Nj. Aebischer, IMMEDIATE AND DELAYED-EFFECTS OF A GALE IN LATE SPRING ON THE BREEDING OF THE SHAG PHALACROCORAX-ARISTOTELIS, Ibis, 135(3), 1993, pp. 225-232
At the beginning of May 1982, a westerly gale destroyed or damaged 49%
of 761 Shag Phalacrocorax aristotelis nests on the exposed west side
of the Isle of May, southeast Scotland; 518 nests on the sheltered eas
t side acted as controls against which to assess subsequent effects of
the gale on Shag reproduction and recruitment. On sites affected by t
he gale, 90% of pairs rebuilt their nest and laid a second clutch, on
average 18 days after the loss of the first one. First-time breeders n
ested closer to the sea, suffered greater damage to their nests, and d
eserted their damaged nests more readily after the gale than did exper
ienced ones; a quarter of potential recruits to the west side were det
erred from breeding in that year. By the end of the season, the number
of chicks fledged per pair was 31% lower on the west side than on the
east. The difference was caused partly by nest desertion, partly by g
reater hatching failure of full clutches in apparently undamaged nests
and especially by lower fledging success of pairs that renested. Irre
spective of breeding experience, delayed early breeders produced more
chicks than late breeders nesting at the same time, showing that late
breeders were of poorer intrinsic quality than early breeders. This wa
s one reason for a seasonal decline in Shag productivity, although env
ironmental factors also played a role. During April-July, gales like t
hat of May 1982 occur on average once every 5 years on the Isle of May
. Despite the disruption that they may cause to nesting Shags, the imp
act on the long-term growth of the colony is small.