
Twelve sweeps of the experimental killing area between April 
22 and May 23 resulted in a kill of 4788 adult, 1371 young, and 107 
albatrosses of unimown age, a total of 6266 (see Table 7), 
A total number of albatrosses using the area this season was 
calculated to be 6216 adults and 2511 chicks, a total of 8727. These 
figures are based on a count of all nests in the area on January li, 
and February 25, 1957. 
Laysan Black-footed 
albatross albatross Total 
Total count of nests 2455 56 2511 
Estimated original nests 2602 62 2664 
Total breeding population 5204 124 5328 
Estimated unemployed birds 867 21 888 
Twelve "clean sweeps" spread over a one-month period resulted 
in the elimination of 77 percent of the adult albatrosses known to be 
using the area this season, and the chicks were virtually eliminated. 
The considerable difference between the number of chicks killed and the 
nest count in January and February resulted from mortality of nestlings 
during construction work along the south side of the area. 
_Discussion.=--Two factors must be considered in evaluating the 
results of the population reduction program. (1) The number of years 
the young birds remain at sea before returning to the island is still 
unknown. Studies of the royal albatross in New Zealand by Richdale* 
show that these birds do not ordinarily return until their sixth or 
seventh year. On the other hand, according to Sorensen**, the light- 
mantled sooty albatross returns at the end of its second year. Data 
on our Laysan and black-footed albatrosses are fragmentary. The 
earliest age at which a Laysan albatross is known to have returned is 
7 years, and for the black-footed, 5 years. Any killing program, to be 
successful, must therefore be carried on for a sufficient number of 
years to eliminate the several generations of birds which may be at 
sea when this program is begun. (2) The frequency with which adult 
birds return to breed is unknown. Data on the royal albatross obtained 
by Richdale* indicate that these birds breed in alternate years if they 
are successful in raising a nestling. Possibly the Laysan and black- 
footed do likewise. Information from returns of banded birds will 
eventually answer these questions. 
The effect of the killing program on the number of 
albatrosses soaring over the runways is difficult to evaluate. The 
*  Richdale, L. E. Post-egg period in albatrosses. 
1952 Biological Monographs, Ortago Daily Times and 
Witness Newspapers Co. Lid., Dunedin 431-166 
** Sorensen, J. H. Light-mantled sooty albatross at Campbell Island. 
1950 Cape Expedition Series 8:1-30 
39 
