Maternal signatures are present in the eggs of some birds, but quantifying interclutch variability within populations remains challenging. Maternal assignment of eggs with distinctive appearances could be used to non-invasively identify renesting females, including hens returning among years, as well as to identify cases of conspecific brood parasitism. We explored whether King Rail (Rallus elegans) eggs with shared maternity could be matched based on eggshell pattern. We used NaturePatternMatch (NPM) software to match egg images taken in the field in conjunction with spatial and temporal data on nests. Since we had only a small number of marked breeders, we analyzed similar clutch images from a study of Eurasian Common Moorhens (Gallinula chloropus chloropus) with color-banded breeders for which parentage at many nests had been verified genetically to validate the method. We ran 66 King Rail clutches (n = 338 eggs) and 58 Common Moorhen clutches (n = 364 eggs) through NPM. We performed non-metric multidimensional scaling and permutational analysis of variance using the best egg match output from NPM. We also explored whether eggs could be grouped by clutch using a combination of egg dimensions and pattern data derived from NPM using linear discriminant analyses. We then scrutinized specific matches returned by NPM for King Rail eggs to determine whether multiple matches between the same clutches might reveal maternity among nests and inform our understanding of female laying behavior. To do this, we ran separate NPM analyses for clutches photographed over several years from two spatially distant parts of the site. With these narrower datasets, we were able to identify four instances where hens likely returned to breed among years, four likely cases of conspecific brood parasitism, and a within-season re-nesting attempt. Thus, the matching output was helpful in identifying congruent egg patterns among clutches when used in conjunction with spatial and temporal data, revealing previously unrecognized site fidelity, within-season movements, and reproductive interference by breeding females. Egg pattern data in combination with nest mapping can be used to inform our understanding of female reproductive effort, success, and longevity in King Rails. These methods may also be applied to other secretive birds and species of conservation concern.

Eggshell pigments are costly to produce. The sexual signaling hypothesis predicts that the degree of pigmentation in eggshells is positively related to maternal quality. Thus, females in better condition are expected to lay brighter or more maculated eggs. To test this, we quantified the extent of maculation in eggshells of King Rails (Rallus elegans) and Common Moorhens (Gallinula chloropus chloropus) and related this to female body condition. We identified key variables for body condition using principal components analysis of morphometric measures. To evaluate which combination of variables provided the best index of body condition in each species, a series of linear models were ranked using AICc. To estimate the area of surface pigment on each egg, color egg images were converted to binary and we calculated the percent of black pixels within a scaled oval superimposed over the images. We ran linear regressions of mean percent pigmentation on maternal body condition. Neither female King Rails nor Common Moorhens in better body condition laid more maculated eggs. Thus, the sexual signaling hypothesis was not supported. Common Moorhen eggs were slightly larger, on average, and their eggshells had more pigment per unit area and per egg than King Rail eggs.