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The City Nature Challenge is a yearly community science event for folks in cities all over the world to observe and document biodiversity in their own backyards, and 2025 was the 10-year anniversary. To participate, people make observations of any organism – plant, animal, insect and more – on iNaturalist for a few days in late April to early May. This is followed by a short identification phase – where a community of naturalists work on identifying all species observed. The biodiversity data crowd-sourced through iNaturalist contributes important information to scientists and land managers.

In the Denver-Boulder metro area, more than 9,714 observations were submitted by 764 people of 1,260 species! We nearly doubled our number of observations and observers compared to 2024, and we broke our previous record in 2020 of ~7,000. This year, our most observed species was Chokecherry ( Prunus virginiana ). Fun species observed included a silver fox , long-eared owl , Abert’s squirrel , bobcat , prairie violet , beaver , black-crowned night heron , little brown bat , American mink , elk , moose , Northern Harrier and black bear . We even had 145 research-grade observations of 26 species that are listed as rare, endangered, or threatened by NatureServe or the U.S. Fish and Wildlife Service (over twice as many as last year).

For 2025’s global challenge, there were 3.3 million observations of almost 74,000 species made by 103,000 people from over 62 countries around the world. This brings the total number of observations made during the past 10 years to almost 13 million! The leading city for numbers of observations, species, and observers was La Paz, Bolivia.

Thank you to everyone who participated in this year’s City Nature Challenge. We are looking forward to participating with you next year.

Shout out to the winners of the Denver-Boulder City Nature Challenge: Most observations: @Phyllisholst with 405 observations of 150 species Most identifications: @Andershastings with 2,265 observations

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Denver-Boulder City Nature Challenge Sets New Record in 2025

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