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Egretta
About: Egretta is a research topic. Over the lifetime, 528 publications have been published within this topic receiving 7136 citations.
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TL;DR: The feeding strategy of the first group appeared to be one of searching for new high-quality food patches rather than staying and exploiting food patches that were declining in quality, suggesting that factors affecting bird density at feeding sites may also have affected population size.
Abstract: Reduced prey availability has emerged as a primary hypothesis to explain population constraints on wading birds in numerous wetlands around the world. However, there is almost no understanding of which component of prey availability (i.e., prey density or vulnerability of prey to capture) is affecting populations and whether the relative effects of each component differ among species. In this study, I manipulated prey density and water depth (i.e., prey availability) in 12 0.2-ha ponds to determine their relative effects on the numeric response of eight species of free-ranging wading birds (White Ibis, Eudocimus albus; Wood Stork, Mycteria americana; Snowy Egret, Egretta thula; Glossy Ibis, Plegadis falcinellus; Great Egret, Ardea alba; Tricolored Heron, Egretta tricolor; Great Blue Heron, Ardea herodias; and Little Blue Heron, Egretta caerulea). The experiment was conducted in a constructed wetland adjacent to, and west of, the northern tip of the remnant Everglades, in Palm Beach County, Florida, USA. Each pond was set to a water depth of 10 cm, 19 cm, or 28 cm, and was stocked with golden shiners (Notemigonus crysoleucas) at a density of either 3 fish/m2 or 10 fish/m2. Total bird use (all treatments pooled) increased from day 1 (day after stocking) to day 6, stabilized for several days at ∼280 birds, and then decreased until day 16, when bird use nearly ceased. Fish were depleted most rapidly in the shallow treatment and least rapidly in the deep treatment. The giving-up-density (GUD) of prey increased with increasing water depth. There was no significant difference among species in the slope of that relationship; however, a visual inspection of the data showed that differences in GUDs were becoming more apparent in the deepest treatment. At that depth, the White Ibis, Wood Stork, and Snowy Egret had higher GUDs than did the Glossy Ibis, Great Egret, Tricolored Heron, Great Blue Heron, and Little Blue Heron. Also, the first three species were affected significantly by both prey density and water depth, whereas the latter five species showed a decidedly weaker response to one or the other component of prey availability. The first three species were more abundant in the shallow treatments and the high prey density treatments, and they abandoned the study site before other species reached their maximum density. The feeding strategy of the first group appeared to be one of searching for new high-quality food patches rather than staying and exploiting food patches that were declining in quality. Species that employed a searching strategy also have shown the most severe population declines, suggesting that factors affecting bird density at feeding sites may also have affected population size.
328 citations
TL;DR: The levels in tissues that are associated with adverse effects in birds from laboratory studies are reviewed and compared with levels found in wild bird populations in the New York Bight to provide a basis for interpreting values in avian populations.
250 citations
TL;DR: Comparing numbers of Ardeidae and their prey in paired old- and new-style areas at six sites in central Japan from May to August 1995 found greater numbers and biomasses of frogs, crayfish Procambarus clarkii, loach Misgurnus anguillicaudatus, and other fish in old-style paddy fields, and inold-style ditches the authors found more frogs, tadpoles and fish, but generally fewer cray fish.
158 citations
TL;DR: The area used and habitats selected by herons nesting in a colony near Beaufort, North Carolina are described to support the hypothesis that colonies can act as "information centres," wherein unsuccessful birds follow successful ones to better feeding locations.
