Regulation of Development Time and Hatch Synchronization in Black Brant (Branta bernicla nigricans)

Nicolai, C; Sedinger, J; Wege, M

1. Eggs of precocial bird clutches hatch more synchronously than they are laid. The widely accepted hypothesis to explain hatching synchrony has been that vocalizations from earlier laid embryos accelerate development of later laid embryos. The relationship between position in the laying sequence (hereafter PILS) and time to hatching was investigated in Black Brant (Branta bernicla nigricans L.; hereafter brant). Factors associated with variation in incubation duration were also examined. 2. Experimental clutches comprising eggs laid on the same day from the same PILS were assembled to eliminate the effects of earlier laid eggs on those laid later. This experiment allowed us to examine developmental time in clutches without the effects of interactions between eggs laid earlier in the sequence and those laid later. In a separate experiment, clutches were manipulated so that the full complement of laying sequences was maintained in each clutch, but each egg originated from a different female. This experiment allowed us to separate the influences of genetic-maternal effects from the influence of nest environment and incubation behaviour. Developmental time was also monitored in a set of clutches that were unmanipulated. 3. Metabolic rates of eggs from each PILS were measured at mid-incubation and the day before hatch for both experimental and control nests. By measuring metabolic rates, it was possible to examine changes in metabolic rates of embryos as hatch approaches, which may be another mechanism to synchronize hatch. 4. No difference was detected in incubation period between control and manipulated clutches. There was a steady decline in incubation period from first to last laid eggs independent of the clutch type. Fifth laid eggs required >3 days less to hatch than those laid first. These data suggest that sounds produced by brood mates and/or female incubation patterns are not the principal mechanisms for hatching synchrony. Both genetic and host mothers influenced overall developmental time, indicating that genetic-maternal effects and incubation behaviour and nest environment also influenced developmental time. 5. Embryonic metabolic rate was negatively correlated with number of days before hatch, but there was not a positive relationship between PILS and metabolic rate. Our findings show that embryonic metabolic rate may affect development more than vocalizations between brood members in synchronizing hatch.

Regulation of Development Time and Hatch Synchronization in Black Brant (Branta bernicla nigricans)

Series