Green-rumped parrots appear to have high rates of adoption and infanticide, showing two very different sides of life in the animal kingdom. a study published May 6 in the journal Proceedings of the National Academy of Sciences (PNAS) describes what drives them to go to two extremes when it comes to interacting with another bird’s chicks.
Green-rumped parrots (Forpus passerinus) area very small and cozy bird found in parts of South America and the Caribbean. They feed fruits, seeds and different flowers and are known for their bright green hues. Unlike other parrots that prefer to live higher in the canopy, green-rumped parrots tend to nest in hollowed out trees or fence posts in grasslands.
These parrots aren’t the only animals that have been observed adopting killing each other’s babies. Numerous species amphibians, fish, rodents, felines and primates Babies of their own species have all been observed being killed and – in some cases –their own descendants. Both men and women can kill the offspring of their rivals to secure a social or sexual advantage for themselves. A male animal may kill the offspring of a female whose mate has died so that he can do so reproduce faster with her. Others have been observed caring for the babies of dead or missing animals.
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For Green-rumped parrots, both infanticide and adoption involve finding two necessities: a nest and a mate.
“Most infanticide attacks occurred when a breeding pair was attacked by another pair trying to take over a coveted nest site,” study co-author and wildlife biologist Steven Beissinger of the University of California, Berkeley. said in a statement.
In the studya team created artificial nesting sites from PVC pipes and installed them on a cattle ranch in Guárico, Venezuela. Colorful bands were also placed on the parrots to track the individual birds and their relationships. They found dead baby birds in the nest with no clear indication of what had killed them.
“We couldn’t tell if something had attacked them, or if they died of a disease, or something else,” Beissinger said. “But when we were looking at some of the nests, all of a sudden a male came in that wasn’t one of them – who wasn’t a parent at that nest – and he came out with a little bit of blood on his beak.”
The team began identifying and referencing examples of the behavior observations of more than 2,700 nests taken between 1988 and 2015 in the study. In psittacines, it appears that competition for breeding sites is the main motivation for attacks, rather than reproduction.
In the nests the team monitored, parrots killed or injured nestlings and eggs at 256 locations. Most attacks appeared to be carried out by a single parrot or breeding pair entering and then claiming the breeding site for itself. The attacks also occurred more often when the parrot population was high and there was more competition for good breeding grounds.
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“It’s not that everyone is born a killer, but the urge to breed is very strong,” study co-author and University of Texas Rio Grande Valley avian ecologist Karl Berg. said in a statement. “If the resources provided by the environment are not sufficient for all individuals to reproduce, they look for alternative strategies. Unfortunately, this involves killing innocent little offspring.”
So was infanticide observed in nests where one parent had died and the living parent had found a new mate. The new partners might as well adopt unrelated offspring or kill them. Ultimately, the choice to become a stepparent did not harm their changes in reproductive success. The males who adopted chicks unrelated to them and nested with females also started breeding at a younger age.
According to the teamadoption has since become harder to understand challenges older ideas about natural selection. An evolutionary goal for most animals is to get as many copies of your genes into the next generation as possible. Adopting a niece or nephew can make biological sense since they share about 25 percent of your genetic material. However, the benefit of adopting offspring from an unrelated animal is not as logical, but still occurs.
“It was very interesting to see that the reproductive fitness outcomes were about the same between adoption and infanticide, suggesting that they have an alternative strategy,” Berg said. “Adoption can be a non-violent way to carry genes into the next generation.”
