How Frogs and Lizards are Telling Us About Climate Change
Brumation is different from hibernation - reptiles and amphibians can wake up to drink water during warmer periods before returning to dormancy.
In the sun-drenched landscapes of Italy, Greece, and their surrounding islands, a silent, ancient clock is ticking. This clock isn't made of gears and springs, but of life itself. It dictates when frogs emerge from the mud to sing their choruses, when tortoises stir from their long sleep, and when snakes first bask on sun-warmed stones. Scientists are now listening to this clock more intently than ever, discovering that its ticks are shifting—and revealing profound truths about our changing world.
At its heart, phenology is the science of timing. It's the study of recurring biological events and how they are influenced by seasonal and interannual variations in climate. For amphibians and reptiles—collectively known as herpetofauna—these events are critical to their survival and include:
The driving force behind these rhythms? Primarily temperature and precipitation. A warm spell in late winter can trigger emergence; a dry spring can delay breeding or cause reproductive failure.
To understand how scientists uncover these patterns, let's dive into a landmark long-term study that exemplifies research in this field.
Objective: To determine if the breeding phenology of the Appenine Yellow-Bellied Toad (Bombina pachypus), a vulnerable species endemic to Italy, has shifted over a 20-year period (2002-2022) in response to local climate change.
Researchers chose a well-preserved, temporary pond system within a national park in southern Italy.
Weekly visits for two decades to record arrival, calling, and egg-laying events.
Nearby weather station provided temperature and precipitation data.
"The data revealed a clear and statistically significant trend. Over the 20-year period, all three phenological events—arrival, calling, and egg-laying—occurred progressively earlier."
| Phenological Event | Average Date in 2002 | Average Date in 2022 | Average Shift (Days Earlier) |
|---|---|---|---|
| First Arrival at Pond | March 15 | February 28 | 15 days |
| First Male Call | March 22 | March 7 | 15 days |
| First Egg Mass Observed | April 5 | March 19 | 17 days |
Figure 1: Correlation between temperature and breeding date
Figure 2: Impact of precipitation on breeding start
This study provided concrete, local evidence that an amphibian species is directly responding to climate warming by altering its fundamental reproductive schedule. This has cascading effects: earlier breeding might allow tadpoles more time to develop before the pond dries up in summer, which could be beneficial. However, it also risks exposing early adults to more unpredictable late-winter weather events, creating an ecological mismatch if their food sources (insects) haven't also advanced their own schedules .
How do researchers gather this precise data? It requires a blend of traditional fieldwork and modern technology.
The absolute basics. Recording accurate observations, dates, and on-site microclimate temperatures is fundamental.
Used to capture and analyze frog calls. Sophisticated software can even identify species by their call, aiding in monitoring.
Precisely marks the location of observed animals, nests, or egg masses for long-term study and population mapping.
Small, weatherproof devices left in the field to continuously record temperature and humidity at the study site.
Modern tools that allow the public to upload photos and dates of sightings, vastly expanding the dataset available to scientists .
The shifting rhythms of amphibians and reptiles in the Central Mediterranean are a powerful bio-indicator. They are a silent alarm, telling us that the delicate balance of ecosystems is being altered by a warming climate. These changes are not just about earlier frog songs; they are about potential mismatches in food webs, increased competition, and the heightened vulnerability of species already on the brink.
By understanding these phenological patterns, scientists can better predict future changes, identify the most vulnerable species, and inform conservation strategies. The next time you hear the first frog chorus of the year, listen closely. It's not just a sound of spring; it's a vital message from the natural world about the state of our planet .