Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forestry, Wildlife, and Fisheries

First Advisor

Robert B. Hamilton

Abstract

I studied the nesting ecology of the White-faced Ibis (Plegadis chihi) during the summers of 1994 and 1995 in three colonies in Lacassine National Wildlife Refuge, southwestern Louisiana. Data were collected on colony-site characteristics, chronology (with abundance) of colony formation, reproductive success, and growth and development of ibis nestlings. Small colonies nested in dense buttonbush (Cephalanthus occidentalis) and water willow (Decodon verticillatus) "islands." The largest colony nested in black willows (Salix nigra) (3.2 ha)--a habitat unique to ibis populations in Louisiana--with nests heights up to 7.5 m. Cattle egrets (Bubulcus ibis) (62%) and ibises (36%) were the most abundant species. Ibis nesting began on 23 May; hatching occurred between 19 June and 16 July. I assessed reproductive success of 292 nests with 262 chicks. In 1994 and 1995, clutches averaged 2.8 and 2.6 eggs; hatching rates (fertility) were 90% and 93%; hatching success was 41% in 1994 and 1% (in 64% of the colony) and 74% (elsewhere) in 1995; 14-day fledgling success was 33% and 37%. Survival was highly correlative with hatching order: first hatched were most likely to survive. Estimated colony success was 491 fledglings from 1,292 nests (0.38) in 1994 and 149 from 622 nests (0.24) in 1995. Major environmental differences between years were higher water, more alligators (Alligator mississippiensis), and fewer mammalian predators in 1994. Extensive predation by raccoons (Procyon lotor), mustelids, avian predators, alligators, and snakes caused most nest failures (67% and 96% each year). Minor causes included infertile eggs and collapsed and abandoned nests. Nests were more successful when substrate was black willow (vs. other tree species), over water (vs. land), in upper or lower tree heights (vs. middle), and on the edge of the colony. Nearest-neighbor species did not affect success, but nearest-neighbor distance had some effect. Measurements of the culmen, forearm, tarsus, and mass were taken of 92 chicks, the oldest was 20 days old. A chick's growth was not affected by brood size or if it survived to fledge, but was slightly affected by year and hatching order. Nestlings' regurgitated pellets contained water bugs, beetles, and horsefly and dragonfly larvae.

ISBN

9780591035193

Pages

172

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