S (survival rate) = Number of adults in population (or sample) / Total size of population (or sample). 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. Processing of Samples Thorough processing of large samples of birds killed accidentally is time-consuming. We were fortunate in having considerable assistance; even so, all desirable data could not be obtained from the 1090 birds of the present sample. As aids to others conducting studies of this kind we should mention a few points which may be of assistance. Birds should be picked up as soon as possible after death, certainly by the end of the day after the accident and preferably much sooner. They should be weighed as soon as possible after collection (weights decrease rapidly, even under refrigeration), and the weights (in grams, to one tenth of a gram) written on tags attached to a leg of each specimen. The sample should then be sorted by species or groups of species of approximately equal size (to avoid crushing of smaller birds by larger ones), placed in boxes, paper bags, or better, air-tight containers clearly marked with date, locality, and other necessary particulars, and relegated to a deep-freeze compartment. For all but the smallest samples, such freezing units are indispensable to complete study. Once frozen, the birds may be selected for study at leisure, but time is still important, as, even when frozen, gonads may eventually deteriorate, and birds eventually become desiccated which is a disadvantage if skins are to be made.