iNaturalist Big Days


Current known record is @gwark on July 13, 2018, with 492 species as iNat counts them!! (511 including non-verifable observation)

Here is a table of all the days over 300 species I know of (additions welcome and strongly encouraged!).

Observer Date Verifiable Species (as iNat counts them)
@gwark 13-Jul-18 492
@gwark 15-Jun-18 404
@reuvenm 13-Jul-19 386

Original Text:

Back on July 1st, I made a special attempt to photograph as many species as I could in one day, and ended up finding just under 400:

I could easily have done a lot more by spending more time and a different strategy. So I’m sure there are some better “big days” out there on iNaturalist. I’m curious to hear about people’s biggest days? What is the record number of species anyone has photographed in a day?


I’m guessing my record is 125-150. It would be neat if the site could generate that info though.

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The calendar feature does.

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If I want to look by day. But I’d have to page through all my days and years to find my biggest.

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My most is 101. I’ve never actually tried to get as many as possible, so I could probably get more if I tried.

I tried doing the same thing on the same day, for the Canada Day Bioblitz. Unfortunately I could not get out until mid day, so that really impacted my numbers. I’d never gone out before with the express purpose of quantity of records. I also approached it with a seconday goal of doing my level best not to record trees, as that seemed a shortcut to the 152 goal. In retrospect, maybe I should have recorded them and then just subtracted them from my total.

The biggest issue I hit was that to do it, you need to be a really good plant identifier, or hope that the good plant identifiers see and review your records. Too many of my plants got left unidentified.


Note that the calendar actually doesn’t work if you have more than 200 observations on any given day. It will only count species from 200 observations.


Here is the link to this year’s Canada Day (July 1) Biodiversity Challenge that Chris is referring to and that Reuven was the top contributor to (in both observations and species).
It’s impressive that collectively, across Canada, we were able to document nearly 3,000 species on Canada Day!


Well, I think I just identified several more for you. A bunch of them don’t show the features needed for ID unfortunately.

But yeah, plants are absolutely vital for this. It takes practice just to be able to pick out when something is different. I also specifically targeted a bunch of nearby areas with very different habitats that hold very different species. Including trees - I think I photographed every tree species growing natively within ~15 minutes of my house except Butternut (I definitely walked past at least one), Swamp White Oak (very local, didn’t visit the right areas), Tamarack (the one site isn’t publicly accessible) and probably a couple of willows (which I haven’t learned to identify yet).

I imagine mothing could be comparable for getting a ton of species, which I didn’t do. I think 700+ species in a day would be possible in Ontario if your group included people skilled at plant, moth, and lichen/fungi identification, and you went to a high-quality area. Maybe that’s too optimistic. Mid to late June likely the best time (anyone interested for next year?).


Cheers for that info, didn’t know about that limit.

This is such a great idea! Definitely going to chat to my amateur naturalist friends about this idea… So moths and plants would be the way to do it? What else would people suggest?

My biggest day was a paltry 60 taxa, but that was from snorkelling a reef, so not your normal day! I reckon if you got into particularly biodiverse water you could really ratchet numbers up…


This would definitely be a good motive for iNaatters to improve their plant ID. When I’m doing vegetation surveys at sites in WNY in the middle of summer 150-200 species is typical for a few hours in any site with two or more natural communities present. Some end up closer to 300 given more survey time to find them all, but if you knew where they all were and just wanted to put up a max “big day” number you could do it.


Some ideas:

  • fungi

  • birds (depends very much on time of year and habitat but I can easily get 30-35 [more like 40-50 with actual walking and effort] species during migration just from my house without really trying)

  • don’t forget to include signs like: leaf mines, galls, feathers, tracks, scat, etc.

  • moths can be helpful especially if you try to focus on abundant micros

  • microfauna and flora of all kinds!


I think this is key as well, I specifically went to a series of places, that with 1 exception I had never been to before, so I din’t know what was present, or where I could find any specific targets.

It also takes real discipline to photograph and document stuff you would normally walk past.


So far, 76 last year, and 51 this year. Interestingly, both days were in places I had never been before.

Now I wasn’t trying for volume those days. I wonder how well I could do in my regular haunts if I really tried…

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Most observations - just shy of 2 hours
94 observations 78 taxa 66 species 14 life list firsts

Most life list firsts first day as well
21 observations 18 taxa 18 species 65 life list firsts :) (Since first day, all higher leveled taxa tripped when lower level taxa picked, plus wrong guesses)

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I think that 700 is doable if mothing and sweep netting is included. To make sure very few of the sweep netted bugs escape before being photographed, perhaps an ice pack could be utilized prior to photography to cool the bugs.

Since time is an issue, the songs and calls of the birds, amphibians and orthoptera could be recorded instead of attempting a photograph to save time.

