Pairs are established or confirmed through aerial courtship displays in which a male and a female fly in wide circles up to or more, calling all the while, before the two birds descend together in zigzag glides. If the male is carrying a fish, he may attract the attention of other males too. On the ground, the male courts the female by circling her with his tail and neck raised, head pointing down, and wings partially open. If she responds, they may both adopt a posture with the head pointed skywards. The male may tease a female with the fish, not parting with his offering until she has displayed to him sufficiently. Once courtship is complete, the male makes a shallow depression in the sand, and the female scratches in the same place. Several trials may take place until the pair settle on a site for the actual nest. The eggs may be laid on bare sand, gravel or soil, but a lining of debris or vegetation is often added if available, or the nest may be rimmed with seaweed, stones or shells. The saucer-shaped scrape is typically deep and across, but may extend to as much as wide including the surrounding decorative material. Breeding success in areas prone to flooding has been enhanced by the provision of artificial mats made from eelgrass, which encourage the terns to nest in higher, less vulnerable areas, since many prefer the mats to bare sand. The common tern tends to use more nest material than roseate or Arctic terns, although roseate often nests in areas with more growing vegetation.