A standardized method for quantifying eggshell spot patterns

Abstract

Spottiness is an important component of the morphology of bird eggs and a number of methods have been developed for characterizing variation in spottiness. We developed a quantitative method for measuring and comparing eggs to determine if female European Cranes (Grus grus) lay eggs with individually distinct color and spotting patterns. We used photographs taken under standard conditions and developed a computer program (ESPANA) to quantify egg‐spot patterns. The goal of the analysis was to create a “fingerprint” of each eggshell by measuring reflection along virtually drawn lines (transects) on an egg's image. Values measured in the same positions along transects can be compared among eggs by considering them as separate variables defining the pattern. Data were analyzed using cluster analyses and by performing analyses of similarity (ANOSIM). We found that the eggs of female European Cranes (N = 11) had individually distinct color patterns, with eggs laid by a given female more similar to each other than to the eggs of other females. Beyond its potential use for identifying the eggs of specific females, we believe our method could also be useful for investigators quantifying differences in egg‐spot patterns for other reasons, for example, examining possible relationships between egg‐spot patterns and female quality. The program ESPANA is implemented using the Java programming language and is available as supporting information on the Journal of Field Ornithology website.

Unscrambling variation in avian eggshell colour and patterning in a continent-wide study

“…To provide an objective, quantitative estimate of maculation, photographs were processed using an automated image-processing tool SpotEgg [55]. A number of digital image processors have been developed to quantify egg maculation [56], many of which focus primarily on the extent of parasitic egg mimicry [12,57,58]. We chose SpotEgg (run in Matlab v. 2012b) to measure maculation, as this program allows one to define the characteristics of the maculation (i.e.…”

Quantifying the maculation of avian eggs using eggshell geometry

“…Considering this distortion becomes particularly important when using images to estimate maculation metrics such as percentage cover (Ornés et al . ) or to link visible maculation with the underlying pigment concentration (Brulez et al . ).…”

“…Testing these various hypotheses requires a means of accurately quantifying various aspects of eggshell maculation, including the area covered by regions of maculation, which is commonly used to calculate a percentage coverage (Ornés et al . ). To achieve this, researchers typically take their measurements directly from photographs of eggs.…”

SpotEgg: an image‐processing tool for automatised analysis of colouration and spottiness

“…Images should not contain partial shadows, artefacts, and overexposed/underexposed areas. Ornés et al () introduced the use of a ‘black‐box’ to help in controlling lighting conditions in the field, but also other resources as neutral colour reflectors or diffusive neutral colour umbrellas could be used, especially in places of controllable illumination conditions (lab, museum, etc.). If only spottiness is required, camera bracketing may be useful to produce High Dynamic Range (HDR) versions of the scene (note that HDR alter colours). Finally, since SpotEgg runs the programmed analyses for all the pictures in the selected folder, we recommend to create new folders for each species because the parameters for spottiness analyses are defined only once for a whole dataset (input folder).…”

“…Images should not contain partial shadows, artefacts, and overexposed/underexposed areas. Ornés et al (2014) introduced the use of a 'black-box' to help in controlling lighting conditions in the field, but also other resources as neutral colour reflectors or diffusive neutral colour umbrellas could be used, especially in places of controllable illumination conditions (lab, museum, etc.). If only spottiness is required, camera bracketing may be useful to produce High Dynamic Range (HDR) versions of the scene (note that HDR alter colours).…”