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THOUGH THE CALENDAR says that spring started on March 20, the many clues that nature offers to those who watch and listen add up to a more complex and layered unfolding over time. Inspired by a new book called “Phenology,” a primer on the why and how of taking sharper notice of what happens when outside, I’m learning to read nature’s signals better and becoming what its author calls “an everyday phenologist,” which feels really good and also allows a gardener like me to share my observations with science.
Today’s guest is Theresa Crimmins, author of the new book and Director of the USA National Phenology Network, which since 2009 through its community science app called Nature’s Notebook, has collected more than 40 million records of phenological data that can help in natural resource management and decision-making, especially critical in a time of a fast-changing climate. Theresa is a plant ecologist and an associate professor at the University of Arizona, where the network is based. (Above, a shadbush or Amelanchier flower bud starting to swell; photo by Ellen G. Denny.)
Plus: Enter to win a copy of the new book by commenting in the box near the bottom of the page.
Read along as you listen to the March 24, 2025 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify (and browse my archive of podcasts here).
phenology, with theresa crimmins
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Margaret Roach: I read your book, “Phenology” [affiliate link], and we spoke a couple of weeks ago for a “New York Times” garden column, and so I’ve gotten to know more and more and more [laughter], and I’ve got the bug of being an everyday phenologist now. Since we collaborated on the Times story, I’ve really kind of been looking and listening in my very familiar, longtime garden with sort of enhanced eyes and ears this pre-spring, this early spring, and wondering as the headline of the Times story said, “Is It Spring Yet?” [Laughter.] And that’s what you kind of have been doing, too, in your home in Arizona.
Theresa Crimmins: Absolutely. And yeah, I love how you phrased that, with enhanced eyes and ears, because that is something that I have observed that has evolved in Me too. I’ve been with the network since its beginning, back in actually 2007, that was when our network was established. But like you said, we did launch Nature’s Notebook, the observation platform, in 2009. And at the get-go, I participated in our new observation platform basically so that I could tell other people how to do it [laughter], and to make the very first materials for a series of videos and some content for our website. And so I was just going through the mechanics of like, oh, how do I know when this flower is open, and how do I know when these leaves are fully expanded?
And I’ve been doing it ever since, because I have experienced so much more in the practice of going out regularly and looking at the same tree in my backyard over and over again. I’ve seen so much, it’s revealed to me just so much beauty and botanical nuance in the flowers, these trumpet-shaped flowers on this desert willow tree that just have gotten so big in my yard. I’ve seen so many organisms, other things buried in, not buried in but tucked into the flowers in the tree. And I’ve just really actually come to view these other beings in my yard as friends. Honestly, it has really turned into deep, deep relationships. And so yeah, it’s not just for the data, it’s absolutely because it feeds my soul.
Margaret: And I love that, because in the book, even though you’re a scientist and you have all these credentials and expertise, and this is your field of study, you really shared that, the soul-feeding part. And that experience, that emotional experience, also enriched your awareness that it added something for you. And so that’s kind of what’s happening to me because I feel like I know my plants outside; I know who they all are, but I haven’t really looked in the same way.
When we were doing the Times story, we were talking about red maple trees, for instance, which I have some of, and the fact that they have male and female flowers; there are two sexes of flowers. And I thought, “Ooh, I want to go look when that, soon, soon I’m going to go look, I’m going to; which is it?” And we don’t look closely enough a lot of times. And with Nature’s Notebook, if we register and become a user of Nature’s Notebook, the tool, the community science app that the network has, we can also, besides all these good feelings that we’ve been just talking about, and this more intimate knowledge that we’ve just been talking about, we can also make a contribution by saying: This is what I saw today, essentially, by noting our observations, and we are asked to then answer some specific questions about what we saw. [Below, female flowers of red maple; photo by Ellen G. Denny.]
Theresa: Yes, absolutely. And I should probably preface that with, if folks are brand new to Nature’s Notebook, when you first register and get observing, it can feel a little overwhelming because you’re confronted with a whole lot of questions right out of the gate. We’re actually in the midst of revamping our app right now, because we know that can be a barrier. It can be overwhelming to new folks. So by next spring, we should have a much more enhanced, improved observer experience, where you can start at a simple, basic level and then graduate through to more complex questions.
