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City Nature Challenge

What’s the first thing that comes to mind on hearing the word “nature”? A big National Park such as Yellowstone or the Smokey Mountains? May a jungle such as the Amazon Basin or the wilds of Borneo?  Well, I have good news for you: You can enjoy nature in your own backyard and be part of a worldwide competition. The City Nature Challenge, or CNC, is a great way to observe nature all around you.

What is the CNC?

The City Nature Challenge, or CNC, is a worldwide effort to document biodiversity in and around cities! Biodiversity describes the diversity or variety of life, be it in a specific habitat or in a larger view like a whole forest or even the whole world. An area with high biodiversity has many different kinds of life, or different species of organisms. A bioblitz is an activity where people document the biodiversity of an area at a specific point in time. A bioblitz gives a great snapshot of what’s there right then! The CNC is a four day bioblitz in cities around the world, followed by six days of identifying what was found. More on this later…

A lot of people think they need to go “away” to experience nature, but nature is all around us! Nature can be found right in your own backyard; even if you don’t have a backyard, wild things are growing out of sidewalk cracks, flying overhead, or crawling over fenceposts. The CNC is intended to help people discover that they are surrounded by natural things, to give a resource to document what those things are, and to offer motivation to learn about their natural environment.

How do you participate in the CNC?

The CNC uses the platform iNaturalist. INaturalist is a website or phone application where users can submit an observation of a wild or natural organism, associated with a time, date, and location stamp, and then the community of people on the site can help identify the observed species. It’s a great way for individuals to engage with nature, even if they don’t know what they’re looking at. An observation in iNaturalist is the set of pictures or sound clips submitted in reference to a single occurrence of an organism at a specific time and place. For example, someone can submit an observation of a wildflower just starting to emerge in their front yard in March, and then submit a new, separate observation of the same wildflower in the peak of summer. These would be two separate observations since they are two distinct times, even though it is referring to the same organism. Observing the same species at different times of the year is actually a really useful way for scientists to see how species react to changing seasons. This could also provide long term evidence for changing life cycles and behaviors, such as plants blooming earlier or later in the season on average than 10 years ago. The CNC is a great example of a concerted effort worldwide to document biodiversity at the same time every year! So how did the CNC come to be?

CNC past and future

The CNC started in 2016 as a friendly competition between San Francisco and Los Angeles to see which city could document the most biodiversity in their urban environment within a week. The Boston Area, along with 13 other cities in the US, joined the competition in 2017. The same year, the observation period changed to just 4 days, immediately followed by an identification focused few days. Over 4000 people across the country were involved in submitting observations in their areas on iNaturalist for the 2017 CNC, identifying 8,600 species! By 2018, the CNC went international and has continued to grow ever since. In 2018, the Boston Area even came in 3rd place out of 68 cities in the world for the number of iNat observers who participated- we were just shy of 1000 observers and clocked in at 992. The competition got stiffer as more and more cities joined in on the fun, so even though in 2019 we had a whopping 1107 participants, we came in 10th for participants out of 159 cities. However, that year had more than 35,000 participants across the world- so 10th place maybe isn’t that bad! 2020 was a bit of a different year for the CNC, as the global COVID-19 pandemic prevented people and organizations from hosting events and gathering in person for guided walks or programs. In response, the CNC was advertised as a collaborative celebration instead of a challenge, taking pressure off of people and organizers, and promoting health and safety. The Boston Area still turned out strong, with 1071 observers putting us in 7th place, just barely squeaking past the Triangle Area of North Carolina which had 1070 observers!

The Boston Area is hard pressed to get into the top spots for number of observations or individual species though. The CNC is international and the goal is for it to take place at the same time for everyone! Since it comes during the still early/ mid stretches of the spring for us here in the northeast United States, there aren’t as many species that are out, active, or visible for us. In 2019, we had an impressive 20,000 observations, but all the cities in the top 10 had over 30,000! Our confirmed species here in the Boston Area has continued to grow with each passing year though, from 1,321 species in 2018, to 1,439 in 2019, to 1,672 in 2020- even though we had fewer individual observations and observers in 2020! Even still, we only came in 20th place for number of species in 2020, as the top 11 cities all had over 2,000 species observed. 

In 2021 as we continue to promote health and safety, and continue avoiding gathering in groups due to the ongoing COVID-19 pandemic, we can still work towards increasing our CNC numbers! Let’s get 1200 participants, back to 20,000 observations, and identify 1800 species for the Boston Area!

When is the 2021 CNC?

The 2021 City Nature Challenge is fast approaching, with the observation period to take place April 31- May 3. While taking observations is a critical component of the project, a very important part is identifying all of the observations that have been submitted! May 4- May 9, 2021 is the identification period, where people can go onto iNaturalist and help identify what was seen. Even if you aren’t confident in a species identification, it’s even helpful to identify things labeled as “unknown” to “plant” or “animal” for example. Or, if you’re confident about identifying some species, consider taking some time out of your week to look through the Boston Area 2021 CNC project and share your knowledge in early May!

Why is the CNC important?

Events like the CNC are great opportunities to get the community involved in science. Anyone can participate in taking pictures and uploading them to iNaturalist, and that information can be used by scientists for years to come! INaturalist is a fun and interactive way to see your observations, and those of others, change from “unknown” to a specific species identification. With more eyes on the environment, we’re more likely to find new or different things that individuals in the strict science community might have missed. For the last two years, over 1,100 rare, endangered, or threatened species have been documented in the CNC across the world! This and similar events give a really great pulse of what’s going on in nature, especially in and around cities, and how we may be able to react. 


Join us in the Boston Area in the 2021 City Nature Challenge at the end of April, and watch our numbers climb as we discover biodiversity together. Visit the Boston Area City Nature Challenge Website here ( to learn more, check out this “What is the CNC 2021?” video (, and join our project on iNaturalist here ( To learn more about the global CNC effort, go here ( You can learn how to use iNaturalist with this helpful tutorial (


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