Showing papers on "Nycticorax published in 1996"

Design and management of bird nesting habitat: tactics for conserving colonial waterbird biodiversity on artificial islands in Hamilton Harbour, Ontario

Abstract: Hamilton Harbour, at the west end of Lake Ontario, supports breeding colonies of six piscivorous waterbirds: double-crested cormorant (Phalacrocorax auritus), black-crowned night-heron (Nycticorax nycticorax), herring gull (Larus argentatus), ring-billed gull ( Larus delawarensis), common tern (Sterna hirundo), and Caspian tern (Sterna caspia). Most breeding pairs of all species nest on privately owned mainland locations that are subject to multiple industrial and development activities. The construction of three artificial islands in the eastern basin of Hamilton Harbour in the winter of 1995-1996 presents an opportunity to simultaneously reduce current land-use conflict and maintain the existing avian biodiversity. Accordingly, we used ecological information to determine suitable substrates and vegetation to satisfy nesting habitat preferences and to facilitate the occupation of the islands by nesting waterbirds. Our recommendations for habitat design and management emphasize techniques to prevent displacement of both tern species by ring-billed gulls and of night-herons by cormorants. We propose long-term management procedures based on aspects of the biology and known ecological interactions among the various species. Resume : Le havre de Hamilton, situe a l'extremite ouest du lac Ontario, heberge des colonies reproductrices de six oiseaux aquatiques piscivores : le cormoran a aigrettes ( Phalacrocorax auritus), le bihoreau gris (Nycticorax nycticorax), le goeland argente (Larus argentatus), le goeland a bec cercle (Larus delawarensis), la sterne pierregarin ( Sterna hirundo) et la sterne caspienne (Sterna caspia). Chez toutes ces especes, la plupart des couples de reproducteurs nichent sur la terre ferme, sur des terrains prives soumis a de multiples activites industrielles ou travaux d'amenagement. La construction de trois iles

Reproductive success, growth and survival of black-crowned night-heron ( Nycticorax nycticorax ) and snowy egret ( Egretta thula ) chicks in coastal Virginia

Abstract: ABsTRAcr.-We studied reproductive success, growth, and survival of Black-crowned NightHeron (Nycticorax nycticorax) and Snowy Egret (Egretta thula) chicks in two mixed-species heronries on marsh islands in Chincoteague Bay, Accomack County, Virginia in 1992 and 1993. We attached radio transmitters with mortality sensors to the oldest chicks (A-chicks) in 11 to 22 nests of both species to monitor survival during the mid- to late nestling period and into the postnesting dispersal period. For both species, we found significant differences between 1992 and 1993 in growth rates and survival. Mass growth rates of chicks were higher in 1993 than in 1992 for both species. Culmen-length growth rates varied significantly due to year-colony effects for night-herons, but only for hatching order for egrets. Differences in survival rates due to hatching order were found for the egrets in both years, but were found only in 1992 for night-herons. As with mass growth rates, survival of chicks was higher in 1993 than 1992. Survival of radio-marked A-chicks did not differ between species or years for the period from hatching to fledging or from fledging through the end of the study (ca. two months postfledging). Survival ranged from 0.80 to 1.00 from the time radio transmitters were attached (ca. two weeks of age) until dispersal age (53-55 days for egrets; 55-60 days for night-herons). After birds left the colony, survival rates were lower during the next 40 to 55 days, ranging from 0.25 to 0.60. These results suggest that, at least for Snowy Egrets, A-chicks may be buffered from annual variations in food conditions, but that growth and survival of other brood members may provide a barometer of local conditions. Despite problems of variability in measurement, some of these parameters show promise as bioindicators of estuarine conditions. We recommend that a cost-efficient wading-bird monitoring program would include: (1) estimating numbers of nesting birds of selected species (e.g. Snowy Egrets) at particular estuaries, and (2) monitoring "initial brood sizes" and survival of young to at least two weeks of age in a sample of nests for each focal species. However, additional biomonitoring (e.g. marsh forage fish, contaminant loads) is necessary to evaluate how well top trophic-level organisms such as fish-eating birds respond to changes in estuarine production or quality. Received 12 December 1994, accepted 18 March 1995.

