Diet of the White Stork (Ciconia ciconia) in a heterogeneous Mediterranean landscape: the importance of the invasive Red Swamp Crayfish (Procambarus clarkii)

Abstract

Limited quantitative data are available on food habits of the White Stork (Ciconia ciconia) in Mediterranean environments, particularly in ricefields where a relatively new food resource, the invasive Red Swamp Crayfish (Procambarus clarkii), is abundant. We studied the diet of the White Stork in a heterogeneous landscape (Central Portugal) in order to compare the importance of the Red Swamp Crayfish as a food resource in a dominant agricultural/ricefield area in rela - tion to a predominant woodland/agricultural area. White Storks´ diet was analysed spatially (two sites) and seasonally (winter, spring, summer) using pellets (n = 122) collected between December 2012 and July 2013. Overall, from 1570 prey items identified, crayfish was the second most frequent and abundant prey in the diet (frequency of occurrence, FO = 79.5%; numerical fre- quency, NF = 22.9%, respectively), only surpassed by coleopterans (FO = 94.3%; NF = 57.7%). However, in terms of consumed biomass (global PB) crayfish dominated the diet (PB = 44.0%),representing 1.8 times the consumed biomass of coleopterans (PB = 24.2%). Consumption of crayfish was higher in the site with highest abundance of ricefields (NF: 32.0% vs. 17.7%; PB: 51.3% vs. 38.4%). Although no significant seasonal variations were detected in terms of the number of crayfish consumed by storks, consumed crayfish biomass was significantly higher in summer in relation to other seasons. Our findings suggest that in Mediterranean heterogeneous areas the White Stork feeds upon a wide range of prey taxa though, when available, coleopterans along with Red Swamp Crayfish dominate the diet.