Some penguin parents maintain specific duties – dads guard, moms forage – and they don’t alter these roles around no matter what. But according to a new Behavioral Ecology and Sociobiology study, penguin moms and dads who can’t switch or share parental duties aren’t provisioning their chicks as well during years when climate warming reduces their food supply.
Being flexible typically allows animals to respond adaptively to changing conditions, whereas inflexible sex-specific parental investment might worsen breeding success. This is especially a problem for vulnerable and endangered species – such as crested penguins facing population declines because of climate-induced nutritional stress.
Most penguins avoid long periods of fasting by switching up brooding and chick-provisioning obligations between both sexes. However, eastern rockhopper penguins (Eudyptes chrysocome filholi) in New Zealand are one of seven Eudyptes species that show a fixed division of labor between parents during the first three to four weeks after their eggs hatch. The dads fast ashore while guarding the chicks from predatory seabirds, and moms do all of the provisioning, taking foraging trips almost every day. Then during the five to six weeks before fledging, chicks form little “daycare” groups called crèches where they’re fed by both parents who make extended trips out to sea.
To see if this uniquely rigid division of roles during chick-rearing exacerbates their vulnerability during times of poor food availability and quality, a team led by Massey University’s Kyle Morrison tagged nearly 200 male and female eastern rockhopper penguins living in Penguin Bay on Campbell Island. The team measured adult foraging trip durations, provisioning rates, reproductive success, and chick sizes during an abundant year of good diet quality and a lean year of nutritional stress.
As predicted, the penguins made longer foraging trips and provisioned less for their chicks during the leaner year. During the crèche phase of the low diet quality year, males reduced their provisioning rate more severely than the females: Dads searched for food at sea for longer stretches of time in order to regain the mass they lost while on guard duty. And the chicks fed less often and grew more slowly as a result.
Even though this strict parental division of labor is maladapted to the less predictable food supply expected with further climate change, the team thinks that crested penguins will remain anchored to their breeding strategy. The smaller, less aggressive females aren’t as effective guards. If the parents were to share their guarding and foraging duties equally, however, the chicks could end up receiving as much as 34.5 percent more feeds.
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