. Bulletin. Natural history; Natural history. 386 Illinois Natlral History Survky Bulletin Vol. 28, Art. 3 30-[ulv 4. lulv lU-12, 14-15. 1958; in central Illinois—Mav 22-23. 27-29, 31, lulv 9-13. 15, 1907: June 22-26. 28-29. 1909; lune 18-19. 21-24. [ulv 8. 10. 12. 1957; and June 15. 17. 23-28. July 10. 1958; in southern Illinois— [une 4-8. 10-14. 17-21. 25-29. July 1. 1907; June. Fig. 4.—Areas (indicated by black squares) in which the strip census method of estimating bird populations was used in 1956, 1957, 1958, and 1959. In most areas, censuses were made in both summer and winter, in a few
. Bulletin. Natural history; Natural history. 386 Illinois Natlral History Survky Bulletin Vol. 28, Art. 3 30-[ulv 4. lulv lU-12, 14-15. 1958; in central Illinois—Mav 22-23. 27-29, 31, lulv 9-13. 15, 1907: June 22-26. 28-29. 1909; lune 18-19. 21-24. [ulv 8. 10. 12. 1957; and June 15. 17. 23-28. July 10. 1958; in southern Illinois— [une 4-8. 10-14. 17-21. 25-29. July 1. 1907; June. Fig. 4.—Areas (indicated by black squares) in which the strip census method of estimating bird populations was used in 1956, 1957, 1958, and 1959. In most areas, censuses were made in both summer and winter, in a few areas in only one of these seasons. The boundaries be- tween the northern, central, and southern zones discussed in this paper are shown by heavy lines. S-11, 14-17, July 13-15, 1909; June 11-17, ful\ 8-10, 1957; and June 13-14, 18-21, July 8-9, 1958. The winter censuses were made during the following; periods: in northern Illinois —December 3, 6-8. 10. 1906; January 2-5, 8-11, 14-17, 1907; December 4-6, 1956; January 22-23, 1957 ; February 27, 1958; in central Illinois—December 11, 13, 17-18, 1906; January 21-25, 27, 29-30, February 1. 1907; December 14, 17, 1956; February 4-8, 1957; February 5_6. 12-14. 24-26. 1958; in southern Illi- nois—February 6-8. 9, 11-14. 18-21, 1907; December 27-28, 1956; January 8-13, 1957; and February 7-11, 1958. Forbes & Gross (1923:436) stated that the strip census method used in their studies limited them "to birds of more or less open ; Although reduced visibility in woodlands and dense shrub habitat undoubtedly affected the accuracy of the method, data for such habitats were gathered both in the earlier field work and in our own. However, in considering the value of the method, we were con- cerned primarily with open-field areas. In defining habitats, we placed primary em- phasis on the nature of the land cover, not on the land use. Thus, we classified a stand of alfalfa as a kind of hayfield even if it had b
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