Nest size and structure variation in two ground nesting passerines, the Skylark Alauda arvensis and the Short-toed lark Calandrella brachydactyla

摘要

We analysed variation in size and weight of 127 Skylark Alauda arvensis and 179 Short-toed Lark Calandrella brachydactyla nests studied over four years in central Spain. More specifically, we explored three groups of hypotheses: hypotheses based on (1) thermoregulation and past reproductive parental investment, (2) predation, and (3) clutch size. Variables recorded were dry nest weight inner diameter outer diameter nest edge,,, thickness, nest cup depth and percentage of lining layer cover, which were related to laying date, clutch size, geographical orientation, shrub cover, year, and predation rate. Weight and nest edge thickness were negatively correlated with laying date in both species, and with percentage of lining layer cover in the Short-toed Lark. Skylark inner nest diameter varied positively with shrub cover. Three nest measurements varied with year in the Short-toed lark: nest edge thickness, nest cup depth, and inner diameter. In this species, nest cup depth was associated with orientation, while inner diameter varied also with laying date. Neither predation, clutch size nor phenology were correlated with nest size and weight in either species.