Tanner (ms., and letter, April 21, 1955) recently devoted considerable ingenuity to computing by actuarial methods the longevity of the Oven-bird, using the adult-immature ratio in samples killed at a ceilometer at Knoxville, Tennessee. Tanner's computations were based on the simple assumption that

Further application of such techniques may prove desirable and rewarding. It would seem at present, however, to be a risky procedure, as it has been abundantly shown (see above) that adults and immatures often do not migrate at the same times and rates, and the ratios of adults to immatures in samples of migrants are likely to be far from representative of the true proportions in the populations concerned. It should be added that Tanner is perfectly aware of this objection.