326 



Annals of the Carnegie Museum. 



fauna, or else by species of the Tropical which are more elastic, adapt- 

 ing themselves to the different environments caused by the periodical 

 rainy and dry seasons. 



Altitudinal Migration of Resident Species. 



A peculiar phenomenon, affecting the problem of the distribution 

 of a considerable number of resident birds, is the seasonal migration 

 from higher to lower altitudes and the congregation of certain species 

 into a small area where their favorite food is found in abundance. 

 The only species known to make these migrations are some of the 

 fruit-eating tanagers, and some of the cotingas and honey-creepers, 

 and there can be no question that the descent into lower regions 

 is made in search of certain fruits and berries which ripen at those 

 times and of which the birds are very fond. Perhaps one of the most 

 marked is that of the bell-bird {Procnias tricarunculata) , which is 

 normally a resident and breeds in the Cordilleran and sub-Andean 

 Zones. About the first of December they begin to drift into the Car- 

 ibbean lowlands, becoming very abundant in the upper part of the 

 Humid-Tropic Zone (600 to 1,500 feet), where they remain until late 

 in February, feeding upon a small nut-like fruit. 



Other examples are Euphonia minnta and E. luteicapilla, which 

 come down earlier and stay longer, appearing in large numbers in the 

 vicinity of Carrillo in September, gradually working their way into 

 the lowlands, until in December they were quite common about El 

 Hogar, in company with Dacnis venusta and Cyaneipes lucidus, which 

 are never seen in that region at any other time of the year. Tangara 

 icterocepha/a, T. guttata ckrysop/irys, T. fiorida and T. gyro hides 

 also appear in considerable numbers during August and September in 

 the lower part of the Rio Sucio gorge, in the vicinity of Carrillo, while 

 Tangara dowi comes down as far as La Hondura (3,500 feet) in great 

 numbers. Little or nothing is known concerning the range of Tangara 

 fiorida and T. icterocephala, beyond the fact that they are found in 

 the vicinity of Carrillo at certain times of the year, but it is quite 

 probable that they breed in the dense forests of the foot-hills in that 

 vicinity at an altitude of from 2,000 to 4,000 feet, congregating in the 

 lower gorge to feed on a small berry-like fruit abundant during August 

 and September. However T. guttata and T. gyroloides are species 

 of wider range and are met with during the breeding season at much 

 higher altitudes, while I found T. dowi abundant late in October in 

 the Sub-Andean Zone of the Volcano Turrialba. 



