ScienceShot: More Babies, More Problems
Raising offspring is so stressful that it could take years off your life. That’s the conclusion of a new study on Western jackdaws (Corvus monedula), crowlike birds that live in both cities and rural areas across Europe. Over an 8-year period, researchers manipulated the number of young that 186 parent birds across the Netherlands had to raise. They tracked the jackdaws with colored leg bands, ensuring that those who received extra nestlings one year also did so the next year, and those who lost nestlings always raised smaller broods. Over time, both mother and father birds who parented more young—about six or seven birds instead of two or three—had a 34% to 64% drop in remaining life expectancy, the researchers report online this month in Ecology Letters. A 2-year-old parent bird’s average remaining lifespan, for example, dropped from 2.64 years to 1.73 years. In reality, these numbers probably underestimate the total lifespan cost of reproduction, the scientists hypothesize, because the experimental setup didn’t take into consideration the effects of producing and incubating eggs. The results likely hold true for other bird species—the jackdaw’s parenting behaviors are typical for nesting birds. No word yet on whether they apply to humans.