Look: Thousands rally outside UK parliament in biodiversity protest

Thousands of protesters descended on Britain's parliament Saturday as part of a four-day campaign designed to "highlight the environmental failures" of government.

Environmental group Extinction Rebellion (XR) kicked off the event on Friday, promising less disruption and more inclusion than the blockades that became its trademark.

A demonstrator wears a costume as people protest during the Extinction Rebellion's 'The Big One' event, in London, Britain.

Saturday's protest focused on nature and biodiversity, and started from Westminster Abbey with attendees, many of them children, wearing animal costumes and masks.

An activist from the Extinction Rebellion wears a costume while they demonstrate, as a part of 'The Big One' event, in London.

The march ended in Parliament Square with a mass "die-in", which the activists described as "a symbolic spectacle" where participants "lie down in silence, in memory and mourning for the heartbreaking 70 percent decline in wild animal populations since the first Earth Day in 1970."

Protesters take part a mass 'die-in' outside of the Treasury Offices.

Members of performance troupe Red Rebel Brigade march in central London at a demonstration by the climate change protest group Extinction Rebellion.

Members of performance troupe the Green Spirits march in central London.

Scientists for Extinction Rebellion line up at 'The Big One' environment event which coincides with "Earth Day", in London, Britain.