SIGNIFICANCE OF INTRACLUTCH EGG SIZE VARIATION IN THE PURPLE HERON

We studied patterns of intraclutch egg size variation (profiles) in 53 clutches belonging to a population of Ardea purpurea breeding in the Ebro Delta (North-east Spain) during 1988 and 1989. The analytical met hod used (MANOVA of repeated measurements) is a substantial improvemen t relative to those used up to now, which are critically reviewed in t he paper. We found no relationship between clutch size and profiles of intraclutch egg size variation. Only year affected profile variation. This is consistent with the view that profiles are outcomes of the in teraction between physiological and environmental factors. We also ass essed whether laying relatively small last eggs constitutes significan t energy savings for females, concluding that the savings are irreleva nt in relation to the females' estimated daily energy budgets. We also evaluated the influence of the size of the last-laid egg on the sibli ng mass hierarchy; its effect was insignificant compared with mass dif ferences arising from asynchronous hatching. In our view, profiles sho uld no longer be indiscriminately considered as adaptive.