Cytochrome P450 and contaminant concentrations in nestling black-crowned night-herons and their interrelation with sibling embryos

Abstract: Hepatic cytochrome P450-associated monooxygenase activities were measured in 11-d-old nestling black-crowned night-herons (Nycticorax nycticorax) collected from a reference site (next to Chincoteague National Wildlife Refuge, VA, USA) and three contaminated sites (Cat Island, Green Bay, WI, USA; Bair Island, San Francisco Bay, CA, USA; and West Marin Island, San Francisco Bay, CA, USA). Arylhydrocarbon hydroxylase and benzyloxyresorufin-O-dealkylase activities of nestlings from contaminated sites were only slightly elevated (less than threefold) compared with the reference site. Organochlorine pesticide and total polychlorinated biphenyl (PCB) concentrations in nestlings were greatest at contaminated sites, although much lower than found in concurrently collected eggs and pipping embryos. Pollutant concentrations of nestlings were rarely associated with monooxygenase activity. In contrast, concurrently collected pipping heron embryos (often siblings of the nestlings) exhibited pronounced monooxygenase induction (means at contaminated sites were elevated up to sevenfold and values of some embryos exceeded 25-fold induction). Furthermore, monooxygenase activity of pipping embryos was significantly correlated with total PCBs, arylhydrocarbon receptor-active PCB congeners, and toxic equivalents. The modest monooxygenase responses of heron nestlings suggest that this biomarker may have only limited value during this rapid-growth life stage.

Predation at intermountain west fish hatcheries

Abstract: During 1993-94, we observed predators and surveyed managers at Intermountain West fish hatcheries to quantify the extent and species responsible for depredation losses. Our field study confirmed hatchery managers' impressions that great blue herons (Ardea herodias), black-crowned night herons (Nycticorax nycticorax), ospreys (Pandion haliaetus), and California gulls (Larus californicus) were the most important predators. At 2 intensively monitored hatcheries, we calculated losses to avian predation to be 7.0 and 0.6% of annual production, in contrast to the managers' estimates of 15% at each hatchery. Feeding mostly on dead or moribund fish, feral cats (Felis catus), raccoons (Procyon lotor), and striped skunks (Mephitis mephitis) had little effect on fish production. Private hatchery managers estimated higher (13%) total depredation losses than did managers of state owned hatcheries (5%). Hatchery managers viewed netting to be the only effective nonlethal control measure.

Heavy metal and selenium levels in birds at Agassiz National Wildlife Refuge, Minnesota: Food chain differences.

Abstract: The levels of heavy metals and selenium in the eggs and in breast feathers of adult doublecrested cormorant (Phalacrocorax auritus), black-crowned night heron (Nycticorax nycticorax), and franklin's gull (Larus pipixcan) nesting at Agassiz National Wildlife Refuge in Marshall County, northwestern Minnesota were examined. Also examined were metal levels in the feathers of fledgling night herons and gulls, in the feathers of adult and fledgling American bittern (Botaurus lentiginosus), in eggs of American coot (Fulica americana) and eared grebe (Podiceps caspicus), and in feathers of adult Canada geese (Branta canadensis). These species represent different levels on the food chain from primarily vegetation-eating species (geese, coot) to species that eat primarily fish (cormorant). A clear, positive relationship between level on the food chain and levels of heavy metals occurred only for mercury in feathers and eggs. Otherwise, eared grebes had the highest levels of all other metals in their eggs compared to the other species. No clear food chain pattern existed for feathers for the other metals. For eggs at Agassiz: 1) lead, selenium, and manganese levels were similar to those reported in the literature, 2) mercury levels were slightly higher for cormorants and night herons, 3) all species had higher chromium and cadmium levels than generally reported, and 4) eared grebes had significantly higher levels of cadmium than reported for any species from elsewhere. For adult feathers: 1) gulls had higher levels of lead than the other species, 2) cadmium levels were elevated in gulls and adult herons and cormorants, 3) mercury levels showed an increase with position on the food chain, 4) selenium and chromium levels of all birds at Agassiz were generally low and 5) manganese levels in adults were generally higher than in the literature for other species. Adults had significantly higher mercury levels than fledgling gulls, night herons, and bitterns.

