1914] Crandall: Notes on Costa Rican Birds. 337 



uniting in good-sized flocks which searched the woodland for 

 anything edible. The Jays seemed to act as sentinals for the 

 rather stupid Caciques, giving their shrill alarm notes at the 

 slightest sign of danger. It is of interest to note that a similar 

 association of a Jay and a Cacique, both of different species 

 from the ones here mentioned, has been recorded from British 

 Guiana, by Mr. C. Wm. Beebe.^ 



As the Jays were calling, an audible popping noise could 

 be distinguished, following the note. Careful observation 

 showed a distension on the fore-neck, which was alternately 

 inflated and collapsed, the cracking sound occurring at the point 

 of greatest inflation. Examination of a freshly killed bird dis- 

 closed a sac of skin at a point just anterior to the point of the 

 sternum. It was quite flat and measured 14 mm in length. 



A captive specimen of Psilorhinus moi'io morio (Wagl.) in 

 the Zoological Park exhibited a similar character. This bird 

 never uttered a vocal note, but distended the cervical sac when- 

 ever 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. Dissection showed this 

 protusion to have been formed by a simple evagination of the 

 dermal covering of the neck. A narrow band of muscle fibres 

 lying in the skin surrounded the base of the sac, but as these 

 bands occur in closely allied forms (as Cyanocitta cristata) it 

 is doubtful if they perform a special function in this case. The 

 sac communicated directly with the praebronchial or interclavi- 

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

 ing in the furcular membrane, and doubtless received its air 

 from this source. 



Seirus novehorace7isis noveboracensis (Gmel.). Northern 



Water-Thrush. 



One living specimen was taken on April 9th and a second 

 on the 15th. Two others were noticed during the same period. 



^ Our Search for a Wilderness, p. 174. 



