Basil Davies, The Zoologist (1898)
“ The two parent birds would be unequal to catering for the wants of a larger brood than five; neither could a hen of this size well produce more than five eggs. Indeed, four is not an uncommon clutch by any means in districts where insect-food is not specially abundant. On the other hand, a Blackcap Warbler must produce five young in a season to prevent her species diminishing; and as the breeding season is curtailed by migration, which the young must be old enough to undergo when the time arrives, we see that a smaller clutch would not be convenient. ”
