Showing papers on "Heron published in 1978"

Competition between Cattle Egrets and Native North American Herons, Egrets, and Ibises

Abstract: Cattle Egrets (Bubulcus ibis) recently invaded and spread across North America, nesting in existing heronries. The spread of this species into the Western Hemisphere is well documented (Crosby 1972, Weber 1972), yet many aspects of its breeding biology are incompletely understood. Cattle Egrets do not appear to compete with native herons and egrets for food since their foraging methods and food items differ (Jenni 1969, 1973). Cattle Egrets tend to breed later than native North American ardeids, thus eliminating competition for nest sites (Dusi 1966, Dusi and Dusi 1968, Jenni 1969, Dusi et al. 1971, Weber 1972). In 1968, Dusi suggested that Cattle Egrets may compete with Little Blue Herons (Florida caerulea) when some late-arriving Cattle Egrets take over deserted nests, often adding their own eggs to those already present. Dusi, however, stated that the existing competition was not "greatly harmful" to the Little Blue Herons. Further study, however, indicated that Cattle Egrets arrive when Little Blue Herons have chicks, and that the egrets take over nests by forcing some of the heron chicks out of their nests (McKitrick 1975). While Cattle Egrets steal nest material from each other in Africa (Siegfried 1971a, 1972) and Colombia (Lancaster 1970), they have not been reported to steal material from other nesting herons in North America. Presumably, nesting much later than the native species eliminates some competition for nest sites and materials, as well-established incubating herons can successfully defend their nests.

An Aerial Survey of Waterbird Colonies Along the Upper Mississippi River and Their Relationship to Dredged Material Deposits.

Abstract: : Aerial surveys of 1040 km of the Upper Mississippi River, Locks and Dams 1-26, showed 35 active colonies of five species of larger waterbirds (great blue heron, great egret, black-crowned night heron, double-crested cormorant, and Forster's tern) nesting in the floodplain. In addition, green herons and yellow-crowned night herons are reported as nesting, although location by aerial survey was not possible due to cryptic coloration and nest placement beneath the tree canopy. No species were found nesting on dredged material. In general, colonies were located on isolated insular natural sites on the east side of the river below dams and/or tributaries. Dredged material sites were found to be unsuitable for nesting because of high human recreational use of dredged material and the early succession of vegetation stages present. (Author)

Feeding Behavior and Food Habits of the Boat-billed Heron (Cochlearius cochlearius)

Abstract: Boat-billed herons (Cochlearius c. ridgwayi) were observed with a night vision device as they fed nocturnally in a Pacific Guatemalan marsh. They used two basic heron/egret feeding techniques previously described for other species. No specialized feeding behaviors were observed that could be related uniquely to the expanded bill. Food taken by boat-bills was similar to that of black-crowned and yellow-crowned night herons (Nycticorax nycticorax and Nyctanassa violacea) feeding in the same marsh. Because of the limited information on Cochlearius, none of the existing hypotheses are adequate to explain the shape of the bill as a feeding adaptation, and only a previous observation of the bill as a display character provides a plausible explanation. THE FUNCTION of the oddly expanded bill of the boat-billed heron (Cochlearius cochlearius) has for years been assumed to be associated with some specialized feeding technique. Bock (1956) suggested that ". . . Cochlearius feeds in a manner different from that of other herons. A broad bill may be used as a scoop or may enable the bird to feed on smaller animal life." More recently, Mock (1975) proposed a hypothetical "touch-feeding" technique specialized to exploit a seasonal abundance of mud-dwelling organisms. Some brief observations of feeding appear in the literature. In Nicaragua, Boavalius (fide Rendahl 1920) said they "waded about, picking up fishes with a surprising rapidity." Wetmore (1965) reported that "they stand or walk in shallow ripples in the rivers, where they scoop at aquatic animals rather than spear at them in heron style." Feeding behavior under an attempted simulation of natural conditions was described by Carpenter (1971). Sys,tematized field studies, of the boat-bill have only recently been made. Two studies at San Blas, Nayarit, Mexico provided the first details on the boat-bill's breeding biology (Dickerman and Juarez 1971) and breeding display repertoire (Mock 1976). The present paper records the first detailed observations of nocturnal feeding of boat-billed herons (subspecies Cochlearius c. ridgwayi Dickerman 1973) and includes a description and discussion of their food habits.

The use of feeding habitat by a colony of herons, egrets, and ibises near Beaufort, North Carolina

Abstract: Nine species of herons were followed to their feeding sites from a nesting colony near Beaufort, North Carolina, by airplane. Except for the Cattle Egret, which flew exclusively to fields and dumps, all other species flew mainly to saltmarsh habitat. In addition, habitats were selected in relation to tidal depth and it appears, at least for the Great Egret, that low tide habitats were preferred. Most Great Egrets, White Ibises, Louisiana Herons, and Snowy Egrets flew close to the colony and numbers decreased farther from the colony. The Great Egret, Black-crowned Night Heron, and White Ibis flew farther from the colony at high than at low tide. In addition, the species differed in distance flown from the colony. Great Egrets traveled farther from the colony when they used thermals. Rate of travel to feeding sites, however, was the same whether Great Egrets used thermals or not. Aggressive encounters were observed in the Great Egret, Louisiana Heron, Snowy Egret, and Black-crowned Night Heron. Cattle Egrets and White Ibises followed other individuals to feeding sites and it appeared as though they were using the colony as an information center. The Great Egret is the only species to effectively use eelgrass beds near Beaufort. The Great Egrets use of this habitat was restricted to about 1.5 hours on either side of low tide. We suspect that other shorterlegged species did not use eelgrass regularly because of its depth. (The author did not submit a manuscript for publication)