But yes, and so with that in mind, if folks do start and do feel overwhelmed by all of the questions, answer as many or as few as you wish, and all of them are valuable, every single record that we get is a really valuable piece of a huge quilt of data that we’re stitching together across the whole country for almost 2,000 different species of plants and animals now. And we’re starting to really tell stories about when different events, like leaf out or flowering, are occurring in different parts of the country and in different species, and what are the conditions that are associated with those events and how are they changing? And then how those changes actually stand to impact not just ecological functioning, but us directly? There’s a lot of direct impacts to us and our economy, actually, as a consequence of changing phenology.
Margaret: So those changes, those moments of change, the different stages are called phenophases. And you I think maybe it was last December or something, not so long ago, published on the website, something that we can all access called the Phenophase Primer. It’s this massive, beautifully illustrated book essentially about flowering plants specifically, but it takes us in intricate detail through, as I mentioned before, was it a male flower or a female flower or whatever…every detail of every phase of the flowering process in all these different species. And it’s just, again, even though I feel like I know a lot about plants, and I’ve been around them a long time and I’ve made them my life’s work, so to speak, I was blown away. So there’s also a lot of learning for people if they want to dig in deeper. You’re providing a lot of support learning so that they can then answer those questions that you just talked about in a little more informed manner.
Theresa: Yes. We have two primers actually, and they were born out of volunteers’ questions, repeated questions of, “What do you mean? How do I know if this bud has broken?” In some species, a broken bud, a breaking leaf bud, is very clear and apparent. And in others, it is surprising how challenging it is to evaluate that even with the instructions that we provide. So yes, both primers, the first one’s the Botany Primer, and that is really just more of basic botany, an orientation to what are the male parts of the flower, what are the female parts of the flower? When you’re looking at a dogwood, what you might think are petals are actually bracts [photo above by Dave Skinner], they’re not the petals. The flowers of a dogwood are much smaller and the little tiny parts on the inside. And then the second primer that you just mentioned, yeah, the Phenophase Primer, is very in-depth, it’s almost 300 pages chock full of these incredibly detailed photos and so much good information. And I have to give credit, I was not an author on either of these. The women that prepared, especially the Phenophase Primer, just went to extreme levels of detail. And the end result is so phenomenal, and I’m learning so much by paging through it and reading the really informative text. And so yes, I just can’t say enough great things about it. And the wonderful thing is that they’re available; both resources are free for download as PDFs on our website.
Margaret: Yes. So that’s the Phenophase Primer that has the whole detail about all the flowering plants and so forth. Yeah, and it’s funny because you just said that they were phenomenal [laughter], and of course, phenomenon and phenology come from the same root word. Yeah. So that’s good.
This taking notice we’re talking about phenology and you direct the USA National Phenology network, and so it sounds all very scientific and so forth, but this taking notice of the what happens when in sort of all these subtle incarnations in nature was not invented by scientists. It was a practice of Indigenous cultures throughout history, and allowed them to really survive and thrive, yes?
Theresa: Yeah. Yes, yes. I want to make sure that we acknowledge that. Yes, the practice keeping track of when stuff happens seasonally has been part and parcel of human survival since the beginning. And so yes, our ancestors, there’s actually proof of this in cave paintings that date back tens of thousands of years that people were keeping track of when different herds were migrating, because that’s was so necessary for survival. And then in more recent times, there are a lot of these sometimes what are referred to as wives’ tales [laughter], these recommendations of plant peas when … oh, shoot, I can’t remember that one exactly. The one that always comes to mind is plant corn when the oak leaves are the size of a squirrel’s ear or a mouse’s ear, and that we might think that, “Oh, it’s so quaint. How cute is that?”
It has its roots in indigenous cultures. People have for many millennia lived on the land here and used nature signals to cue when to do things. And there’s so much wonderful evidence of this being documented and carefully protected now by different tribes, because it is wisdom and it is cultural knowledge, and it is critically valuable. So absolutely, absolutely don’t like the use of something like wives’ tales as a name for these kinds of knowledge and wisdom. [Above, bud scales unfolding on Magnolia soulangeana flower bud; photo by Ellen G. Denny.]
Margaret: Conventional wisdom at least is a little less nasty sounding than old wives’ tales or whatever. But, and you call them adages, yeah?
