PRE-1941 EGGSHELL CHARACTERISTICS OF SOME BIRDS1 D. R. OSBORNE AND R. WINTERS, Department of Zoology, Miami University, Oxford, Ohio 45056; 127 Balyeat Ave., Van Wert, Ohio 45891 Abstract. Parameters and techniques used to characterize avian eggshells are reviewed. Elongation, volume and thickness indices were calculated to estimate the shape and size of 1145 eggs (328 sets) representing 18 orders, 54 families and 253 species of the Clark K. Lloyd Collection at Miami U., Oxford, Ohio. The study includes eggs of species from 13 countries and 37 states collected prior to the widespread use of pesti- cides. Fifty four species came from Ohio and 43 from California. Sixteen species are considered rare or endangered, or have declining populations. A comparison of egg volumes as determined by Paganelli et al (1974) was made and differences ranged from 0.7% to 22%. OHIO J. SCI. 77(1): 10, 1977 During the last quarter of the 19th and collection contains 328 egg sets from 18 early portion of the 20th century many orders, 54 families and 253 species, mostly oologists attempted to build up compre- from North America, which were obtained hensive collections under regulations set between 1887 and 1940 (table 1). It in- forth by national and international so- cludes eggs of species from 13 countries cieties. These collections are presently and 37 states. Most species are repre- housed in museums and undoubtably sented by only one clutch of eggs. The some are still in private collections. At collection is important because it was the request of the American Ornitholo- accumulated prior to the widespread use gist's Union's Committee on Research, a of pesticides and because it contains a project was initiated in 1966 to survey large sample collected from a localized egg and bird collections in the United area in the interior of North America. States and Canada. Of the 160 egg col- Fifty four species (57 sets) are from lections found, five are housed in Ohio Ohio; with 50 from Butler County. museums (Banks et al, 1973; Clench et al, Because of the limited area of the col- 1976). Most collections consist of full lection the data should not be considered clutches (sets) along with date and lo- as a representative cross-section of Ohio cation collected and are important re- birdlife. sources for determining variability within clutches as well as intraspecific relation- METHODS ships. Changes in eggshell character- Traditionally figures in texts report the size of istics can also be related to geographic egg by average value of length and breadth (e.g. ffrench, 1973), and sometimes range value location and to different aspects of breed- (e.g. Bent, 1919). Recent texts such as the ing biology before and after the wide- Handbook of North American Birds (Palmer, spread use of persistent pesticides. 1962) have included measurements of the cur- vature of the two ends of the egg. This more The present paper reviews the various accurately specifies the shape of the egg, in- parameters and techniques used in stud- dependent of its size. The rationale for these ies on eggshells, and documents eggshell measurements is discussed by Preston (1968). characteristics of 1145 eggs from the We reported standard measurements of Clark K. Lloyd collection, presently length, breadth and weight because they are housed at Miami University, Oxford, easily obtainable in the field and laboratory. These values were then used to calculate the Ohio. The history of the collection has eggshell indices of elongation, volume, and been described by Hefner (1974). The thickness (table 1). Greatest length and breadth were measured with a vernier caliper 'Manuscript received March 25, 1976, and in to the nearest 0.1 mm and weight to the nearest revised form August 9, 1976 (#76-31). 0.1 mg. Species and scientific names are 10 No. 1 EGGSHELL CHARACTERISTICS 11 listed and arranged according to the AOU prolate ellipsoids. A coefficient of 0.51 1957 check-list. was used to allow for the imperfect ellip- EGGSHELL PARAMETERS soid form of a number of seabird eggs (Stonehouse, 1966; Coulson et al, 1969). Shape Index. Eggs of various species The coefficient is not suited for humming- differ considerably in shape, ranging from birds which lay blunt-ended eggs nor for the near spherical eggs of the Hooded grebes and tinamous which lay eggs Merganser {Lophodytes cucullatus) to the pointed at both ends (Preston, 1974, conical eggs of the Golden Plover Tatum 1975). (Pluvialis dominica). Several different Actual measurements of internal vol- indices have been used to approximate umes are more accurate than external shape. Most involve the dimensions of volumes calculated from egg dimensions, length and breadth. The shape index, but such measurements are not always B/L x 100, developed by Romanoff and practical for eggshells, and indices must Romanoff (1949), has been used in the