Variation in antimicrobial protein activities in eggs from nine lark species in relation to precipitation, temperature and aridity, during the breeding season. Activities of lysozyme and ovotransferrin respectively in relation to (a and d) mean precipitation, (b and e) mean ambient temperature and (c and f) the aridity index AM during the breeding season. A lower value of AM indicates a more arid environment. Raw data values are shown in grey, and mean values (based on mean values per nest) for each population are shown in black. The line of best fit is generated from a general linear mixed model containing only the variable of interest as predictor.