44 BIRDS OF THE REPUBLIC OF PANAMA PART 4 



sheltered from wind, but also isolated from other trees that would give 

 predators easier access. Lawton and Lawton found that nests in more 

 wind-protected sites were more likely to be successful than nests in 

 more exposed sites. 



The eggs are bluish gray "thickly covered with fine brown speckles, 

 which on the thicker end nearly obscure the ground color." Seven eggs 

 measured from 32.5-36.5x23.8-25.4 mm. The incubation period 

 ranged from 18 to 20 days. The young at hatching have a yellow skin, 

 sometimes darker on the upper surface, and are without down. Bill and 

 feet are yellow, and the inside of the mouth is red. Skutch noted that 

 the bills of the immature birds darkened slowly with age. 



Lawton and Guindon (Condor, 1981, pp. 27-33) found that all mem- 

 bers of the flock bring food to the nest. Over the course of the nesting 

 season inexperienced young birds become more efficient at bringing ap- 

 propriate food items. 



The curious inflatable breast sac found in all races of this species of 

 jay appears to have been noted first by Samuel Cabot, Jr. ( Journ. Bost. 

 Soc. Nat. Hist., vol. 4, 1844, pp. 460-467), in the race P.m. vociferus in 

 Yucatan. He speaks of their calls as loud and disagreeable and in a 

 male and female that he collected, records "a most peculiar formation 

 in the trachea, being a membranous bag, coming off between the rings, 

 about halfway down, and intimately connected with the skin of the 

 neck." There can be no doubt that he noted the peculiar air sac, though 

 his interpretation of it as connected with the trachea was in error. 



Lee S. Crandall (Zoologica, vol. 1, no. 18, 1914, p. 337) in observa- 

 tions near Guapiles, on the base of Volcan Turrialba, Costa Rica, in 

 early 1914, made careful observations on the air sac in the field, verified 

 later by data from a captive bird at the New York Zoological Society's 

 Bronx Zoo. He described the popping noise heard in the field, and in 

 the zoo recorded that the bird "never uttered a vocal note, but distended 

 the cervical sac whenever he was excited, making a popping sound which 

 could be heard at a distance of several yards. On examination of this 

 bird after death, the sac was found lying between the branches of the 

 furculum, 1 mm anterior to their point of union. Deflated, it measured 

 13 mm from base to tip and 19.5 mm along the base, the tip being 

 rounded. . . . The sac communicated directly with the praebronchial or 

 interclavicular air-sac (Saccus interclavicularis) , through a large open- 

 ing in the furcular membrane, and doubtless received its air from this 

 source." 



A more detailed account is that of Sutton and Gilbert (Condor, 

 1942, pp. 160-165, figs. 59, 60) based on observations and specimens 



