Red-tailed Tropiebird ( Phaethcn rubricauda) 
Current Status : Common nesting species* POBSP mximum population estimate; 1000 
in July* 1963 • POBSP minimum population estimatej 20 in February* 1964 . 
Prior Records : As early as 1841* Peale (in Poesch* 1961) recorded that Red-tailed 
Tropicbirds occurred on Enderbury. His journal* however* gives no 
information on this species other than the fact of their occurrence* 
Some 80 years later* in late feroh* 1924* J#G. 
Correia stated that only one Red-tailed Tropiebird had been seen flying over 
the island when it was visited by the Whitney South Sea Expedition* (Correia*field notes) 
In July* 1938 both George C. Monro and Walter R. Donag^ho recorded the presence of 
tropicbirds on Enderbury* and Muhro estimated the population at M up to a few hundred 
birds”. (Munro* 1938a* Donaghho* 1952) In addition* Munro or people aiding him in 
his banding efforts* banded 50 adults in 1938 and 200 more birds between April 2 and 
fey 15* 1939. A single xygB&xgx specimen was collected by L.P. Schultz of the 
U.S* National Museum who visited Enderbury in mid-fey* 1939# 
sr—'? f f '"i" "'| f' 
Population : The population size fluctuates with the stage of the breeding 
cycle and is highest during the summer months and lowest during the winter » 
when only two to five percent of the total population is present. From May 
through June, when the largest numbers of nests have been found, flocks of 
tropicbirds display over the island. In November when almost all nests 
contain young the number of birds seen is only a fraction of the number 
actually using the island, and most birds are at sea. The number of non- 
breeding adults which used the island from 1963 to 1965 is unknown since 
it was impossible to determine their number during our short stays on the 
island. We estimate that 5C0 to 75C pairs nested on the island. 
Annual Cycle : POBSP visits have been made during only five months of the 
years but data collected during these periods indicate an annual nesting 
cycle. If we consider the inclubation period as about 4 3 days and the 
fledging period as about 86 days (Fleet - per. com.), it is possible to 
interpolate the annual cycle from the relatively infrequent visits. 
mth 
The estimated number of nests is given in fable_ 
These numbers are 
based on careful surveys of the entire island but a number of nests were 
certainly overlooked. We believe that our counts have generally represented 
from 50 to 75 percent of the breeding population during any one visit and 
have made our estimates on this basis. 
Table 
^Red-tailed Tropiebird nest cycle on Enderbury 
