Article Review: Egg Coloration is Correlated with Female Condition in Eastern Bluebirds (Sialia Sialis )

Article Review: Egg Coloration is Correlated with Female Condition in Eastern Bluebirds (Sialia Sialis )

Citation for the paper assigned

Siefferman, L., Navara, K. J., & Hill, G. E. (2006). Egg coloration is correlated with female          condition in eastern bluebirds (Sialia sialis). Behavioral Ecology and Sociobiology, 59(5),           651-656.

Determination of if the hypothesis explicitly stated or implied, the alternative hypothesis, and the understanding of the hypothesis

The hypothesis has been explicitly stated that egg coloration is correlated to a condition in the eastern blue birds. The alternative hypothesis would be that the older female eastern bluebirds and female eastern bluebirds in better conditions are highly prone to lay blue and more colorful eggs.

Based on the reading, the hypothesis implies that the female eastern bluebirds that are healthy are highly prone to lay eggs that are colorful compared to their counterparts who are not in better health conditions. Moreover, the hypothesis can also be understood to propose that the color of the eggs of the female eastern bluebirds is a determinant of the health conditions of the birds given that birds that lay colorful eggs tend to be healthier compared to those whose eggs are not colorful. The authors, through the use of the hypothesis, therefore, make an attempt towards offering proof that the healthier eastern bluebirds are not necessarily the young birds but are bluebirds with good health conditions, as well as that the older bluebirds are also capable of laying colorful eggs.

The main point of the paper

The main point of this paper is to prove that the health conditions of the female eastern bluebirds can be proven by their egg coloration as healthier birds tend to lay increasingly colorful eggs than the unhealthy birds.

Summary of the Paper

The study was mainly based on the hypothesis that egg coloration was correlated to a condition in the eastern blue birds. Nevertheless, the researchers did not highlight the research question guiding their study in the paper.

To study the sample population, the researchers made use of the residuals of the body mass regression on tarsus length, along with the ration of the tarsus length to body mass as indicators of the birds’ body conditions. The researchers also carried out ratio analysis and residual analysis on the outcomes. Further, the reflectance of the eggs with different colorations was carried out using a spectrometer, fiber optic probe and a deuterium–tungsten–halogen lamp, and the blue-green chroma was used in the description of the egg reflectance data as the region is known correspond to areas with the least biliverdin absorbance. The normality was after that tested using the Shapiro–Wilk tests, in addition to the parametric tests being used in instances where data were distributed normally, and the nonparametric tests were employed in instances where the assumptions of normality had been violated. Also, SPSS software was employed in the analysis of data and every statistical tests used in the study was two-tailed.

Based on the findings of the study, the authors made the observation that within the [population of the eastern bluebirds that were studied, eggs were laid in three key morphs, namely blue-green, pink and white, and also that there were distinct differences with regards to the spectral shapes between the white, pink and blue-green eggshells.

With regards to the results and conclusion, upon carrying out various tests on the eggs, the researchers observed that, consistent with the study hypothesis, the biliverdin pigmentation found in the eggshells reflected the female conditions and the females in better health and body conditions, and the older females laid the increasingly colorful eggs. Moreover, the study also concluded that egg coloration was directly linked to the cell-mediated immunity in the female eastern bluebirds, and this was also representative of the initial empirical proof indicating that biliverdin pigmentation was interrelated with female health condition. Additionally, the researchers concluded that the condition-reliant egg coloration might be adaptive in instances where the male eastern blue-birds make use of egg coloration in making strategic decisions with regards to the paternal investments, as well as in instances where the female blue birds utilize egg coloration in discriminating between the eggs they have laid and those of brood parasites that are conspecific.