• Ideal method – gives the true value
• Requires that’s the nest is found at the start of the nesting cycle
• Hard to achieve
• Limits the number of nests available for analysis causing low sample size
• A simple percentage of the number of successfulnests
• If out of 100 nests 20 fledge young, nestingsuccess would be considered 20 %
• Biased because nests that fail early are often not found, thus inflating the observed nesting success