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Least Bittern Nesting Sites at Reelfoot Lake, Tennessee
Nicholas A. Winstead and Sammy L. King

Southeastern Naturalist, Volume 5, Number 2 (2006): 317–320

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2006 SOUTHEASTERN NATURALIST 5(2):317–320 Least Bittern Nesting Sites at Reelfoot Lake, Tennessee Nicholas A. Winstead1,2,* and Sammy L. King1,3 Abstract - Relatively little is known about Ixobrychus exilis (Least Bittern) nesting sites. We searched for Least Bittern nests on Reelfoot Lake and nearby Black Bayou Waterfowl Refuge, TN, May–July 2003. We located 8 nests at Reelfoot Lake, where Decodon verticillatus (swamp loosestrife) dominated emergent communities. We also discovered 2 nests at Black Bayou, where Zizaniopsis miliacea (giant cutgrass) dominated emergent communities. D. verticillatus was the dominant plant species within 60 m of most nests. Z. miliacea dominated within 5 m of most nests, and most nests were made of Z. miliacea. We found a nest with 2 white-colored chicks and 2 ochre-colored chicks, which may be the first such instance reported. Introduction Ixobrychus exilis J.F. Gmelin (Least Bitterns) are wetland-dependent birds (Gibbs et al. 1992) that are a species of conservation concern in Tennessee (TDEC 2004). Tennessee has lost 59% of its original 810,000 ha of wetlands (Dahl 1990), and much of the remainder is hydrologically altered. Less than 1% of what remains is dominated by herbaceous vegetation (Wear and Greis 2002) that Least Bitterns typically use for nesting habitat (Gibbs et al. 1992). Least Bitterns usually construct nests in tall, grass-like emergent vegetation such as Typha sp. L. (cattails), Carex sp. L. (sedges), and Scirpus sp. L. (rushes) (Weller 1961), and Least Bitterns commonly used Z. miliacea on Reelfoot Lake in the past (Simpson 1939). Shifts in plant species composition can alter nesting habitat associations; thus, Least Bittern nesting habitat associations near Reelfoot Lake may have changed. We conducted nest searches and analysis of nest-site characteristics on Reelfoot Lake and Black Bayou Waterfowl Refuge to determine nesting habitat associations. Study Site Reelfoot Lake is a 6300-ha publicly owned lake in west Tennessee. Zizaniopsis miliacea (Michx.) Doell and Aschers. (giant cutgrass) formerly occupied 1000 ha of the lake (Burbank 1963) coincident with exceptionally high densities of Least Bitterns (Mengel 1965). However, hydrologic alterations and excessive inputs of sediments and nutrients have shifted the emergent vegetation community from a grass-dominated (Z. miliacea) community to one dominated by the shrub Decodon verticillatus (L.) Ell. 1Department of Forestry, Wildlife, and Fisheries, University of Tennessee, Knoxville, TN 37996. 2Current address - Mississippi Department of Wildlife, Fisheries and Parks, Mississippi Museum of Natural Science, 2148 Riverside Drive, Jackson, MS 39202. 3Current address - US Geological Survey, Louisiana Cooperative Fish and Wildlife Research Unit, 124 School of Renewable Natural Resources, Louisiana State University AgCenter, Baton Rouge, LA 70803. *Corresponding author - 318 Southeastern Naturalist Vol. 5, No. 2 (swamp loosestrife; Winstead 2004). Marsh area has declined to 500 ha, with 93% now consisting predominantly of dense uninterrupted stands of D. verticillatus (Winstead 2004). Black Bayou Waterfowl Refuge is a wetland with semi-permanently flooded units adjacent to Reelfoot Lake. The 21-ha Black Bayou unit surveyed during this study was dominated by an even interspersion of Z. miliacea and open water (hemi-marsh). Methods We searched Reelfoot Lake and Black Bayou for Least Bittern nests during May–July 2003; Reelfoot Lake was searched from the open water edge by boat, and Black Bayou was searched on foot. The search area encompassed approximately 18 km of shoreline on Reelfoot Lake and 21 ha on Black Bayou. We examined the