An exploration of inter-clutch variability and eggshell patterning in two species of rail
Johnson, Emily Wittenberg
The avian egg has long fascinated researchers with its diverse colors, patterns, and shapes. Variation within and between species provides opportunities to address the question of why eggs are pigmented the way they are. Numerous hypotheses have been suggested, including that maculations act as maternal signatures or that they act as signals of female quality. The confamilial King Rail (Rallus elegans) and British Common Moorhen (Gallinula chloropus chloropus) lay large clutches of protoporphyrin spotted eggs, allowing us to address questions of eggshell maculation. Both species face a diversity of ecological pressures, which may have influenced how their eggs are patterned. This thesis combines modern pattern detection technology, field collected data, and aspects of evolutionary and breeding biology to attempt to determine whether females of these two species of rails lay distinctive eggs. In Chapter 1, I investigate whether King Rail eggs have maternally unique signatures, and if so, whether these signatures can be used to identify non-invasively renesting females, returning breeders, and to identify instances of conspecific brood parasitism (CBP) for this secretive species. To address the first question I used a program called NaturePatternMatch (NPM) that matched eggs based on pigment patterns. Additionally, I explored whether eggs could be matched to clutches using a combination of pattern data derived from NPM and physical egg dimensions. I validated these methods using clutch images from a study of British Common Moorhens with confirmed parentage. NPM was only able to match a small proportion of eggs to their corresponding clutch, but the inclusion of egg dimensions did increase this slightly. Furthermore, I used the output from NPM in conjunction with spatial and temporal information for King Rail nests to identify previously unrecognized cases of returning breeders, CBP, and within-season renesting attempts. This method of combining egg pattern data with field data may be applied to other sensitive species as a means of non-invasively informing researchers about reproductive effort and success and breeder return rates and longevity. In Chapter 2, I tested a key prediction of the sexual signaling hypothesis to determine whether eggshell maculations are a post-laying signal of maternal quality. This hypothesis contends that females in better body condition will be able to produce eggshells with more pigment if pigment is costly to produce. Few studies of non-passerine species with protoporphyrin pigmented eggs have tested the sexual signaling hypothesis. To test this hypothesis, I measured black pixels (proxy for pigmentation) on binary images of eggs from female banded King Rails and Common Moorhens. Female body condition in each species was based on a principal components analysis of morphometric measurements taken in the field. I then related the estimated percent pigmentation on a female's eggs to her body condition. There was no relationship between amount of pigment and body condition in either species. Moorhens produced larger eggs with significantly more pigment per unit area of eggshell on average. In conclusion, this thesis contributes valuable information on egg variation in two rail species. It also utilizes available tools, such as NPM, in a novel way to identify individual females based on their eggs, a method that can be further refined and applied to other species of conservation concern.
Johnson, Emily Wittenberg. (May 2021). An exploration of inter-clutch variability and eggshell patterning in two species of rail (Master's Thesis, East Carolina University). Retrieved from the Scholarship. (http://hdl.handle.net/10342/9141.)
Johnson, Emily Wittenberg. An exploration of inter-clutch variability and eggshell patterning in two species of rail. Master's Thesis. East Carolina University, May 2021. The Scholarship. http://hdl.handle.net/10342/9141. August 19, 2022.
Johnson, Emily Wittenberg, “An exploration of inter-clutch variability and eggshell patterning in two species of rail” (Master's Thesis., East Carolina University, May 2021).
Johnson, Emily Wittenberg. An exploration of inter-clutch variability and eggshell patterning in two species of rail [Master's Thesis]. Greenville, NC: East Carolina University; May 2021.
East Carolina University