Nest attentiveness in several Neotropical suboscine passerine birds with long incubation periods

Many species of tropical birds have prolonged incubation periods compared to other tropical species and to most species in temperate latitudes. One hypothesis for prolonged incubation is that these tropical species reduce nest attendance to minimize the risk of predation. The resulting decrease in average egg temperature would reduce embryo growth rate and lengthen the embryo development period. We sampled six species of Neotropical, lowland, inner forest antbirds (Thamnophilidae) and flycatchers (Tyrannidae) with average incubation periods between 17. 9 and 23. 3 days. Estimated total integrated 24-h nest attendance between clutch completion and hatching ranged between 14. 2 and 19. 5 days, representing 71-84 % of the incubation periods. Because total nest attendance in these species exceeded the incubation periods of most small passerine birds in temperate latitudes, and because average nest attendance per day did not differ substantially between these tropical species and temperate species, reduced nest attendance does not appear to cause their prolonged incubation periods. Instead, these extended egg periods likely reflect slower embryonic growth and development at a given egg temperature. Prolonged incubation can increase time-dependent mortality in the nest, which would require an increase in either post-fledging survival or adult reproductive success to favor a slow-growth evolutionary strategy. Mechanisms underlying the postulated trade-off between incubation period length and individual quality merit further investigation.