Eggshell Thickness Variation in Red-legged Partridge (Alectoris rufa) from Spain

—Eggshell thickness is commonly used as an indicator of habitat quality and effects of environmental pollution on avian reproduction. We present the first data available on eggshell thickness for Red-legged Partridge (Alectoris rufa) in Spain. We compared eggshell thickness between eggs collected in an agricultural area (wild eggs) and eggs from game farms (farm eggs). Wild eggs had shells significantly thicker (x̄ 0.32 mm, n 74) than farm eggs (x̄ 0.28 mm, n 89), despite game farm partridges being fed a diet rich in calcium and not exposed to agricultural pollutants. Eggshell thickness did not affect hatching success of wild partridges, and population decline observed in this species cannot be linked to reduction in egg viability due to eggshell thickness. Received 8 February 2008. Accepted 6 May 2008. Reduction of egg viability is an important cause of reproductive failure and has been suggested to contribute to decreases of bird populations (Drent and Woldendorp 1989, Cooper et al. 2005). Eggshell quality and reproduction of bird species is greatly affected by levels of calcium availability (Graveland and Drent 1997, Dhondt and Hochachka 2001, Tilgar et al. 2005), which in turn can be affected by levels of pesticides (Dauwe et al. 2006) or acidification (Nybø et al. 1997, Pollentier et al. 2007). 1 Estación Biológica de Sanaüja (CSIC), Ministerio de Ciencia e Innovación; Ap. Correos no 35, 25280 Solsona, E-Lleida, Spain. 2 Department of Biodiversity and Evolutionary Biology, Museo Nacional de Ciencias Naturales de Madrid (CSIC), C/José Gutiérrez Abascal 2, E-28006 Madrid, Spain. 3 Área de Defensa del Bosc, Centre Tecnològic Forestal de Catalunya, Pujada del seminari, s/n, E-25280, Solsona, Spain. 4 Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA. 5 Roskilde University Library, P. O. Box 258, DK4000 Roskilde, Denmark. 6 Corresponding author; e-mail: [email protected] High levels of pesticides are related to reduction in eggshell thickness in many species (Bunck et al. 1985, Peakall and Lincer 1996, Falk et al. 2006). Thus, eggshells are reasonable indicators of polluted areas, and can be used to monitor health of populations over long periods (Falk et al. 2006). However, long-term thinning of eggshells may not universally be related to pollution. A large decline in eggshell thickness in different species of thrushes (Turdus spp.) from different countries has been observed since before the introduction of organochlorine pesticides, but the cause of the decline is still unknown (Green 1998, Scharlemann 2003). The Red-legged Partridge (Alectoris rufa) has been decreasing throughout its range (Meriggi and Mazzoni 2004 and references herein). Lack of reproductive success has been mainly attributed to food scarcity due to agricultural practices and nest predation (Potts 1980). However, the reproductive biology of this species is poorly known (Cabezas-Dı́az et al. 2005) and little information is available about eggshell characteristics, which could affect reproductive success. Our objectives were to measure shell thickness of eggs of Red-legged Partridge from a wild population to compare with those from a population where partridges had no food limitations, were putatively not subjected to agricultural pollution, and were known to have high hatching success. We tested the prediction that eggshells from the wild population should be thinner than those from the game farm population.