As we reach the height of summer and our beloved bats get busier, what the heck does phenology have to do with all of it?
07.09.25
By Wendy K. Probst
Summer travel plans are all about expectations: of good weather, some good vibes, and good food – oh and also making sure the kids are having fun. And that goes for bats, too!
So, as we reach the height of summer in temperate climates, and the birds, bees, and our beloved bats get busier (pun intended), what the heck does phenology have to do with all of it? Answer: quite a bit. And it’s complicated.
First, if you are wondering what phenology is, you’re not alone. Although, for the Bat Conservation International team of scientists, studying things like phenology is their jam. Some might even call it “fun-ology!”
Imagine you’re gearing up for a lively, balmy summer complete with all the fresh tasty moths you can gulp down. But an unexpected storm suddenly changes your moth buffet options from all-you-can-eat to “closed due to inclement weather.” This kind of bad timing doesn’t just mean missed meals, because, when you are a bat with a high metabolism who needs their calories, every meal matters. The bigger the bug-buffet, the better. This is why phenology – or timing – is everything to bats.
Phenology is quite simply the timing of when plants and animals are active, and how this timing relates to weather and climate. So, it doesn’t just impact bats but has an effect on everyone – from when we have allergies to when the mosquitos are biting or when fresh produce is available. And of course, our summer plans.
It also means that “sciency things”: shifting conditions like photoperiod (daylight length), precipitation, and temperature, are triggers for bats to be active in the spring, mate and give birth in the early summer, hibernate or migrate in the fall, and so on. Which can throw things out of whack if occurrences like abrupt or intense weather pattern shifts create an adverse domino effect.
BCI’s Conservation Research Coordinator, Kathy Gerst studies and has posed some fun phenology questions that have no straight or final answer (spoiler alert?) but, like most good questions, will hopefully make us all ponder more about the role that bats play in helping to maintain an ecological balance.
Watch and Learn
Let’s start with why BCI monitors. Bats play a pinnacle role in the balance of the world’s ecosystems – minus Antarctica – and everything is an ecosystem. So, BCI’s science and conservation teams need to monitor them as closely as possible. And they are always up for this not-so-easy-breezy task. What they find can provide information about population sizes and ranges from before and after bats encounter threats or experience change. This consistent, long-term research is the key that unlocks what Kathy Gerst and her BCI colleagues aptly describe as a “rich treasure trove of information about the past, present, and future of life on Earth.” A mystery unfolding in real-time.
When is the best time to monitor?
Timing is everything when observing bats. And, like all seasonal things, it’s cyclical. Listening for baby bat “babble” is one example. In early to mid-summer, when baby bats are still learning to fly, they are also still learning how to “speak.” In this case, monitoring is all about timing. Knowing when bats are pregnant, lactating, having pups, and when those pups leave the roost is vital. Acoustic monitoring of these babbling baby bats can help to locate maternity roosts so that researchers can return to these areas and gather consistent information to keep populations protected.
The Attitude of the Atmosphere
Are bat activity patterns shifting with climate change?
Yes. Think about your own summer travel plans. Or any plans that could be impacted by the weather for that matter. What if your travel route was suddenly wiped out by a hurricane? Or the temperature soared too high for comfort.
In one recent instance, for two years in a row when early summer temperatures reached well above 105 degrees in California’s Central Valley, baby Mexican free-tailed bats were literally dropping to the ground from the heat below a maternity site in Bakersfield. As a vital part of the ecosystem in the agricultural Central Valley, these migratory bats consume their body weight or more in insects each night – unless it’s too hot.
Situations like these can be paradigms for studying climate change effects because of bats’ sensitivity to temperature and migration patterns. They also serve as indicators, like an early warning system.
We’ve all seen or experienced some extreme weather conditions in recent years. Migratory bats know the feeling. Events like tropical storms, typhoons, and hurricanes are increasing around the world, bringing extreme flooding, high wind, and damage to vegetation. This causes bats to lose habitat and insect prey, as well as clean water, causing fewer pups to be born or survive to adulthood. Because of this, migration routes are often altered, causing bats to travel farther to find resources necessary for survival.
Cause and Effect
Can plant and insect phenology be used to predict bat activity?
Again, yes. It’s important that bats emerge from hibernation when there are insects to eat – and insects respond to those cues as well. The emergence of insects depends on predictable seasonal shifts – so shifts or overlaps in seasonal cues can cause, well, a butterfly effect.
As Kathy Gerst explains, “If the cues to migrate don’t align with the cues in the area where the insects are emerging then there can be mismatch.” Another important factor for nectar bats like the Endangered Mexican long-nosed bat (Leptonycteris nivalis), is the importance of nectar availability along migratory corridors. These sweet little night flyers feed primarily on the nectar of several species of agave and are important pollinators for this economically valuable plant. By understanding this pollinator partnership between nectar-feeding bats and wild agave, BCI aims to restore agaves that sustain the bat populations that rely on them.
Moving and Doing
What are the climate drivers that signal bats to migrate, mate, and hibernate?
Many bats choose their summer travel destination by finding the best spots to start a new family. In the eastern U.S., acoustic sampling can tell us more about big brown bats (Eptesicus fuscus) and eastern red bats (Lasiurus borealis) and their habitat use within the summer reproductive period. Climate shifts can throw this timing out of kilter, which leaves the potential for phenology mismatch between bats and essential food resources (in this case delicious moths and other flying insects) during critical life stages like adolescence. Bat “tweens” need this time to build strength and agility before they wing-it to warmer climates during migration or before they hibernate.
To put it more technically: species of insectivorous and pollinating bats that undergo long-distance migrations and depend on seasonal timing of food resources to fuel migrations could be negatively impacted by shifts in phenology of available resources (e.g.; flowering plants or seasonal insect abundance). Of course, those insect-filled summer nights do end at some point – deep sigh – and when they do, bats need to plan ahead for the hibernation months or start to migrate south.
Teamwork = Dreamwork
Last but never least, all of this data collection at just the right times of year requires consistency. That’s why BCI collaborates with organizations like the North American Bat Monitoring Program (NABat), USA National Phenology Network, and their Nature’s Notebook community science program, which allows regular people to collect data on phenology, all of which helps gather data to answer these questions.
Keepin’ On
More questions than answers? Yup. And these are the kinds of questions we could use phenology data to answer. With every answer, the mysterious role of bats in the larger picture unfolds. Final question: Why should you care? So that the second largest order of mammals on the planet with more than 1,400 wide-ranging species are protected and thrive. Well-studied bats + healthy, balanced ecosystems = pollinated plants, pest management, and pioneer and native plant seed dispersal, which means thriving habitats.
Well-studied bats + healthy, balanced ecosystems = pollinated plants, pest management, and pioneer and native plant seed dispersal, which means thriving habitats.
In other words: healthier planet, healthier everything!
More research and monitoring will tell a larger narrative. Talk about a cliffhanger! Or perhaps a “choose your own adventure” story. Either way, what’s better than a riveting summer read? So read on, follow along, and help to support BCI as they work hard to gather clues in this vital big-picture adventure to conserve the world’s bats and their ecosystems to ensure a healthy planet.
Wendy K. Probst is the editor of The Bat Pub, and a freelance editor and writer who has devoted her career to working with stellar conservation organizations like Bats Conservation International and the Appalachian Trail Conservancy. She is both driven and anchored by her desire to dream, create, preserve, educate, and empower others.
