The U test (Hoel 1954) shows this to be significant at the .0024 level; that is, bay-breasted warblers lay significantly larger clutches during years of bud worm outbreaks. There are not sufficient data to make a corresponding comparison for Cape May warblers. It is known (Wangersky and Cunningham 1956) that an increase in birth rate is likely to lead to instability. The easiest way to increase the stability, while still maintaining the large clutch which is desirable for the fluctuating food supply, is to have the clutch especially large when food is abundant. This is apparently the solution which the bay-breasted warbler, at least, has taken.