It would be quite a grind to process that many observations. My own maximum is a paltry 37 observations in a single day, but since I am not done going through that day it actual number of observations with likely be between 50 to 60 observations.

Last year (2018) I did two different big day attempts where I live in Sitka, Alaska. The first was on June 15 and the second on July 13

I ended up with over 400 unique species or higher taxa on the first attempt, but realized there were some ways I could improve my efficiency of getting to different habitats to cover more ground, and made it to over 500 on the second attempt.

I live on the coast, and there’s a lot of diversity in the intertidal, so my days were chosen to correspond with good low tides during the summer when more plants are out and easily identifiable. I didn’t manage to maximize the potential of low tide (suboptimal timing) either day, so that could be a place for improvement.

I think in principle it should be possible to get to 1000 species here where I live in one day. However, in addition to knowing the local vascular plants well (which I already do), I will need to have a solid knowledge of lichens and bryophytes, as well as a better knowledge of the intertidal critters and algae. This means not just the ability to recognize them quickly in the field, but also awareness of how/where to find them.

I think it’s very important to already know/recognize the majority what you are observing, as that makes for much more efficient observing. You can just target things you know are species, and not spend a lot of time hunting around for things that might be different (plus you’re less likely to have lots of redundant observations of the same thing).

I was pretty much only out during daylight (or dusk) hours, but days are long here in the summer, and I was pretty wiped out by the end of each (and that was before I needed to process photos and/or add names to iNaturalist observations). I suspect I’ll try again at some point in the future, but probably not until after I get a better handle on at least one of intertidal organisms, bryophtes, and/or lichens.


Just for fun, I tried to think through the best approach for getting as many species as possible in a day, and came up with this:

Run several moth sheets with miscellaneous lights (UV, mercury vapor) starting at dusk the evening before; at midnight of the Big Day, start photographing everything that’s on them already or comes to them. Intersperse with roaming about for night insects not attracted to light and other night creatures. Collect water samples from nearby water sources and alternate the outdoor patrols with looking for microorganisms under a microscope (so as to get some of these without using up daylight hours). Hopefully catch a nap during the night so your eyes won’t burn out before the day is over!

When dawn approaches, start hiking. Try to record bird calls. As it gets light enough, go for anything that moves—birds, herps, mammals, arthropods, etc. When there are none of these to be seen, photograph all the plants, fungi, lichens, slime molds, and so on that you can find. Check under rocks and logs, sift through leaf litter, etc. Hop around from one location to another, trying to balance the lesser efficiency of time spent travelling against the benefits of varied spots. Altitude variation would be great, if possible, and some riparian habitats.

At low tide, get to the shore and photo all the beach/tide pool creatures, algae, seashells, etc. you can find (yes, you’re starting near a beach—a tropical one!). Next, snorkel the shoreline photographing all the fish, coral, sponges, echinoderms, and so on. Then do a dive or two to get the species that are down deeper. Return to land and continue working on plants/everything that moves until it gets dark, and return to your moth sheet/roaming/microscope approach (working a different area than the previous night) until midnight rolls around again!

Of course, to really optimize like this would involve finding a good locale ahead of time, with multiple habitat types on land; good tide pools, reef, and maybe muck diving quickly accessible from the same area; and preferably at least two base buildings, one per night, where you could set up a microscope, access water for microorganisms, and get a lot of insects at your moth sheets. You’d also need good equipment, including a microscope setup with the ability to take photos, a good underwater camera (the better the camera, the more species you can get from each photo), snorkeling and scuba gear and access to a boat, moth lights, etc.

I’m sure adjustments could be made to get taxa that I haven’t considered. Also, a group of specialists in different fields could take this on together, helping each other see species that one observer might overlook, or could act as a support team to help a single observer get as many species as possible.

More theoretical than practical, but fun to think about! I wonder how many species a person could find in one day, in a biodiverse spot, with this approach?


In a biodiverse area, the speed at which you can find and photograph organisms is critical. Some species will just take too long to justify it.

Spending five minutes trying to catch a stubborn dragonfly is too much. If you couldn’t get that dragonfly on the second swing forget it.

A sweep net or beating sheet that can find dozens of species in seconds is balanced by the time required to get good macros possibly from many different angles.

I have had occasions where I have caught a hover fly in a net very fast, but I spent more time taking it out of the net and unless it is an easy ID, you need to photograph it from the top, sides and front while holding it in your fingers or in a little plastic bottle.

That bring up a point – what rules would you set up for your count. Would you use a net? Would you go as far as making specimens of athropods (some species require microscopic examination)? Attract birds with recordings or not?

As far as moths are concerned, sugaring a few trees could help. Night-vision goggles could find a few nocturnal animals, I wouldn’t bother at my latitude though (46 degrees north).