CLUM, N.J.*; PREEST, M.R.: Incubation History and Embryonic Development in Boat-tailed Grackles

Synchronicity of hatching in birds can have significant effects on the survival of individual chicks and entire broods. Hatch synchrony in birds is assumed to be primarily under the control of the incubating female, with incubation at the start of laying resulting in asynchronous hatching, and incubation at the end of laying resulting in synchronous hatching. Data collected during a previous study of boat-tailed grackles (Quiscalus major) revealed that the hatching pattern of eggs could not be explained by the incubation behavior of the female, regardless of when incubation is hypothesized to have begun. During April 2001, we monitored laying, incubation, hatching, and development of boat-tailed grackles in coastal North Carolina, with the objectives of documenting the onset of incubation and investigating developmental differences in hatchlings of different rank as a possible explanation for hatching patterns. Temperature logging of nests revealed that birds began incubating after the laying of the second egg, and that the intensity of incubation increased after the third egg. Temperatures in nests with unincubated (single) eggs did not differ from ambient. Unincubated first eggs pipped 17.5h earlier than expected based on their lay date, suggesting that significant development was occurring despite the lack of incubation by the female. Higher ambient temperatures in 2001 than in the previous study were associated with shorter incubation periods for all eggs. Unlike the previous study, but consistent with incubation beginning with laying of the second egg, the lay to pip time was not significantly different for second and third eggs. Our results suggest that temperature differences associated with ambient variation and incubation intensity may significantly affect incubation period and hatch synchrony.