Effectiveness of Alarm–Distress Calls for Frightening Herons from a Fish Rearing Facility

Abstract: We evaluated the effectiveness of using alarm-distress calls of the black-crowned night heron Nycticorax nycticorax and the great blue heron Ardea herodias for frightening these piscivorous bird species from a rearing unit for rainbow trout Oncorhynchus mykiss. Heron alarm–distress calls reduced black-crowned night heron numbers 48% during the 11-d treatment period, compared with the pretreatment period, but did not affect the number of great blue herons. The number of black-crowned night herons using the rearing unit and the proportion that remained immediately after the broadcast of alarm–distress calls increased from nights 1 through 11 of the treatment period, which indicates that this predator quickly habituated to the calls. We did not find any differences between the proportions of black-crowned night herons and great blue herons that remained on the rearing unit immediately after playing calls of the respective species. Alarm–distress calls were mostly ineffective in reducing heron predat...

Dispersal and habitat use by post-fledging juvenile snowy egrets and black-crowned night-herons

Abstract: ABSTRACr.-We studied the post-fledging dispersal movements and habitat use of juvenile Snowy Egrets (Egretta thula) (SNEG) and Black-crowned Night-Herons (Nycticorax nycticorax) (BCNH) in coastal Virginia using a dye (picric acid) and radiotelemetry. Results from monitoring radiomarked birds revealed significant differences both years between species, with SNEGs dispersing more widely than BCNHs. BCNH juveniles usually remained south of Delaware, but SNEGs often moved into Delaware and southern New Jersey. The maximum dispersal distance found for a SNEG was ca 340 km north of the natal colony. Temporal patterns of movement followed logistic relationships, with rapid initial movements, but relatively few movements after about 2-3 weeks for most birds. Cumulative distances moved by juvenile SNEGs during August-September differed from 1992 to 1993. No such year difference was found for BCNHs. Compared to SNEGs, BCNHs used manmade impoundments relatively more often than natural wetlands; however no quantitative assessment of habitat preferences could be made. Received 25 May 1995, accepted 9 Dec. 1995.

Descripción de una colonia mixta de aves acuáticas en Laguna Iberá, Corrientes, Argentina

Abstract: In the breading season 1991-1992 a mixed water-bird colony of about 400 nests of Egretta thula. Casmerodius albus. Nycticorax nycticorax. Ardea cocoi and Anhinga anhinga appeared at Laguna Ibera, Corrientes Provinee, Argentina. It was unique for its type in the arca, Observations were carried out during two breeding seasons. The dominant species during the first season was E, thula (52.5 %ofthe nests) followed by C. albus, During the next season the colony expanded in area and in number ofnests (87 %). The dominant speeies was now C. albus, with 80,5 %of the nests and a growth of399 %. AII the remaining speeies declined, andN. nycticorax was apparently absent. Evaluation ofthe impaet ofhuman visitors on the eolony require further monitoring.

