What is ‘Scent Trailing’?
In the animal world there are many forms of communication and sensations which we, as humans, commonly overlook. One such sense is called scent trailing, a form of chemical communication (Butler & Graham, 1995). Scent trailing is the ability of an individual to follow a conspecific (an individual of the same species) based on a pheromonal (secreted chemical scent) trail they leave behind (Brown & MacLean, 1983). Similar to the trail of breadcrumbs used in Hansel and Gretel. This behavior has been widely studied and confirmed in snake species, typically allowing the pursuit of mates or hibernacula (overwintering areas) (LeMaster et al., 2001; Mason & Parker, 2010). Male Box Turtles, which native to the USA, are believed to use scent trailing during mating season to find a mate (Huff, 2005). A similar observation was found in Desert Tortoises, where males would sniff the ground to track females for courtship (behavior or communication used to attract a mate) (Berry, 1986). These findings suggest the possibility that scent trailing could also be used by turtles in Ontario.
Photo: Desert Tortoise by Joshua Tree Provincial Park - Flickr (1) Flickr (2)
What animals display this behavior?
As previously mentioned, animals such as reptiles are known to use scent trailing. An animal that has had lots of attention in this field of research are snakes (Mason & Parker, 2010). Snakes and other squamates use a characteristic tongue movement which allows them to sample the chemosensory (scent and taste) cues in the environment. The tongue delivers the cues near an organ in the mouth or nose called the vomeronasal or Jacobson’s organ (Mason & Parker, 2010). The Jacobson’s organ is located in the nasal cavity and uses specialized skin to detect stimuli (scents or taste cues) left in the environment (Gillingham & Clark, 1981; Negus, 1956). Various papers have confirmed that adult and juvenile snakes use chemicals left in their environment by other individuals of the same species to find mates and hibernacula (Brown & MacLean, 1983; Burger & Zappalorti, 2011; Mason, 2009; Brown & MacLean, 1983; Martin, 2019). Male snakes will use these scent trails to track females during mating season, whereas females are much less likely to scent trail other turtles of the same species (Mason, 1992). In a study by Joanna Burger (1979) Pine Snake snakelets were seen switching courses to follow adult trails to winter hibernacula. This behavior is highly advantageous in regions with harsh winters as locating hibernation dens significantly increases juvenile snake survival (Martin, 2019).
Photo: Pine Snake from iNaturalist by Springhunter - https://www.inaturalist.org/observations/105231115
Another reptile species that is known to use scent trailing are Spotted Salamanders. Juvenile Spotted Salamanders metamorphosize in ponds and wetlands before coming ashore to find hideaways (Greene et al., 2016). Exploring their new habitat comes with high risks and it is believed that these efts (baby salamanders) scent trail other individuals of the same species to suitable habitats. In a study by Kathryn Greene and colleagues (2016), efts were frequently found to choose hideaways with adult salamanders when introduced to two hideaways (one with adults and one without). These observations suggest that efts use chemical cues to locate appropriate and safe habitats to increase their chance of survival.
Photo: Spotted Salamader by U.S. Geological Survey - Flickr
A gap in knowledge exists in the present literature on how turtle hatchlings make their way to a suitable overwintering site as they are given no parental assistance (Pappas et al., 2009). Scientists speculate that many environmental or innate traits may be involved in orienting hatchlings to their critical first overwintering site, but they are generally not well understood (Warner & Mitchell, 2013).
Could scent trailing adults in the area assist hatchlings on this critical journey?
Do hatchlings use scent trailing to find overwintering sites? Why is this a concern?
Since various reptiles have been known to use scent trails to discover important areas in their habitat, it may be possible that hatchling turtles also possess this ability. Once eggs are laid, they receive no further parental care. Therefore, upon hatching from eggs, freshwater turtles need to use innate abilities and environmental cues to find their way to inhabitable areas (Pappas et al., 2009). The current literature contains very little information on turtle hatchlings as they are difficult to detect and track at their small size (Paterson et al., 2012). Various cues have been implicated in hatchling navigation including; solar, visual, olfactory (smell), and social facilitation (following other hatchlings or turtles) (Mason & Parker, 2010; Pappas et al., 2009; Butler & Graham, 1995).
Photo: Snapping Turtle Hatchlings - The Land Between
In a study conducted by Amelia Whitear and colleagues (2017), the chemical cue preference in Spiny Softshell hatchlings, a highly aquatic turtle species, was investigated. Scientists found that hatchlings preferred water scented by individuals of the same species (conspecifics) over unscented water. Potentially indicating that hatchlings use scent cues to move towards conspecifics and increase chances of survival by leading them toward areas with high quality resources or hibernacula. The scientists also investigated this phenomenon in Blanding’s and Snapping Turtles but no preference was found. These findings may have been due to the fact that these two species are semi-aquatic and thus may have reduced abilities to detect chemical cues in the water, compared to Spiny Softshell Turtles. It is possible that semi-aquatic turtle species instead rely on terrestrial chemical cues left on materials in the area (i.e. grasses, vegetation, rocks, etc.) (Whitear et al., 2017). In the future, further investigations should focus on this possibility to assist in determining recovery activities and assess aspects of turtle population stability.
Why is this important & directions for future studies:
Staff at The Land Between are excited to see whether future studies can confirm if turtle hatchlings in Ontario use scent trailing to navigate their new environment to find overwintering sites. Understanding this phenomenon is a huge conservation priority because as adult turtles are lost, it is expected that fewer scent trails are available for hatchlings to follow. As these paths disappear, we anticipate that recruitment of juveniles into the adult population will also experience a serious decline should this be the main means of locating hibernacula. One of the greatest challenges a turtle will face is surviving the first year of life, which scent trailing may facilitate (Berman; Brown & MacLean, 1983). Should this be the case, then by protecting adult turtles, mitigation strategies will also support hatchling survival.
By: Andrea O’Halloran - March 2022
Edited by: Sabrina Hasselfelt
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