Clutch Enlargement in Lesser Gray Shrikes (Lanius Minor) in Slovakia When Food is Superabundant: A Maladaptive Response?

Abstract

Abstract Food abundance influences various aspects of birds' breeding ecology, such as onset of laying, clutch size, and reproductive success. Here, we examine the effects of a natural superabundance of food—cockchafers (Melolontha melolontha, Coleoptera)—on nesting success of a monogamous long-distance migrant, the Lesser Gray Shrike (Lanius minor). In that species, cockchafers make up 88% of adult and 48% of nestling diet in years with cockchafer outbreaks. We compared timing of egg laying, clutch size, and fledging success in three years and chick development in two years with and without cockchafer outbreaks. In cockchafer years, laying date was advanced by about one day, clutch size increased by about one egg, and heavier chicks were produced. Fledging success, however, did not change (fledgling number in non-cockchafer years: 5.3 ± 0.2, 5.0 ± 0.2, and 4.0 ± 0.5; in cockchafer years: 4.1 ± 0.7, 5.4 ± 0.2, and 4.2 ± 0.5), because more eggs failed to hatch during cockchafer years. Thus, increased clutch size in periods of superabundant food do not always result in increased fledgling production. Limited incubation ability or intrinsic physical egg properties, resulting in inefficient incubation, are the most likely explanations for increased hatching failure in years of food superabundance in our study population of Lesser Gray Shrikes.