Theresa: Yes, for lack of a better term. But now I’m even kind of wishing I would have used wisdom or something like that, because truthfully, it is information that reflects a deep appreciation for why things happen when they do. And these things can be disentangled and kind of explained from a more Western science perspective. The reason why it works to plant your corn seeds when the oak leaves are a particular size is because oaks are responding to temperatures. And it’s an indication that days are long enough and we are past the risk of frost and soil is warm enough that if you put those seeds in the ground, they’re likely to be successful. They won’t freeze. The chutes won’t come up and die. And it’s not too late. It’s sufficiently early that the plants should come, they should bear fruit and give you the corn that you’re seeking before the season is too late.
Margaret: And the adage or whatever, or the wisdom about the peas, was plant pea when the peepers peep, I believe.
Theresa: That’s right. Thank you.
Margaret: And then there’s that one for gardeners that was like prune roses when the forsythia blooms and so forth. So there’s lots of those observations like that that have been made and seem to correlate.
Now speaking of correlations, though, one of the kind of scariest parts of all those 40 million observations you have in Nature’s Notebook, in this giant database and so forth: One of the things that can be noted is that in some cases there are mismatches happening now, plant and animal species that had a relationship maybe are no longer doing that thing that was the heart of the relationship at the same time. And so there’s these, well, not good things, and that’s because they might, the plant and the animal that used to be so connected intimately, might be responding to different triggers or something. Is that what’s going on?
Theresa: Yes, largely, and we don’t have a ton of super-concrete examples of these, mainly because in order to document emerging mismatches requires really careful watching of both species in a relationship ideally over time. And species are dynamic, they’re constantly responding to different cues. And if it’s an animal, they’re trying to adapt, both animals and plants are plastic in their responses, meaning they usually have some flexibility. One way in which we see plasticity is if a year is warmer, typically an individual species will undergo its activity earlier in the year. But different species have different levels of plasticity or flexibility in how much they can track those varying conditions and how much they can shift, really.
And so phenological mismatches are largely something that we wave hands about in the scientific community and argue about how big of a problem it is. But there are some concrete documented cases, and some of the most widely understood ones are in migratory birds and their food sources, because typically long-distance migrants are cued, in the Northern Hemisphere, to come north in the spring by daylength. And so how many hours of daylight are they experiencing? There’s something in their brain that says, O.K., the days are long enough. Now start flying north with the expectation that when they arrive to their breeding grounds in the summer, the food source that they rely upon, which is oftentimes caterpillar larvae, or sorry, larvae for Lepidoptera, moths and that sort of thing will be fat and juicy and abundant on the plants. And so these tired, hungry birds arrive and they’ve got lots of food.
So because they’re cued by daylength, they’re coming north the same time every year. However, as temperatures have warmed in recent decades, plants have started largely undergoing their leaf-out activity earlier in the year. And the insects that rely on those leaves as food sources are likewise following that cue. And they are emerging and they’re hatching eggs earlier, too. And so those larvae that the birds need as food are in years with really early springs, where the plants leaf out very early and the insect eggs hatch very early, in some cases, those birds are arriving and they don’t have a whole lot to eat, because those insects have already undergone various lifecycle stages and moved past when they would be really a good food source for the birds.
And so we’ve seen the birds respond in a number of different ways. Sometimes they just keep on moving north even though they’re tired and hungry; they just have to keep going because they’re trying to find some food. In other cases, we’re seeing less success in breeding and rearing of young, because they just don’t have the fat stores and other resources that they need. And so again, these are more like dotted lines rather than straight lines that we can draw yet. But we are seeing impacts on bird populations, bird numbers, because of these mismatches. And it is what you said, it’s that the interacting species are responding to different cues to initiate activity in the spring, and so they’re not coinciding any longer in the way that they do.
Margaret: I think when we spoke previously, I think you explained to me that just as far as the plants and insects that they may have a relationship with, many plants respond to, and like get up and get growing, from warmth, right?
Theresa: Yes.
Margaret: And insects may become active according to day length, I believe.
Theresa: Yeah. I think it depends. I honestly should revisit the literature on that, because I wonder if it breaks down by taxonomic group.
Margaret: Probably, so we can say some insects, but there’s certainly… That’s the kind of thing that could cause a mismatch.
