Physiognomic Variation in Dotterel Charadrius morinellus Clutches

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Abstract
Much interest has focused on why birds lay variably marked and coloured eggs. We quantified the physiognomy of dotterel eggs and used discriminant function analysis to compare clutches. Two background colours, feint scribbles and primary spots around the egg apex were particularly significant in discriminating between clutches. On the basis of other studies we suggest that females can be identified consistently according to these physiognomic features of their eggs. Of 109 clutches examined in the field, 6.4% had one markedly old egg (possibly laid by a brood parasite), but none had extra eggs (only 0.8% of 657 clutches have ever had 4 eggs). As the Dotterel can be polyandrous (we suggest at least 3-5% of females), we postulate that a shortage of males, variable nest losses and an ability in some females to produce many eggs may facilitate brood parasitism. There were no convincing relationships between nest site features and clutch physiognomy, suggesting that individual females do not choose particular nest sites to match their distinctive eggs.