Aechmophorus occidentalis occidentalis
Status: Common, locally abundant, regular spring and fall migrant west and central, uncommon east. Locally common regular breeder western Sandhills, rare casual elsewhere north and west. Rare regular summer visitor west and west-central, rare casual elsewhere. Rare casual winter visitor lower North Platte River Valley.
Documentation: Specimen: UNSM ZM14365, summer 1982 Keith Co.
Taxonomy: Two subspecies are recognized, occidentalis in western North America and ephemeralis in western Mexico (Clements et al 2016). Nebraska birds are occidentalis.
This species and Clark’s Grebe, A. clarkii, were formerly considered color morphs of a single species, but a high degree of assortative mating (Ratti 1979, Nuechterlein 1981, Nuechterlein and Storer 1982), led to elevation of the morphs to species status (AOU 1983). The two species are sympatric, although Clark’s Grebe is predominant southward (Sibley and Monroe 1990).
Hybridization occurs between the two Aechmophorus species. Konter (2011) found around 3.5% of birds in sympatric breeding populations in California and Oregon were intermediate, and that the percentage of intermediates had increased since earlier studies (Ratti 1979, 1981). Nevertheless, Konter (2011) found sufficient assortative mating between the two species to continue to consider them separate species. Pyle (2008), however, considered the two conspecific.
Two intermediates at Lake McConaughy, Keith Co 27 Sep 1996 had bright orange bills typical of Clark’s Grebe and dark lores typical of Western Grebe; Ratti (1981) noted that bill color is “not as discrete as the facial pattern” and “alone should not be used to identify these species.” Other reported intermediates were at North Platte NWR, Scotts Bluff Co 15 Aug 1997, 1-2 at Lake McConaughy 18 Apr and 9 May 1998, and one with an orange bill and black feathering below its eye was in Dodge Co 27 Nov 2014.
Spring: Mar 19, 21, 22 <<<>>> summer (west and west-central); Apr 10, 11, 14 <<<>>> Jun 10, 12, 14 (elsewhere)
Migration peaks in late April; fewer birds occur in the east. There are earlier westerly reports of three on 4 Mar 2001 at Lake Ogallala, Keith Co, 13 on 9 Mar 2001 Lake McConaughy, and 16 Mar 1962 Lincoln Co, and an easterly report 30 Mar 2011 in Platte Co. A later date was of three at Harlan Co Reservoir, Harlan Co 19 Jun 2017.
- High counts: 30,000 at Lake McConaughy 30 Apr 2018, 18,000 there 22 Apr 2000, 14,500 there 19 Apr 1997, and 14,100 there 16 May 2008. An estimate of 100,000 at Lake McConaughy 23 Apr 2014 was based on a “few birds per acre” on this 14,164 hectare (35,000 acre) lake.
Summer: Highest breeding densities occur in western Sandhills (Wampole and Fichter 1946; Rosche 1982) as well as on Lake McConaughy and Keystone Lake in Keith Co, where breeding was first observed in 1993 (Rosche 1994). Away from these locations records are few; of a family group including three half-grown unfledged young was on the south pond at North Platte SL, Lincoln Co 16 Sep 2010, it bred at Carson Lake, northwest Garfield Co (Blake and Ducey 1991), and an adult carrying a chick was photographed at Harlan Co Reservoir, Harlan Co 16 Jun 2018. Ducey (1988) cited reports of nesting in McPherson Co in 1969 and Lincoln Co in 1972, but no details are available.
Western Grebes routinely occur at lakes away from breeding areas in late Jun and early Jul, primarily in the west. Large numbers at Lake McConaughy from Jun-Jul, far in excess of the breeding population there, are presumably non-breeding immatures, such as the 1715 there 19 Jun 2004. Elsewhere there are numerous reports statewide away from breeding areas of small numbers during late Jun-Aug.
- Breeding Phenology:
Eggs: 6 Jun-11 Jul
Dependent Young: 21 Jun-16 Jul
Fall: summer <<<>>> Dec 6, 6, 7 (west, central)
Sep 15, 19, 27 <<<>>> Dec 2, 2, 3 (east)
Earlier dates include three on 13 Aug 2006 on the Missouri River near Niobrara, Knox Co, and later dates away from Lake McConaughy and Sutherland Reservoir are of singles at Branched Oak Lake, Lancaster Co 5-6 Dec 2009, in Sarpy Co 7 Dec 2015, in Frontier Co 12 Dec 2010, at North Platte NWR 12 Dec 1997, at Offutt Air Force Base Lake, Sarpy Co 13 Dec 1996, on the North Platte CBC 21 Dec 2014, and at Harlan Co Reservoir 1 Jan 2000.
