Reliable deer censuses may be used to determine 4 values relative to reproduction, namely: (1) The average annual rate of increase (r); (2) The annual gain (%), i = r[long dash]I; (3) The no. of fawns per doe in winter (y), where y = 2(r[long dash]l); and (4) the survival no. of fawns per adult doe in winter [y[image]). The paired values of y - / are: 0.4-0.5, 0.7-1, 1-1.5, and 1.3-2. After the derivation of y, the corresponding value of y[image] is found by interpolation. A high value of y[image] definitely reveals a high fertility during the previous summer, whereas a low value of y[image] indicates either low fertility or unusual losses. The basic formula is P = Ar l, where P is final population growing from A pop. in t-years at rate r. Also, r = 1 4- 1/2y, where the 1/2 indicates even sex ratio, and is termed the "female fraction". If all 9 yearlings are sterile, the max. value for each of the 4 terms is: r = 1.66; i = 66%, y = 1.34; and y[image] -2. These 4 values were very closely approximated by a deer herd in its first 6 years on the Ed. S. George Reserve, Ann Arbor, Mich. A typically hunted herd in Utah had comparable values of 1.155, 15.5%, 0.31, and 0.4. In contrast, r averaged 0.924 for a 10-yr. period during the decline of the Kaibab deer herd. This means the herd lost 7.6% of its pop. each year. When r < 1, it is called "rate of survival". The calculations are illustrated by use of numbers and logarithms.