This method is appropriate provided that successful and unsuccessful nests are discovered with equal probability, a condition that may be met in studies of artificial nesting structures, small islands, or other small units of habitat that can be intensively searched for terminated nests. Apparent nest success estimates are biased when applied to samples of clutches gathered by flushing hens from their nests. Advanced clutches are more likely to hatch than young clutches because of the shorter interval between discovery and hatching. The probability of hatching for clutches found 5 days after initiation is because they have already survived 5 days and need to survive only 30 additional days to hatch. Apparent nest success, applied to a sample of active nests, reflects the true success rate only when all clutches are found on the day they were initiated.
Apparent success overestimates true success when clutches are found at a later date.
When the day of destruction or abandonment is unknown, it is assumed to have occurred midway between the last two visits. For nests observed on 2 or more days but not revisited to determine their fate, the day of the last visit marks the end of the exposure interval. A basic assumption of the method is that the daily survival rate for the intervals that nests were under observation is the same for all nests and all intervals. This method has gained acceptance by ornithologists. However, computations are difficult and use of a computer is advised.