Determinants of eggshell strength in endangered raptors

Abstract

We compared eggshell strength in a group of falcon taxa including the peregrine falcon (Falco peregrinus peregrinus), the red shaheen falcon (F. peregrinus babylonicus), the saker falcon (F. cherrug), the gyr falcon (F. rusticolus) and some interspecific and intraspecific hybrids. Our results showed that smaller falcons (<1,000 g) of the peregrine group have eggshells that are significantly softer (x=13.3 N) and thinner (x=0.26 mm) (n=107 eggs) than larger falcons (>1,000 g) of the gyr-saker group (x=20.8 N and 0.39 mm, respectively, n=81 eggs). We found a significant positive correlation between egg hardness and eggshell thickness. Linear mixed models showed that clutches from heavier females consisted of larger and harder eggs with thicker shells and thicker egg membranes. Eggs produced by older females and eggs laid later in the laying sequence were relatively smaller and softer and had relatively thin egg membranes and eggshells. Individual females, irrespective of their age, contributed significantly to the observed variation in egg strength. Egg size and hardness of hybrid eggs were similar to that of the pure species suggesting that hybridization does not affect eggshell hardness or thickness. Our study provides quantitative evidence of several factors, other than levels of contamination, which may affect eggshell thickness and hardness in falcons.

The effect of developmental stage on eggshell thickness variation in endangered falcons

“…When possible, measurements were taken from the pale spots of the egg in order to reduce variation of thickness due to differences in pigmentation (see Gosler et al, 2005). All measurements were conducted without the membrane, since membranes are rather thick in falcon eggs (Castilla et al, 2009b). The outer thick eggshell membrane and the thin vascularized chorioallantoic membrane were removed from the eggshells after immersing them in water (see Castilla et al, 2010).…”

“…Despite the considerable body of research devoted to eggshell characteristics, either in poultry science (Hunton, 1995;Carnarius et al, 1996) or in wild birds Davis, 2004, 2005;Castilla et al, 2007Castilla et al, , 2009b, the effect of developmental stage on eggshell thickness or strength remains unknown for most wild species. Since developing embryos utilize calcium from the eggshell, developmental stage can be expected to cause eggshell thinning (Vanderstoep and Richards, 1970;Bunck et al, 1985;Bennett, 1995;Castilla et al, 2007;Karlsson and Lilja, 2008).…”

“…Since developing embryos utilize calcium from the eggshell, developmental stage can be expected to cause eggshell thinning (Vanderstoep and Richards, 1970;Bunck et al, 1985;Bennett, 1995;Castilla et al, 2007;Karlsson and Lilja, 2008). Additionally, eggshell thickness appears to be influenced by many factors including genetics, egg colour and size, the time the eggs spend in the uterus, female characteristics (condition, age, stress, health status), and the diet of the females (Kennedy and Vevers, 1973;Nys et al, 1991;Francesch et al, 1997;Ciftci et al, 2003;Boersma et al, 2004;Riczu et al, 2004;Castilla et al, 2007Castilla et al, , 2009bBirchard and Deeming, 2010). More recent studies have shown that Mycoplasma infection also produced egg abnormalities and eggshell thinning (Feberwee et al, 2009).…”

“…Because of the endangered nature of many raptor species (Cramp and Simmons, 1980), eggshell thinning has been the focus of much research in these species (Cade et al, 1971;Peakall and Lincer, 1996;Falk et al, 2006;Castilla et al, 2009b). Population collapse and reproductive failure in raptors have occurred in many parts of the northern hemisphere from about 1950 onwards, and 2 have often been attributed to the use of biocides in agriculture and forestry management (Wegner et al, 2005;Falk et al, 2006;Fernie et al, 2009).…”

The Effects of Rodenticide Residues Deposited in Eggs of Tyto alba to Eggshell Thickness

“…There was no significant difference (p>0.05) of eggshell thickness within and among treatments in all breeding seasons of T. alba. The results indicated that bromadiolone and chlorophacinone do not affect eggshell thickness unlike other pesticides (Jaspers et al 2005;Mendenhall et al 1983) or environmental pollutants such as mercury (Castilla et al 2009) and rodenticides such as brodifacoum and walfarin (Naim et al 2012). Naim et al (2012) stated that mean eggshell thickness of T. alba under rat baiting with warfarin and brodifacoum ranging from 0.276 -0.286 mm (n=18) and 0.260-0.291 mm (n=18), respectively, while the mean eggshell thickness in rodenticide free area and biorodenticides ranges from 0.285-0.293 mm (n=9) and 0.283-0.286 (n=14).…”