When forming a pair bond, the hen approaches the cock on his territory with a hunched, submissive posture, while making begging calls (similar to those emitted by young gulls). If the cock chooses not to attack her and drive her away, he responds by assuming an upright posture and making a mewing call. This is followed by a period of synchronised head-tossing movements, after which the cock then regurgitates some food for his prospective mate. If this is accepted, copulation follows. A nesting site is then chosen by both birds which is returned to in successive years. European herring gulls are almost exclusively sexually monogamous and may pair up for life, provided the couple is successful in hatching their eggs.