PROTHONOTARY WARBLER 27 



Enemies. — Dr. Walkinsliaw (1941) says that the house wren is a 

 serious competitor with the prothonotary warbler in Michigan, con- 

 tending with it for nesting sites in the bird-boxes. 



The cowbird is a persistent enemy of this warbler in spite of its 

 hole-nesting habits ; perhaps if the warbler nested in deeper holes it 

 might find some relief from this pest. Among 70 sets of eggs of this 

 warbler in the J. P. Norris collection, 18 contain cowbirds' eggs. Dr. 

 Friedmann (1929) found no less than 36 records of such parasitism 

 in the literature, and says: "As many as four eggs of the Cowbird 

 have been found in a single nest together with four of the Warbler's. 

 There are several cases on record of doubled-storied nests of this bird, 

 with a Cowbird's Qgg buried in the lower story. Such cases are, how- 

 ever, not common, and usually the Warbler seems to make no attempt 

 to get rid of the strange eggs." E. M. S. Dale wrote to me of a nest, 

 found near Toronto in 1933, that contained seven eggs of the cowbird 

 and none at all of the warbler ! 



Snakes sometimes destroy the eggs or young. 



Fall. — Dr. Walkinsliaw (1938) says that "the majority of the Pro- 

 thonotaries leave our rivers [Michigan] by the second or third of 

 July. One may canoe some years a good many miles during the latter 

 part of July or the early part of August without finding a single 

 Prothonotary, whereas in other years many groups can be found. 

 The majority evidently are early migrants. Very few remain until 

 late August or early September, the latest date being September 9, 

 1934, at Battle Creek." 



The 1931 A. O. U. Check-List states that this warbler apparently 

 crosses the Gulf of Mexico in migration "and is not found in Mexico 

 north of Campeche," but probably some migration is along the coast 

 of Texas and Mexico, as suggested by George G. Williams (1945). 



Dr. Chapman (1907) says : "The route of the Prothonotary Warbler 

 in its fall migration is interesting; the breeding birds of the Middle 

 Atlantic States apparently pass southwest to northwestern Florida 

 and then take a seven-hundred-mile flight directly across the Gulf of 

 Mexico to southern Yucatan, instead of crossing to Cuba and thence 

 to Yucatan." 



Alexander F. Skutch writes to me : "Unrecorded from Guatemala, 

 the prothonotary warbler is a rare bird of passage and very rare 

 winter resident in the more southerly portions of Central America. 

 Wlien Carriker published his list of Costa Rican birds in 1910, he 

 had a few records from the highlands — apparently of migrating 

 birds — and from the Pacific lowlands, but none from Caribbean low- 

 lands. But on March 4, 1934, I found it not uncommon at Puerto 

 Limon, where I saw one among the royal palms in Vargas Park, and 



