Premiers - Outil de Suivi des Contrats

Annexe III
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success and not consider them separately (Hewavisenthi & Parmenter, 2001; Ji et al., 2001). It
is all the more important that hydric and thermal conditions fluctuate during all the incubation
period within the nest (Packard et al., 1985).
Change in egg mass during the course of incubation
We assumed that changes in egg mass (i.e. egg growth rate) correspond to different quantities
of water absorbed by eggs during incubation time (Ackerman et al., 1985). Whatever the
moisture substrate, we observed a significant egg growth rate over the course of incubation
and these changes were strongly and differentially affected by water potential profile of
substrate during incubation (Figure 1). So, as Cagle et al. (1993), we found that water
potential is a good predictor of water exchanges between eggs and its incubation environment,
affecting strongly changes in egg mass. We found that egg growth rate significantly varied
with the current water potential of the incubation substrate encountered by the egg (see Table
2.1), with a more important gain of water in the wet substrate than respectively in the
intermediate and the dry substrates. We also found that the water exchange between eggs and
the substrate was significantly different between the three periods of incubation (Table 2.1 &
Figure 1). All eggs increased in mass until approximately day 40 of incubation whatever
water potential of substrate, while egg growth rate strongly differed between water potential
treatments in the last period of incubation. These observations are confirmed by a significant
influence of the substrate moistures on egg growth rate only during the two last periods of
incubation time with a stronger effect in the last one (Table 2.1, model 2).
In addition, we found a significant interaction between incubation periods and water potential
encountered by eggs (Table 2.1, model 1): eggs in wet and intermediate substrates gained
mass continuously during all the incubation, with a higher egg growth rate in wetter substrate.
In contrast, eggs on dry substrate gained mass during the first two-thirds of the incubation and
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