differs from CRP in the United States in that haying and grazing are allowed annually in PCP. In Canadian aspen parkland, occurred significantly more frequently in PCP than in cropland (McMaster and Davis 1998). However, their frequency of occurrence did not differ between hay and pasture sites within the parkland PCP sites. In North Dakota, were present in areas seeded to native grasses 1 year after seeding occurred (Higgins et al. 1984). In Wisconsin, occurred in a restored native tallgrass prairie site 3 years following seeding (Volkert 1992).

Monitoring Requirements: See Bollinger et al. (1988) for methods for estimating population density (line transects and circular-plot techniques both overestimate density).
Biological Research Needs: Greatest priority should be focused on the ecology and social behavior of Bobolinks during their austral summer in the southern hemisphere. Little is understood about the species? conservation status during the several months spent each year in South America; trapping, involvement in the caged bird market, and purposeful killing to reduce crop depredation are subjects we know little about. This species is potentially vulnerable to rapid population declines if efficient control measures are developed; control would be facilitated by habitat destruction and flocking behavior that might concentrate birds during the austral summer. Little information exists on these important issues, which can have significant impacts on the breeding densities of Bobolinks in North America. The species appears to spend much time in migratory transit to and from South America. Little is known about behavior, movement patterns, and specific concentration locales during migration (Martin and Gavin, 1995).
Population/Occurrence Delineation
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Group Name: Passerines

Use Class: Breeding
Subtype(s): Foraging Area, Nest Site, Nesting Colony
Minimum Criteria for an Occurrence: Evidence of historical breeding, or current and likely recurring breeding, at a given location, minimally a reliable observation of one or more breeding pairs in appropriate habitat. Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.

Mapping Guidance: Breeding occurrences include nesting areas as well as foraging areas.

For swallows and other species that have separate nesting and foraging areas, separations are based on nest sites or nesting areas, not to locations of foraging individuals. For example, nesting areas separated by a gap larger than the separation distance are different occurrences, regardless of the foraging locations of individuals from those nesting areas. This separation procedure is appropriate because nesting areas are the critical aspect of swallow breeding occurrences, tend to be relatively stable or at least somwhat predictable in general location, and so are the basis for effective conservation; foraging areas are much more flexible and not necessarily static.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Significant dispersal and associated high potential for gene flow among populations of birds separated by tens of kilometers (e.g., Moore and Dolbeer 1989), and increasing evidence that individuals leave their usual home range to engage in extrapair copulations, as well as long foraging excursions of some species, make it difficult to circumscribe occurrences on the basis of meaningful population units without occurrences becoming too large. Hence, a moderate, standardized separation distance has been adopted for songbirds and flycatchers; it should yield occurrences that are not too spatially expansive while also accounting for the likelihood of gene flow among populations within a few kilometers of each other.

Be careful not to separate a population's nesting areas and foraging areas as different occurrences; include them in the same occurrence even if they are more than 5 km apart. Mean foraging radius (from nesting area) of Brown-headed Cowbird females was 4.0 kilometers in California, 1.2 kilometers in Illinois-Missouri (Thompson 1994). Yellow-headed Blackbirds, Brewer's Blackbirds, and probably Red-winged Blackbirds all forage up to 1.6 kilometers away from breeding colony (Willson 1966, Horn 1968). In one study, Brewer's Blackbirds were found as far as 10 kilometers from nesting area (Williams 1952), but this may be unusual.

For swallows and other parrerines with similar behavioral ecology, separation distance pertains to nest sites or nesting colonies, not to locations of foraging individuals. For example, nesting areas separated by a gap of more than 5 km are different occurrences, regardless of the foraging locations of individuals from those nesting areas. This separation procedure is appropriate because nesting areas are the critical aspect of swallow breeding occurrences, tend to be relatively stable or at least somwhat predictable in general location, and so are the basis for effective conservation; foraging areas are much more flexible and not necessarily static.

Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.

Unsuitable habitat: Habitat not normally used for breeding/feeding by a particular species. For example, unsuitable habitat for grassland and shrubland birds includes forest/woodland, urban/suburban, and aquatic habitats. Most habitats would be suitable for birds with versatile foraging habits (e.g., most corvids).

Date: 10Sep2004
Author: Hammerson, G.

Use Class: Migratory stopover
Subtype(s): Foraging Area, Roost Site
Minimum Criteria for an Occurrence: For most passerines: Evidence of recurring presence of migrating individuals (including historical) and potential recurring presence at a given location; minimally a reliable observation of 25 birds in appropriate habitat.

