BLUE-HEADED VIREO 297 



During tlie winter months hibernating pentatomids constitute one of the most 

 important sources of food for the blue-lieaded vireos, as shown by the November 

 and January percentages of 48.7 and 20.02, respectively. * * * 



Considering the enormous numbers of beetles available, it is somewhat sur- 

 prising that not more are eaten. The blue-heads manage to seek out enough, 

 however, to make up 13.51 percent of their entire diet. Of this, the ladybird 

 beetles make up 4.88 percent, or more than a third. It is certain that there are 

 not a third as many ladybird beetles as all other beetles combined ; and thus it 

 must be considered that the blue-headed vireos, like the warbling, either find 

 these brilliantly colored forms in abundance in their environment or else make 

 special search for them, a most undesirable habit economically. Roughly, a 

 second third of the total bulk is composed of the metallic wood borers, the 

 longicorns, and the click beetles. The remaining portion includes, among others, 

 the weevils, which comprise 1.8 percent of the food. 



The average of Hymenoptera for the year was 6.86 percent, and of 

 flies Diptera, 4.29 percent. Other insects eaten include stoneflies, 

 dragonflies, grasshoppers, crickets, and locusts (6.56 percent for the 

 year). 



The small percentage of vegetable food was mostly "in the form of 

 fleshy fruits, such as wild grape, dogwood, viburnum, and wax 

 myrtle. No cultivated fruit was identified, and it is practically certain 

 that none is eaten." The average for the year was 3.68 percent, but in 

 January it formed nearly a quarter of the total food, 24.37 percent. 



Aaron C. Bagg (Bagg and Eliot, 1937) says: "The height of the 

 Blue-head's migration coincides with the emergence of tent-cater- 

 pillars. At Holyoke on May 10, 1926, 1 watched one of these Vireos 

 take most of the young catei'pillars in one web, then fly to another and 

 repeat the heavy meal." 



Alexander F. Skutch writes to me: "Once in the highlands of 

 Guatemala I saw a blue-headed vireo pick up a very long caterpillar, 

 possibly an inch in length. At first the bird seemed puzzled to know 

 what to do with it, and crossed to the other side of the tree with the 

 larva dangling from its bill. Here he laid it along a twig, held it there 

 with a foot, and took a few nibbles or tugs at it. Then he took it in 

 his bill again, still nearly or quite intact, and swallowed it whole. The 

 habit of using the foot for holding food, while it is torn apart with the 

 bill, appears to be very imperfectly developed among the vireos, but 

 has attained a high degree of efficiency in the related families of shrike- 

 vireos (Vireolaniidae) and pepper-shrikes (Cyclarhidae)." 



The blue-headed vireo lives mainly in the trees of the forest and 

 obtains most of its food among the twigs and foliage, where it gleans 

 quietly and thoroughly. But Ora W. I^iight (1908) says: "I have 

 also on several occasions seen one of these birds spring into the air 

 after passing insects after the style of a Flycatcher, in fact this man- 

 ner of feeding would seem to be more characteristic of this species 

 than of any other Vireos with which I am acquainted." 



Behavior. — One of the chief characteristics of the blue-headed 



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