Seasonal and Interannual Variability in Laying Date, Clutch Size, Egg Volume and Hatching Asynchrony of Four Lark Species in Mediterranean Spain

—Seasonal and interannual variability in laying date, clutch size, egg volume and hatching asynchrony of four lark species in Mediterranean Spain Aims: To describe the variation in laying date, clutch size, egg volume and hatching asynchrony of four lark species (Skylark Alauda arvensis, Short-toed Lark Calandrella brachydactyla, Thekla Lark Galerida theklae and Lesser Short-toed Lark Calandrella rufescens) and at two different time scales: between years (large-scale variation), and within seasons (short-scale variation). Location: Two climatically contrasting Mediterranean areas: Layna, located in the centre of the Iberian Peninsula and with a continental Mediterranean climate, and Cabo de Gata, located in the south-western Iberian Peninsula and with a semi-arid climate. Breeding Skylarks and Short-toed Larks occur in Layna, whereas breeding Thekla Larks and Lesser Short-toed Larks occur in Cabo de Gata. Methods: During the study period between 1991-95 in Layna and between 1991-94 and 1996-97 in Cabo de Gata, searches were carried out for nests of the four species and laying date, measured egg-length and width, and hatching asynchrony recorded. Overall, 118 nests of Skylarks, 165 of Short-toed Larks, 334 of Thekla Larks and 259 of Lesser Short-toed Larks were studied. Between-year variations in breeding parameters were analysed with General Linear Models (GLM’s). To investigate the presence or absence of asynchronous hatching in relation to year, laying date and clutch size, bi and multinomial logistic regression models were fitted. Results: The breeding season in Cabo de Gata started earlier (60 days before) and was longer (15-25 days) than in Layna. The frequency distribution of laying dates was unimodal in all cases, with the exception of Lesser Short-toed Larks. Annual mean laying dates did not vary significantly among years in Layna, but the opposite was found in Cabo de Gata. However, mean laying dates of clutches from the 25 percentile show large between-year variations in all cases. Regarding the among-year variation in clutch size, all species studied except the Thekla Lark show a high degree of constancy in this parameter. The seasonal pattern of clutch size variation was similar in all species studied, with maximum clutch sizes on intermediate dates, and smaller early and late clutches. Mean clutch volume appears relatively constant in relation to annual variation in three of the species studied. Nevertheless, in Thekla Larks a significant inter-annual variation was observed in this breeding parameter. Finally, the incidence and/or the extent of hatching asynchrony are similar in all the species studied, increasing with clutch size and laying date. Conclusions: This study shows that the four lark species have different reproductive strategies which cannot be explained solely in terms of their body mass or biogeographical affinities. More studies are needed to evaluate how these factors could affect breeding success in larks in Mediterranean habitats and the implications on demography and population dynamics.