From the figures in table 1, it may be seen that Laysan Island 
is the most important breeding station for North Pacific albatrosses. It 
is utilized by 46 percent of the total breeding population of Laysan 
albatrosses, and by 61 percent of the total breeding population of 
black-footed albatrosses. 
Midway Atoll. panics second with 36 percent and 15 percent, 
respectively, of the total breeding populations of the two species. 
Only four atolls - Laysan, Midway, Iisianski, and Pearl and 
Hermes Reef ~ are the breeding growmds of 96 percent and 94 percent, 
respectively, of the total world populations of Laysan and black- 
footed albatrosses. It is obvious that the future of North Pacific 
albatross populations hinges largely upon the maintenance of adequate 
breeding colonies on these four atolls, particularly Laysan and Midway. 
A more detailed report on albatross populations throughout 
the Leeward Chain will be published elsewhere by Karl W. Kenyon and 
the writer. 
Be ologi te 
The present report contains only brief summaries of those 
aspects of life history and ecology that have an immediate bearing on 
the airoraft hazard problem or on the application of control measures. 
A more detailed report covering the basic biological aspects will be 
published separately. 
Age at Which Albatrosses First Return to the Breeding Grounds 
Present data are inadequate to determine the age at which 
young albatrosses normally return to the nesting islands for the 
first time. None of the 5,000 albatross chicks color-banded in May- 
June 1957 returned during the 1957-58 nesting season. The youngest 
banded birds of known age recaptured on the islands were a single 4- 
year-old Laysan albatross and a single 4-year-old black-footed 
albatross. No known 5~-year-old albatrosses have been recaptured. 
Returns of birds banded as chicks are fairly evenly distributed after 
the fifth year following banding (table 2). ‘This suggests that the 
majority of young birds return for the first time sometime between the 
ages of 4 and 6 years. The royal albatrosses (Diomedea epomophora) of 
New Zealand first return to their breeding grounds between the ages of 
4} and 8 years (Richdale 1952). Further information is necessary to deter- 
mine what proportion of our North Pacific albatrosses first return at 
each age, and if any return before the age of 4 years. Without this infor- 
mation it is impossible to determine the number of immature birds at sea. 
