Abstract

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Faber, R.A. 1992. Incubation behavior and artificial nest structure usage in black terns nesting along the Mississippi River. Final report submitted to Nongame Wildlife Program, Minnesota Department of Natural Resources. 27 pp.

Abstract:

Night incubation behavior of black terns was studied in 1991 by use of an 8 mm camcorder operated in time-lapse mode and linked to a night vision device. While some birds remained on the nest throughout the night, others let the nest unattended the entire night or left during the night. In each case that a nest was left unattended during the night, a bird returned to incubate near sunrise and incubation then proceeded without significant interruption throughout the day. During the day, the nest was frequently left for very short periods (usually two minutes or less) and incubation duties were exchanged between male and female frequently, usually within the hour. Two instances of owls approaching near the nest during the night were observed in 14 nights of taping. In one case the tern remained on the nest; in the other, it fled the nest and did not return until sunrise. In neither case did the owl make any attempt to take the eggs, suggesting that owls are not significant predators of black tern eggs.

Two sizes of artificial platforms were tested as nesting substrates in both 1990 and 1991. Platforms were distributed in four marshes in 1990 and in five marshes in 1991. Despite previous significant colonies in these marshes, little nesting occurred in any of them except Trempealeau National Wildlife Refuge in 1990 and 1991. Platforms were used only by birds in TNWR in 1990 and 1991. In each year, five platforms of each size were available for use in TNWR. In 1990, seven of the platforms were used and accounted for ten nest attempts. In 1991, five of the platforms were used and accounted for six nest attempts. Overall, 12 of 20 platforms were used for 16 nest attempts. Large platforms were preferred over small ones with eight and four being used, respectively. A ring of hardware cloth was added to the platforms in 1991 to help retain nesting material. Hatching success was nearly identical on large and small platforms. Large platforms were used for four renest attempts over the two years while none of the small platforms were re-used. Hatching success was significantly greater on artificial platforms (89%) compared with that on natural platforms (52%) in 1990 (X2 = 4.36, p = 0.036). Hatching success was similar on artificial and natural platforms in 1991, but was greater on small artificial platforms in 1989 (50% versus 29%). Widespread usage of large artificial platforms may significantly increase hatching success and renesting of black terns and offers hope of reversing their population decline.

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