The migrating group, R migrates with complete retention. After this occurs, mesenchymal tissue migrates under the ectoderm. Haze migrates to adjacent countries and thereby pollutes other countries as well. The northern herd migrates west into southwestern Montana in the winter. During embryological development, the thymus migrates downwards, dragging the inferior glands with it. In winter, the subtropical ridge migrates towards the equator, making rainfall much more likely. The Abdim's stork is another migrant, albeit one that migrates within the tropics. However, when grown the Kaluga constantly migrates back and forth between upstream and downstream. It migrates mainly by day, often in large flocks. It migrates to more southerly areas in winter. This takes place several years before the loggerhead migrates to a mating area. A notable species of moth that migrates long distances is the bogong moth. Long-range travellers include the Arctic tern, which migrates from Antarctica every spring. Silicone easily migrates as either a liquid or vapor onto other components. It migrates during the daytime, in loose flocks of 5 to 250 birds.