Will the real cactus flowers please stand up?

All field scientists know that getting out into nature to do your work means problem solving. Usually, you have to do this on the fly and with limited time, internet, communication… limited everything basically. But that’s where the creativity and decision making skills come in handy. Sometimes it’s a simple obstacle like breaking your tape measure or cactus spines lodged in your shoes. But then other times, it’s a seemingly catastrophic event—like flash floods destroying your study species, or political unrest in your study area—that disrupts your plan. Or, if you’re me, cold weather delaying cactus blooming in a cactus flower experiment.

This winter in the Mojave was unusually cold and rainy. The average high in January 2019 was 10.5°F—normally it’s a high of 57°F. Rain is great for flowers, it means there will be much more of them when they bloom. But cold means delayed blooms. And this Spring, it was delayed by about a month. Four weeks was how long I had planned to be in the desert, so after about two weeks of no flowers and a chilly forecast, I knew we needed to come up with some solutions.

The Buckhorn Cholla just wasn’t blooming. But at least it was beautiful.

The most obvious: stay longer. Duh. But this wouldn’t help if the cacti never bloomed, and I had to be back in Toronto to TA eventually. So I planned to hang out in the desert (no complaints here, it’s beautiful out there), but I knew we needed more options. Hire help? Working with birds means access to a large pool of citizen scientists who would give their time to look at birds in a place they otherwise couldn’t go. And I could hire a paid assistant from the area. These two options seemed great, but getting anything done with the public takes several months advanced notice, and there simply wasn’t any interest in my for-hire ad. So help was out. I kept thinking, and waiting, and hoping the flowers would just bloom and I could work extra long days and get it done. But that didn’t happen.

I had one last idea. Perhaps it was my most hair-brained scheme: use fake flowers (more appropriately called mimic flowers). After all, the problem was there were no flowers, and the end goal was to have flowers. A few papers had studied bird (hummingbird, specifically) visits to mimic flowers, and had success. This idea, which we didn’t know would even work, required a lot of experimental design rewiring. Two semester’s worth of planning and design scrapped and reinvented in a hour was terrifying. Whoever I told about my woes all echoed the same reaction, “That’s field ecology for you!” For a worrier and a planner like me, it’s a nerve-wracking line of work.

But I had to do something. I’d finished walking transects to look at birds and needed to start an experiment, any experiment. So I bought a bunch of fake flowers at Michael’s (Michael’s, would you like to sponsor an up-and-coming ecologist??) that looked like the Buckhorn Cholla’s flowers I’d seen on google, and pinned them onto the un-opened buds of my focal cacti. I had four levels of manipulations, set out camera traps, and watched for an hour. I was on the edge of my camping-chair-seat for the first session. There were thirty flowers pinned on this plant, my highest volume of flowers. Would they come? I needed proof of concept, proof that the birds would visit these cacti in some capacity, or else my findings are nothing but “birds don’t visit cacti”. Nothing wrong with this from a scientific perspective, but there’s not much to explore after the fact. A huge part of my Master’s relied on this next hour.

I was lucky. Within seven minutes, a Costa’s Hummingbird visited the cactus and attempted to pollinate the fake flowers. And then 6 more did the same over that hour. Funnily enough, this would be my busiest session for the rest of the field season. But it was peace of mind—the birds came, and no matter what else happened for the rest of the Spring, I had something to compare all my results to. After the 10 day experiment observing these mimic flowers, they finally began to bloom. The flowers really did look similar to the mimics, and I figured next we could see how different concentrations of real flowers on a cactus influenced bird behavior.

The first visitor to the mimic flowers.
The cacti had finally bloomed, now it was time for the second experiment.

The experimental design for the real flowers was exactly the same as the mimic flowers, but this time, there were real flowers on the plants instead of fake ones. So I watched and waited, this time with less anxiety. But the first day passed, and no birds visited the cacti. Strange, but it was a particularly hot day, perhaps they just weren’t out and about. The next day came and went, and still, no birds at the cacti. This stayed true for the rest of the experiment. Birds were still coming to the procedural control (a poll with 30 mimic flowers glued to the top), but not to the real flowers. Not even once in the 10 day experiment. And just like that, the experiment ended. Science waits for no one.

During the second experiment, birds still visited the mimic flowers. Just not the real ones.

Now, I’m back in Toronto. Data analysis is next up on the docket, but one thing is clear even without the statistics: birds will pollinate flowers on a cactus, just not the flowers that a cactus actually produces. It’s not the entire structure of the cactus that deters birds, but something about the flower itself that tells them not to come.

We know that most cacti are primarily pollinated by bees, and now we can say, at least for Buckhorn Cholla, they are absolutely not pollinated by birds. Could the flower have ultraviolet patterns advertising to the birds that this flower is not for them? Or perhaps a chemical signal from the flower deters them? Essentially, what is the mechanism associated with the flower that keeps birds away?

But perhaps even more interesting is this: what is the cactus flower actually saying to different pollinators? Two signal options exists, exclusionary or inclusionary. The flowers may signal that birds should not come here. Or perhaps, the flowers signal that the nectar is explicitly for bees. Imagine a sign outside a young boys treehouse saying, “No girls allowed.” This is an exclusionary signal, telling girls that they cannot come in (but I mean, smash the patriarchy). Now consider a “Man Cave” sign outside a basement. This is an inclusionary signal, suggesting that this space is for men. In the end, these signs have the same outcome: no women are in the space. An observer who cannot read English could observe that no women entered either of these spaces, but would need to be able to interpret the signs to know whether the signal is exclusionary or inclusionary.

This is fascinating, because in our human signage example, the interaction individuals of men, women, and sign-maker all are the same species speaking the same language. But in our bird-bee-cactus scenerio, we have three extremely different taxa (a plant, an insect, and a vertebrate) all possibly “reading” the same language. And they do all this interspecific signalling avoid niche overlap and wasted energy.

Now, we just got to test it. Easier said than done.

All these questions were… not what I was expecting to come home with at the start of my field season. Had the flowers bloomed when I arrived, I would have performed our original experiment manipulating the number of flowers on different sized cacti. And I would’ve gotten a whole lot of nothing. I’m a scientist, so I don’t like to say fate had a hand in this, but it was some good luck that I was so unlucky.

A male Costa’s Hummingbird, possibly a bilingual genius.