This is apparently what happens in populations of Cape May and bay-breasted warblers. Ken deigh (1947), examining older material, established the fact that these species are abundant when there is an outbreak of Chorist oneura fttlniferana
(Clem.), the spruce budworrn. More recent in formation confirms this. To correlate with the fact (Greenbank 1956) that there have been continu
ously high budworm populations since 1909, there
is the statement of Forbush (1929) that the Cape
May warbler became more common about 1909.
and the statement of Bond (pers. comm.) that the
winter range of the species has been increasing in
size. An outbreak of spruce bud worms started in
northern Maine in the late 1940's, and Stewart
and Aldrich (1951) and Hensley and Cope (1951)
studied the birds during 1950 and 1951. Cape
May and bay-breasted warblers were among the
commonest birds present, as in the earlier out
breaks, although both species were formerly not
common in Maine (Knight 1908). The outbreak
has continued through New Brunswick, where
current bird studies (Cheshire 1954) indicate that
bay-breasted is again the commonest bird, although ior unknown reasons the Cape Ma
observed, In conclusion, it appears that all
primarily regulated by density de
and that a limiting factor is food
breasted and Cape May warblers.