For swallows: Evidence of recurring presence of migrating flocks (including historical) and potential recurring presence at a given location; minimally a reliable observation of 100 birds in appropriate habitat (e.g., traditional roost sites).

Occurrences should be locations where the species is resident for some time during the appropriate season; it is preferable to have observations documenting presence over at least 7 days annually.

EOs should not be described for species that are nomadic during nonbreeding season: e.g., Lark Bunting.

Be cautious about creating EOs for observations that may represent single events.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Separation distance somewhat arbitrary but intended to define occurrences of managable size for conservation purposes. Occurrences defined primarily on the basis of areas supporting concentrations of birds, rather than on the basis of distinct populations.

For swallows and other species with similar behavioral ecology, the separation distance pertains to communal roost sites rather than to foraging areas; the former tend to be more stable and specific over time than the latter.

Date: 03Sep2004
Author: Hammerson, G., and S. Cannings

Use Class: Nonbreeding
Subtype(s): Foraging Area, Roost Site
Minimum Criteria for an Occurrence: Any area used traditionally in the nonbreeding season (used for populations that are not resident in a location year-round). Minimally, reliable observations of 10 or more individuals in appropriate habitat for 20 or more days at a time. For G1-G3 species, observations of fewer individuals could constitute an occurrence of conservation value. Sites used during migration should be documented under the 'migratory stopover' location use class.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Separation distance is necessarily arbitrary but attempts to balance the high mobility of birds with the need for occurrences of reasonable spatial scope. Note that a population's roost sites and foraging areas are parts of the same occurrence, even if they are more than 5 km apart.

For swallows and other species with similar behavioral ecology, the separation distance pertains to communal roost sites rather than to foraging areas; the former tend to be more stable and specific over time than the latter.

Date: 03Sep2004
Author: Hammerson, G.

Use Class: Nonmigratory
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a particular location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals in or near appropriate habitat.

These occurrence specifications are used for nonmigratory populations of passerine birds.

Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Significant dispersal and associated high potential for gene flow among populations of birds separated by tens of kilometers (e.g., Moore and Dolbeer 1989), and increasing evidence that individuals leave their usual home range to engage in extrapair copulations, as well as long foraging excursions of some species, make it difficult to circumscribe occurrences on the basis of meaningful population units without occurrences becoming too large. Hence, a moderate, standardized separation distance has been adopted for songbirds and flycatchers; it should yield occurrences that are not too spatially expansive while also accounting for the likelihood of gene flow among populations within a few kilometers of each other.

Be careful not to separate a population's nesting areas and breeding-season foraging areas as different occurrences; include them in the same occurrence even if they are more than 5 km apart. Blue jays have small summer home ranges but fly up to 4 kilometers to harvest mast (Tarvin and Woolfenden 1999). Flocks of pinyon jays range over 21-29 square kilometers (Ligon 1971, Balda and Bateman 1971); nesting and foraging areas may be widely separated. Tricolored blackbirds forage in flocks that range widely to more than 15 kilometers from the nesting colony (Beedy and Hamilton 1999).

Unsuitable habitat: Habitat not normally used for breeding/feeding by a particular species. For example, unsuitable habitat for grassland and shrubland birds includes forest/woodland, urban/suburban, and aquatic habitats. Most habitats would be suitable for birds with versatile foraging habits (e.g., most corvids).

Date: 10Sep2004
Author: Hammerson, G.
Notes: These specs pertain to nonmigratory species.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 25Nov2014
NatureServe Conservation Status Factors Author: Hammerson, G.; Modified by Jue, Dean K.
Management Information Edition Date: 15Jul1999
Management Information Edition Author: DECHANT, J.A., M.L. SONDREAL, D.H. JOHNSON, L.D. IGL, C.M. GOLDADE, A.L. ZIMMERMAN, AND B.R. EULISS. REVISIONS BY M. KOENEN, G. HAMMERSON, AND D.W. MEHLMAN
Management Information Acknowledgments: Eric Bollinger provided a thoughtful review of a draft of this abstract. Parts of this abstract were originally researched and written by staff of the Northern Prairie Wildlife Research Center and published as Dechant et al. (1999). Additional support for the preparation of this abstract was provided by the National Fish and Wildlife Foundation's Neotropical Migratory Bird Conservation Initiative, through challenge grant number 97-270 to The Nature Conservancy, Wings of the Americas Program. Matching funds for this grant were donated by Canon U.S.A., Inc.
Element Ecology & Life History Edition Date: 18Mar2009
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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    doi:10.2173/bna.176


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