In a nutshell: A meta-analysis found small effect sizes for positive and negative pro-environmental behavior spillover. Positive spillover was more likely if behaviors were similar and the interventions promoted intrinsic motivations for change.
Behavioral spillover occurs when participating in one behavior increases or decreases the probability of participating in a second behavior, potentially amplifying or mitigating the effectiveness of behavior change programs. While the research in spillover behaviors is nascent, there are an increasing number of studies examining pro-environmental behavioral spillovers, and their moderating and mediating factors.
To examine overall spillover effects, Maki et al. (2019) conducted a meta-analysis (basically an analysis of analyses) of published and unpublished behavioral spillover studies. These studies induced a pro-environmental behavior and tested how this influenced the study participants’ intention to engage or engagement in another pro-environmental behavior. This allowed them to make broader inferences about behavioral spillover. They examined results from 22 studies for spillovers in relation to measures of pro-environmental behavior (behavioral intentions, actual behavior and policy support).
Overall the authors found:
- A small positive spillover effect for intentions to perform a second pro-environmental behavior
- A even smaller negative spillover effect for actual behavior and policy support
The authors helpfully summarized their main findings as: ‘if 100 people were successfully encouraged to adopt a pro-environmental action…approximately 5 would develop stronger intentions to adopt a second pro-environmental action, and fewer than 1 would reduce engagement in a second action’.
Other results:
- Intrinsic motivations may increase the likelihood of positive spillover
- Positive spillover is more likely to occur between similar behaviors
- Increased guilt increased negative spillover of behavioral intentions
- Financial incentives were found to constrain both positive and negative spillover effects
They note that the concern of promoting individual actions will undermine support for more governmental interventions such as environmental policy is not supported by the data. Additionally, the data does not support pathways from easy to perform pro-environmental behaviors (e.g. signing a petition, turning off the lights) to more challenging but behaviors of higher impact (e.g. advocacy, donating time and money).
At the moment behavioral spillover is under studied in biodiversity conservation (see Shreedhar and Murato 2019). More investigation in conservation contexts, will provide insights specific to biodiversity behaviors and contribute to greater understanding of spillover more generally. Key take home message here is don’t expect getting people involved in an easy to perform environmental behavior will lead to more significant changes in other behaviors, at least in the short term. It’s also important to keep in mind if we promote individual behavior change, it does not diminish support for policy or structural changes in society. To get a more biodiversity-friendly future, we will most certainly need both.
Please keep to the path 
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