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Declining egg viability explains higher hatching failure in a suburban population of the threatened Florida scrub-jay Aphelocoma coerulescens


R. A. Aldredge, Archbold Biological Station 123 Main Drive Venus, FL 33960, USA. E-mail:


Hatching failure occurs in approximately 10% of all avian eggs, but varies both within and among species. This reduction in viable offspring can have significant fitness consequences for breeding parents; therefore, it is important to understand which factors influence variation in hatching failure among populations. Previous research suggests that hatching failure is higher in a suburban than in a wildland population in the Florida scrub-jay. From 2003 to 2007, we performed two experiments to examine whether increased hatching failure in the suburbs resulted from 1) increased length of off-bouts during incubation (predation risk hypothesis, 2003–2004) or 2) increased exposure to ambient temperature during laying (egg viability hypothesis, 2005–2007). Hatching failure was higher for females that took fewer off-bouts, but the length of those off-bouts did not influence hatching failure. Thus, nest predation risk does not appear to explain higher hatching failure in the suburbs. Alternatively, hatching failure increased with increasing exposure of eggs to ambient conditions during the laying period. First-laid eggs in the suburbs had the greatest pre-incubation exposure to ambient temperature and the greatest rate of hatching failure, consistent with the egg viability hypothesis. Urbanization influences hatching failure through a series of complex interactions. Access to predictable food sources advances mean laying date in suburban scrub-jays, leading to larger clutch sizes. Because scrub-jays begin incubation with the ultimate egg, first-laid eggs in the suburbs may be exposed to ambient temperatures for longer periods, thus reducing their viability.