Costs of maternal care revealed through body condition in Northern Resident killer whales (Orcinus orca)

In species with prolonged parental investment, extended care imposes considerable costs. In Northern Resident killer whales (Orcinus orca), maternal investment is demanding due to long gestation, extended lactation, and lifelong care of non-dispersing offspring. Using 10 years of aerial images, we assessed whether reproduction and maternal care affected body condition in 66 reproductive-aged females. Females in late pregnancy had significantly higher body condition than those not pregnant or with unsuccessful pregnancies, while females in the first two years of lactation had significantly lower condition. By year three, body condition rebounded, coinciding with weaning. To evaluate long-term costs, we analyzed body condition in 75 adult females relative to: (1) number of living offspring (life-long parental care hypothesis), (2) lifetime births (successive reproduction hypothesis), and (3) number of living sons (expensive sons hypothesis), while accounting for prey abundance. Maternal condition declined with increasing numbers of living offspring and lifetime births, independent of Pacific Salmon Commission Chinook salmon (Oncorhynchus tshawytscha) abundance index. Living offspring was the strongest predictor of the reproductive history covariates, supporting the life-long parental care hypothesis. We found no support for the expensive sons hypothesis. These findings highlight energetic costs of extended maternal investment in long-lived, socially complex species.