For humans, raising children is expensive, and parents take on different strategies to afford the costs of childcare, buying food, and paying for college. Some choose to save up ahead of time and only raise kids once they have a large enough savings account, others live paycheck to paycheck, and many fall somewhere in between. Ungulates also need a budgeting strategy to raise their offspring. But, instead of money, the currency many mammals rely on to finance reproduction is energy from the food they eat. Although all ungulate moms need to eat for two (or sometimes three, or four), the timing of when they must obtain the calories differs depending on their strategy. The strategies that animals use to finance reproduction fall on a spectrum between ‘income’ and ‘capital’ breeding. Income breeders are those who rely on continuous availability of quality food resources, or
‘live paycheck to paycheck’. Capital breeders are those who rely on energetic resources ahead of time to ‘save up’ before reproduction.
In anticipation of the costs of reproduction, some moms will save up beforehand by accumulating fat reserves before reproductive events occur. They then rely on that ‘savings account’ to provide enough energy to produce and raise offspring. When they need more energy to raise their offspring, often at a time when resources are far less abundant, they rely on those fat stores to supplement the additional energy needed.
Other moms actively consume more food, and therefore energy, at the time of reproduction to account for the additional costs of raising their young. The animal relies on consistent incoming energy to support their offspring. Income breeders don’t store up energy ahead of time as capital breeders do, which means the timing of reproduction is ever more important because those resources must be there when they are needed to support young.
How do these strategies come about?
When might a person need to ‘save up’ before raising a child versus rely on income as needed? Perhaps if the parents’ future financial situation is unclear, it would be useful to have some funds saved up. Alternatively, if the parents have stable jobs with predictable income, it wouldn’t be as important to save up ahead of time. Animals adapt to their life situations and their environment in similar ways. Animals that don’t have a reliable nutritious food source year-round may need to save up extra energetic reserves before reproducing. In contrast, if an animal has a consistent food source during the expensive times of reproduction, they don’t need to save up ahead of time.
LIVING AT THE EXTREME
Ungulates aren’t the only ones who budget for reproduction. Emperor penguins are extreme capital breeders. After a mother lays an egg, she leaves the father to incubate
it for two months while she stocks up on food for herself. Because of the extreme cold, the father can’t leave the egg, so he doesn’t eat at all during the two-month incubation period. He relies entirely on his fat stores to survive and keep the egg warm.