US Geological Survey


Date of this Version



Published in Wildlife Society Bulletin, Vol. 13, No. 1 (Spring, 1985), pp. 51-53.


Waterfowl investigators are now generally convinced that the usual way of estimating nest success, dividing the number of nests from which eggs hatch by the number of nests found, may be highly biased and misleading. The bias is caused by the greater chance of finding a successful nest (which persists for a rather long time) than an unsuccessful one (which might be present for only a few days). Hammond and Forward (1956) mentioned problems with this apparent rate of nest success, but the deficiencies were widely ignored by waterfowl biologists until Miller and Johnson (1978) brought attention to them again and noted that Mayfield (1961, 1975) had proposed a solution. More recently, Johnson (1979) provided a maximum-likelihood estimator of nest success that was closely approximated by Mayfield's method for several examples. Both methods require the investigator to determine the length of time each nest is under observation and exposed to risk. The estimator we propose here is easier to compute, requires less information about each nest, and approximates the maximum-likelihood estimator. The computations of necessary roots and powers are easily made on any hand-held calculator with yx capability.