Why parrotlets adopt or kill their rivals’ babies

A green-rumped parrotlet widow and her nestlings. The behavior of the nestlings—spilling out of the cavity begging for food—indicates that they aren't getting enough food. Credit: Karl Berg.

In the bustling world of green-rumped parrotlets, love and competition take center stage, sometimes leading to unexpected behaviors like caring for or even harming others’ babies.

A recent study sheds light on why these tiny South American birds exhibit such extreme actions.

Led by Professor Steven Beissinger from the University of California, Berkeley, researchers spent nearly three decades studying these feathered creatures in Venezuela.

They discovered that parrotlets engage in infanticide and adoption, driven by their quest for love and prime nesting spots.

The drama unfolds in the grasslands, where parrotlets prefer nesting in hollowed-out trees and fence posts.

To study their family dynamics, Beissinger and his team installed artificial nesting sites and began tracking individual birds using color-coded bands.

Infanticide, where babies are killed by rival parrotlets, often occurs during fierce competition for nesting sites.

This aggressive behavior is more common when the parrotlet population is high, and resources are scarce. Male intruders, seeking to claim territory and mates, may attack existing nests, leaving behind a trail of tragedy.

Surprisingly, some parrotlets choose a different path. When a parent dies, leaving behind offspring, a new mate may adopt these unrelated babies. This act of adoption challenges traditional views of natural selection but provides a nonviolent way to pass genes to the next generation.

Interestingly, adopting parrotlets don’t lose out on reproductive success. They still find mates and start breeding at a younger age than their rivals. For them, adoption offers both love—a new mate—and real estate—a ready-made nest site.

This study unravels the complex motivations driving parrotlet behavior, showcasing the delicate balance between love, rivalry, and survival. It underscores how competition for resources can lead to both compassion and aggression in the animal kingdom.

Funded by organizations like the National Science Foundation and the National Geographic Society, this research opens a window into the intriguing world of avian parenthood.

As we peer deeper into nature’s mysteries, we gain a deeper appreciation for the diverse strategies animals employ to thrive in a competitive world.

Source: UC Berkeley.