I calculated various shell properties, water vapor loss, and hatching success of eggs of the Pearly-eyed Thrasher (Margarops fuscatus) using measurements obtained during a long-term study in the Luquillo Mountains, Puerto Rico. Empirical results were comparable to standard reference formulae, demonstrating that published formulae can be used with confidence by field biologists studying this and other passerine birds laying prolate spheroid shaped eggs. Shell mass averaged 0.66 g and shell thickness averaged 0.12 mm. Egg surface area averaged 19.31 cm2 (range =18.4-20.34 cm2) as derived from published allometric relationships. Observed and derived eggshell densities were 2.06 g/cm3 and 2.05 g/cm3, respectively. Average egg density was 1.32 g/cm3. Water vapor flux resulted in an average egg-mass loss of 0.087 g each day, culminating in a 1.22-g reduction over the entire 14-d incubation period. Based on a fresh egg mass of 8.02g, 3,009 fertile eggs lost 15.2% of their initial mass. Whereas the total loss of egg mass (in grams) was about the same for all eggs in the laying sequence, smaller (3rd—and 4th-laid) eggs lost a higher percentage of total mass than did the larger ones (1st—and 2nd-laid). There were inter-breeding season differences in mass (= water) loss. The rate of daily water loss increased significantly as the incubation period progressed. The pattern of increase was intermediate between that of small passerines and typical non-passerine species. Hatching success declined throughout the study due to environmental and biological factors.
ARENDT, WAYNE J. 2005. Shell Properties, Water Vapor Loss, and Hatching Success of Eggs from a Rain Forest Population of the Pearly-eyed Thrasher (Margarops fuscatus). Caribbean Journal of Science, Vol. 41, No. 2, 283-295,