suffice. Worth (1940) found for eggs of studies on egg characteristics in House domestic fowl {Gallus gallus) that vol- Wrens, Troglodytes aedon, (Kendeigh el umes obtained by water displacement al, 1956) and Shags, Phalacrocorax aris- were 15% less than those calculated by totelis, (Coulson et al, 1969). A low in- the ellipsoid formula. Coulson estimates dex indicates a relatively long and nar- the internal volume from external mea- row egg; a high index a short and broad surements to average about 0.487 LB2, egg- about 9.3% less than the ellipsoidal Recently, Preston (1968) derived math- formula would give. Of this, 3% is due ematical formulae to quantify the amount to bicone and about 6% to shell thickness of curvature of the two ends of eggs in (Preston, 1974). terms of asymmetry and bicone. These Equations have been developed relat- measurements can be made with a pro- ing surface area to fresh egg weight and file-copying machine (Preston, 1953) or a shell volume (Paganelli et al, 1974; Shott modified spherometer (Gemperle and and Preston, 1975). Although error Preston, 1955; Preston, 1957). In addi- ranges only from 1-3%, most of these tion, Preston (1968) used the length equations are not applicable to eggs divided by the breadth (L/B) as a mea- whose contents have been blown. Egg sure of elongation (K of Schon wetter, volumes have been shown to vary accord- 1960-72), and argues that this plus the ing to the sequence of laying (Kendeigh values of asymmetry and bicone define el al, 1956) and season (Coulson et al, egg shape and size with virtual complete- 1969), and have been useful in estimating ness. We have used Preston's (1968) the age composition of populations (Coul- elongation as an index of shape, recogniz- son et al, 1969). ing its limitations, and have omitted Thickness and Thickness Index. Thick- asymmetry and bicone since the instru- ness of whole eggshells can be measured ments required for these measurements with a modified Starett 1010M dial were not available. Elongation is high micrometer having a curved rod which is for long narrow eggs and low for short inserted through the blow-hole (Anderson broad eggs. Preston (1969) summarizes and Hickey, 1970a). Measurements by elongations of eggs from 63 North Ameri- this method would also include the firmly can families. attached membranes. The main dis- Volume and Volume Index. An esti- advantage of this technique is that it mate of volume was computed by the can only be used on large eggs with large equation of Kendeigh, et al (1956): blow-holes. Another method is a Vicker's Image V = ^LB 6 Splitter attached to a microscope (Alsop, 1972). With this technique measure- where V, the volume, is mm3, L maximum ments can be made in microns regardless length, and B maximum breadth in mm. of the size of the blow-hole. Micro- The coefficient TT/6 is approximately scopic observation enables shell mem- 0.524 and holds for eggs which are true branes to be visually separated from the 12 D. R. OSBORNE AND R. WINTERS Vol. 77 eggshell itself and not be included in the same eggs contributed little to the sam- thickness dimension. ple variance, whereas differences among Shell thickness is directly related to eggs within clutches contributed nearly egg volume (Olsson, 1936) and many as much as differences among clutches. species which lay small eggs have rela- They concluded that it is more efficient tively less shell and thinner shells than and less costly to collect entire clutches, larger eggs of other species (Grossfeld, and estimated 8-11 clutches were ade- 1938; Asmundson et al, 1943; Romanoff quate for detecting differences of 10% in and Romanoff, 1949). Shell thickness is shell thickness. also related to total egg weight. Ar et al, (1974) calculated the change in eggshell RESULTS thickness with egg weight from data of Elongation, volume and thickness in- Schonwetter (1960-72), which then were dices were calculated for 1145 eggs (328 used to predict total functional pore area sets) representing 18 orders, 54 families in 29 species of birds. Thickness of egg- and 253 species of birds (table 1). shells was found to be proportional to the Thirteen countries and 37 states are 0.456 power of fresh egg weight but this represented. The largest sample comes is not applicable to eggshells void of their from Ohio (54 species) followed by Cali- contents. fornia (43 species). Because of the small Thickness index is denned as the weight sample size (most species are represented (mg) of the shell divided by the product by only one clutch) species common to of length and breadth in mm (Ratcliffe, two localities were not compared sta- 1967; 1970). We used Ratcliffe's index tistically for geographic differences. Egg of thickness because of its reliability parameters are also included for 16 species (Anderson and Hickey, 1970b; Burger, considered rare or endangered, or which 1973).