Summary The Gannet lays only one egg, and replacements are common. In 1962 in Scotland the Gannet was shown to be capable of hatching two eggs and rearing two young of the same age. If one of the brood of two was younger it did not survive. In striking contrast, S. leucogaster and S. dactylatra hardly ever manage to rear two young even though they normally lay two eggs. The results of artificial “twinning” showed that hatching success was as high for two eggs as for one, though the incubation period was two days longer, and that fledging success was 83% against 94% (of eggs hatched). This gave the parents of twins a 76% greater output than singles. The twins grew almost as well as singles, though weighing slightly less than a single of the same age, and taking on average four days longer to fledge. These figures refer only to twins of approximately the same age. The twin growth curves are compared in detail with normal single‐chick curves and with twin‐Shag growth curves, The results are discussed in terms of a possible causal mechanism related to feeding behaviour, since, though twin Gannets grow equally as well as each other, and, in the later stages, as well as singles, they are always slightly behind due to a lag which occurred early in growth when the actual amount of food consumed was extremely small. The results are thus apparently at striking variance with the theory that the Gannet rears the maximum number of young that it can feed; but it is still necessary to know how well the twinned Gannet young survive to breeding, and whether the rearing of an extra chick imposes a real strain on the adults (signs of which were beginning to show by the time the young fledged) which in long‐lived birds might offset the reproductive advantage of producing twins. It is suggested that, particularly in sea‐birds, this problem is worth exploring more systematically than has yet been done. Catastrophic years are thought unlikely to weed out twins, since to offset the 76% reproductive advantage would require such years to occur improbably often. Finally, the results are discussed in terms of the Gannet's social behaviour, in particular its well‐developed aggression, which is concerned with site‐defence, and affects the Gannet's food gathering power by requiring constant site attendance by one or other parent throughout the nestling period. In this sense, aggression may partially act as a population control mechanism. The relevance of these results to Wynne‐Edward's theory of animal population control mechanisms is briefly considered.

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Participants disengaged more from images compared with verbal thoughts, and the insomnia patients reported feeling less calm and relaxed at the end of the salient verbal thought compared with the good sleepers.

SUMMARY The Bass colony is increasing—in 1962 there were 5,350–5,700 breeding pairs; 1,340–1,430 pairs of non‐breeders with nests or sites (mainly pairs in their season before first breeding) and 2,000–2,500 “club” birds without nest or site. 15% of nests were occupied by both birds of a pair at the time of the count. Oldest males return to the colony in January, followed by experienced females, considerably later by young adult‐plumaged birds, immature birds later still, and the few one year‐olds that return usually not until May and June. Mid‐cliff sites are the first to be re‐colonized each year. Gannets usually breed in their fifth year and there is some evidence that females breed earlier than males. The characteristics of Gannet nests and sites are described. Nests function in raising the egg and young above the morass of the breeding colony, and reach a density of about 2.3 per square metre. Nests are demolished and their positions changed more often than might be suspected. The extremely strong social tendency which causes Gannets to establish their sites amongst or very close to existing breeders probably is the factor ensuring high density and this contributes to synchronization of laying. Egg laying is analysed. Experienced pairs forming an isolated group of 20 nests began laying later and showed less synchronization than two other groups of the same size but from the middle of a dense mass, probably due to the greater social stimulation experienced by the non‐isolated groups. The date for first and median eggs was also earlier in larger than smaller groups in the same year. The effect of density as distinct from group size is also discussed. Early eggs are mainly laid on cliff or cliff‐edge sites and in large nests. Different groups within the colony produced the median egg within 2–3 days of the end of April each year. In the fullest documented group the mean date was also constant from year to year and closely approached the median, implying a considerable degree of synchronization within the gannetry as a whole. Laying in the observation colony became progressively earlier in successive years, probably due to recovery from previous disturbance. Nevertheless, individual females tended to lay in a fixed position each year with relation to the mean for the group. Increasing age of the female causes earlier egg laying and heavier eggs for up to at least five years. It is suggested that the survival value of seasonally synchronized laying in the Gannet is maximum utilization of a seasonally dependable and abundant food supply for the production of young with the optimal chance of post‐fledging survival. The spread of laying acts as an insurance against possible adverse conditions. There is a considerable reserve of unutilized breeding capability within the colony (adult non‐breeders, a pre‐maturity period longer than physiologically necessary for egg production, and a one‐egg clutch when in fact two young can easily be reared). The mean of 393 Gannet eggs was 104.5 gm. (range 81–130). Eggs constitute ab...