SURVIVAL IN RELATION TO BROOD-SIZE IN TITS

Authors


SUMMARY

  • 1In most years the mean weight of nestling Great and Blue Tits was lower in larger than smaller broods, but it was similar in 1948, when food was exceptionally abundant.
  • 2In most years, the commonest clutch of the Great Tit was nine or ten, and the average number of young surviving per brood was highest from broods of nine or ten. But in 1947 and 1948, when food was unusually abundant, clutches were unusually large and survival was as high from broods of above average size as from those of average size. The results for the Blue Tit seemed similar.
  • 3Few Great Tits have late broods, and, as compared with normal broods, the clutches are smaller, the young weigh less, have higher losses in the nest and survive much less well after leaving the nest. Much the same holds for the Blue Tit.
  • 4These findings accord with the view that the normal breeding season of the Great and Blue Tits is that when they can raise most young, and that their clutch size is in general adapted to the number of young that they can raise.

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