Shell-shocked: When turtle nests become buffets for raccoons

Authored by Clay Shearer and Katie Black

June is the peak of the turtle nesting season in our area. Now that we're half-way through August, we can reflect on our turtle nesting observations. During nesting season, it is common to see turtles nesting along the roadside, but also shallow pits with scattered egg fragments indicative of nests lost to predators.

We’ve been recording depredated turtle nests during our road surveys*, with the most significant cluster located along County Road 20 where it crosses Kemptville Creek in North Grenville. Here we’ve counted over 30 depredated nests, some of which were laid last year, but most were from 2023. Most nests were found along an open, sandy bank of Kemptville Creek which appears to be used as an access point for anglers and non-motorized watercraft. Other nests at this site were found along the gravel road shoulders, including under the guardrails.

Fred Schueler and Aleta Karstad of Fragile Inheritance recommended this site for our study based on their numerous observations of nesting Snapping Turtles. Running the Bishop’s Mills Natural History Centre just down the road, they have a great deal of turtle nesting data for the area dating back to the early 1990s. Our turtle observations for this site combined with those from Fragile Inheritance and iNaturalist show that this area provides habitat for a diversity of turtle species including Snapping Turtle, Eastern Musk Turtle, Midland Painted Turtle, Northern Map Turtle, and Blanding’s Turtle.

Raccoons are a common predator of turtle nests in Ontario. At the Kemptville Creek site, we’ve seen raccoon prints and scat along the road shoulder and along the sandy bank. Fragile Inheritance’s database has numerous instances of raccoons at the Kemptville Creek bridge during peak nesting time. We also thought we saw evidence of digging by raccoons, which was later confirmed by Fred and Aleta. They observed a young raccoon digging the exact holes that we saw right next to two freshly depredated Snapping Turtle nests.

So, what can be done to protect turtle nests from hungry raccoons and other predators? Individual wooden nest protectors are an option, but this relies on the installer to be present at the right moment after nest construction, but also before depredation. As we have seen, this can be a small window of time when dealing with raccoons, sometimes less than 48 hours. Another possibility for areas known to have a high concentration of nests would be installing an electric fence around the nesting area that allows turtles to enter and exit but prevents raccoon entry (Streeting et al., 2023). This method is less practical for areas where nests are spaced further apart.

*A note about counting depredated nests: at the start of the study, we would bury depredated nests to avoid double-counting them. However, this led to animals digging up the nest a second time. It's unknown whether this was due to the smell of the remaining egg fragments, or geosmin, the chemical made by microbes that creates the smell of freshly dug soil that can attract predators (Geller, 2015; Buzuleciu et al., 2016). Also, the egg fragments that we buried that were not dug up a second time were often exposed after a heavy rain. We now collect and discard the egg fragments to avoid double counting and to prevent re-attracting predators.

Please share your thoughts below!

References

Buzuleciu, S. A., Crane, D. P., & Parker, S. L. (2016). Scent of disinterred soil as an olfactory cue used by raccoons to locate nests of diamond-backed terrapins (Malaclemys terrapin). Herpetological Conservation and Biology, 11(3), 539-551.

Geller, G. (2015). A test of substrate sweeping as a strategy to reduce raccoon predation of freshwater turtle nests, with insight from supplemental artificial nests. Chelonian Conservation and Biology, 14(1), DOI: https://www.researchgate.net/publication/281129702_A_Test_of_Substrate_Sweeping_as_a_Strategy_to_Reduce_Raccoon_Predation_of_Freshwater_Turtle_Nests_with_Insights_from_Supplemental_Artificial_Nests

Posted on August 16, 2023 09:23 PM by knoir