Joss Carr, from the Biological Recording Company, shares his top tips for getting the most out of City Nature Challenge 2026, a four-day long global bioblitz organised through iNaturalist in which cities around the world compete to see who can document the most observations and species of wildlife. This year’s competition runs from April 24th–April 27th 2026.
The four-day weekend of City Nature Challenge every April has, for the past two years in which I’ve taken part, marked simultaneously the most fun yet chaotic episode of wildlife recording in my yearly calendar. City Nature Challenge, for those not already in the know, is a friendly competition between cities around the world, taking place over a long weekend at the end of April, during which people go outside and see who can document the most observations and species of wildlife. The competition is both local (between individuals in a city), national (e.g. between cities in the UK) and global (between cities in the world). It’s so much fun.
Deliberately timed to coincide with the onset of ‘spring proper’ in the Northern Hemisphere, it’s the perfect time to be outside recording wildlife – flowers are blooming, birds are calling, flying insects are out on the wing, and bashing a bug net through any patch of vegetation yields more invertebrates than you’ll know what to do with. It’s also dead easy to take part.
The initiative is organised through the biodiversity citizen science platform iNaturalist. If you go outside and make wildlife observations using iNaturalist during the City Nature Challenge dates, your observations will automatically count towards it – simple as that. You can then view the national and global leaderboards on the iNaturalist website to see whereabouts in the rankings you, and your city, stack up. Plus, iNaturalist records that meet certain criteria1 flow onwards to iRecord and GiGL, so your records do all the usual good stuff of contributing towards biodiversity science and conservation. What’s not to love?
City Nature Challenge 2025
- 19,352 total observations
- 662 people took part
- Over 1,600 species recorded!
The City Nature Challenge (or CNC) was originally conceived in 2016 as a friendly competition between the Natural History Museum of Los Angeles County and the California Academy of Sciences (CAS) in San Francisco. Today, the challenge has grown to now involve hundreds of cities around the world, from Cochabamba to Christchurch and Houston to Hyderabad, hundreds of bioblitz events are held, and top competitors rack up thousands of wildlife observations. And London is no exception. In last year’s competition, Greater London edged out the ‘Chester Region’ to come out on top for number of total observations in the UK (19,352 vs. 19,118) in a nail-biting finish, 662 people took part in total across the capital and as a city we collectively observed around 1,600 species!
How to Take Part
This year’s competition runs from the 24th–27th April. Loads of green spaces, nature reserves, and community groups will be running BioBlitz events to take part in, so keep an eye out for these (a list will be available on the Natural History Museum’s website soon[BG2.1]). Even if there aren’t events near you, grab some friends and go out in your local park, garden or nature reserve – you can take part from anywhere.
Now – my top tips for getting the most out of the CNC weekend. As someone who (a) has put my body on the line for CNC two years in a row now to rack up 1,842 and 2,273 observations in 2024 and 2025 respectively (last year I was outside recording for 10 hours each day Friday through Monday!), (b) is totally obsessed with iNaturalist – even writing my recent Master’s thesis all about it, and (c) is a newly minted ‘iNaturalist ambassador’, I feel I am at least somewhat qualified to give this advice. So, what do I recommend?
Top Tip #1 – Take good photos!
One of the fantastic things about iNaturalist is that it lets you upload observations of species you don’t yet recognise. You can take a photo of an unfamiliar wildflower, or beetle, or mushroom, and either through iNaturalist’s in-built ‘computer vision’ image recognition software, or with the help of the amazing community of other naturalists on the platform, you can learn the name of what you saw. In this scenario especially – but in general too – it is super important to take a good suite of photos of your target organism. A single blurry shot of a plant or insect taken at a distance is very unlikely to yield a species-level identification. Instead, take good quality, well-focused photos from multiple angles. If it’s a plant you’re photographing, take photos of the flowers, leaves, fruits, stem, and the whole plant in context. If it’s an insect, try and get photos from the top down and of its underside, if possible. Provided such photos, the likelihood of getting a species-level identification is much higher. But also, don’t be put off if your observation can’t be identified to species level.
Top Tip #2 – Sort out your licenses!
