Denver-Boulder Bioblitz: April 30 – May 9, 2021

Which city has the most nature? 

The 2021 City Nature Challenge will help us find out! Last year Denver Metro Area competed against 244 cities throughout the globe and came up with some impressive numbers: 

  • 5,847 total observations
  • 838 plant and wildlife species identified
  • 443 observers
  • 373 identifiers

Throughout the globe, 41,165 observers from 244 cities collected 814,258 observations of 32,500+ species (including more than 1,300 rare/endangered/threatened species) during the four-day bioblitz! Read more about the 2020 results and view some of the standout observations from the Denver-Boulder region.

Help us show the world how biodiverse our region is by documenting observations of wild plants and animals from April 30 – May 3, 2021! Document nature in your home, backyard, neighborhood, or nearby parks or trails during off hours, and upload your observations to iNaturalist, an online platform for citizen scientists. Any observations of plants, animals, and fungus found throughout our boundary will count.

The Denver-Boulder City Nature Challenge is organized by

About the City Nature Challenge

The City Nature Challenge (CNC) is an ongoing project to document urban biodiversity and engage city residents in the nature around them. The project is framed as a competition between cities to see which can make the most observations, identify the most species, or have the most participants. The program was started in 2016 by the Natural History Museum of Los Angeles and the California Academy of Sciences as a competition between Los Angeles and San Francisco. 

The 2021 City Nature Challenge will take place from April 30– May 9. The first four days, April 30 – May 3, are the days that observations will be collected (aka the Bioblitz), and the last six days, May 4 – May 9, are when those observations will be identified and verified. Participants can also continue to upload observations during this six-day period as long as the sightings took place during April 30 – May 3.

Where can you go to make observations in Denver-Boulder?

The Denver-Boulder Metropolitan Area City Nature Challenge encompasses Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, and Jefferson Counties.

In short: anywhere wild nature exists! Document wild nature in places such as:

  • Your backyard and neighborhood
  • City/neighborhood parks
  • Open space, mountain parks, and natural areas
  • State parks
  • Urban areas
  • And more!

In light of the COVID-19 pandemic, we ask that participants please be respectful of all people and wildlife around you, follow all social distancing requirements, and abide by local land and facility closures. Avoid overcrowded areas and instead visit popular trails during off days/times. 

Remember that your own backyard is teeming with wild nature! Your home is a complex ecosystem and contributor to the larger landscape. Be sure to spend lots of time in your yard and/or neighborhood exploring the diversity of plants, birds, insects, mammals, and other wildlife coming through at all hours. You might meet some neighbors you never knew you had!

*If you are concerned about revealing the location of a sensitive organism (or where your house is), you can hide the exact location from the public by changing the “geoprivacy” of the observation to “obscured.”

Why should you participate?

There is nature all around us, even in our cities! Knowing what species are here and where they are helps us study and protect them, but the ONLY way to effectively do that is by working together (scientists, land managers, community members, you name it) to find and document nature in our area. By participating in the CNC, not only do you learn more about local nature, but you can also make our urban areas a better place – for you and other species!

Get involved!

There are many ways that you can get involved with various levels of commitment. Some suggestions are listed below. If you are interested in contributing in any way, do not hesitate to contact us!

Spread the word

Whether it’s informing your email lists, posting on your Facebook or Twitter accounts, distributing some of our posters and flyers, or just telling your friends, it all helps. The more promotion CNC has the more successful it will be!

Offer extra credit to students

We realize the CNC takes place right before finals week for many universities in the area. Offer extra credit to your students by encouraging them to take a study break to get out into nature and contribute to the Denver-Boulder CNC.

Host a virtual event

Teach others how to use iNaturalist, challenge others to a friendly competition, host a City Nature Challenge presentation or webinar…the possibilities are endless!

Make it a class project

If you’re an educator, you could create an assignment to get your students outside and teach them the value of citizen science. They don’t even have to put their phones down!

Make observations

Whenever you’re outside between April 30 – May 3, whether you’re on a hike, walking the dog, or taking the trash out, pause a moment to observe the nature around you. You might discover something you’ve never noticed before!

Sponsor the Denver-Boulder CNC

Make a donation or sponsor a prize for iNaturalist participants. We’re looking for items like binoculars, a variety of outdoor gear, nature guide books, outdoor attire, gift cards, and more.

Make species identifications

We can only count observations toward our project if they are identified down to the species level by 11:59pm on May 3. We will need lots of help assigning those IDs as the observations roll in! You could do this in your PJs from your couch, or you could make it a social event by planning a virtual ID party. 

2020 Event & Outreach Partners

Bird Conservancy of the Rockies

Bluff Lake Nature Center

Boulder County Parks & Open Space

Butterfly Pavilion

City of Aurora Open Space & Natural Resources

City of Boulder Open Space & Mountain Parks

High Line Canal Conservancy

Majestic View Nature Center

Regis University

University of Colorado Boulder

How to contribute observations


*While any observation will count, we encourage you to only upload wild and non-captive observations.  Please, no photos of people, pets, or potted-plants.*

*If you are concerned about revealing the location of a sensitive organism (or where your house is), you can hide the exact location from the public by changing the “geoprivacy” of the observation to “obscured.*

City Nature Challenge Events

March 30, 6:30-7:30pm: Louisville & Lafayette Open Space Webinar

Webinar led by Louisville and Lafayette Open Space divisions

Learn how to use iNaturalist, a free interactive tool to explore, document, and conserve biodiversity in your backyard and around the world. Once an iNaturalist user, you can participate in the Spring 2021 City Nature Challenge, a global effort with a local component in the open spaces, parks, and backyards of Louisville and Lafayette!

This program is jointly hosted by the Louisville and Lafayette Open Space divisions. Louisville Senior Natural Resource Specialist, Dr. Steve Roels, will introduce the iNaturalist platform and how aspiring citizen scientists can get started exploring their communities. Also inspiring local residents to become citizen scientists will be: 1) Lafayette resident and author of the Smithsonian Field Guide to the Birds of North America, Ted Floyd; 2) Ted’s daughter and Centaurus High School student, Hannah Floyd; and 3) Dave Sutherland, retired naturalist from Boulder City Open Space and Mountain Parks!

After attending the webinar, you will be prepared to join the free City Nature Challenge, running April 30–May 9.

To register, visit:

Registered participants will receive an email through EventBrite two days prior to event, which will contain the Zoom link to attend.  Please make sure to check your email.