Abstract

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Allen, J.H., G.L. Nuechterlein, and D. Buitron. 2005. Lake Christina reclamation: consequences of biomanipulation on use by nongame waterbirds. Final report submitted to the State Wildlife Grants Program. 53 pp. State Wildlife Grants Program final report.

Abstract:

We examined the use of Lake Christina, Minnesota, by nongame waterbirds, following an application of rotenone to eliminate its fish base in the fall of 2003. During weekly shoreline surveys conducted during the open water seasons of 2004 and 2005, individuals of 17 species of nongame waterbirds were counted. Migrant flocks of up to 95 double-crested cormorants (Phalacrocorax penicillatus), 74 pied-billed grebes (Podilymbus podiceps) and 2,100 ring-billed gulls (Larus delawarensis) were seen briefly during spring or fall counts. The most common summer residents were western grebes (Aechmophorus occidentalis), American white pelicans (Pelecanus erythrorhynchos), great egrets (Ardea alba) and black terns (Chlidonias niger). Western grebes were the most numerous nesting waterbird on the lake. Although over 240 western grebes were counted on Lake Christina in the spring of 2004, by the middle of June most had left the lake and no successful nesting occurred. During this same period, very few fish of the appropriate size for grebes were being trapped in the lake, and we suggest that although the emergent vegetation (bulrush, Scirpus spp.) was suitable for nesting, the lack of food prevented all but a few attempts. Shoreline counts of western grebes on neighboring Pelican Lake suggest that many western grebes originally on Lake Christina temporarily moved to this fish-rich lake in June and July. The only non-game waterbirds observed attempting to nest in 2004 were black terns, but they failed to hatch any young.

In 2005, minnow numbers were much higher throughout the spring and summer, and over 200 western grebes were counted on the lake by early June. Western grebes began nesting on 15 June, with over 100 nests initiated during the next 4 days. We located a total of 315 western grebe nests, of which 198 hatched at least one young (63% of all attempts). Complete clutches averaged 3.1 eggs, and all but one nest had hatched by August 10. Over 50 black terns were counted on Lake Christina in the spring of 2005. Of the 10 black tern nests located, three hatched young. Three additional nongame waterbirds nested successfully during 2005: Clark's grebe (A. clarkii), red-necked grebe (Podiceps grisegena), and pied-billed grebe.

In addition to the variety of nongame waterbirds observed using lake Christina, 16 species of ducks, geese and coots were also observed, primarily during migration. By far the most numerous species of all was the American coot (Fulica americana), with over 41.000 seen in the fall of 2004 and over 132,000 in the fall of 2005. Over 300 blue-winged teal (Anas discors), Canada geese (Branta candensis), wood ducks (Aix sponsa) and ring-necked ducks (Aythya fuligula) were also counted within single surveys during spring and fall migrations.

The presence of minnows was critical to the successful breeding of western grebes on Lake Christina. Sufficient emergent vegetation existed to support a large colony of western grebes, with 215 simultaneously active nests in 2005. Considering that many of the 315 nests were probably second or third nesting attempts, this important colony appeared to have very high nesting success in 2005. Lake Christina is clearly an important nesting lake for the colonially nesting western grebe, as well as a major stopover for a variety of both game and nongame waterbirds during the spring and fall migrations.

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