Abstract: -Nine species of herons, egrets, and ibises were followed by airplane from a nesting colony near Beaufort, North Carolina to their feeding sites. Except for Cattle Egrets, which flew exclusively to fields and dumps, the birds flew mainly to saltmarsh habitat. The selection of feeding habitats by Great Egrets and Louisiana Herons was directly related to tidal depth. The Great Egret was the only species that effectively used eelgrass beds, and its use of this habitat was restricted to between 1.5 h before and after low tide. We suspect that shorter-legged herons did not use eelgrass regularly because the water was too deep. Most Great Egrets, White Ibises, Louisiana Herons, and Snowy Egrets used areas near the colony (<4 km). Great Egrets, Black-crowned Night Herons, and White Ibises flew farther from the colony at high than at low tide. Great Egrets traveled farther from the colony when they used thermals; rate of travel to feeding sites was the same, however, whether or not they used thermals. Aggressive encounters were observed at the landing sites of Great Egrets, Louisiana Herons, Snowy Egrets, and Black-crowned Night Herons. In contrast to the other species studied, Cattle Egrets and White Ibises often flew in groups to feeding sites. Indirect evidence supports the hypothesis that colonies can act as "information centres," wherein unsuccessful birds follow successful ones to better feeding locations. Received 31 January 1978, accepted 7 May 1978. THE use of wetland habitats by herons, egrets, and ibises (here collectively termed herons) is not well known. Jenni (1969) found that Snowy Egrets (Egretta thula) feed in open areas, Little Blue Herons (Florida caerulea) in heavily vegetated areas, and Louisiana herons (Hydranassa tricolor) along banks or floating vegetation where the water level drops rapidly. Kushlan and Kushlan (1975) described the feeding habitat preferences of the White Ibis (Eudocimus albus) in southern Florida, and Meyerriecks (1962), Kushlan (1976a), and Custer and Osborn (1978) found that longer-legged herons feed in deeper water than shorter-legged ones. The distance herons travel from a colony to feeding sites is also poorly understood. Published estimates of the maximum distance (km) for various species are as follows: Cattle egret (Bulbulcus ibis) 28.5 (Bateman 1970), 25.8 (Hopkins and Murton 1969), 19.3 (Craufurd 1966, Skead 1966), and 29 (Siegfried 1971); Roseate Spoonbill (Ajaia ajaja) and Grey Heron (Ardea cinerea) 32.2 (Beetham 1910) and 19.3 (Nicholson 1929); Wood Stork (Mycteria americana) 40 (Kahl 1964) and 130 (Ogden et al. in press); and White Ibis, 22.9 (calculated from Bateman 1970) and 44 (Kushlan 1976b). However, the distribution of distances flown from the colony is known only for the Cattle Egret (Bateman 1970, Siegfried 1971), Wood Stork (Kahl 1964), and White Ibis (Bateman 1970). In this study we attempt to describe the area used and habitats selected by herons nesting in a colony near Beaufort, North Carolina. Unmarked herons were followed by airplane from the colony to their first landing site. Using this approach, we were able to gather information that indirectly supports the hypothesis that colonies may act as "information centres," wherein unsuccessful birds follow successful ones to better feeding sites (Ward and Zahavi 1973, Krebs 1974). l Present address: Office of Biological Services, National Western Energy and Land Use Team, Fort Collins, Colorado 80521 USA. 733 The Auk 95: 733-743. October 1978 This content downloaded from 157.55.39.206 on Sat, 17 Dec 2016 05:22:44 UTC All use subject to http://about.jstor.org/terms 734 CUSTER AND OSBORN [Auk, Vol. 95
143 citations
TL;DR: Analysis of nestling regurgitates show that Gambusia makes up a considerable proportion of the diet of four species of Camargue herons, and that the majority of Gambusian taken are females, suggesting that females represent a much more profitable prey.
Abstract: Sex-ratios of Gambusia affinis populations in freshwater marshes in the Camargue (Rhone Delta), are highly biased in favour of males, whereas the sex-ratios in ditches are close to unity. Studies of the diet of free living birds and experimental studies on prey size selection in captivity show that the abnormal sex-ratios in marshes can be attributed to differential heron predation. Ditches are relatively free from predation. Mature female Gambusia are larger, and have an energy content 5–25 times greater than that of mature males. Handling times of Grey Heron (Ardea cinerea) and Little Egret (Egretta garzetta) are only slightly longer for female Gambusia than males. Hence, females represent a much more profitable prey.
128 citations