Antipredator strategies of Alaskan moose: are maternal trade-offs influenced by offspring activity?

• Published in: Canadian Journal of Zoology
• Main Authors: White, Kevin S, Berger, Joel
• Format: Article in Journal/Newspaper
• Language: French
• Published: Canadian Science Publishing 2001
• Subjects: Alces alces; Canis lupus; Ursus arctos; Alaska
• Online Access: http://dx.doi.org/10.1139/z01-170; http://www.nrcresearchpress.com/doi/pdf/10.1139/z01-170

To maximize fitness, mothers must both provision and protect neonates, demands that may be in conflict, particularly in systems that still experience high levels of natural predation. Whether variation in offspring behaviour alters this putative conflict is not known. The objective of this study was to test hypotheses about the extent to which neonatal activity and ecological variables mediate trade-offs between maternal vigilance and foraging. To address these questions we contrasted data from behavioural observations on female moose (Alces alces) that differed in parity, calf activity, and habitat use at a site in south-central Alaska where they are subject to high levels of grizzly bear (Ursus arctos) and wolf (Canis lupus) predation. Our analyses revealed that females with active juveniles were more vigilant (and as a consequence spent less time feeding) than those with inactive young; vigilance of females without attendant young was intermediate. Distance to apparent protective refugia (e.g., vegetative cover) was positively related to vigilance for all calf-status categories, but lactating females spent more time closer to thick vegetation than did nonlactating females. These results suggest that (i) mothers adjust vigilance when young are inactive to compensate for the loss of foraging opportunities during periods of neonate activity, thereby reducing juvenile vulnerability and increasing the overall feeding rate, and (ii) females with young reduce foraging compromises and, presumably, predation risk by spending more time close to protective cover than do nonlactating females. We conclude that maternal trade-offs can be highly labile and that mothers are able to adjust rapidly to environment-specific situations.