City Nature Challenge

CNC 2023

Started in 2016 as a competition between San Francisco and Los Angeles, the City Nature Challenge (CNC) has grown into an international event, motivating people around the world to find and document wildlife in their cities. Run by the Community Science teams at the California Academy of Sciences and the Natural History Museum of Los Angeles County, the CNC is an annual four-day global bioblitz at the end of April, where cities are in a collaboration-meets-friendly-competition to see not only what can be accomplished when we all work toward a common goal, but also which city can gather the most observations of nature, find the most species, and engage the most people in the event.

The majority of sightings are recorded using iNaturalist available as a free app or via the website. Visit iNaturalistUK or read more about how we use iNaturalist in the UK.

In the UK, we have been taking part since 2018 with Bristol leading the way. The term ‘city’ has also evolved over this period and includes wide urban areas eg Birmingham and the Black Country; the North East as well as City of Nottingham and Gloucester. The Natural History Consortium are leading on co-ordinating the UK’s involvement. Take a look at their CNC pages and wider website for information and resources.

The next City Nature Challenge will take place between Friday 26 April – Monday 29 April 2024. There will be 291 cities in 51 countries on all seven continents participating!

City Nature Challenge 2024 North and South America

City Nature Challenge 2024 Eurasia, Africa and Oceana

Take a look at the FAQ page for much more information about the event.

See what happened across the UK in 2020, 2021 and 2022.

What happened in 2023?

View pdf of the above graphic.

The City Nature Challenge in 2023 was once again a collaborative event with 482 cities from 46 countries taking part. In the UK, 22 urban areas took on the challenge. You can see the cities that took part on the City Nature Challenge UK Leaderboard. The leaderboard also includes observations made across the UK, so not in the CNC participating areas.

Observations that are included are those made between Friday 28 April and Monday 1 May 2023. When collating the results the figures were taken as at 9 am, local time, on Monday 8 May in each respective country. The week following the event was to allow time for observations to be added to iNaturalist and the community to identify observations to the highest level possible at that time.

The UK tally* for the UK cities registered for the City Nature Challenge is as follows:

Total Observations: 78,854

Total Species Recorded: 3,797

Number of Observers: 2,610

(*The tally is declared straight after the CNC weekend and whilst the numbers will change as observations are added after the date and more species are identified, this is the official reported figure for observations, species and observers.)

Worldwide, the most commonly recorded species was Mallard. Garlic Mustard, Common Daisy and Herb Robert topped our tally.

Blackbird, Mallard, Robin and Wood Pigeon topped our bird list. The 7-Spot Ladybird, Garden Snail and Common Carder Bee were also commonly observed. The Orange-Tip was the most observed butterfly.

To view the results in depth and see the current, up to date numbers, the UK City Nature Challenge species list is available on iNaturalistUK.

You can view the collective results from across the world on the Global Leaderboard 2023.

Do you want to take part in 2025?

Would you like to find out more about becoming a City Nature Challenge Organiser for your city in 2025? Complete the sign up form which can be found on the City Nature Challenge participate page to register your interest. Please email the Natural History Consortium team at to let them know you are signing up. They may be able to link you up with other people or groups who want to take part in your local area. They can also offer help and advice on what’s involved.