And in a poll conducted for the non-profit Center for Biological Diversity, more than half said society has a "moral responsibility to address the problem," the Los Angeles Times reported Friday.
Unlike most other environmental groups the center has targeted population growth as part of its campaign to save wildlife species from extinction.
To that end, it has distributed more than half a million condoms at music concerts, farmers markets, churches and college campuses.
One reason for the poll was to demonstrate to other environmental groups that the public would not be alienated by bringing up population matters in the debate, Kieran Suckling, the center's executive director, said.
When the center initiated its condom campaign other environmental leaders "reacted with a mix of worry and horror that we were going to experience a huge backlash and drag them into it," he said.
Instead the campaign has swelled the center's membership to about 500,000 and increased donations, he said.
In the poll, 61 percent of respondents expressed concerned about disappearing wildlife and that human population growth was having an adverse effect.
The survey of 657 registered voters was conducted Feb. 22-24 by Public Policy Polling of Raleigh, N.C., and had a margin of error of plus or minus 3.9 percentage points.