for successful breeding, common starlings are omnivorous and can also eat grains, seeds, fruits, nectar and food waste if the opportunity arises. The Sturnidae differ from most birds in that they cannot easily metabolise foods containing high levels of sucrose, although they can cope with other fruits such as grapes and cherries. The isolated Azores subspecies of the common starling eats the eggs of the endangered roseate tern. Measures are being introduced to reduce common starling populations by culling before the terns return to their breeding colonies in spring. There are several methods by which common starlings obtain their food, but, for the most part, they forage close to the ground, taking insects from the surface or just underneath. Generally, common starlings prefer foraging amongst short-cropped grasses and eat with grazing animals or perch on their backs, where they will also feed on the mammal's external parasites. Large flocks may engage in a practice known as "roller-feeding", where the birds at the back of the flock continually fly to the front where the feeding opportunities are best. The larger the flock, the nearer individuals are to one another while foraging. Flocks often feed in one place for some time, and return to previous successfully foraged sites. There are three types of foraging behaviours observed in the common starling. "Probing" involves the bird plunging its beak into the ground randomly and repetitively until an insect has been found, and is often accompanied by bill gaping where the bird opens its beak in the soil to enlarge a hole. This behaviour, first described by Konrad Lorenz and given the German term zirkeln, is also used to create and widen holes in plastic garbage bags. It takes time for young common starlings to perfect this technique, and because of this the diet of young birds will often contain fewer insects. "Hawking" is the capture of flying insects directly from the air, and "lunging" is the less common technique of striking forward to catch a moving invertebrate on the ground. Earthworms are caught by pulling from soil. Common starlings that have periods without access to food, or have a reduction in the hours of light available for feeding, compensate by increasing their body mass by the deposition of fat. Nesting Unpaired males find a suitable cavity and begin to build nests in order to attract single females, often decorating the nest with ornaments such