Turtle Route Fidelity, by Kiara Duval - November 2021
Edited by: Andrea O’Halloran and Leora Berman
Researchers have found that turtles are creatures of habit when it comes to seasonal activities. Though it is very species-dependent, the majority of turtles display some sort of fidelity (faithfulness) to their home regions. That is, they return to the same areas for various activities year after year. Studies have shown that some species of turtles have fidelity to nesting, overwintering, and foraging sites (Schofield et al., 2010; Casale et al., 2007). For a specific example, painted turtles have been observed to show fidelity to nesting areas (Roth and Krochmal, 2015). There is also another type of fidelity that turtles exhibit: route fidelity. This is defined as loyalty to migration routes used to travel between various habitat types. However, route fidelity in turtles is not as well-studied as the other types of fidelity.
Studies focused on migration routes are important for many ecological and conservative reasons. Understanding a population's distribution and habitat requirements allows us to better understand how to protect species and support their conservation (Schofield et al., 2010; Siegwalt et al., 2020). The long-term viability of different species can be directly impacted by environmental processes, human activity, and many other factors (Schofield et al., 2010). Predicting nesting sites, migratory pathways, foraging sites, and over-wintering sites are some of the main priorities when it comes to the turtle conservation effort (Broderick et al., 2007). Knowing when and where turtles spend their time can help us to understand where protection efforts are needed. These efforts can also help us to realize the effects human activities can have on their critical habitats (Casale et al., 2007). Understanding the level of fidelity that turtles have to their migratory routes when traveling between foraging, nesting, and overwintering sites is key to discerning where to focus conservation efforts (Broderick et al., 2007). For example, assessing where painted turtles nest, as it is close to the same area yearly (Rowe et al., 2005), would allow us to protect this nesting area more effectively. However, this is not as easy to assess as it may seem.
Predicting population distribution of turtles has always been difficult due to their elusivity and extensive home ranges (Horton et al., 2017). For example, Snapping Turtles have been observed to follow their migration routes very carefully, although they do periodically change their preferred sites (Keevil et al., 2018). However, there is hope for these studies with the advancements of modern technology, such as satellite tracking, which has made it possible to remotely track an animal's movement (Horton et al., 2017). This allows researchers to analyze trajectories and pinpoint patterns of navigation that different individuals use year after year (Horton et al., 2017). By being able to point out these migratory corridors, researchers can make recommendations for mitigation strategies for these regions. For example, monitoring or controlling fisheries activity during the turtle's migratory season can have a substantial impact on turtle conservation, as shown in a study done by Boderick and colleagues (2007). They showed that Green and Loggerhead sea turtles spent a lot of time resting on the seabed, making them highly susceptible to demersal (groundfish) fishing gear (Broderick et al., 2007).
The results of turtle route fidelity studies have been somewhat inconsistent. That is, there appears to be a great deal of variability in route fidelity, especially among different species of turtles. To demonstrate this, I will present examples from a few different studies.
First, for sea turtles: in a study by Schofield and contributors (2010), the movement of male Loggerhead Sea Turtles was tracked. Though these turtles did return to their original foraging sites each year, they did so by using a myriad of different routes. In a different study conducted on female Hawksbill Sea Turtles, Hawkes and contributors (2012) showed there was not always strong fidelity to migratory routes, and that routes varied in some cases by hundreds of kilometers. However, strong nest and foraging site fidelity was still observed (Hawkes et al., 2012). Further, Boderick and her colleagues (2007) were able to demonstrate some route fidelity in female Green Sea Turtles and Loggerhead Sea Turtles when examining post-nesting migration to foraging grounds. These turtles were tracked for many years and used highly similar routes to return to their foraging and over-wintering areas.
The results are a bit more regular for freshwater turtles where studies demonstrate more definitively that some species may use the same routes to get to their overwintering sites. This appears to be the case for the European Pond Turtle studied by Thienpoint and colleagues (Thienpont et al., 2004). In another study performed on Painted Turtles, a native Ontario species, incredible route precision when returning to sites was observed year after year (Ross and Krochmal, 2015).
Overall, however, there is still uncertainty in the literature with regards to turtle migratory route fidelity. However, all the information presented here was taken from studies where route fidelity was not the main focus. This highlights the need for future studies to focus specifically on turtle migratory route fidelity. This will further inform the need for conservation efforts focused specifically on turtle migration routes.
Fidelity patterns in turtles can be very important for their prolonged survival. They can also be highly variable between different species. As you may already know, many turtle species travel incredibly long distances, both by water and over land, between the sites they use for various life activities including hibernation, mating, and feeding (Shimada et al., 2020; Thienpont et al., 2004). You might be wondering: why would they spend so much time and energy going back and forth to the same spots every year? To answer this question, we will look at a few different factors.
Firstly, maintaining fidelity to specific sites is considered by many to be a low-risk strategy (Schofield et al., 2010). The turtles know that specific sites have provided them with the resources they needed in the past, and this offers them security (Schofield et al., 2010). This means that returning to a site that they’ve used previously can be much more beneficial than searching for a new, unexplored site. Most turtles will return to the same foraging sites every year and only stray if their existing site has suffered degradation and is no longer profitable (Schofield et al., 2010). Studies have also shown that both locally raised and newly released turtles show site fidelity to the area where they were released or born (Attum et al., 2013). The released turtles in particular might choose to remain in the area of their release, as this is the area that becomes familiar to them. Other factors that could impact a turtle’s fidelity to a particular site could also be related to familiarity accompanying easier defense of the territory, or the quality of the site (Broderick et al., 2007).
Turtles are incredible animals with very interesting, if variable migratory patterns. The ability of some species to pinpoint specific locations over hundreds of kilometers and return to them is a fascinating subject to many researchers. Knowing what sites they favor and when they are likely to return can facilitate our studies and present opportunities to learn more about them. Being able to study these patterns will not only increase our understanding of their behavior, but will also allow us to better guide conservation efforts to protect native turtle species.