More than 100,000 people participated in the City Nature Challenge 2025 in 650 cities worldwide, making 3,310,131 observations.
If you close your eyes and I ask you to picture a place where you can find wild things, it is likely that your mind will take you to a far-off place. You might be picturing a national park with open fields or towering forests, rushing waters, mountains, and valleys, with no humans in sight. Sure, many wild things live away from human settlements, however, if we take a moment to pay just a bit more attention to urban areas, you might be surprised just how much you can find. Rabbits grazing on grass in city parks, lichens covering trees lining a campus walkway, birds building nests in backyards, sea slugs in small tidal pools underneath the boardwalk, mushrooms growing out of a small patch of dirt beside a storm drain, bees visiting flowers on balconies, ants creating mini super-highways along cracks in the sidewalk… There is plenty of life here too.
In fact, our cities are teeming with nature and wild things, and sometimes, we forget to notice. So, how do we fix that? Well, what better way to bring our attention to the flora and fauna around us than through a little healthy competition? Enter The City Nature Challenge.
The City Nature Challenge (CNC for short) started back in 2016 – on the first Citizen Science Day in the USA – when Lila Higgins from the Natural History Museum of Los Angeles County and Alison Young and Rebecca Johnson from the California Academy of Sciences decided to take the spirit of competition between two cities and turn it into a driving force for citizen science, conservation, and community. This friendly competition started as a way to get everyday people involved in citizen science by recording observations of wild flora and fauna in urban areas, as well as get them excited about inner-city biodiversity. By 2018, it became a global event, and the participation goes up every year!
So, how does it work? Participants can take photos of wild things within (and around) cities and upload them as observations to the iNaturalist app, where it can later be identified by other community members. During the challenge, groups go out and see which city can make the most observations and capture the most diversity in their city. Ideal observations are clear pictures from multiple angles, such as the bark, leaves, and flowers of a tree in one observation, but any observations that you can get of wild things around your city can help!
Co-founder of the CNC and current Director of Outreach Programs Alison Young commented on the importance of the CNC by stating that challenges like this one can really help people realize that you do not have to go out to a national park or drive far away to enjoy nature and wildlife, because there is plenty of life within our cities and towns as well! Additionally, the observations made during the competition can be, and are, used by scientists who are researching inner city biodiversity and ecology. In fact, multiple research papers have been published over the years using data from the CNC.
This year, the City Nature Challenge 2025 had an amazing turnout. Across 650 cities worldwide, more than 100,000 people took part, making 3,310,131 observations! Participants recorded 73,765 different species that were identified with the help of 23,196 dedicated identifiers. Alison and her team were thrilled to see even more participants than last year. The high turnout was partly thanks to the iNaturalist team really coming on as a promoter of the event, but it is also a trend, as they have seen nothing but growth in the 10 years since starting the challenge.
Every year, there are interesting and exciting observations that shock the world (some of the highlights from this year can be seen here). In April 2025, one observation that really stood out was the recording of a species that hadn’t been seen since it was first described, more than 160 years ago! This incredible little nudibranch, a kind of charismatic sea slug, was found in Visakhapatnam, India. The species Phidiana unilineata was basically re-discovered thanks to an observation by CNC participant @srichakrapranav on iNaturalist. This incredible observation is just one example of how much good this challenge can do in only a few short days.
According to Alison, the CNC’s future looks bright. The teams are confident that participation will continue to grow as the word spreads and more cities join in on the fun. This next year, they also want to focus on growing the challenge to function as an annual global biodiversity survey, really optimizing observations for their use in current and future biodiversity research.
For those wanting to get involved next year, there is a form for new organizers and plenty of information on the website. Anyone who wants to participate can find a group already doing so, become an organizer for their own city, or reach out to local natural history museums, universities, or other groups to help form part of the City Nature Challenge for 2026. They are also hoping for more people to help out as identifiers in the coming years, as that tends to be a bit of a bottleneck in the program. Alison really emphasizes that you do not have to be an expert to help out, even marking unknown things as a “plant” or labeling the order of insects can go a long way in helping others identify observations to a higher level. The more people who help out, the more the CNC can reach its full potential.
Though it is almost a year away, Alison encourages people to start preparing for next year right away by getting out and practicing making observations with the iNaturalist app, finding interesting spots around your city where you can find wild plants and animals to observe for next year, and just enjoying a bit of your urban flora and fauna all year long.
The City Nature Challenge, which started out as a friendly competition and a small citizen science initiative, has quickly grown into a global event. This bioblitz-like competition fosters the awareness and protection of inner-city biodiversity and aids in the collection of important biodiversity data for research now and as a crucial baseline for the future. We hope to see you join in next year!
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