La Prospección de placeres del oro y otros minerales densos

[eng] Alluvial prospecting is the most widely used method in heavy mineral exploration. Heavy minerals are resistant to meteoric agents. Economically, the most important heavy minerals are: precious metals (gold, silver and platinum group minerals), gems (diamonds, rubies, sapphires, emeralds, etc), the tin base metal group (cassiterite), technologic metals such as titanium (ilmenite and rutile), tungsten (wolframite and scheelite), zirconium (zircon) and the rare earths. The most usual techniques used in alluvial prospecting and the different criteria employed in exploration, mineral benefit and evaluation of alluvial ore deposits known as placers are presented.[cat] La prospecció al.luvionar es un mètode excepcional per la recerca de minerals de interès econòmic, com los minerals densos d'elevada resistència física i química. Entre ells son d' interès els metalls preciosos (or, plata i platí), gemmes (diamant, rubí, zèfirs, maragdes, aigua-marina, etc.), metalls de base com l'estany (cassiterites), minerals tecnològics com el titani (ilmenites i rutils), wolfram (volframita i scheelita), zirconi (zircó), de terres rares (monacites), etc.. En aquest text, és presenten las tècniques mas usuals en Prospecció al.luvionar com la batea, així com els distints criteris a seguir per dur a termini una prospecció, un benefici i una avaluació dels seus jaciments que es coneixen com ¿placeres¿.[spa] La prospección aluvionar es un método excepcional para la búsqueda de minerales de interés económico, como los minerales densos de elevada resistencia físico-química. Entre ellos son de interés los metales preciosos (oro, plata y platinoides), gemas (diamante, rubíes, zafiros, esmeraldas, aguamarinas, etc.), metales de base como el estaño (casiteritas), minerales tecnológicos como el titanio (ilmenitas y rutilos), wólfram (volframita y scheelita), circonio (circón), de tierras raras (monacitas), etc.. En este texto, se presentan las técnicas mas usuales en prospección aluvionar como la batea, así como los distintos criterios a seguir para llevar a cabo una prospección, un beneficio y una evaluación de sus yacimientos que se conocen como ¿placeres¿

Parental energy and fitness costs in birds

De kosten die aan reproduktie verbonden zijn kunnen op twee verschillende manieren worden opgevat. Naast de direkte uitgaven, in termen van energie, kan men ook de repercussies voor (toekomstig) reproduktief succes in rekening brengen. Deze twee benaderingen, die in de literatuur verwarrend genoeg vaak door elkaar gebruikt worden, zijn gestoeld op verschillende biologische concepten. Toch bestaat er een verband tussen de beide begrippen. De aard van die relatie tussen de huidige energetische uitgaven en het reproduktief succes is het thema van dit proefschrift. Zie: Samenvatting.

Spring staging in Brent Geese Branta bernicla:feeding constraints and the impact of diet on the accumulation of body reserves

The diet composition of Brent Geese Branta bernicla on a salt-marsh was quantified. Puccinellia maritima was the principal food species, while Plantago maritima and Triglochin maritima were less commonly taken. Festuca rubra only acted as a substitute for Puccinellia when production of the latter species dropped. The metabolizable energy of the food plants ranged from 5 to 11 kJ . g-1. By assessing the ingestion rates of geese feeding on different food species, the net intake rate could be derived. Plantago and Triglochin appeared to be the most profitable plants to eat. The proportion of these species in the diet was restricted by (1) the capacity of the alimentary tract, since high intake rates combined with high water contents of the food plants easily led to overfill; and (2) the limited distribution of these plants, in combination with their rapid depletion by grazing geese. These latter factors led to an unequal allocation among individual geese. Most Plantago and Triglochin was obtained by dominant pairs within the flocks. The high quality of Puccinellia allowed geese to gain mass in spring, but the metabolizable energy of this plant species declined during the staging period, and Plantago and Triglochin increased in importance in supplying the geese with components with which to build their body reserves. The timing of the onset of spring growth of the various food species differed between years, and plant phenology was shown to have a profound effect on the final body reserves of the geese

Increased daily work precipitates natural death in the kestrel

1. Costs of reproduction have been assessed experimentally by measuring subsequent survival and reproduction of parent animals raising enlarged and reduced numbers of offspring. Reported effects on survival have so far always referred to local survival of marked individuals in the study population. They do not provide definitive proof of a cost of reproduction, since reduced local survival may be due either to reduced survival or to an increased tendency to emigrate from the study area. Therefore, it is important to assess mortality rates in connection with brood size experiments. 2. We report an analysis of the time of death in 63 cases where kestrels, Falco tinnunculus L. had raised broods of manipulated size and were subsequently reported freshly dead. 60% of the parents raising two extra nestlings were reported dead before the end of the first winter, compared to 29% of those raising control or reduced broods. This result confirms our interpretation of the manipulation effects on local survival as due to mortality rather than emigration. The extra mortality occurred in the winter following the brood enlargement. 3. Kestrel parents in these experiments have been shown to adjust their daily energy expenditure to the modified brood size. Increased parental effort in this species thus entails an increased risk of death half a year later.