This was based on grass farming, which produced large quantities of forage and pasture. At times, they forage from agricultural crops and may be considered pests. Though foraging is usually solitary, they occasionally forage in groups. Rats prefer to forage in forest habitats. Pelagic birds feed on planktonic crustaceans, squid and forage fish. The result can be rich feeding grounds attractive to the plankton feeding forage fish. There was also a shortage of forage livestock. There are of two broad types of forage legumes. They forage in leaf litter on the forest floor, eating earthworms and insects. Salmon farming leads to a high demand for wild forage fish. They may forage in flocks in winter, when they mainly eat grasshoppers. Occasionally, breeding pairs may forage and hunt together. Workers may forage in households, but nest in soil mounds. Though primarily ground feeders, they will also forage in larger plants. In winter, they often forage in flocks.