THE GULLS 229 



accepted as typical for the genus. Another classical account is that of 

 the black-headed gull by Kirkman (1937). Both accounts, which 

 appeared simultaneously, have done much to increase our knowledge 

 of gull behaviour. Paludan (1951) and Tinbergen (1953) have followed 

 with other intensive studies. 



These two gulls make an interesting comparison. As a rule the 

 black-headed gull arrives quite suddenly and in a large flock at its 

 breeding ground, much as the puffin does, but almost a month earlier, 

 in the first fortnight of March; although some scouts pay visits in Feb- 

 ruary. But it does not settle down immediately. Its visits are somewhat 

 spasmodic, and always during those early weeks it withdraws to roost 

 away from the breeding ground. When the adults settle at the nesting 

 sites in March and April, they appear to be paired like gannets, 

 rooks, and other social nesters. We know very little as to the actual 

 pairing up, which is said to take place before arrival. Kirkman 

 insisted that the birds "have arrived paired at the breeding place," 

 but Tinbergen (1952) provided proof that the male and female arrive 

 separately at the breeding ground and there discover each other or a 

 new mate on or near the familiar nesting site. There appears to be no 

 firm evidence that any gull remains with its mate throughout the 

 winter; or that they pair regularly before they leave for the breeding 

 ground in early spring, in February and March. In short, we only 

 know that the birds are faithful to the colony and nest-site. This 

 applies also to the migratory lesser black-backed gull, which arrives in a 

 body at the nesting ground in March (with a few scouts earlier), and 

 it would appear to apply to all the gulls (as well as to the terns) which 

 perform mass movements from wintering to breeding grounds. 



Faithfulness to the old nesting site, however, is very strong. Kirk- 

 man suggests that the big nest in the centre of a group of smaller 

 nests in a black-headed gull colony may be the parents' home, and 

 the other nests round about are those of the children. Extensive ringing 

 alone can prove this attractive explanation of the grouping of nests, 

 and might also explain the interiorly family (or neutral) attitude of 

 the owners, who adopt an exteriorly aggressive attitude to all others 

 outside the family group. But other factors operate, and Kirkman 

 himself notes that the size of the nest is largely determined by the 

 number of times a bird is prevented from sitting on its eggs ; if its mate 

 refuses to leave the eggs the frustrated bird finds an outlet (displacement 

 activity) for broodiness by collecting and depositing material in the 

 nest. 



