Seabird Abstracts

The behaviour of the Shag

Snow BK (1963) British Birds 56(3):77-103 & (5):164-186

  1. An account is given of the behaviour of the Shag {Phalacrocorax aristotelis), based on four years' study of the breeding population on Lundy, Bristol Channel.
  2. Adult males normally re-use their nest-sites of the previous year. Females may either return to their previous nest-sites or move to others. Thus some pairs persist in successive years, and some change. Previously mated pairs engage in the same courtship behaviour as newly formed pairs.
  3. The social and courtship displays are described and figured, and are analysed with reference to their aggressive and submissive elements. The main aggressive element consists of pointing the head and beak at the opponent; this is avoided in submissive postures and the advertising displays. Postures and movements are of particular importance as the Shag's vocal repertoire is extremely limited.
  4. The males perform advertising displays which attract unpaired females. An unpaired female will visit a number of males before visiting one more frequently and forming a pair with him. Displaying males recognise the sex of other Shags from their postures. Pairs usually mate only on the nest or nest-site; this has probably evolved because it is necessary for the eggs to be kept covered and protected from predators.
  5. Some observations indicated that Shags recognise one another primarily by the face, and it is suggested that the appeasement gesture, which involves turning the back of the head towards the aggressor, is linked with this.
  6. Most nest-building is done after pair-formation, the material being largely collected by the male and built in by the female. There is a strong association between nest-building activity and copulation.
  7. Both sexes incubate the eggs. The incubation routine, with typical changeovers, may start several days before eggs are laid. The ending of incubation behaviour seems not to be internally determined, but depends on the external stimulus situation, and so may be hastened or retarded by manipulating the nest contents, e.g. introducing a chick soon after incubation has begun. After hatching, both parents brood the chicks and undertake guard duty.
  8. Both parents feed the young. The female probably gives more feeds than the male in the first few days, a difference perhaps correlated with the larger size of the male. When the young are larger, male and female may concentrate on feeding different individuals. Each chick typically receives only three or four feeds per day. Nest sanitation is efficient, involving several different behaviour patterns.
  9. Experiments in which chicks were exchanged between nests indicated that strange chicks are accepted up to the age of about 29 days, and that after this age (at which sex differences begin to become apparent) strange chicks are more likely to be accepted by an adult of opposite sex.
  10. After leaving the nest, the juveniles congregate on the sea-rocks, where each is fed by its own parents, though they often try unsuccessfully to snatch food from other adults.
  11. An account is given of the development of the young Shag's behaviour, including its departure from the nest and the development of its locomotory ability, voice, social behaviour and displays.


Links at this site

Links to other sites