Orsini's viper pursues a reproductive strategy of switching between reproductive and non-reproductive behavior in alternate years, finds a new study.

Orsini's viper snakes are the smallest snakes in Europe. The species is considered to be rare and patchily distributed. They are found in open meadows and hillsides across several European Union countries. The viper species is facing a risk of extinction in three countries including France, Italy and Greece.

Researchers from Centre de Recherche en Ecologie Expérimentale et Predictive (CNRS/ENS), and the Université Paris Sorbonne, have been monitoring a population of Orsini's vipers in France's Mont Ventoux for the last 30 years. A total of 160 females were observed throughout their lives.

They found that the Orsini's vipers switch between reproductive and non-reproductive years. Based on a mathematical model developed using field data collected over the years, researchers have confirmed that the viper follows a reproductive strategy where the adult female reproduces once in every two years.

During non-reproductive years, the snakes spend time building fat reserves and acquiring resources needed for their body growth, which influences their fertility. Larger females produce more offspring. In the reproductive years, the females stop growing and spend all their resources in reproduction. They reproduce successfully and there is no psychological impact on the mother, a report from CNRS said.

This reproductive strategy of the vipers is completely different from the viviparous snake species. Viviparous snakes become thin after giving birth to their offspring. Their resources "melt away," which could threaten their survival. In the case of the Orsini's vipers, they give birth to healthy offspring and the risk of parental survival is also low.

This study could help explain cases of intermittent reproduction in other plant and animal species, said the researchers.

The findings of the study, "Intermittent breeding and the dynamics of resource allocation to growth, reproduction and survival", are published in the journal Functional Ecology.