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Fish Crow Predation on Eggs of the White Ibis at Battery Island, North Carolina

Mark A. Shields and James F. Parnell
The Auk
Vol. 103, No. 3 (Jul., 1986), pp. 531-539
Stable URL: http://www.jstor.org/stable/4087124
Page Count: 9
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Fish Crow Predation on Eggs of the White Ibis at Battery Island, North Carolina
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Abstract

We studied predation by Fish Crows (Corvus ossifragus) on eggs of the White Ibis (Eudocimus albus) during the 1983 and 1984 nesting seasons at Battery Island, southeastern North Carolina. Crow predation accounted for the loss of 32% (n = 223) of ibis eggs in 1983 and 44% (n = 538) in 1984. Crows usually took all eggs in a clutch. An estimated 6 pairs of Fish Crows nested on the island each year. We believe these individuals were responsible for most egg loss. The predation rate of ibis clutches was highest in plots nearest crow nests and lowest in two plots that contained observation blinds. Results of experiments using simulated ibis nests suggested that crows were wary of the blinds. Predation declined with nest age, apparently due to increased nest attentiveness by adult ibises during the last week of incubation. The overall predation rate in 1984 was significantly higher than in 1983. Greater nest densities and less synchronous breeding by ibises in 1984 may have contributed to the higher predation rate. Ibis productivity was estimated at 1.22-1.30 fledglings per pair in 1983 and 1.05-1.12 in 1984. This level of reproduction appeared sufficient for maintenance of the population. Thus, egg predation by Fish Crows during our study did not appear to be a serious threat to the productivity of this White Ibis population.

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