Does risk of nest failure or adult predation influence hatching patterns of the Green-rumped Parrotlet?

Parent birds may adjust the onset of incubation to minimize periods of high risk of nest failure due to predation (the Nest Failure Hypothesis) or of mortality to adult birds (the Adult Predation Hypothesis). We examine tempo ral patterns of risk of nest failure and predation on adult females in a po pulation of Green-rumped Parrotlets (Forpus passerinus) to determine whethe r those patterns explain observed patterns of incubation. Over one-third of nests (38.6%) failed completely, and an additional 2.2% failed after fledg ing one or more young. Most nests failed due to predation and infanticide. Because parrotlets begin incubation on the first egg, we examined a range o f hypothetical failure rates for the period prior to the onset of incubatio n. Daily survival probabilities for nests were higher during the nestling s tage than during incubation or hedging. Survival of adult females varied li ttle through the nesting cycle, but was highest while attending nestlings. Model predictions were highly dependent on assumptions made about survival rates during the pre-incubation period. When empirically based values were used for this period maximum productivity was achieved with first-egg incub ation, consistent with observed patterns. Models were most sensitive to tho se parameters most difficult to estimate. This study represents the first t est of the Nest Failure model with a nonpasserine or tropical species, and the first assessment of the Adult Predation model using field data.