City Nature Challenge

Participate in the City Nature Challenge

April 24-27, 2026

Lexington’s Conservation Division and Lexington Living Landscapes are teaming up to promote Lexington’s participation in the City Nature Challenge. The Challenge is a “bioblitz”, an event that focuses on finding and identifying as many species as possible in a specific area over a short period of time, involving volunteer scientists as well as families, students, teachers, and other members of the community. The City Nature Challenge was launched in 2016 and quickly became a worldwide phenomenon. Last year, more than 100,000 people in 669 participating urban areas on six continents recorded more than 3 million observations!

Urban biodiversity matters (see side bar). Which is where you come in! The City Nature Challenge is an easy and fun way for people without PhD’s to help scientists understand the distribution and trends in urban and suburban biodiversity. All you need to participate is a smartphone loaded with the iNaturalist app and a little time to make observations between April 24-27.

Lexington is part of the City Nature Challenge in two ways. Officially we are part of the Boston Area CNC, and our data will contribute to their records. In addition, informally we’ve created a separate Lexington CNC that will keep track of all species observations in town, which will add to our records from when we participated from 2022-2024.

Why care about urban biodiversity?

The earth is in the midst of a biodiversity crisis, and the evidence keeps piling up every day. In 2019 the U.N. estimated that one million animal and plant species are threatened with extinction, many within decades, more than ever before in human history. The population of North American birds is estimated to have declined by three billion (almost 30%) since 1970. The Living Planet Index estimated in 2024 that wildlife populations across the globe have declined an average of 73% since 1970. It’s common to talk about how globally we’re in the midst of a sixth mass extinction, with many causes: habitat loss, climate change, pollution, invasive species, and overharvesting, among others.

One might think that the battle to save our biodiversity will be won or lost in rural areas and nature reserves, but urban and suburban areas turn out to be surprisingly biodiverse, and can be key contributors in the fight to halt the decline. These areas have lots of small pockets of diverse habitat that act as refuges, sometimes for species at risk in the rural landscape, or serve as migratory stopovers. The urban biodiversity of some wildlife groups may equal or exceed that of the surrounding countryside. Urban biodiversity matters.

Lets participate together! Just follow these simple steps:

Download the iNaturalist app to your smartphone. There’s one version for Android phones and two for Apple (iOS) phones; choose the more recent one, not “iNaturalist Classic.” They’re free.

Learn how to use the app. You have three options:

1. Follow the instructions on the Boston Area CNC website.

2. Attend the Zoom webinar on Thursday, April 23, at 7:00 pm, when Lexington resident and iNaturalist expert Barbara Katzenberg will walk us through how to record observations for the City Nature Challenge. Details under Upcoming Events.

3. Attend one of the conservation area walks on Saturday, April 25th (Paint Mine Conservation Area, 1:00 – 2:30 pm) and Sunday, April 26th (Dunback Meadow Conservation Area, 12:00 – 1:30 pm). We’ll spend 1½ hours walking and making observations on our smartphones. Come even if you don’t intend to make official observations yourself; help us find plants and animals to record, and see how the process works. Details below Upcoming Events.

Then if you wish, record more observations on your own, in your backyard, neighborhood, or local conservation area. There’s one key limitation: the CNC only records observations of wild organisms (so no pets, animals in a zoo/aquarium, plants in your garden, potted plants, plants at a botanical garden, people, etc.). Insects in your backyard are great, as are volunteer plants, but not ones you planted, even if native. Observations must be made between April 24-27 to be counted in the official City Nature Challenge, and all uploaded observations made within Lexington will be automatically included in the City Nature Challenge.

You do not have to identify what you record, though if you can, that’s helpful. iNaturalist relies on a community of experts to review observations and provide identifications; that happens in a second time window from April 28 – May 10. The challenge during the April 24-27 window is to record as many good observations as we can; learn how at one of the learning opportunities mentioned above.

So join us, learn about Lexington’s biodiversity, and have fun! Questions? Email lexlivingland@gmail.com.

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