In a groundbreaking study, scientists from the University of Oxford have, for the first time, captured and analyzed the courtship communication of European fiddler crabs (Afruca tangeri) using advanced geophone technology. Published in the Journal of Experimental Biology, this research sheds light on how these coastal creatures use vibrational signals to attract mates in the acoustically challenging intertidal zones.
Vibrational Courtship: The Seismic Love Language of Fiddler Crabs
Male fiddler crabs are known for their distinctive courtship rituals, which include producing vibrational signals by drumming the ground with their oversized claws or shells. Until now, how effectively these seismic signals conveyed information amidst the noisy seashore environment remained unclear.
The University of Oxford’s Animal Vibration Lab deployed a novel approach—using GoPro cameras paired with sensitive geophones—to record over 8,000 seismic courtship signals in the southern mudflats of the Iberian Peninsula. This allowed the team to capture and analyze the detailed vibrational patterns of courting male fiddler crabs in real-time.
Larger Claws, Louder Signals: Honest Signaling in Crabs
The study revealed that male crabs perform a complex four-step mating routine: beginning with a subtle wave, followed by sequential claw waves and body drops, escalating to simultaneous movements and ending with an underground drumming display when a female approaches. Each phase increases in seismic intensity, producing distinct vibrational profiles.
Crucially, the research found that claw size plays a significant role in the strength and honesty of these seismic signals. Males with larger claws generated higher-energy vibrations with greater amplitude. This natural constraint prevents smaller males from faking their fitness, allowing females to assess a potential mate’s quality based solely on the vibrational cues—without needing visual confirmation.
Lead author Tom Mulder (Department of Biology, University of Oxford) explains, “It appears that males cannot—or do not—deceive about their physical size. Females can rely on the loudness of seismic signals to honestly evaluate a mate’s suitability.”
Machine Learning Identifies Crab Behaviors via Vibrational Patterns
Interestingly, while the frequency of the signals remained constant, variations in loudness, rhythm, and duration allowed researchers to distinguish between different behaviors—such as body drops versus underground drumming. These distinctions were so consistent that a machine learning algorithm was able to classify crab behaviors based solely on seismic data with up to 70% accuracy.
This innovation opens the door to future applications of AI in wildlife monitoring. From detecting endangered species in remote regions to identifying pests in agricultural fields, vibrational analysis paired with machine learning offers a non-invasive method for environmental and ecological research.
Seismic Communication: A Smart Strategy in Noisy Coastal Habitats
Unlike vocal signals, the percussive vibrational cues used by fiddler crabs are more reliable in noisy coastal habitats. Simple changes in volume and repetition allow these small animals to effectively communicate over long distances. The study highlights how larger-clawed males have a distinct advantage in being heard by distant females, although smaller males still participate successfully using other parts of the courtship routine.
Dr. Beth Mortimer, corresponding author and researcher at Oxford’s Department of Biology, concludes, “Larger claws help overcome background seismic noise, giving males a better chance of attracting distant females. Yet, even smaller males contribute meaningfully, as drumming is just one element of their complex mating display.”
Citation:
Mulder, T. et al. Constraints on percussive seismic signals in a noisy environment by European fiddler crabs, Afruca tangeri. Journal of Experimental Biology, 2025. DOI: 10.1242/jeb.249323
Source: University of Oxford