Egg characteristics in relation to skipped days of laying in the Grey Partridge

Birds sometimes skip a day along the sequence of egg laying, which may vary the mass or the composition of delayed eggs compared with those that were laid consecutively. Our literature review shows that this has been interpreted as a short-term adaptation that enables females to overcome energetic constraints during the laying period, but other hypotheses implying the influence of weather, pollution, or hormonal cycles have also been proposed. We collected freshly laid Grey Partridge Perdix perdix eggs to determine the effects of laying gaps on egg characteristics. Egg shape, as well as egg components (beta-carotene, avidin and lysozyme concentrations) did not vary in relation to skipped days. Eggs were slightly heavier when one or two days were skipped (0.72% and 0.45%, respectively). However, when examining the hatching rate, we found a significant decrease in relation to skipped days, hence eggs following laying gaps showed a lower hatching rate than other eggs. The pattern observed could indicate the presence of some physiological stress that caused females to skip one or two days and to lay eggs that hatched less.