This is a bit technical but very important. The default license for records on iNaturalist is CC-BY-NC, or, in common English, a ‘creative common non-commercial attribution license’. This is technical lingo for “people can only use your records if it’s for a non-commercial purpose and if they give you credit”. This sounds good in principle, right? But in practice – very bad. Local Environmental Record Centres, like our beloved GiGL, need to generate income through commercial activities, even if they operate as non-profit organisations. If you don’t change your license from the default, GiGL cannot use your data. You don’t want to see all your hard work from CNC go to waste, do you? So go into your settings and change your default license to either CC-0 (public domain) or CC-BY (creative commons by attribution). That way your data is free as a bird!
Top Tip #3 – Provide your real name
In the UK recording context, being able to link records to the recorders who made them is a matter of high importance. To do this requires knowing the recorder’s real name. That might sound like information that would obviously be provided, but in fact on a platform like iNaturalist you can get by with just a username instead. Unfortunately, many recording scheme organisers – volunteers who collate records for particular taxonomic groups (e.g. hoverflies or lichens) – won’t accept records if they come from ‘fluffybunny372’. So, you need to let them know your real name. Fortunately, on iNaturalist, you can provide your real name by entering it under ‘Display Name’ in Settings. Once provided here, it’s this name that will be shared alongside your records when they’re exported onwards to iRecord and so on.
Top Tip #4 – Don’t ‘blind agree’
When you are lucky enough to receive an identification from another iNaturalist user on one of your observations, it can be very tempting to hit the ‘agree’ button as a way of saying ‘thank you, I trust that you are correct’. It is very important that you don’t do this. iNaturalist uses a community identification system wherein every user’s vote is worth 1, and every user’s identifications represent their best knowledge of that species at the given time. By ‘blind agreeing’ with other users, you break that system by bolstering another user’s opinion and making it worth 2. What happens if they’re then wrong? Even users who appear to be total experts in their field make mistakes.
Instead of ‘blind agreeing’, let your own identifications represent your best knowledge at the time. If you are ‘corrected’ by someone who seems more knowledgeable than yourself, you can always ‘withdraw’ your original identification so the observation’s overall identification switches to the new one provided. Also, do not be afraid to provide ‘coarse’ identifications for organisms you don’t recognise. It’s perfectly acceptable to upload a photo of an unknown plant as just ‘plants’ (Kingdom: Plantae), or an unknown beetle as just ‘beetles’ (Order: Coleoptera). These observations can then be found and their identification refined by other users who are specialists in those groups of species.
Top Tip #5 – Location, location, location
This is an important one. When making records on iNaturalist from your phone, a location is automatically provided based on your phone’s internal GPS unit, and this is attached to the observation. This works well in theory but is not very consistent in practice. Constant variations in satellite signal can fling your phone’s perceived location hundreds of metres away from your true location (as you’ll know if you’ve ever tried to use Google Maps in a forest). Before uploading records, then, always double check your location data is correct. Is the provided pin where you actually were? If not, adjust it so it’s correct. At the same time, make sure to provide an appropriate site name in the ‘locality notes’ field. iNaturalist has a tendency to provide rather random or non-specific site names in situations where more appropriate site names are obvious. For example, if recording on Hampstead Heath, iNaturalist might suggest the site name ‘England, GB’ or ‘Number 4 Pond, London, England, GB’ when the much more appropriate ‘Hampstead Heath, London, UK’ is the logical best choice.
If you want to get more into the nitty-gritty of making high quality observations on iNaturalist, I’ve written an extensive journal post on the topic which you can find here: https://www.inaturalist.org/journal/josscarr/100039. Other than that – I hope you enjoy the City Nature Challenge weekend. Get out there and observe some wildlife with your friends and family, and let’s see if we can take home gold for London for the second year in a row!
- To flow onwards to iRecord – and then to Local Environmental Records Centres like GiGL – iNaturalist records must (1) be within the UK, Isle of Man, or Channel Islands, (2) be of a species known to occur in the UK, (3) be ‘Research Grade’, and (4) have a license that permits sharing (ideally CC-0 or CC-BY). ↩︎