Interbredding of a tricolored heron and a snowy egret in South Dakota

Abstract: Reports of interbreeding among herons are uncommon and include a Little Blue Heron (Egretta caerulea) and a Cattle Egret (Bubulcus ibis) in California (Bailey et al. 1989), a Little Blue Heron and a Snowy Egret (E. thula) in Florida (Sprunt 1954), and a Little Blue Heron and a Tricolored Heron (E. tricolor) in Arizona (Phillips et al. 1964). In addition, a possible hybrid between a Snowy Egret and a Tricolored Heron was photographed in Florida in 1960 (Dickerman and Parkes 1968). In this paper, we report interbreeding between a Tricolored Heron and a Snowy Egret. To our knowledge, this hybrid combination has not been reported previously. Tricolored Herons and Snowy Egrets occur sympatrically along the Atlantic coast from New York to South America, and along the Pacific coast from Mexico to Peru (Hancock and Elliott 1978). Tricolored Herons rarely nest inland as far north as South Dakota (Schmidt 1979, Skadsen 1986), whereas Snowy Egrets have been locally common breeders in eastern South Dakota since at least the early 1980s (South Dakota Ornithologists' Union 1991). On 23 June 1995, we observed a Tricolored Heron in a mixed-species heronry in Brown County, South Dakota (45?40'N, 98?05'W). This observation was only the fifth record of a Tricolored Heron in South Dakota (South Dakota Ornithologists' Union 1991). The heronry was in a flooded, 5-ha stand of dead Russian olive (Elaeagnus angustifolia) trees. Extensive flooding in 1993 and 1994 had increased the available aquatic habitat and probably contributed to the establishment of the heronry. Nesting species included Cattle Egrets, Great Egrets (Ardea alba), Snowy Egrets, Little Blue Herons, and Black-crowned Night-Herons (Nycticorax nycticorax). About 1,200 pairs of herons (mostly Cattle Egrets) nested in the heronry in 1994 (Peterson 1995), and about 5,950 pairs (95% Cattle Egrets) nested there in 1995 (Naugle unpubl. data). On 30 June 1995, we marked a nest site after observing the Tricolored Heron perched on the rim of a nest bowl. This nest contained four light-bluish eggs and was constructed of Russian olive branches about 30 cm above the water. On 2 July, a Snowy Egret was incubating the remaining two eggs in the marked nest, which also contained two nestlings. While we were observing the incubating Snowy Egret, a Tricolored Heron landed near the nest. Subsequently, we observed a "nest relief ceremony," in which the Tricolored Heron and the Snowy Egret raised their head plumes and began bill-nibbling and vocalizing (see Rodgers 1977). Following the nest relief ceremony, the Tricolored Heron settled on the nest and incubated the eggs. All four eggs had hatched by 6 July. During that visit we photographed and recorded a nest relief ceremony on standard 1.25-cm VHS tape. The Snowy Egret fed the chicks regurgitated food. The Tricolored Heron also fed the chicks in the absence of the Snowy Egret. On 1 August, photographs were taken of the four juveniles (which were in the late branching stage of development) at the nest site (VIREO accession batch V06/24/001-005; Academy of Natural Sciences, Philadelphia). Their plumage and soft-part colors were unlike those typical of juvenile Snowy Egrets or Tricolored Herons (McVaugh 1972, 1975). Their heads were marked with a gray-brown crown that extended down the nape of the neck and graded to a slate gray on the back and wings (see Fig. 1). The sides of the neck and breast varied among individuals from slate gray to pale rufous. All juveniles were white on the head and undersides of the neck and body. Their irides were yellow, and their bills were black above and dark orange below, grading to black distally. The legs were yellow-green proximally and posteriorly, grading to dark on the distal anterior surface. There was no brownish-red color on the primary or secondary coverts or on the sides of the neck or breast, as would be typical of juvenile Tricolored Herons.

Dispersal and habitat use by post-fledging

Abstract: ABSTRACr.-We studied the post-fledging dispersal movements and habitat use of juvenile Snowy Egrets (Egretta thula) (SNEG) and Black-crowned Night-Herons (Nycticorax nycticorax) (BCNH) in coastal Virginia using a dye (picric acid) and radiotelemetry. Results from monitoring radiomarked birds revealed significant differences both years between species, with SNEGs dispersing more widely than BCNHs. BCNH juveniles usually remained south of Delaware, but SNEGs often moved into Delaware and southern New Jersey. The maximum dispersal distance found for a SNEG was ca 340 km north of the natal colony. Temporal patterns of movement followed logistic relationships, with rapid initial movements, but relatively few movements after about 2-3 weeks for most birds. Cumulative distances moved by juvenile SNEGs during August-September differed from 1992 to 1993. No such year difference was found for BCNHs. Compared to SNEGs, BCNHs used manmade impoundments relatively more often than natural wetlands; however no quantitative assessment of habitat preferences could be made. Received 25 May 1995, accepted 9 Dec. 1995. Little is known about survival, movements, or habitat use during the post-breeding period for most North American migratory birds (Finch and Stangel 1993). Even for large, conspicuous species such as colonial waterbirds, few quantitative dispersal data have been published. Numerous anecdotal reports indicate that many terns, gulls, and wading birds move northward along the coasts and large interior rivers of the United States after the nesting season. In some regions, the movement pattern is constrained by geography, with waterbirds often following major drainages (Gill and Mewaldt 1979) regardless of the cardinal direction or following a peninsula or island archipelago (e.g., in Florida, Powell and Bjork 1990, Strong and Bancroft 1994 on Great White Herons, Ardea herodias occidentalis). Studies of individual species revealed some extensive northward dispersal after breeding; e.g., Black-crowned Night-Herons (Nycticorax nycticorax) in the eastern United States (Bartsch 1952, Byrd 1978), Little Blue Herons (Egretta caerulea) in Mississippi (Coffey 1943) and elsewhere in the southeast (Townsend 1931), Great White Herons in Florida (Powell and Bjork 1990), and Cattle Egrets (Bubulcus ibis) in Africa