Podilymbus podiceps - (Linnaeus, 1758)
Pied-billed Grebe
Other Common Names: Mergulhão-Caçador
Taxonomic Status: Accepted
Related ITIS Name(s): Podilymbus podiceps (Linnaeus, 1758) (TSN 174505)
French Common Names: grèbe à bec bigarré
Spanish Common Names: Zambullidor Pico Grueso, Macá de Pico Grueso
Unique Identifier: ELEMENT_GLOBAL.2.100209
Element Code: ABNCA02010
Informal Taxonomy: Animals, Vertebrates - Birds - Other Birds
Image 11197

© Larry Master

Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Podicipediformes Podicipedidae Podilymbus
Genus Size: B - Very small genus (2-5 species)
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Concept Reference
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: Podilymbus podiceps
Taxonomic Comments: May constitute a superspecies with P. gigas (AOU 1998).
Conservation Status

NatureServe Status

Global Status: G5
Global Status Last Reviewed: 09Apr2016
Global Status Last Changed: 20Nov1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Nation: United States
National Status: N5B,N5N (05Jan1997)
Nation: Canada
National Status: N5B,N4N5N,N5M (16Jan2018)

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 (S3B,S5N), Alaska (S2S3B), Arizona (S5), Arkansas (S3B,S5N), California (SNR), Colorado (S5B), Connecticut (S1B), Delaware (S1B,S3N), District of Columbia (S4S5N), Florida (SNRB,SNRN), Georgia (S4S5), Idaho (S3), Illinois (S3), Indiana (S3B), Iowa (S4B,S4N), Kansas (S2B), Kentucky (S1B,S4N), Louisiana (S4B,S5N), Maine (S4B), Maryland (S2B), Massachusetts (S1B,S4N), Michigan (S4), Minnesota (SNRB), Mississippi (S5N), Missouri (S3), Montana (S5B), Navajo Nation (S4B,S3N), Nebraska (S5), Nevada (S4), New Hampshire (S2B), New Jersey (S1B,S3N), New Mexico (S5B,S5N), New York (S3B,S1N), North Carolina (S3B,S5N), North Dakota (SNRB), Ohio (S2S3), Oklahoma (S5), Oregon (S5), Pennsylvania (S3B,S4N), Rhode Island (S1B), South Carolina (SNRB,SNRN), South Dakota (S4B), Tennessee (S4), Texas (S5B), Utah (S4B,S3S4N), Vermont (S2S3B), Virginia (S1S2B,S4N), Washington (S4B,S5N), West Virginia (S2B,S4N), Wisconsin (S4B), Wyoming (S5)
Canada Alberta (S4B), British Columbia (S4B), Manitoba (S4S5B), New Brunswick (S4B,S4M), Newfoundland Island (S1B,SUM), Northwest Territories (S3B), Nova Scotia (S4B), Ontario (S4B,S4N), Prince Edward Island (S4B), Quebec (S4), Saskatchewan (S5B), Yukon Territory (S1S2B)

Other Statuses

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: >2,500,000 square km (greater than 1,000,000 square miles)
Range Extent Comments: BREEDING: southeastern Alaska through southern Canada to Nova Scotia, south locally through North America, Middle America, West Indies, and South America to central Chile and southern Argentina (AOU 1983). Breeding populations in the northeastern U.S. are more localized and less abundant than in other regions of the U.S. or Canada (Gibbs and Melvin 1992). NON-BREEDING: southern British Columbia, western and southern U.S. south through South America. Rare visitor in Hawaii (AOU 1983). Areas of highest winter concentration include southern and central Texas, Great Salt Lake (Utah), Lake Mead (Nevada-Arizona), and the San Joaquin Valley (California) (Root 1988).

Overall Threat Impact Comments: Has declined locally due to degradation, disturbance, and loss of wetlands. The greatest threat to populations in the northeast is alteration and loss of wetland habitat through draining, dredging, filling, pollution, acid rain, agricultural practices, and siltation (Gibbs and Melvin 1992). Palustrine emergent wetlands, including inland freshwater and brackish marshlands frequented by grebes, are among the most threatened wildlife habitats in the U.S. Over 4.75 million acres (1.92 million ha) of such wetlands were destroyed in the U.S. between the mid-1950s and mid-1970s, and losses continue at > 160,000 ac/year (64,777 ha) (Tiner 1984). Pollution and environmental contaminants may degrade wetland ecosystems and impair reproductive capacity in industrialized portions of the range. Carbamate pesticides have had lethal effects in New York (Stone 1979). Although acidification of wetland nesting habitats could potentially reduce food supplies, grebes usually occupy wetlands of circumneutral pH with dense growths of emergent vegetation (Gibbs et al., in press; Gibbs and Melvin 1990) that may provide effective chemical buffering against acidification. In agricultural areas, siltation resulting from erosion of farmlands and run-off containing insecticides may degrade nesting habitats and reduce availability of invertebrate foods. Highly susceptible to oil toxicosis, although this does not pose a major threat to overwintering grebes because they occur in small groups and favor sites at inland, fresh waters generally well-protected from large, ocean-borne oil spills (Clapp et al. 1982). One died after choking on a fish (Behrstock 1981). These birds sometimes mistake wet roads for water bodies from which they are unable to take off. Human exploitation historically has had an important impact on numbers. Warren (1890) reported that large numbers were shot and sold to milliners and furriers who fashioned ear-muffs and hat ornaments from the silver-white breast and abdomen feathers. The grebe has long been persecuted because of the challenge it poses as a target for hunters (Bent 1919, Forbush 1925, Palmer 1949). Its predilection for using managed impoundments during migration may predispose it to accidental or malicious shootings by duck hunters. Human disturbance can greatly disrupt patterns of nest attendance and incubation (Forbes and Ankney 1988, Davis et al. 1985).

