EASTERN OVENBIRD 471 



In Ohio, Lawrence E. Hicks (1934) found 41 nests out of 112, or 36 

 percent, parasitized by the cowbird. According to Sage, Bishop, and 

 Bliss (1913) 11 outof 30, or nearly 37 percent, of the nests found in 

 Connecticut contained eggs of the cowbird. H. W. Hann (1937) re- 

 ports that 52 percent of those he found in southern Michigan were 

 parasitized. Herbert Friedmann (1929) had over 150 records of 

 parasitized ovenbirds' nests ranging from southern New England, 

 New York, Pennsylvania and west to Illinois, Minnesota, and Iowa. 

 In contrast it is interesting to note that of 15 ovenbirds' nests I have 

 seen, and of many others reported in Maine, not one contained cow- 

 bird's eggs. Although the cowbird is an abundant bird in that State 

 the ovenbird seems to be comparatively free from molestation in this 

 part of New England. 



According to Hann (1937) the cowbird lays early in the morning 

 before the ovenbirds lay and requires only 40 to 60 seconds to deposit 

 the egg. In 13 cases an egg of the ovenbird was removed by the cow- 

 bird before the latter deposited an egg, and the number of eggs thus 

 removed was 75 percent of the number of cowbirds' eggs laid. The 

 ovenbird seems to make no attempt to remove the cowbird eggs. The 

 incubation of the cowbird's eggs averaged 11.6 days which is 0.6 of 

 a day less than the average period of the ovenbird. Young ovenbirds 

 in parasitized nests grew approximately as well as those in non-para- 

 sitized nests, so that the chief loss to the ovenbird was in the removal 

 by the cowbird of an estimated 18 percent of the total number of eggs 

 laid by the parasitized ovenbirds. However, the survival rate of the 

 cowbirds was low, since out of 40 cowbird's eggs laid, only 22 hatched, 

 10 birds left the nest, and probably not more than 5 left the woods. 



Fall. — Early in August ovenbirds are to be seen just south of their 

 breeding range, indicating that the autumn migration has started. 

 The earliest recorded dates for the Carolinas are in the first week of 

 August. They reach southern Florida by August 20 and by the end 

 of August the first fall migrants arrive in Cuba and Puerto Rico. The 

 bulk of the individuals do not pass over this route until a month later. 

 From mid-September to mid-October waves of these warblers are to 

 be seen passing through and leaving the Florida Peninsula. 



The last individuals leave Manitoba, Ontario, New Brunswick, and 

 other sections of these parts of the northern nesting range by the last 

 week of September. In the northern States of the Middle West and 

 in New England they leave by the first week of October, but some 

 linger as late as November. The last ones are generally seen in Ken- 

 tucky, Virginia, and the Carolinas during the last week of October, 

 a few are known to winter in South Carolina. From this latitude 

 south to Florida and the Gulf States it is difficult to determine the 

 date when the last birds leave this region for the islands of the West 



