We determined whether nests that did not receive eggs was attributable to cryptic nest predation (i.e. predation of eggs laid between nest checks) or nest abandonment in Common Grackles (Quiscalus quiscula). Nest predation was extremely low (∼2%), whereas more than 44% of 427 nests found during nest building never received an egg; this indicates that nest abandonment accounted for most nests without eggs. Nest construction was completed for 32% of nests that were abandoned. Few nests known to have received eggs were abandoned. As the breeding season progressed, both nest abandonment and time from nest completion to first egg decreased. It has been proposed that the delay in egg laying early in the season allows females to optimize timing of egg laying. Nest abandonment may also serve this purpose, but seems an unnecessarily expensive mechanism. Alternatively, nest abandonment could be involved with mate switching. Understanding why nests are abandoned requires data on the associated ecological circumstances, in addition to accurate identification of instances of abandonment. The latter requires distinguishing abandonment from cryptic predation. Rates of nest abandonment can be estimated for populations by using rates of known nest predation during egg laying. For individual nests, however, distinguishing abandonment from cryptic predation requires detailed observation (e.g. video cameras), except in circumstances such as ours, where predation is extremely low.

Nidos sin Huevos:?Abandono o Depredación Críptica?