Short-term Trend Comments: North American Breeding Bird Survey (BBS) data indicate a small but significantly (P < 0.01) larger proportion of BBS routes showing increases in populations (0.51) than decreases (0.44) during the 1966-1989 period in the U.S. No significant trends were evident for the eastern U.S., but published accounts suggest that long-term declines have occurred in southern and central New England, New Jersey, Delaware, and possibly New York (Gibbs and Melvin 1992). BBS data for 1966-1993 indicate a significant decline (mean 2% per year) for North America, primarily due to a decline in the northern Great Plains (S. Droege, pers. comm.). Christmas Bird Count data for 1959-1988 indicate a significant increase (mean 1.4% per year) in North America, but recent drought conditions were not included in the study period (S. Droege, pers. comm.); CBC trends for the upper Atlantic seaboard were negative.

Other NatureServe Conservation Status Information

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: southeastern Alaska through southern Canada to Nova Scotia, south locally through North America, Middle America, West Indies, and South America to central Chile and southern Argentina (AOU 1983). Breeding populations in the northeastern U.S. are more localized and less abundant than in other regions of the U.S. or Canada (Gibbs and Melvin 1992). NON-BREEDING: southern British Columbia, western and southern U.S. south through South America. Rare visitor in Hawaii (AOU 1983). Areas of highest winter concentration include southern and central Texas, Great Salt Lake (Utah), Lake Mead (Nevada-Arizona), and the San Joaquin Valley (California) (Root 1988).

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 AK, AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, 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, NT, ON, PE, QC, SK, YT