Theresa: Absolutely, yes. And for sure, plants and pollinators are a big one. That’s one we all care about for so many reasons. One is that every third bite of food you can thank bees for, because they pollinate so much of what we eat. And so yes, if we don’t have abundant pollinators present, when the flowers are looking for that pollination service, everybody loses, including us, the consumers of those fruits that those plants might be producing. So yeah, it’s a real serious concern, and one that folks in agriculture are tracking, are trying to keep an eye on and figure out ways to address before it really becomes a major problem.
Margaret: So I wanted to talk a little bit more about if I want to contribute my observations to Nature’s Notebook. So I signed on and made an account and so forth. And the idea is that I don’t just say, “Oh, the red maples are flowering today.” I have to pick a red maple, and I have to look at that same plant at different times, or you hope I will look at that same plant, that same individual, at different times. And it doesn’t have to be a red maple. It could be the forsythia, or it could be the lilac in my front yard or whatever. But I have to sort of name my individual subjects, my plants in my account; I name them, and then I hopefully repeatedly make observations about what phenophase they’re at.
And so in that way, it’s different from when I go to my eBird account or my iNaturalist account, when I’m just simply saying, “I saw this” by uploading my observation. I say I saw whatever today, what bird or what plant, because it’s about that distinction of what phase it’s in. Right? That’s what we’re trying to get at. [Above, male flower of red maple; photo by Ellen G. Denny.]
Theresa: Yes, yes. Right, eBird and iNaturalist primarily are encouraging the documentation of species presence, like you said: I see this thing today in this location.
We’re asking you to ideally help us construct a picture over the whole season of what is happening on your target. If it’s a plant, then on your plant. We also will take observations on animals at a site. People are generally less likely to observe animals simply because so many of the observations are, “I don’t see it today,” but what we are trying to do is construct a picture of when those different activities are happening in animals, too, like breeding or fledging or hatching, that kind of thing.
But yes, each time, once you get set up, which involves creating a profile or an account, and registering a site where you’re going to make observations, and we recommend it be someplace very convenient, like your yard. And then if you’re going to do plants, selecting, like you said, individuals that you’ll make repeated observations on. Then each time that you step out to make observations, you’re confronted with a series of questions that are phrased such that the answer will be a yes or a no. And so it’s things like do you see flower buds? And then do you see open flowers? And again, sometimes there are a bunch of them. It can be as many as 13 different questions that you are confronted with for a single organism. You can answer as many or as few of those as you wish. You can just ignore the rest. And then you’re also invited if you happen to say, “Yes, I do see flower buds,” you’ll be confronted with, “Well, how many flower buds are there?”
And all of that information is just intended to help us construct, again, a picture of what’s happening on that organism over the whole season, ideally, and then extra ideally over multiple years. Where the data really become valuable is when we can track those and see what happened on those individual organisms from one year to the next. And so we are asking a lot. We know that, and take whatever we can get.
Margaret: Yeah, no, but I think also it’s making me think more sharply and look more sharply. So I think there’s a benefit to the observer, too, frankly, by being asked the questions. Yeah, I think it is a consciousness-raising exercise. [Laughter.]
Theresa: Yes. You’re in it for the long haul, hopefully, and we really celebrate that. We really do try to share back what we can see in these data that are coming in. We do a lot to hopefully support our participants across the whole country in the form of summarizing scientific studies that use the data and report that back through newsletters and webinars and emails and that sort of thing. So we do try to help folks see the value in sticking with it for the long term.
Margaret: Well, Theresa Crimmins, I’m so happy to speak to you, and now let’s both go outside and go look around, O.K.? [Laughter.]
Theresa: That sounds fantastic. Thank you so much.
Margaret: Happy spring. Talk to you soon again.
more from usa national phenology network
enter to win a signed copy of ‘phenology’
I’LL SEND A signed copy of “Phenology,” by Theresa Crimmins, to one lucky reader. All you have to do to enter is answer this question in the comments box below:
Have you ever recorded your nature observations to a community science app? Which one? (Ready to try watching for the unfolding phenophases of some favorite plants and maybe sharing those?)
No answer, or feeling shy? Just say something like “count me in” and I will, but a reply is even better. I’ll select a random winner after entries close Tuesday April 1, 2025 at midnight. Good luck to all.
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prefer the podcast version of the show?
MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 15th year in March 2024. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the March 24, 2025 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify (and browse my archive of podcasts here).
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