Showing papers on "Nycticorax published in 1999"

Optimal' colony size for least terns : An inter-colony study of opposing selective pressures by predators

Abstract: , I compared breeding success and causes of nesting failure for Least Terns Sterna antillarum nesting in 11 colonies ranging from 2 to 606 nests in Connecticut, USA. Although the percentage of nests lost due to predation decreased with increasing colony size, the relationship between colony size and the impact of predators varied with the type of predator. A significant positive correlation was observed between colony size and nest loss due to Black-crowned Night-Herons (Nycticorax nycticorax). In contrast, a significant negative correlation was observed between colony size and nest loss duc to small mammals, Herring Gulls (Larus argentatus), and American Crows (Corvus brachyrhnchos). Thus, colonies of approximately 150 nests appear to be large enough for low impacts by small mammals, gulls, and crows, but small enough to be relatively unattractive to Black-crowned Night-Herons. Nest losses and chick mortality were significantly higher during 1988, mainly the result of increased levels of Black-crowned Night-Heron predation on large colonics. Overall, both hatching and fledging success of Least Terns did not increase with increasing colony size, although all colonies with fewer than 10 nests failed completely. Hatching and fledging success did not correlate with increasing nesting synchrony or increasing nest density during either year. However, nesting synchrony showed a significant negative correlation with both hatching success during both years and fledging success during 1988. Thus, less synchronous colonies showed a tendency to be more successful.

Foraging Flights of Nesting Egrets and Herons at a Hong Kong Egretry, South China

Abstract: -Observations of the foraging flights of nesting Great Egrets (Casmerodius albus), Little Egrets (Egretta garzetta), Black-crowned Night Herons (Nycticorax nycticorax) and Cattle Egrets (Bubulcus ibis) in 1997 and 1998 from the A Chau Egretry in Starling Inlet, Hong Kong, China, showed that shallow coastal waters were the major feeding habitat of Great and Little egrets, whose habitat use greatly overlapped. Black-crowned Night Herons, the dominant breeders in the colony, preferred mangroves and fishponds, while Cattle Egrets made most use of freshwater marsh and abandoned paddy fields. Cattle Egrets showed the highest use of feeding habitats outside the Inlet. In both years, Cattle Egrets made the longest median flights at both high and low tides. Black-crowned Night Herons made the shortest flights at high tide in both years while Great Egrets and Black-crowned Night Herons flew the shortest distance at low tide in 1997 and 1998, respectively. In both years, Great and Little egrets flew farther at high tide, when nearby shallow waters were too deep for feeding. Foraging flight distances varied significantly between years only for Cattle Egrets. More Black-crowned Night Herons and Cattle Egrets were involved in group flights. The feeding habitats in Starling Inlet supported far more breeding ardeids than expected for their area, probably because of their high productivity. The short foraging flight distances of Black-crowned Night Herons may reduce foraging costs and help explain the dominance of this species in the colony. Conservation of all wetland feeding habitats in Starling Inlet will be necessary to maintain the present size and diversity of nesting ardeid populations. Received 26 January 1999, accepted 22 September 1999.

Effects of Agricultural Development on Colonial Ardeid Populations in Southwestern Spain

Abstract: -Agricultural development has been considered a major factor influencing changes in species, species' distributions and abundances. We examine the effects of this process on colonial ardeid populations in a Mediterranean ecosystem in south-western Spain, where an ambitious irrigation plan has lead to structural homogeneity of a large area. During this process Cattle Egret (Bubulcus ibis) and Grey Heron (Ardea cinerea) populations have increased in the area. The Cattle Egret population was strongly associated with irrigated land while the Grey Heron population increased in the general area as a consequence of the recent colonization of it, but avoided local areas with extensive irrigated lands. Little Egret (Egretta garzetta) and Black-crowned Night-heron (Nycticorax nycticorax) populations were independent of the changes in agricultural practices. Received 10 September 1997, revised 6 October 1998, accepted 15 May 1999.

Documentation of vertebrate fauna in mangalavanam mangrove area

Abstract: ertebrate fauna of Mangalavanam mangrove area was studied from V May 1998 to May 1999 mainly based on observational methods. Three species of reptiles and seven species of fishes were collected from the area. Forty-two species of birds were recorded, representing 12 Orders and 24 Families. The most common bird species found at Mangalavanam were little cormorant (Phalacrocorax niger) and night heron (Nycticorax nycticorax). Highest species richness of birds was found in the months of May and July. Nesting of little cormorant and night heron was observed from February to July. House crow was the main predator of eggs and nestlings of these two species. The area is an ideal roosting site for little cormorant and night heron. Total roosting population was the highest in the month of December and lowest in June. Peak time of arrival of little cormorant was from 1720 to 1800 hours, and in the case of night heron, maximum number of birds left the roost between 1845 and 1900 hours. Five species of mammals were recorded from the area. The major factors which are detrimental to the ecosystem are: 1. Proposal to lease part of the land to a Trust. 2. Parking of oil tankers in the Salim Ali Road, 3. Dumping of waste in the lake. 4. Air pollution due to the unloading of cement. 5. Encroachment of puramboke land on the eastern side and 6. Uncontrolled growth of weeds in the lake. Recommendations for better management of the Mangalavanam have been provided.

Population dynamics and nesting of three species of egret on Xiamen Dayu Island

Abstract: This paper deals with the population dynamics and nesting of Nycticorax nycticorax, Egretta garzetta and Ardeola bacchus in the Egret Naturel Reserve on Xiamen Dayu Island. The number of three egret species vary greatly with the season. May, June and July is the peak seasons. When the total birds reach about 5000 in each month. Especially, 5610 birds are sighted in May,and three species account for 50.8%, 32.0% and 17.2%, respectively. In April, most egrets begin to nest on the branchs of Acacia confusa, and nests come to 6000 during middle May and the beginning of June.The results show that the three species of egret are all resident and breeding birds of the Island.