INTRACLUTCH EGG-SIZE VARIATION IN THE BARNACLE GOOSE BRANTA-LEUCOPSIS- AN EGG-REMOVAL EXPERIMENT

We carried out an egg-removal experiment on Barnacle Geese Branta leuc opsis to test the hypothesis that tactile contact between the brood pa tch and eggs accumulating in the nest during laying was causally relat ed to intraclutch egg-size variation, acting through the development o f incubation behaviour. Egg removal had no effect on mean egg mass, re laying interval or clutch size: mean (+/- s.e.) clutch sizes for first clutches were 4.9 +/- 0.9 and 4.7 +/- 0.9 eggs for control and experi mental females, respectively, We therefore conclude that Barnacle Gees e have a determinate pattern of egg laying, Daily removal of all eggs from the first-laid egg did not affect the within-clutch pattern of eg g-size variation: in both control and experimental clutches the first egg was relatively small, the second or third egg was largest and ther e was a linear decline in egg size to the smallest, last-laid egg, The re was no significant difference in either the absolute or relative si ze of the last-laid eggs in control and experimental clutches, Tactile contact with eggs in the nest, therefore, is not required for the exp ression of intraclutch egg-size variation in Barnacle Geese, In this r espect, determinate-laying Barnacle Geese differ from species with ind eterminate laying patterns (e.g. gulls) where egg removal does affect the normal pattern of within-clutch egg-size variation. If hormonal ch anges (e.g. prolactin) associated with onset of incubation are causall y related to the intraclutch decrease in egg size, then the stimuli in volved appear to differ between determinate and indeterminate layers.