Measuring egg size using digital photography: testing Hoyt's method using Florida Scrub-Jay eggs

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Abstract:

ABSTRACT. 

Egg volumes are most often estimated using a mathematical model that incorporates length and width measurements and a species-specific shape variable. Although adequate in many respects, this technique does not account for intraspecific variation in egg shape. We developed a computer-automated technique that uses calibrated digital photographs to render precise measurements of several egg-size parameters including length, width, volume, and surface area. The system extracts egg outlines from photographs, and divides each egg into latitudinal slices that are subsequently regarded as simple geometric shapes (cylinders or cone frustra) with volumes and surface areas that can be summed to generate size parameters for the entire egg. We tested this technique using 491 eggs from Florida Scrub-Jay (Aphelocoma coerulescens) nests and compared the resulting egg volumes with volumes calculated using the preeminent method of estimating volume from linear measurements. Our method was highly accurate, and differences between the volumes from our method and the alternative method were strongly associated with variation in egg shape. Advantages of our technique include decreased handling of eggs and increased accuracy. Software resources and additional information regarding the technique are available at http://www.archbold-station.org/abs/data/birddata/Bridge-JFO-eggsize.htm.

Keywords: Aphelocoma coerulescens; Florida Scrub-Jay; egg volume; field techniques; measurement error; surface area

Document Type: Research Article

DOI: http://dx.doi.org/10.1111/j.1557-9263.2006.00092.x

Affiliations: 1: Archbold Biological Station, 123 Main Drive, Venus, Florida 33960-2039, USA 2: Centre for Ornithology, School of Biosciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK 3: University of Memphis, Department of Biology, 3774 Walker Ave, Life Sciences 201, Memphis, Tennessee 38152, USA

Publication date: March 1, 2007

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