Personality traits, defined as differences in the behavior of individual animals of the same species that are consistent over time and context, such as ‘boldness,’ have been shown to be both heritable and be influenced by external factors, such as predation pressure. Currently, we know very little about the role that early environmental factors have upon personality. Thus, we investigated the impact of incubation temperature upon the boldness on an oviparous reptile, the bearded dragon (Pogona vitticeps). Eggs, from one clutch, were incubated at two different average temperatures within the normal range. After hatching the lizards were raised under the same environmental conditions. Novel object and novel environment tests were used to assess personality. Each test was repeated in both the short term and the long term. The results revealed that incubation temperature did impact upon ‘boldness’ but only in the short term and suggests that, rather than influencing personality, incubation temperature may have an effect on the development of behavioral of oviparous reptiles at different stages across ontogeny.

Normal tables provide an objective step-wise description of the morphological development of an embryo. Such tables have been described for the chicken, turkey, quail, and duck embryos, but there is no such staging table for goose embryos. As the goose has one of the longest incubation periods of all the poultry species and embryo mortality during incubation is relatively high, a normal table of goose embryo development would be useful in assessing the morpho-genetic status of the goose embryo before and during incubation. In this study, embryos were isolated from commercial White Koluda goose eggs stored no longer than four days in a cool room (18°C) prior to incubation and after 4, 8, 12, and 16 h of incubation. Embryo staging was based on the normal tables described for the chicken by Eyal-Giladi and Kochav (EGK) and Hamburger and Hamilton (HH). Goose embryos from unincubated eggs were at Stage X and XI EGK and after 16 h of incubation the majority of embryos were between Stages 2 and 4 HH. Our results suggest that while the stage of development of the embryo in the unincubated goose egg is similar to that reported for the chicken, although the diameter of goose embryo is slighter larger. Following incubation, a goose embryo advances more slowly than a chicken embryo up to 16 h of incubation.

The influence of a developing bird embryo on eggshell thinning is well known, however this phenomenon has been described mainly for poultry, and in wild birds is poorly understood. This study focussed on Capercaillie (Tetrao urogallus), in which the effect of a developing embryo on the change of eggshell thickness has not been described. However, problems relating to a large number of dead embryos and eggs cracking during incubation are observed in captive breeding centres giving us the opportunity to test how the developing embryo affects the eggshell and thereby its properties, including eggshell strength and thickness. In total, 196 unhatched eggs, including 146 infertile and 50 eggs with embryos which died at various stages of development, were analysed in relation to eggshell shape, thickness and strength. Moreover, 102 posthatched eggshells were also examined. Although the strength of eggshell was affected by egg shape and shell thickness, contrary to expectations, the stage of embryonic development had no significant influence on eggshell strength. As has been demonstrated in other species, etching of eggshells by the developing embryo reduces shell thickness in Capercaillie but it has minimal effect on the strength of the eggshell. Egg viability is not compromised during the later stages of development by contact incubation with the female. The eggshell of infertile eggs or eggs containing earlydead embryos were 10% thicker than posthatched eggshells and eggs with late-dead embryos, confirming that eggshell thinning in Capercaillie is typical for precocial species.

Capercaillie behavior, both in the wild and in captivity, is poorly known due to this species’ secretive way of life. Female-male and female–female social organization and interactions are especially poorly documented. The research was conducted in Capercaillie Breeding Center in Wisła Forestry District where a breeding flock is kept throughout the year. Thanks to video monitoring, we were able to observe mate choice, and then later, female–female interactions during laying and incubation period. Male individual variation in tooting latency and duration were recorded. Females’ interest in males was related to males’ tooting activity, but when males became too insistent and started to chase the females, the females avoided contact with them. There was a significant relationship between calendar date and when tooting starts, and between the tooting duration the female spent with a male. Two incidents of female-male aggression caused by competition for food were observed. Female intruder presence and competition for nesting place was observed in 66.67% nests. Most female–female interactions were limited to threat posturing, but fights and attempts to push out the intruder from the nest occurred as well. Such interactions may lead to nest abandonment and egg destruction, lowering the breeding success.

Despite numerous studies, intra-species variation in bird eggs is still not well explained. In the presented studies, we investigated the possible sources of this variation: female factor, laying order, and season, using the following traits of Capercaillie eggs as an example: egg size and shape, eggshell lightness, and thickness. Samples were collected for three years from three Capercaillie breeding centres located in different parts of Poland, where birds are kept in conditions close to their natural habitat and have a similar diet. The obtained results showed no significant impact of laying order on egg size, shape, pigmentation, nor eggshell thickness. This indicates that the provided nutrition ensures an adequate supply of minerals for the entire laying period. Most results did not show statistically significant differences between eggs from different breeding centres, but in one breeding centre, eggshells had lighter pigmentation. We assume the observed differences may result from females’ individual features or local environmental conditions. Egg traits were highly consistent for individual females, proving that visual identification can be useful in identifying the eggs of different females.