Movement away from breeding sites may occur as early as mid-Jul shortly after juveniles are capable of flight. Lake McConaughy is a major fall staging area for the species; high count there is 44,000 carefully estimated on 27 Sep 2000. Large numbers occur on occasion at Sutherland Reservoir, Lincoln Co; 2300 were there 16 Oct 2016, and 1000 on 18 Aug 2005.
At Lake McConaughy and Sutherland Reservoir, a few birds linger late into Dec and may overwinter (see Winter).
- High counts: 44,000 at Lake McConaughy 27 Sep 2000, 37,000 there 21 Sep 2014, and 35,000 there 26 Sep 1999.
Winter: Recently, small numbers have overwintered in the Kingsley Dam, Keith Co vicinity; first midwinter report there was of two at Lake Ogallala 5 Feb 1995. One wintered 1996-97, and in the mild winter of 1997-98 as many as 342 were present 3 Jan, 71 on 15 Jan, and 14 were still present 22 Feb. As many as 365 were at Lake McConaughy 1 Jan 1999, but only one remained as late as 19 Feb. During the winter 1999-2000, numbers declined from 656 on 2 Dec to 155 on 19 Feb. In 2010-2011, 776 were still present 2 Jan, but only one remained 31 Dec 2016. There were 255 counted on the Lake McConaughy CBC 29 Dec 2012, but only one was found by 16 Feb. In 2018-2019, 79 were still present 5 Jan and one on 13 Jan. It is not known whether declining numbers through winter are due to departure or death.
At Sutherland Reservoir, first known overwintering was in 1997-98, when two were noted 14 Jan; one was there 3 Jan 2011, “a few” were there 7 Jan 2007, and 1-2 were there 10-18 Feb 2017, and 1-2 20 Dec-2 Feb 2019.
CBC: Christmas Bird Count
NWR: National Wildlife Refuge
SL: Sewage Lagoons
WMA: Waterfowl Management Area (State)
Photograph (top) of a Western Grebe near Chadron, Dawes Co 24 Jun 2013, courtesy of NEBRASKAland Magazine/Nebraska Game and Parks Commission.
American Ornithologists’ Union [AOU]. 1983. The AOU Check-list of North American birds, 6th ed. Allen Press, Lawrence, Kansas, USA.
Blake, L., and J. E. Ducey. 1991. Birds of the eastern Sandhills in Holt County, Nebraska. NBR 59: 103-132.
Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2016. The eBird/Clements checklist of birds of the world: v2016, accessed 30 January 2018.
Ducey, J.E. 1988. Nebraska birds, breeding status and distribution. Simmons-Boardman Books, Omaha, Nebraska, USA.
Konter, A. 2011. Interbreeding of Aechmophorus grebes. Wilson Journal of Ornithology 123: 132-136.
Nuechterlein, G.L. 1981. Courtship behavior and reproductive isolation between Western Grebe color morphs. Auk 98:335-349.
Nuechterlein, G.L., and R.W. Storer. 1982. The pair-formation displays of the Western Grebe. Condor 94: 351-69.
Pyle, P. 2008. Identification Guide to North American Birds. Part II, Anatidae to Alcidae. Slate Creek Press, Bolinas, California, USA.
Ratti, J.T. 1979. Reproductive separation and isolating mechanisms between sympatric dark- and light-phase Western Grebes. Auk 96: 573-586.
Ratti, J.T. 1981. Identification and distribution of Clark’s Grebe. Western Birds 12: 41-46.
Rosche, R.C. 1982. Birds of northwestern Nebraska and southwestern South Dakota, an annotated checklist. Cottonwood Press, Crawford, Nebraska, USA.
Rosche, R.C. 1994. Birds of the Lake McConaughy area and the North Platte River valley, Nebraska. Published by the author, Chadron, Nebraska, USA.
Sibley, C.G., and B.L. Monroe, Jr. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, Connecticut, USA.
Wampole, J., and E. Fichter. 1946. Western Grebes nesting at George Lake, Grant County. NBR 14: 45.
Silcock, W.R., and J.G. Jorgensen. 2018. Western Grebe (Aechmophorus occidentalis), Version 1.0. In Birds of Nebraska — Online. www.BirdsofNebraska.org
Birds of Nebraska – Online