Peterson, R. T, Alexander, H. G, Alexander, H. G & Peterson, R. T / January 1950 – vol. 43, issue 1–32 SIRS,--I have delayed answering the letter on the above subject from Mr. P. H. T. Hartley (British Birds, xli, pp. 254-255) because the data then available only served to justify his remark that " more investigation is needed." I examined the two sets of winter frequencies statistically, and assuming the validity of both methods, could only conclude that (statistically) he and I were working on " dif... This article is only available to registered users.To read more, please log in or purchase a subscription.