AN EXPERIMENTAL-STUDY OF INCUBATION EFFORT IN HIGH-ARCTIC BARNACLE GEESE

1. We examined the cost of reproduction in high-Arctic barnacle geese (Branta leucopsis Bechstein) by manipulating the length of the incubat ion period by +/-5 days. Unmanipulated clutches were used as controls. 2. Nests with prolonged incubation suffered a higher egg loss to pred ators than control nests and nests with shortened incubation. 3. Among females with prolonged incubation, body condition at hatching was sig nificant lower than among females with shortened incubation. These, ho wever, did not increase their feeding effort to compensate for mass lo ss. 4. Increased levels of parental effort did not affect adult return rate or date of arrival to the breeding ground the following season. Accordingly, there is no evidence from this study that barnacle geese invest in young at the expense of their own survival or future fecundi ty. 5. We propose that breeding females retain some reserves at the en d of laying in order to (i) incubate more continuously, thus shortenin g the incubation period and minimizing the risk of egg predation, and/ or (ii) have a buffer against weight loss due to increased energy expe nditure during inclement weather.