To estimate reproductive success in a population one ideally would like to determine the number of young fledged per nesting female. However, this is difficult because often (1) the adults are not individually marked, (2) the colony is not visited daily, and (3) the investigator is unable to monitor all young until they fledge. If adults are unmarked and successful renesting occurs, reproductive success will be underestimated. If a colony is not visited daily and nests are initiated and lost between visits, reproductive success will be overestimated. The Mayfield method is one approach to overcoming this latter problem. Finally, nestling colonial birds are often able to move away from the nest site well before fledging and thus avoid being detected. To overcome this problem capture-recapture methods and enclosures have been used. In this paper we discuss these limitations and evaluate methods of dealing with them.