Sex ratios of migrating southern hemisphere humpback whales: A new sentinel parameter of ecosystem health.

Southern hemisphere humpback whales have evolved energetically demanding capital breeding and migratory life-history behaviours. It has been hypothesised that not all individuals of a population participate in the seasonal migration each year, or only undertake partial migrations. Given the cost of migration and reproduction, we explored the possibility that specifically, not all mature females participate in the seasonal migration every year, or significantly delay or shorten their migration, in response to poor feeding conditions.