Light pollution bird survey begins

The British Trust for Ornithology (BTO) is asking the public to take part in a survey to assess the effect of light and heat pollution on garden birds.

The charity is asking people to get up before sunrise (about 08:00 GMT) on Thursday 9 January, to monitor their garden bird feeders.

Participants should record the times at which they see up to 10 different species arrive.

This project is a follow-up to the charity's 2004 Shortest Day Survey.

Clare Simm from the BTO explains why the team wants to focus on light pollution.

Video journalist: Victoria Gill