Boris Johnson's partner Carrie Symonds has made her first public speech since moving into Downing Street last month.
In a speech at a Birdfair event, Ms Symonds said politicians have a "gigantic responsibility" to care for the environment.
She also joined a question and answer session with Chris Packham, presenter of BBC Springwatch.
The 31-year-old quit her role as a director of communications for the Conservatives last year.
The prime minister's girlfriend is now a senior adviser for US environmental campaign group Oceana.
She works with the charity's marketing operation in London and a profile on its website describes her as being "passionate about protecting the oceans and marine life".
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In her speech Ms Symonds said she was a newcomer to bird-watching, having become interested after visiting a puffin colony at Bempton in East Yorkshire.
She said she had been alarmed at seeing a picture of a slaughtered bird in a newspaper shortly afterwards, and condemned the trophy hunting of puffins.
However, Ms Symonds said she was "profoundly optimistic" that the people who care "far outnumber the people who don't, especially among young people".
She said while she is not "perfect", she is "learning" and referred to the floral print sustainable dress she wore to the event.
The £225 garment is reported to be eco-friendly, having been made locally in London from a cotton blend that is biodegradable and which does not contain microplastics or dyes that pollute the environment.
More than 24,000 people attended Birdfair last year over three days.
Tim Appleton, founder of the annual event for birdwatchers, said it has raised £40m for global conservation projects in the 31 years that it has been running.
He said: "We're absolutely over the moon that Carrie is supporting us and we hope she will continue supporting us and conservation for many years to come."