Red foxes (Vulpes vulpes) use a complex system of scent communication, relying on several types of scent glands and chemical secretions to convey information about territory, identity, and reproductive status. The anal glands, located near the anus, produce potent-smelling substances deposited with feces to mark territory and signal individual identity. Similarly, the caudal gland at the base of the tail emits a musky odor, likely aiding in social interactions and dominance recognition. Even as they walk, foxes leave chemical trails through their foot pads, creating unique scent signatures that other foxes can detect.
Urination plays a critical role in red fox communication, particularly for marking territorial boundaries and indicating reproductive availability. Foxes’ scent marks are composed of complex chemical mixtures, including sulfurous compounds in urine that serve as long-lasting markers and fatty acids in anal gland secretions that provide strong, distinctive odors. These scent signals change seasonally, with increased marking during the winter breeding season and a focus on den protection in spring and summer.
What is Fox Scent Communication Used For?
Red foxes (Vulpes vulpes) rely heavily on scent communication to interact with each other and their environment. This communication serves several key purposes:
Territory marking: Foxes mark their territories using urine, feces, and secretions from scent glands located near their tail and paws. These scent marks indicate to other foxes that an area is already claimed, helping to avoid conflict.
Mating signals: During the breeding season, females release pheromones in their urine to signal reproductive status, attracting males.
Social hierarchy and individual identification: Foxes use scent to recognize individuals, identify family members, or assert dominance within a social group. Each fox’s scent is unique, like a signature.
Predation avoidance: Scent marking, while effective for communication among foxes, can also attract larger predators like wolves or lynx. To mitigate this, foxes may alter their scent-marking behaviour when they sense the presence of such threats, becoming more secretive or reducing scent intensity.
Cross-species communication: Research has shown that a compound in red fox urine, dihydroactinidiolide, elicits a reaction in felines similar to catnip, indicating a form of cross-species chemical communication between foxes and cats through scent​.
Traditionally, scent marking is understood to be an olfactory (smell-based) form of communication. However, there are indications that scent marks may also carry visual cues, adding a more complex layer of communication.
Can Foxes See Their Own Scent Marks?
Foxes may not only smell their scent marks but also "see" them through chemical components that luminesce, fluoresce or reflect UV light. This idea stems from research suggesting that certain animals, including canids and felids (cats), have the ability to perceive ultraviolet (UV) light. If foxes are also UV-sensitive, they may be able to visually detect scent marks that contain UV-reactive compounds or even bioluminescent chemicals.
UV sensitivity in canids and felids: Some animals, such as reindeer and domestic cats, have been shown to perceive UV light. Red foxes, with their slit pupils and nocturnal behaviour, share some visual adaptations with these species, which suggests they might have similar visual capabilities.
Chemicals in fox scent: Fox urine and glandular secretions are rich in volatile organic compounds, including some that might fluoresce under UV light. Studies on other animals (like cats and maned wolves) indicate that scent-marking chemicals can have additional visual properties.
This theory posits that by using a combination of scent and sight, foxes could have a more sophisticated method of communication. For instance, a UV-reactive or bioluminescent scent mark might indicate how recent the mark is (as it fades), or different visual patterns could signify varying types of information.
An Experiment: Fox Vision and UV Light
Foxes use scent to communicate through markings, but could they also see these markings under ultraviolet (UV) light? Some animals, like certain insects, can detect UV light, and we want to test if foxes possess a similar ability. This experiment explores whether foxes can detect UV signals, like invisible messages, and visually identify markings that are otherwise invisible in normal light.
Materials and Setup:
Fox Training: Train a pet fox to understand basic commands like "sit," "wait," and "touch."
Paper: A4 light blue paper (cut into quarters-A6 sized) and A4 white paper (cut into quarters—A6 sized).
Invisible Ink: UV pens (for writing invisible messages on paper).
Black Light Camera: To check the UV ink’s visibility under UV light.
Fox Treats: Dog treats or other tasty tidbit for rewarding the fox.
Biro: For labeling the back of the paper.
Tupperware: Containers to store paper and prevent scent detection
Step 1: Training the Fox to Identify a Written Cue
Out of view of the fox, take two white sheets of paper.
On one sheet, write the word "FOXY" in biro (visible ink).
Leave the other sheet blank (no writing).
Present the two sheets of white paper in front of the fox: one with the word "FOXY" (written in biro) and one blank.
Command the fox to touch the paper with the word "FOXY."
Reward the fox when it correctly touches the paper with the word "FOXY" (the one written in biro).