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; NatureServe, 2004

U.S. Distribution by County Help
State County Name (FIPS Code)
CT Fairfield (09001), Hartford (09003), Litchfield (09005), Middlesex (09007), New Haven (09009)*, Tolland (09013), Windham (09015)
DE Kent (10001), New Castle (10003), Sussex (10005)
ID Ada (16001), Bear Lake (16007), Bingham (16011), Blaine (16013), Bonner (16017), Bonneville (16019), Boundary (16021), Camas (16025), Canyon (16027), Caribou (16029), Cassia (16031), Custer (16037)*, Fremont (16043), Gooding (16047), Idaho (16049), Jefferson (16051), Kootenai (16055), Nez Perce (16069), Power (16077), Teton (16081)
IL Bureau (17011), Cass (17017), Champaign (17019), Coles (17029), Cook (17031), Douglas (17041), DuPage (17043), Fayette (17051), Ford (17053), Fulton (17057)*, Grundy (17063), Henry (17073), Jackson (17077)*, Jasper (17079), Jefferson (17081)*, Kane (17089), Kendall (17093), La Salle (17099)*, Lake (17097), Lawrence (17101), Lee (17103), Macon (17115), Madison (17119), Mason (17125), Mchenry (17111), Perry (17145), Pulaski (17153), Putnam (17155), Rock Island (17161), Sangamon (17167), St. Clair (17163), Tazewell (17179)*, Union (17181), Vermilion (17183)*, Whiteside (17195), Will (17197)
KY Christian (21047), Daviess (21059), Fulton (21075), Hopkins (21107)*, Jefferson (21111)*, Lyon (21143)*, Menifee (21165), Trigg (21221)*, Union (21225), Warren (21227)
MA Barnstable (25001)*, Berkshire (25003), Dukes (25007)*, Essex (25009), Franklin (25011), Hampden (25013)*, Hampshire (25015), Middlesex (25017), Nantucket (25019)*, Plymouth (25023), Worcester (25027)
MD Anne Arundel (24003), Baltimore (city) (24510)*, Baltimore County (24005), Dorchester (24019), Frederick (24021), Montgomery (24031)*, Prince Georges (24033)*, Somerset (24039), Wicomico (24045), Worcester (24047)
MO Adair (29001), Bates (29013), Boone (29019), Buchanan (29021), Carroll (29033), Clay (29047), DeKalb (29063), Franklin (29071), Holt (29087), Jackson (29095), Jasper (29097), Lafayette (29107), Lincoln (29113), Linn (29115), Mississippi (29133), New Madrid (29143), Pike (29163), Platte (29165), Putnam (29171), Ray (29177), Saline (29195), Schuyler (29197), St. Charles (29183), St. Clair (29185), Sullivan (29211), Texas (29215), Vernon (29217)
NH Belknap (33001), Carroll (33003), Coos (33007), Grafton (33009), Hillsborough (33011), Merrimack (33013), Rockingham (33015), Strafford (33017), Sullivan (33019)
NJ Atlantic (34001), Bergen (34003), Burlington (34005), Gloucester (34015), Hudson (34017), Mercer (34021), Middlesex (34023), Monmouth (34025), Morris (34027), Ocean (34029), Passaic (34031), Salem (34033), Sussex (34037), Warren (34041)
NY Albany (36001), Allegany (36003), Cayuga (36011), Chautauqua (36013), Chemung (36015), Clinton (36019), Columbia (36021), Cortland (36023), Dutchess (36027), Erie (36029), Essex (36031), Franklin (36033), Genesee (36037), Greene (36039), Hamilton (36041), Herkimer (36043), Jefferson (36045), Kings (36047), Livingston (36051), Madison (36053), Monroe (36055), Montgomery (36057), Niagara (36063), Oneida (36065), Onondaga (36067), Ontario (36069), Orange (36071), Orleans (36073), Oswego (36075), Queens (36081), Rensselaer (36083), Richmond (36085), Rockland (36087), Schuyler (36097), Seneca (36099), St. Lawrence (36089), Suffolk (36103), Sullivan (36105), Tioga (36107), Tompkins (36109), Ulster (36111), Washington (36115), Wayne (36117), Westchester (36119), Wyoming (36121), Yates (36123)
PA Armstrong (42005), Beaver (42007), Bedford (42009), Butler (42019), Centre (42027), Clearfield (42033), Crawford (42039), Erie (42049), Fulton (42057), Greene (42059), Huntingdon (42061), Lackawanna (42069), Lawrence (42073), Lycoming (42081), Mercer (42085), Perry (42099), Philadelphia (42101), Schuylkill (42107), Sullivan (42113), Tioga (42117), Venango (42121), Washington (42125)
RI Newport (44005)*, Providence (44007)*, Washington (44009)
VA Fairfax (51059)
VT Addison (50001), Chittenden (50007), Franklin (50011), Grand Isle (50013), Orleans (50019), Rutland (50021), Washington (50023), Windham (50025)
WA Lewis (53041)+
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
01 Upper Androscoggin (01040001)+, Piscataqua-Salmon Falls (01060003)+, Pemigewasset (01070001)+, Merrimack (01070002)+, Contoocook (01070003)+, Nashua (01070004)+, Concord (01070005)+, Merrimack (01070006)+, Upper Connecticut (01080101)+, Waits (01080103)+, Upper Connecticut-Mascoma (01080104)+, Black-Ottauquechee (01080106)+, Middle Connecticut (01080201)+, Deerfield (01080203)+, Chicopee (01080204)+, Lower Connecticut (01080205)+, Westfield (01080206)+*, Farmington (01080207)+*, Charles (01090001)+, Cape Cod (01090002)+*, Blackstone (01090003)+*, Narragansett (01090004)+, Pawcatuck-Wood (01090005)+, Quinebaug (01100001)+, Shetucket (01100002)+, Housatonic (01100005)+, Saugatuck (01100006)+
02 Upper Hudson (02020001)+, Hudson-Hoosic (02020003)+, Mohawk (02020004)+, Middle Hudson (02020006)+, Rondout (02020007)+, Hudson-Wappinger (02020008)+, Lower Hudson (02030101)+, Hackensack-Passaic (02030103)+, Sandy Hook-Staten Island (02030104)+, Raritan (02030105)+, Southern Long Island (02030202)+, Middle Delaware-Mongaup-Brodhead (02040104)+, Middle Delaware-Musconetcong (02040105)+, Crosswicks-Neshaminy (02040201)+, Lower Delaware (02040202)+, Schuylkill (02040203)+, Brandywine-Christina (02040205)+, Cohansey-Maurice (02040206)+, Broadkill-Smyrna (02040207)+, Mullica-Toms (02040301)+, Great Egg Harbor (02040302)+, Chincoteague (02040303)+, Upper Susquehanna (02050101)+, Chenango (02050102)+, Owego-Wappasening (02050103)+, Tioga (02050104)+, Upper Susquehanna-Tunkhannock (02050106)+, Upper West Branch Susquehanna (02050201)+, Bald Eagle (02050204)+, Lower West Branch Susquehanna (02050206)+, Upper Juniata (02050302)+, Raystown (02050303)+, Lower Juniata (02050304)+, Lower Susquehanna-Swatara (02050305)+, Gunpowder-Patapsco (02060003)+, Patuxent (02060006)+*, Conococheague-Opequon (02070004)+, Middle Potomac-Catoctin (02070008)+*, Monocacy (02070009)+, Middle Potomac-Anacostia-Occoquan (02070010)+, Western Lower Delmarva (02080109)+, Eastern Lower Delmarva (02080110)+, Pokomoke-Western Lower Delmarva (02080111)+
04 Little Calumet-Galien (04040001)+, Pike-Root (04040002)+*, Buffalo-Eighteenmile (04120103)+, Niagara (04120104)+, Oak Orchard-Twelvemile (04130001)+, Upper Genesee (04130002)+, Lower Genesee (04130003)+, Irondequoit-Ninemile (04140101)+, Salmon-Sandy (04140102)+, Seneca (04140201)+, Oneida (04140202)+, Oswego (04140203)+, Chaumont-Perch (04150102)+, Upper St. Lawrence (04150301)+, Oswegatchie (04150302)+, Indian (04150303)+, Grass (04150304)+, Raquette (04150305)+, St. Regis (04150306)+, English-Salmon (04150307)+, Chateaugay-English (04150308)+, Mettawee River (04150401)+, Otter Creek (04150402)+, Winooski River (04150403)+, Lamoille River (04150405)+, Saranac River (04150406)+, Lake Champlain (04150408)+, St. Francois River (04150500)+
05 Upper Allegheny (05010001)+, Conewango (05010002)+, Middle Allegheny-Tionesta (05010003)+, French (05010004)+, Middle Allegheny-Redbank (05010006)+, Lower Monongahela (05020005)+, Upper Ohio (05030101)+, Shenango (05030102)+, Beaver (05030104)+, Connoquenessing (05030105)+, Licking (05100101)+, Barren (05110002)+, Pond (05110006)+*, Vermilion (05120109)+, Embarras (05120112)+, Lower Wabash (05120113)+, Little Wabash (05120114)+, Skillet (05120115)+*, Lower Cumberland (05130205)+, Red (05130206)+, Silver-Little Kentucky (05140101)+*, Lower Ohio-Little Pigeon (05140201)+, Highland-Pigeon (05140202)+, Tradewater (05140205)+*
07 Copperas-Duck (07080101)+, Kishwaukee (07090006)+*, Green (07090007)+, The Sny (07110004)+, Salt (07110007)+, Peruque-Piasa (07110009)+, Kankakee (07120001)+, Chicago (07120003)+, Des Plaines (07120004)+, Upper Illinois (07120005)+, Upper Fox (07120006)+, Lower Fox (07120007)+, Lower Illinois-Senachwine Lake (07130001)+, Lower Illinois-Lake Chautauqua (07130003)+, Upper Sangamon (07130006)+, South Fork Sangamon (07130007)+, Lower Sangamon (07130008)+, Lower Illinois (07130011)+, Cahokia-Joachim (07140101)+, Meramec (07140102)+, Upper Mississippi-Cape Girardeau (07140105)+, Big Muddy (07140106)+, Cache (07140108)+, Upper Kaskaskia (07140201)+, Middle Kaskaskia (07140202)+, Lower Kaskaskia (07140204)+
08 Obion (08010202)+, New Madrid-St. Johns (08020201)+
10 Tarkio-Wolf (10240005)+, Independence-Sugar (10240011)+, Upper Grand (10280101)+, Lower Grand (10280103)+, Upper Chariton (10280201)+, Harry S. Missouri (10290105)+, Lower Missouri-Crooked (10300101)+, Lower Missouri-Moreau (10300102)+
11 Current (11010008)+, Spring (11070207)+
16 Bear Lake (16010201)+
17 Lower Kootenai (17010104)+, Pend Oreille Lake (17010214)+, Coeur D'alene Lake (17010303)+, Upper Spokane (17010305)+, Idaho Falls (17040201)+, Upper Henrys (17040202)+, Lower Henrys (17040203)+, Teton (17040204)+, Willow (17040205)+, American Falls (17040206)+, Lake Walcott (17040209)+, Raft (17040210)+, Upper Snake-Rock (17040212)+, Beaver-Camas (17040214)+, Camas (17040220)+, Little Wood (17040221)+, Lower Boise (17050114)+, Middle Snake-Payette (17050115)+, Lower Snake-Asotin (17060103)+, Upper Salmon (17060201)+*, South Fork Clearwater (17060305)+, Clearwater (17060306)+, Nisqually (17110015)
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
Basic Description: An aquatic bird (grebe).
General Description: A small, stocky, and poorly buoyant waterbird, 31-38 cm in length (Cramp 1977), with small, narrow wings, feet placed far back, and a blunt-ended posterior. During the non-breeding period, the bill is unmarked, the throat is white, and the white rear becomes more conspicuous. As adults, sexes are alike, whereas juveniles are distinguished by the lack of a white orbital ring, an unmarked bill, darker brown sides of the head and neck, and a whiter underbelly (Palmer 1962). Downy chicks have a striking, zebra-like pattern of black and white stripes, interspersed with reddish-brown spots, and a bare loral area (Palmer 1962, Storer 1967).

VOCALIZATIONS: During territorial defense, males emit a distinctive prolonged call, a loud "cow-cow-cow-cow-cow- cowp...cowp...cowp..." This call is reminiscent of cuckoos (Palmer 1962), and enables communication over several hundred meters in nesting habitats dominated by dense, visually restricting vegetation. A variety of other calls are also produced during the breeding season (see Palmer 1962), but during the non-breeding season generally silent.

NEST: Build sodden, floating nests of rotting and green plant material and mud. Often anchored to growing, emergent plants. In Iowa, 138 nests averaged 38 cm in diameter (Glover 1953).

EGGS: elliptical to subelliptical, approx. 44.3 x 30.1 mm, smooth and nonglossy (Harrison 1978, Arnold 1989). Although white or tinted bluish or buff when laid, eggs gather a heavy, brown stain from the wet, organic matter comprising the nest.

MOLT: Molt is poorly known. Palmer (1962) noted that a complete molt into basic plumage takes place in autumn, with considerable individual variation in its timing and duration (Cramp et al. 1977). Flight feathers are lost simultaneously, prior to loss of body feathers. Complete molt takes one to two months. Basic molt and late nesting may occur simultaneously (Otto and Strohmeyer 1985). A partial molt into alternate plumage occurs in spring (Palmer 1962).

Diagnostic Characteristics: A short, stout, chicken-like bill with a broad, black band in the middle, large head and elongated neck, white orbital ring, black throat patch and forehead, and drab, brownish plumage throughout except for white under the tail (Palmer 1962, Cramp 1977).
Reproduction Comments: Single- or double-brooded and lay two to ten eggs, usually six to eight eggs per clutch (Sealy 1978, Forbes et al. 1989). Eggs are laid daily. Incubation is initiated after the fourth egg is laid, and occurs during about 90% of a given day (Forbes and Ankney 1988). Incubation is shared equally between sexes during laying and post-laying periods, although females spend more time incubating around hatching (Forbes and Ankney 1988), which occurs at about 23 days (Palmer 1962). Begin incubation before completing the clutch (Cramp et al. 1977) leading to considerable hatching asynchrony among the brood. Two to four eggs generally hatch on the first day of hatching, and the remaining eggs hatch daily over a period of three to seven days (Forbes and Ankney 1987, 1988). A detailed description of the hatching muscle and its development is given by Fisher (1961). The first eggs laid are about 8% lighter than subsequent eggs within clutches (Forbes and Ankney 1988), but variation in egg weight probably has little effect on the vigor of individual hatchlings (Arnold 1989).

Adults usually divide brood. Age at first flight has been estimated at 35 days (Kirby 1976, Forbes and Ankney 1987). Age at first breeding may be as early as 13 months (MacVean 1990). Solitary nesters and defend relatively small territories of as little as less than two ha (Glover 1953) that provide food, cover, and nest sites. Territorial birds also sometimes forage outside their defended areas. Highly territorial and usually only one pair nests at a wetland (Faaborg 1976, Sealy 1978). Wetlands more than five ha, however, may support more than one pair (Palmer 1962, Faaborg 1976), and large marshes with suitable habitat support multiple pairs (Chabreck 1963).

NESTING PERIOD: Initiation of nesting activity varies throughout the range, occurring as early as April and as late as June, and peaking in May in most areas. Examples of nesting periods are 3 May to 10 September for 107 nests in Louisiana (Chabreck 1963), 2 May to 8 August for 138 nests in Iowa (Glover 1953), and 3 May to 22 August in Ontario (Johnsgard 1987). Although some pairing may occur on wintering areas (Palmer 1962), courtship begins soon after ice-out following arrival at nesting areas. Courtship behavior is mutual and less formalized than other species of grebes (Palmer 1962).

NESTS AND EGGS: Both sexes build nests and may add plant material and mud as the season progresses and as nests slowly sink (Fjeldsa 1975). Air-pockets in green plants and trapped gases generated by the fermenting and rotting vegetation give the nest buoyancy. The floating, rotting nest generates substantial quantities of heat, and many aspects of reproduction may be related to their use of a warm, humid nest (Davis et al. 1985). Nests have a hollow to hold the eggs, and may extend 90 cm below the surface but only eight cm above (Glover 1953). The eggs have a threefold increase in pore density, compared to other birds' eggs, which enables the eggs to lose sufficient water within the humid confines of the nest prior to hatching (Davis et al. 1985). When leaving the nest, adults cover their eggs with plant material, and the rotting nest, where temperatures may remain 11-13 degrees Celsius higher than the surrounding water, can provide enough heat to incubate the eggs in the adults' absence (Davis et al. 1985). Time constraints imposed by incubation may thereby be lessened, providing adults with more time for foraging and territory defense.

NESTING SUCCESS: High nest success has been reported in many areas: 70% of 138 nests in Iowa (Glover 1953), 77% of 150 nests in Wisconsin (Otto 1983), 90% of 107 nests in Louisiana (Chabreck 1963), and 90% of 115 nests in Nova Scotia (Forbes et al. 1989) hatched one egg or less. Wind and high waves, fluctuating water levels, and predation can be significant sources of nest loss. Of 42 nests in Manitoba, 69% failed, mostly due to flooding from high waves (Sealy 1978). Half of total nest loss in Iowa was due to wave action or water level fluctuation and 25% to raccoon (PROCYON LOTOR) predation (Glover 1953). In Nova Scotia, nest loss resulted from predation, including crows (CORVUS BRACHYRHYNCHOS) and poor weather (Forbes et al. 1989). In comparison to clutch sizes, observations of relatively small broods, e.g., averaging 4.4 (Chabreck 1963) and 2.9 (Yocum et al. 1958), suggest that substantial chick mortality occurs. Snapping turtles (CHELYDRA SERPENTINA) may represent important predators of young (Coulter 1957). Females are indeterminate layers (Fugle and Rothstein 1977), and frequently replace lost clutches, usually renesting within 50 m of destroyed nests (Glover 1953, Forbes et al. 1989).

CHICK REARING: Adults usually divide broods and provision chicks with a variety of small-sized prey, including dragonfly naiads, dytiscid beetle larvae, leeches, and salamanders (Forbes and Ankney 1987). Chicks usually remain near parents, and frequently ride on the backs of adults, even during foraging dives (Forbush 1925). Initial size disparities of chicks, due to asynchronous hatching, influence food allocation within broods. Aggression among chicks is high when rates of food-delivery by adults are low, and larger chicks win more disputes over food than smaller chicks (Forbes and Ankney 1987). The bare loral area of chicks changes from dull-colored to bright crimson in hungry chicks, however, and adults may use this indicator of nutritional status to allocate food among members of a brood (Forbes and Ankney 1987). Two unusual forms of chick provisioning occur: for unknown reasons, chicks are occasionally fed by adults other than pair members (Forbes 1987), and young grebes from first broods may feed young from second broods (Cramp et al. 1977).

Ecology Comments: Residents in pairs or family groups; more gregarious in winter (Stiles and Skutch 1989), with groups commonly including 100 or more. Generally one nesting pair on ponds up to 4 ha, but sometimes many more. One study recorded defended area of 46 m radius around nest, though nests sometimes closer than this (Johnsgard 1987). Mean distance between successful nests 55 meters (n=96; Chabreck 1963). Average home range 1.3 hectares (n=44; Glover 1953), but some as large as 35 hectares (Muller 1995).

Little is known about sources of mortality. Avian botulism, avian cholera, and gizzard worms are known to occur in grebes (Friend 1987). Predators include cottonmouths (AGKISTRODON PISCIVORUS) (Leavitt 1957), peregrine falcons (FALCO PEREGRINUS) (Buckalew 1948), and American alligators (ALLIGATOR MISSISSIPPIENSIS) (Delany 1986). Coulter (1957) reported substantial predation by snapping turtles in Maine.

Sometimes associate with other birds to enhance foraging opportunities. Have been observed in mutualistic foraging associations with snowy egrets (EGRETTA THULA) in Virginia (Leck 1971), snowy egrets and tricolored herons (HYDRANASSA TRICOLOR) in North Carolina (Mueller et al. 1972), and boat-tailed grackles (QUISCALUS MAJOR) in Mississippi (Jackson 1985).

Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: Y
Mobility and Migration Comments: Northern populations are migratory (south to western Panama), southern populations are sedentary (AOU 1983). Northward migration begins in March, and arrival at nesting areas in April and early May is dependent on timing of spring thaw (Cramp et al. 1977). Occasionally occurs in close-massed flocks during migration. Fall migration is protracted and begins in August, with the majority of migrants moving south between September and November (Cramp et al. 1977). Migration usually takes place at night. Freezing temperatures sometimes force birds to move short distances southward during mid-winter. During winter, may occur in large, dispersed flocks occasionally of more than 1,000 birds and commonly 100 birds.
Estuarine Habitat(s): Bay/sound, Lagoon, River mouth/tidal river
Riverine Habitat(s): Low gradient
Lacustrine Habitat(s): Deep water, Shallow water
Palustrine Habitat(s): HERBACEOUS WETLAND
Habitat Comments: BREEDING: In eastern U.S., occurs in ponds, sloughs, and marshes, in marshy inlets and along edges of rivers, lakes, and reservoirs, and occasionally in estuarine wetlands (Palmer 1962, Chabreck 1963, Cramp et al. 1977, Andrle and Carroll 1988). Nests are typically built in shallow water surrounded by dense vegetation, especially cattail (TYPHA spp.) and bulrush (SCIRPUS spp.), and are farther from shore than from open water (Glover 1953, Stewart 1975, Faaborg 1976, Sealy 1978, Forbes et al. 1989). Wind and waves are major threats to floating nests and surrounding emergent vegetation acts as a wave break, anchors the nest, and conceals the nest from predators (Forbes et al. 1989). Because the direction of wind and waves shifts frequently during the nesting season, sheltered nesting sites can be limiting (Faaborg 1976). In Nova Scotia, avoided nesting on edges of stands of emergent vegetation that were exposed to wave action, and nest-site selection was related to structure but not type of vegetation available (Forbes et al. 1989). In comparison to randomly chosen marsh locations, nests were characterized by greater distance from shore, increased proximity to open water, and deeper water (Forbes et al. 1989).

Microhabitats at Manitoba wetlands included the densest and tallest stands of emergent vegetation available, particularly those in deeper portions of ponds (Nudds 1982). In Iowa, always associated with dense stands of emergent, littoral vegetation, and avoided wetlands with 100% open water (Faaborg 1976). On moist-soil impoundments in Missouri, habitat use was associated with water > 25 cm deep and vegetative cover characterized as "open, sparse, or short" (Fredrickson and Reid 1986). Grebe use was not associated with shallower waters or "dense" or "rank" emergent vegetative cover (Fredrickson and Reid 1986).

NON-BREEDING: Habitats in winter and migration similar to breeding areas (Cramp 1977), but many shift to more exposed areas on brackish, estuarine waters or sheltered inlets on large lakes, rivers, and salt water (Palmer 1962). Root (1988) noted that the densest overwintering populations occur on wide rivers and large lakes.

Adult Food Habits: Invertivore, Piscivore
Immature Food Habits: Invertivore, Piscivore
Food Comments: Dives from surface; eats mainly fishes, crustaceans, insects; also amphibians, other invertebrates, and some plant material (Terres 1980). Forages mainly by short dives in shallow water. Wetmore (1924) analyzed stomach contents of 174 pied- billed grebes collected during different seasons from localities throughout North America. The diet was dominated by fish (24% by volume, including catfish, eels, perch, sunfish, suckers, carp, and minnows), crustaceans (31%), and insects (46%). Most crustaceans taken were crayfish, and insect food was predominantly Odonata (dragonflies and damselflies), Heteroptera (bugs), and Coleoptera (beetles). A strong seasonal shift in diet was observed; fish were important foods during the nonbreeding season, but were relatively unimportant during nesting. Odonates, only 8% of the overall annual diet, constituted 34% of the diet during July and August.

Eight stomachs from British Columbia contained mostly fish, while Odonates comprised most of the contents of stomachs from three downy young (Munroe 1941). Palmer (1962) reported that grebes fed principally on leeches during the breeding season in South Carolina. Stomachs from Pennsylvania contained fish, frogs, aquatic insects, especially beetles, and aquatic plants (Warren 1890). The stout bill and heavy jaw musculature (Zusi and Storer 1969) may be adaptations that enable grebes to take larger fish than other sympatric species of grebes (Forbes 1989).

Feather-eating is an unusual aspect of the diet. Wetmore (1924) observed feathers in 52% of the 174 stomachs he examined, and adults sometimes feed feathers to their chicks (Ehrlich et al. 1988). Feather-eating may pad and protect the stomach and trap fish bones so that bones can dissolve slowly in the stomach rather than passing directly into the fragile intestine (Storer 1961). Also, hard, indigestible materials, such as chitin and bones, may be felted together with feathers prior to regurgitation as pellets (Storer 1961).

Pied-billed grebes have a number of morphological adaptations for pursuing prey underwater. Their toes are lobed and their tail is short and rudder-like. Their feet are situated far back on the body and can be pivoted high above the back to permit quick forward propulsion and a high degree of maneuverability underwater (Fjeldsa 1975, Cramp et al. 1977). Their small, narrow wings also are used for underwater swimming (Forbush 1925). The eyes of pied-billed grebes have cone-dense retinas that permit detection of small prey at close range in shallow waters, compared to more deeply diving grebes that have rod-dense retinas (Begin and Handford 1987). Grebes compress their feathers to expel trapped air and submerge more easily, and, compared to other birds, generally have many more feathers (ca. 20,000), which enable grebes to stay waterborne continuously (Fjeldsa 1975).

In Florida, may stir up sediments with the feet to bring prey into view (King 1974). In California the duration of 154 foraging dives ranged from one to 15 s (average 7.6 s (Bleich 1975)), with grebes moving only 3.7 m, on average, between dives. Escape dives to avoid disturbance lasted longer and ended farther away than foraging dives (Bleich 1975). These grebes frequently sunbathe between foraging dives; this may be an important means of heat conservation, especially for females (Ryan and Heagy 1980).

Adult Phenology: Diurnal
Immature Phenology: Diurnal
Length: 34 centimeters
Weight: 442 grams
Economic Attributes Not yet assessed
Management Summary
Stewardship Overview: Secretive wetland birds that are widely distributed across the Northeast. Little is known about their population size and stability because it is difficult to detect them on bird surveys currently conducted in the Northeast. Specialized surveys using point-counts and tape-recorded vocalizations in wetlands are necessary to determine the presence of breeding birds. Prefer moderately deep wetlands with large areas of aquatic-bed vegetation and open water for feeding, and dense areas of emergents for nesting. Readily use artificial wetlands at managed impoundments. The large clutch size coupled with their ability to raise two broods per year suggest that the management potential for populations is high. Northern populations are migratory and dense wintering populations occur at inland sites in the southern U.S.
Species Impacts: May be aggressive toward other birds with similar diet and habitat requirements, and the presence of grebes is sometimes considered by wetland managers to be detrimental to waterfowl production (Kilham 1954, Kirby 1976).
Restoration Potential: Will colonize artificial wetlands created by surface-mining (Perkins and Lawrence 1985) and abandoned industrial settling ponds (Rickard et al. 1981). Readily uses artificial wetlands at managed impoundments such as at state and federal waterfowl refuges (Andrle and Carroll 1988; Gibbs et al., in press). Artificial impoundments are thought to have reversed population declines in some areas and led to local population increases in others (Bull 1974). Their ability to renest following nest loss and raise two broods per year, its relatively large clutch size (up to seven eggs), and its tolerance of a wide range of habitat conditions, suggest that, given a stable habitat base, management potential for populations is high (Gibbs and Melvin 1992).
Preserve Selection & Design Considerations: Minimum wetland area is an important consideration in preserve design. Grebes typically occur on wetlands above a minimum threshold size, although this "minimum area" varies regionally. Minimum area requirements appear to be as large as five ha in the Midwest and Northeast (Brown and Dinsmore 1986; Gibbs et al., in press; Gibbs and Melvin 1990), although sites in the Midwest as small as 0.5 ha are used occasionally (Faaborg 1976). If provided with suitable habitat, large breeding populations can be supported on a single, managed wetland, e.g., up to 107 pairs have nested on an 81-ha impoundment in Louisiana (Chabreck 1963).

Moderately deep (0.25-2 m), stable waters represent an important feature of habitats for nesting. Key physical features of breeding areas also include large areas of aquatic-bed vegetation and open water, which can serve as deepwater feeding sites, interspersed with dense growth of robust emergents, with some patches over 100 m from shorelines that can serve as predator-free nest sites. Protection from human disturbance is important, e.g., from boats whose wakes can flood nests and recreationists whose presence can disturb incubating birds. Preserves also should be protected from upland run-off that may transport silt and contaminants and thereby lower wetland productivity and reduce food supplies (Gibbs and Melvin 1992).

In Maine, occurred only in wetlands > five ha in size, and were more common on wetlands impounded by beavers (CASTOR CANADENSIS) or humans than in wetlands of glacial origin (Gibbs et al. in press, Gibbs and Melvin 1990). Wetlands used by grebes had, on average, more aquatic-bed (submerged and floating vegetation) and emergent vegetation than did unused wetlands. In Iowa, individuals were observed at only 44 seasonal and semi-permanent wetlands among > 500 ponds and lakes surveyed (Faaborg 1976). Used wetlands of intermediate size (0.6-7.0 ha), but seemed to avoid either smaller or larger wetlands (Faaborg 1976). Another Iowa study suggested that the occurrence was dependent on wetland area because grebes occurred regularly only at wetlands > five ha (Brown and Dinsmore 1986). Wetlands as small as 0.3 ha, however, were used in Manitoba (Nudds 1982). In eastern Washington, 80% of broods were found at potholes of only 0.4-2.0 ha (Yocum et al. 1958).

Management Requirements: In the northeastern U.S., preservation of large, deepwater fresh and brackish marshes is the most important management need; managed waterfowl impoundments often provide prime nesting and migration habitat, and future efforts to protect or create wetlands significant to waterfowl could benefit the grebe (Gibbs and Melvin 1992). Preservation of relatively large (> 10 ha) wetlands with an interspersion of dense, robust emergents, submergent vegetation, and open water, is the most urgent management need in the Northeast. Wetlands used for breeding also need to be protected from chemical contamination, siltation, eutrophication, and other forms of pollution that harm grebes or their food supplies. Vegetative features of preferred habitats represent a particular stage of wetland succession ("hemi-marsh" stage of Weller and Spatcher 1965). Wetland managers, therefore, need to periodically reverse vegetative succession and open up extensive stands of emergent vegetation while maintaining suitable habitats nearby to serve as alternate nesting areas during wetland manipulations. In the northeastern states, wetlands characterized as deep, fresh marshes are perhaps best suited for nesting. For states with substantially reduced populations (e.g., Rhode Island, Connecticut, and New Jersey), creation of nesting habitats may be necessary to restore viable populations. Managed impoundments could also bolster nesting populations in areas where marshlands were scarce originally (e.g., central Pennsylvania, central and western Virginia, and West Virginia).

Because grebes occur in many wetlands managed for waterfowl by state and federal agencies, there is ample opportunity for making minor alterations to existing management schemes to improve nesting habitat. For example, portions of dense stands of cattail and bulrush, which are often removed with cutting, burning, or flooding treatments to improve waterfowl habitat, should be retained as nesting sites. Maintaining stable water levels during the nesting season prevents flooding of nests (a major source of reproductive failure) and predator access. Heavily dependent on aquatic-bed vegetation (floating-leaved and submergent) and management activities that promote establishment and growth of such vegetation will benefit grebes (Gibbs and Melvin 1992). Manipulation of water levels (Fredrickson and Taylor 1982) provides a cost-effective method for establishing dense stands of emergent vegetation while retaining open-water areas preferred by grebes.

Given the dependence of nesting birds on Odonates and small fish (Wetmore 1924), complete drying during wetland drawdowns should be avoided to prevent die-offs of dragonflies, many of which overwinter in late instars rather than in drought-resistant eggs (Orians 1980), and fish. The presence of carp may significantly lower availability of invertebrate foods for grebes and other waterbirds. Liming and fertilizing dikes and adjacent fields can increase the productivity and raise the pH of nutrient-poor, acidic wetlands in the northeastern region. Floating nests are easily washed over and capsized by wave action, and thus large, motorized boats should be excluded from marshes with nesting grebes. Recreation activity should be restricted during the nesting season to avoid disturbance to incubating grebes (Gibbs and Melvin 1992).

Monitoring Requirements: Standardized surveys that adequately monitor population and habitat trends are needed (Gibbs and Melvin 1992). Development of standardized surveys to monitor populations is critical because there are currently few population data on which to base management decisions. Standard monitoring procedures for bird populations encounter grebes at frequencies too low to assess population trends in most areas. They use localized wetland habitats that usually occur away from roads, and the seasonal peak of vocal activity (May) tends to occur earlier in the year than Breeding Bird Survey routes are run. Population monitoring programs should accompany any management activities to determine the success or failure of wetland manipulations.

Surveys of populations should be conducted during the peak nesting season, and can be readily justified if coordinated with surveys of other marshbirds (Swift 1987, Manci and Rusch 1988, Gibbs and Melvin 1990), many of which also are of management concern, e.g., least bittern (IXOBRYCHUS EXILIS), American bittern (BOTAURUS LENTIGINOSUS), and black tern (CHLIDONIAS NIGER). Surveys can evaluate population responses to habitat features in addition to monitoring population trends. Annual surveys (for two to three years) of many sites could provide baseline data on the distribution and abundance in a region. Subsequent surveys (perhaps every five years) could then be used to assess population trends. Broadcast of tape-recorded calls is useful for locating territorial birds (Kibbe 1989, Gibbs and Melvin 1990). Standardization of survey methodology is necessary for results to be comparable between years and among areas, and would be facilitated by having a single regional or national agency or organization responsible for directing and coordinating survey efforts (Gibbs and Melvin 1992).

Management Research Needs: From Gibbs and Melvin (1992): 1) Conduct surveys to better determine relative abundance and distribution in the Northeast. 2) Develop standardized survey techniques and implement programs to monitor trends in populations and habitat availability. 3) Conduct detailed studies of the floristic and structural composition of wetland vegetation, water levels and water quality, and minimum wetland area associated with the occurrence of grebes during nesting and migration. 4) Determine the effects of diseases, parasites, contaminants and weather. 5) Investigate effects of altering management strategies at wetland impoundments managed primarily for waterfowl in order to benefit grebes. 6) Monitor contaminant levels in adults and eggs in agricultural and industrialized regions. 7) Determine major migration stop-over sites and study over-wintering habitats and biology. 8) Evaluate the effects of invasion of phragmites (PHRAGMITES AUSTRALIS) and purple loosestrife (LYTHRUM SALICARIA).
Population/Occurrence Delineation
Group Name: Grebes

Use Class: Breeding
Subtype(s): Foraging Area, Nesting Area
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.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Separation distances are arbitrary. Unsuitable habitat: upland areas.

Home ranges during the breeding season usually quite small; each pair of Red-necked Grebes defends up to about 114 meters of shoreline and associated waters, where all activities take place (Palmer 1962). Pied-billed Grebes: average home range 1.3 hectares (a circle with a diameter of about 130 meters; Glover 1953), although occasionally as large as 35 hectares (Muller 1995).

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): .11 km
Inferred Minimum Extent Justification: Based on conservative home ranges of Red-necked and Pied-billed Grebes.
Date: 28Oct2004
Author: Cannings, S., and G. Hammerson

Use Class: Nonbreeding
Minimum Criteria for an Occurrence: Evidence of recurring presence of flocks (including historical) outside the breeding season; and potential recurring presence at a given location. Normally only areas where concentrations greater than 50 birds occur regularly for at least 20 days per year would be deemed EOs.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Separation distance is arbitrary, set at 10 kilometers to define occurrences of managable size for conservation purposes. Occurrences defined primarily on the basis of areas supporting concentrations of foraging birds, rather than on the basis of distinct populations.

Unsuitable habitat: upland areas.

Date: 28Oct2004
Author: Cannings, S., and G. Hammerson
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
NatureServe Conservation Status Factors Edition Date: 22Apr1987
Management Information Edition Date: 31Dec1992
Management Information Edition Author: GIBBS, J.P., AND S.M. MELVIN; REVISIONS BY D.W. MEHLMAN AND G. HAMMERSON
Management Information Acknowledgments: Parts of this abstract were originally published by the U.S. Fish and Wildlife Service in Schneider and Pence (1992). Funding for the preparation of the original document was made possible by the U.S. Fish and Wildlife Service, Newton Corner, MA. The authors are grateful to the library staff of the Smithsonian Institution, the Patuxent Wildlife Research Center (U.S. Fish and Wildlife Service), and the Peabody Museum at Yale University for bibliographic assistance. J. Longcore and D. McAuley facilitated a bibliographic computer search and provided other logistical support. The Maine Department of Inland Fisheries and Wildlife provided office space and computer access during the preparation of this report. Critical review of an earlier draft of this report was provided by P. Novak. K.E. and H.C. Gibbs provided much indirect support to J.P.G.
Element Ecology & Life History Edition Date: 21Feb1995
Element Ecology & Life History Author(s): HAMMERSON, G.

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