384 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 



On only three occasions during the three seasons I have passed on 

 Barro Colorado have I seen a male Cotinga nattereri near the labora- 

 tory. None of these was in the sand-box tree. Two perched for a 

 few moments at the top of a dead tree about 100 feet from the sand- 

 box tree. They were alone. The third was at the border of the 

 forest, 120 yards from the sand-box tree. A few minutes after he 

 flew back into the forest a female cotinga left the forest from nearly 

 the same place and flew to the nest in the sand-box tree. This was 

 on February 14, 1928, when my observations indicate that the female 

 was lajdng. It is not improbable, therefore, that the sexes were 

 associated on this occasion. 



Thraupis cana. — A pair of blue tanagers nested in the oropendola 

 tree in the season of 1927 and 1928. They selected for their site a 

 large mass of parasitic plants (the lower side of which was occupied 

 by a colony of stingless bees) where it was not possible to watch 

 them closely and I have no notes on the progress of their nesting. 



An iguana {Iguana iguana)^ between four and five feet in length, 

 was usually present in the sand-box tree and on occasions two smaller 

 ones were observed. They would lie motionless for hours stretched 

 out on the larger, upper limbs, apparently sunning themselves. 

 Rarely they ate the leaves of the tree. None of the birds that fre- 

 quented the tree were seen to notice them, nor were the iguanas con- 

 cerned with the birds. 



SUMMARY OF OBSERVATIONS ON A NESTING COLONY OF ORO- 

 PENDOLAS {ZARHYNCHV8 WAGLERI) ON BARRO COLORADO 

 ISLAND, CANAL ZONE 



The tree occupied by the oropendolas, when, in 1924, the laboratory 

 was established, having fallen in June of that year, the present site 

 was selected the following year. The new tree, which is believed 

 to have been chosen chiefly because of its proximity to the former 

 home, does not apparently offer the advantages of the fallen one and 

 the colony appears to be decreasing in numbers. 



The birds exhibit much regularity in the date at which they begin 

 to nest. In 1926 and 1927 nest building began on January 8, in 

 1928, on January 2. A humming bird {Anthracothorax nigri- 

 collis) and a cotinga {Cotinga nattereri) that nested in the oropen- 

 dola tree showed a similar regularity in site and date. While the 

 nesting season coincides roughly with the dry season, the exact time 

 of its inauguration does not appear to be closely dependent on the 

 rainfall. Temperature apparently presents too little variation to be 

 a controlling factor. The return of these birds to the same place year 

 after year illustrates the homing instinct, while the seasonal regu- 

 larity of their visit is in evident response to those annual prompt- 