Repeat this training until the fox reliably touches the paper with the word "FOXY" every time, regardless of position.
The fox should learn to pick the worded paper (the one with "FOXY" written in biro) over the blank paper.
Step 2: Introducing Coloured Paper
Out of sight of the fox, take two sheets of coloured paper (e.g., light blue—similar at reflecting UV to white paper but any colour will do).
On one sheet, write the word "FOXY" in biro (visible ink).
Leave the other sheet blank (no writing).
Present the two coloured sheets of paper in front of the fox: one with the word "FOXY" (written in biro) and one blank.
Command the fox to touch the paper with the word "FOXY."
Reward the fox when it correctly touches the worded paper, regardless of whether it's light blue or another colour.
Repeat this process multiple times, swapping the positions of the papers so the fox doesn’t learn the position but instead focuses on the word.
Switch the colours of the worded and un-worded papers randomly, so that the fox learns to recognize the word "FOXY" without relying on the paper’s colour.
Repeat the process until the fox reliably picks the worded paper (with "FOXY" written in biro) over the blank paper, regardless of whether it's on white or coloured paper.
Step 3: Minimizing Scent Influence
To reduce the fox's ability to rely on scent, seal the papers in transparent containers once they are prepared, so the wording is clearly visible.
This ensures that the fox is not using scent cues from the pens and can only rely on visual cues to select the paper.
Reintroduce the sealed papers to the fox: one with the word "FOXY" in biro and one blank.
Command the fox to touch the container with the worded paper, and reward it for selecting the correct paper.
The fox should still be able to choose the worded paper in a controlled setting where scent cues are minimized. It may take a bit of training and trail and error for understanding to set in.
Step 4: Swapping to UV Pen to Test UV Perception
Out of sight of the fox, take a fresh sheet of white paper and write the word "FOXY" using the UV pen (invisible ink).
Check the UV writing with a black light camera to confirm that it is visible under UV light.
Take a sheet of light blue paper and leave it blank (no writing).
Seal both papers (the UV paper and the plain light blue paper) in transparent containers to ensure no scent influences the fox's decision.
Present the fox with both the sealed UV paper (with "FOXY" written in UV pen) and the plain light blue paper.
Command the fox to touch the container with the paper that has the word "FOXY" on it.
Reward the fox when it correctly selects the white paper with "FOXY" written in UV ink.
If the fox can still correctly pick the worded paper with the UV ink, this suggests that it is not relying on the colour of the paper or scent, but instead can see the UV ink.
Step 5: Repeat
Repetition and Confirmation: Test multiple times, swapping the positions of the papers, and ensure the fox is consistently selecting the paper with the word "FOXY" written in UV ink, even when presented with different coloured papers.
What We Expect to Find
After a few sessions where the fox consistently chooses the white UV-marked paper, it will confirm that the fox is not only recognizing the word "FOXY" but also can differentiate between visible UV ink and other factors like colour. If the fox is reliably selecting the white paper with UV ink, this suggests that the fox is capable of perceiving UV light.
Why This Matters
Proving that foxes can "see" their scent marks using UV light would open up new avenues for studying canid behaviour and communication. It could mean that foxes, like some birds and insects, use hidden wavelengths of light to convey more complex information than scent alone. This discovery could change how we understand not just foxes, but how animals use multisensory cues to navigate and communicate in their environment.
Summary
Red foxes (Vulpes vulpes) use a sophisticated system of scent communication to convey information about territory, identity, and reproductive status. They employ a variety of scent glands, including anal and caudal glands, as well as footpads, to leave chemical signals through urine, faeces, and secretions. These scent marks, rich in complex chemical compounds like sulphurous substances and fatty acids, vary seasonally and are used for territory marking, social hierarchy, and reproductive signalling.
This novel theory suggests that foxes may not only rely on olfactory cues but could also "see" their scent marks through ultraviolet (UV) sensitivity, similar to certain animals such as reindeer and cats. This theory proposes that foxes’ scent marks may contain UV-reactive compounds or bioluminescent chemicals that could help them visually detect these marks. Testing this hypothesis involves experiments in controlled environments, using black light and UV pens to examine the possibility foxes can see UV marks. If foxes show a preference for the cue, whether brio or UV, and not on the blank paper, it could suggest that their communication system is more complex, incorporating both visual and olfactory elements.
The potential discovery of visual scent detection in foxes could revolutionise our understanding of canid communication, indicating that foxes use hidden wavelengths of light to enhance their social interactions, much like some birds and insects.
Supporting Information:
