Showing papers on "Heron published in 1986"

Advantages and disadvantages of egret and heron brood reduction.

Abstract: Data from great egrets and great blue herons were used to test a fundamental assumption of Lack's brood-reduction hypothesis, that mortality is brood-size dependent. This was confirmed for the largest brood sizes (4 and 3), which, in egrets, also have the highest sib-fighting rates. Broods of one, however, experienced paradoxically high mortality, especially early in the season. The hypothesis is advanced that parents desert unprofitably small broods when sufficient time remains for production of a larger brood. A simple game-theory model shows that this parental desertion may hinge primarily on the overall costs of renesting. Egret brood reduction caused by sibling aggression (siblicide) occurred later than less aggressive forms of brood reduction. The inclusive fitness of senior broodmates is maximized by the successful fledging of all sibs, and the physical superiority of seniors (in food-handling for herons; food-handling and aggression for egrets) usually suffices to guarantee their own welfare in brood competitions. Finally, it is shown that the last chick in asynchronously hatching broods represents two kinds of reproductive value (RV) to the parents-"extra RV" (obtained despite the survival of elder sibs) and "insurance RV" (obtained only when at least one elder sib dies first)-which can be distinguished from field data. This approach can be used in comparisons with other asynchronous species for partitioning the fitness contributions of marginal offspring.

Sexual reproduction in Acropora (Isopora) (Coelenterata: Scleractinia) - II. Latitudinal variation in A. palifera from the Great Barrier Reef and Papua New Guinea

Abstract: In contrast to the seasonal gamete and planula production of Acropora (Isopora) palifera on Heron Island reef (Lat. 23° S), populations on Lizard Island reef (Lat. 14° S), sampled in 1979, 1981 and 1983, and Salamaua and Busama reefs (Lat. 7° S), sampled from 1980 to 1983, planulated year-round. Intensive sampling of colonies at Salamaua and Busama showed that gametes ripened at two-month intervals and that up to six cycles of gametes and larvae could be produced by an individual colony. Gametes of only a portion of the population — usually close to 50% — ripened each month. The Salamaua population, on average, produced fewer and smaller planulae than the Heron Island population during each two-monthly reproductive cycle. Hypotheses correlating the annual periodicity of breeding in marine animals with latitudinal variation of temperature were tested. In general, the time of breeding in A. palifera at Heron Island reef is much more restricted than theories based on latitudinal variations of water temperature would predict. It is hypothesized that, in the near subtropical environment of Heron Island reef, this species has evolved a life-history strategy that limits the amount of energy allocated to reproduction and allocates more energy to growth.

Decline of Second-Growth Douglas-fir in Relation to Great Blue Heron Nesting

Abstract: The effects that great blu e heturs (Ar.Jea hercdiB) have upon nesting kees, Douglas,fi. (Pseedorslg@ merz;ert0, sere explored in western Vashington. An explanalion for the decline and d€ath of nesting trees {oliowing use by herons is of{ered. Excrement deposited on the soil beneath nests was analyzed, and found b contain nutrients in anounrs be.eficial ro Douglas fir. Although soil pH decreased foilowing the onset of nesling, this decrease was not su{ficient to adversely change soil nutrienr arailabiliiy. Ho*ever, heron excrenent on needles benealh the nest probab)y acted as a physical barrier to photosynthetic and to transpira, tional processes. Ir was also caustic to needle tissues and resulted in abnormat needle loss. This needle loss vas likelr rhe precur, sor to tree decline. Introduclion In the Pacific Northwest, great blue herons (Ardea herodias) maintain large nesting colonies in the upper branches of Douglas-fir (Pseudotsuga menziesii). When walking through an active heron rookery in spring, one is overwhelmed by the smell of excrement and rotting heron food (fish, shellfish and frogs) which cover the forest floor. Those trees that support nests have lost most of their foliage; rhey appear diseased and near death. The areas directly beneath nesting trees are void ofplant growth, in contrast to the lush understory that surrounds the rookery. The association between the presence of heron excrement and the deterioration of nesting trees and their shrub understory, suggests that excrement has caused the observed changes. Dolesh (1984) suggested this type of deterioration rlas caused by detrimental changes in soil conditions resulting from heron excrement deposits beneath the nesting trees. The objective of this study was to develop a basis for understanding nesting tree decline using (l) a description of the rnorphological changes that nesting trees undergo, (2) a chemical examination of heron excrernent, and (3) an anallsi. of soil pH bencalh nesting lrees.