condition and construction of nests, and recorded nest locations with a GPS. We used aerial photographs with 60-m radius circles drawn around each nest to delineate vegetation types and analyze habitat data. Habitat variables included percent cover of Z. miliacea, D. verticillatus, Nuphar luteum (L.) J.E. Smith (cow lily), woody species, other emergents, and open water. We digitized these photographs in ArcView 3.2, and calculated the area of each vegetation type within 60-m and 5-m radius circles. Results We found 10 active Least Bittern nests, 8 on Reelfoot Lake and 2 on Black Bayou. The average nest had relatively even proportions of open water and vegetation within 60 m, with 49% open water, 30% D. verticillatus, 15% Z. miliacea, and 3% N. luteum (Table 1). D. verticillatus was the dominant species within 60 m at 7 nests and Z. miliacea the dominant species at 3 (Table 1). The average nest had relatively even proportions of open water and vegetation within 5 m as well, with 47% open water, 38% Z. miliacea, 10% N. luteum and 5% D. verticillatus (Table 2). Z. miliacea was the dominant species within 5 m of 7 nests, D. verticillatus was dominant at 1, and N. luteum was dominant at 2, followed by Z. miliacea (Table 2). All nests were < 1 m from an open-water pool > 3 m in diameter. Nine nests were constructed in Z. miliacea and 1 in D. verticillatus. Eight nests were made almost entirely of Z. miliacea. One was constructed in Z. miliacea, but comprised mostly of short sticks (probably Hibiscus sp. L. [marsh mallow] or D. verticillatus). These nests were constructed by bending Z. miliacea leaves into a shallow cup and, in the latter nest, adding short sticks on top of the cup. The nest constructed in D. verticillatus was constructed mostly of D. verticillatus twigs wedged between the basal stems of the nest plant with a few dried D. verticillatus leaves laid on top of the nest. The base of D. verticillatus is the only part structurally secure enough to support a Least Bittern nest. Because stems from the nest plant are too thick for Least Bitterns to manipulate, short sticks must be wedged between adjacent stems from a single root mass, and then more sticks placed on top of one another until a nest is made. The nest in D. verticillatus appeared structurally insecure, and was abandoned. The cup of the nest was very shallow, and the eggs were on the verge of rolling out. 2006 N.A. Winstead and S.L. King 319 Discussion Typha sp. is the most commonly reported plant species used in Least Bittern nest construction (Bogner and Baldassarre 2002, Frederick et al. 1990), and Z. miliacea is structurally similar to Typha sp. in that both are tall, grass-like plants. Therefore, Least Bitterns may be better able to construct nests in Z. miliacea than in D. verticillatus. Although D. verticillatus was the most common plant species within 60 m of most nests, most nests were constructed in Z. miliacea, which was the dominant plant species within 5 m of most nests. Weller (1961) found at least 2 instances of Least Bitterns removing predator-damaged eggs and continuing to incubate those that remained. One nest in this study had fewer eggs on subsequent visits, which may indicate predation. Weller (1961) found 1 nest that was unsanitary and considered it unusual. One unsanitary nest was found in this study, with dried feces on the nest and eggs. Weller (1961) also observed nests that sank under the weight of the adults and chicks, which also was observed in this study. Chicks are covered with soft, ochre-colored down above and white down below (McVaugh 1975). Chicks from different nests may vary from pale to dark ochre, but all chicks of the same nest are reported to be the same color Table 1. Proportions of vegetation types within 60 m of Least Bittern nests at Reelfoot Lake and Black Bayou, 2003. DV = Decodon verticillatus, NL = Nuphar luteum, OE = other emergents, OW = open water, WDY = woody species, ZM = Zizaniopsis miliacea. Nest %DV %NL %OE %OW %WDY %ZM 1 61.2 0.0 0.0 34.4 0.0 4.5 2 23.3 0.0 5.8 3.4 23.7 43.9 3 0.0 0.0 0.0 51.6 0.0 48.4 4 0.0 0.0 0.0 52.2 0.0 47.8 5 17.4 7.0 0.0 75.6 0.0 0.0 6 42.2 5.0 0.0 52.6 0.0 0.2 7 34.6 1.2 0.0 63.6 0.0 0.7 8 43.6 1.2 0.0 54.6 0.0 0.7 9 40.7 9.1 0.0 49.9 0.0 0.4 10 40.7 9.1 0.0 49.9 0.0 0.4 Mean 30.4 3.2 0.6 48.8 2.3 14.7 Table 2. Proportions of vegetation types within 5 m of Least Bittern nests at Reelfoot Lake and Black Bayou, 2003. DV = Decodon verticillatus, NL = Nuphar luteum, OE = other emergents, OW = open water, WDY = woody species, ZM = Zizaniopsis miliacea. Nest %DV %NL %OE %OW %WDY %ZM 1 0.0 0.0 0.0 37.5 0.0 62.5 2 14.3 0.0 0.0 42.9 0.0 42.9 3 0.0 0.0 0.0 50.0 0.0 50.0 4 0.0 0.0 0.0 50.0 0.0 50.0 5 37.5 0.0 0.0 62.5 0.0 0.0 6 0.0 0.0 0.0 75.0 0.0 25.0 7 0.0 0.0 0.0 62.5 0.0 37.5 8 0.0 0.0 0.0 62.5 0.0 37.5 9 0.0 50.0 0.0 12.5 0.0 37.5 10 0.0 50.0 0.0 12.5 0.0 37.5 Mean 5.2 10.0 0.0 46.8 0.0 38.0 320 Southeastern Naturalist Vol. 5, No. 2 (McVaugh 1975). Two of four 1-day-old chicks in 1 nest in this study were ochre and 2 were white above. The white chicks were resting their heads on top of an ochre-colored chick. The other ochre-colored chick was found on the outside of the nest. Wright (1946) reported that chicks were scared out of the nest, but stayed on the sides to return later. This fourth chick was probably flushed from the nest when the boat approached and the adult flushed. The other 3 chicks seemed oblivious to the researcher’s presence. The fourth chick was returned to the nest, but immediately climbed back out. Acknowledgments We thank the Department of Forestry, Wildlife, and Fisheries at the University of Tennessee for funding this project. P. Brown and D. Sams provided lodging, boats, and other in-kind services. J. Yoes helped with fieldwork. D. Buehler and W. Minser provided helpful reviews of the manuscript and technical assistance. Literature Cited Bogner, H.E., and G.A. Baldassarre. 2002. Home range, movement, and nesting of Least Bitterns in western New York. Wilson Bulletin 114:297–308. Burbank, J.H. 1963. An evaluation of the aquatic pest plant control program at Reelfoot Lake. Journal of the Tennessee Academy of Science 38:42–48. Dahl, T.E. 1990. Wetlands losses in the United States, 1780s to 1980s. US Department of the Interior, Fish and Wildlife Service, Washington, DC. 21 pp. Frederick, P.C., N. Dwyer, S. Fitzgerald, and R.E. Bennetts. 1990. Relative abundance and habitat preferences of Least Bitterns (Ixobrychus exilis) in the Everglades. Florida Field Naturalist 18:1–9. Gibbs, J.P., F.A. Reid, and S. Melvin. 1992. Least Bittern. Pp. 1–12, In A. Poole, P. Stettenheim, and F. Gill (Eds.) The Birds of North America, Number 17. The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists’ Union, Washington, DC. McVaugh, Jr., W. 1975. The development of four North American herons II. Living Bird 14:163–183. Mengel, R.M. 1965. The Birds of Kentucky. Ornithological Monographs No. 3. The American Ornithologists’ Union. Allen Press, KS. 581 pp. Simpson, T.W. 1939. The feeding habits of the Coot, Florida Gallinule, and Least Bittern on Reelfoot Lake. Journal of the Tennessee Academy of Science 14:110–115. Tennessee Department of Environment and Conservation (TDEC). 2004. A guide to the rare animals of Tennessee. Tennessee Department of Environment and Conservation, Division of Natural Heritage, Nashville, TN. Available at: http:// Wear, D.N., and J.G. Greis. 2002. The southern forest resource assessment summary report. US Department of Agriculture, Forest Service, Southern Research Station, Asheville, NC. Available at: Weller, M.W. 1961. Breeding biology of the Least Bittern. Wilson Bulletin 73:11–35. Winstead, N.A. 2004. Breeding bird and vegetation communities of Reelfoot Lake. M.Sc. Thesis. University of Tennessee, Knoxville, TN. Wright, E.G. 1946. Incidents in Least Bittern family life. Passenger Pigeon 8:124.