The behaviour exhibited in searching, obtaining and utilising food. A few bird species are real specialists in that they are limited to one prey, while some are (in part of their range) mostly dependent upon one prey out of many possible foods. Many groups though are basically omnivorous, although often having clear preferences. The feeding habits of each species may be divided into two components; the general dietary and hunting habits of the genus, family or order, and the characteristic specific habits or preferences of the species which enable closely related species to live within a single habitat by means of this specialisation. Good examples are the specific preferences of titmice Parus spp. for hunting at different heights, in different trees and in different parts of those trees. The frequency of feeding activity ranges from the almost uninterrupted hunting by small passerines throughout daylight, and the three meals a day of thrushes during an abundant fruit harvest, to the one meal in 48 hours of Great Black-backed Gulls during herring fishery, and the week-long fasts of some marine birds in the breeding season (months long in some penguins). Some species like the Nutcracker Nucifraga caryocatactes store food (in this case hazelnuts) for scarce periods like winter. See also 'food'.