Hello,

In land-fresh water turtle nests, mammalian predators have been reported to destroy >80% of G. insculpta nests (Harding and Bloomer 1979; Brooks et al. 1992) . But in a study on Glyptemis insculpta the researches did not record any mammalian predation despite presence of potential ones (Walde et al. 2007). 

Also, coatis, mongooses, and dogs have been reported to dig up nests and predate the eggs of sea turtles.

I hope this helps.

Brooks, R.J., G.P. Brown, and D.A. Galbraith. 1991. Effects of a sudden increase in natural mortality of adults on a population of the Common Snapping Turtle (Chelydra serpentina). Canadian Journal of Zoology 69:1314-1320.

Harding, J.H., and T.J. Bloomer. 1979. The Wood Turtle, Clemmys insculpta...a natural history. HERP–Bulletin of The New York Herpetological Society 15:9-26.

Walde et al. 2007. NESTING ECOLOGY AND HATCHING SUCCESS OF THE WOOD TURTLE, GLYPTEMYS INSCULPTA, IN QUÉBEC. Herpetological Conservation and Biology 2(1):49-60.

Sea Turtles

Lynn E. Fowler. 1979. Hatching Success and Nest Predation in the Green Sea Turtle, Chelonia Mydas, at Tortuguero, Costa Rica.

Leighton et al. 2008. Predicting species interactions from edge responses: mongoose predation on hawksbill sea turtle nests in fragmented beach habitat.

Herman, D. W. 1986 Herp Review 17(1):24 reports predation of a bog turtle nest on 31 July which would be 3 to 4 weeks after laying.  The suspect predator was an opossum.  I recall someone telling me of ant predation and vole predation, both of which could come from under the nest and might occur many days after laying but I do not have a reference.

Buhlmann and Coffman (2001. Fire ant predation of turtle nests and implications for the strategy of delayed emergence. J. Elisha Mitchell Sci. Soc. 117: 94–100) reported fire ants to predate cracked eggs of yellow-bellied turtles, Trachemys scripta, causing a hatchling mortality rate of 45%.

The Fowler (1979) study cited above found that most nests were predated LATE in the season, not early.  Most of this predation was done by dogs that were more likely to destroy nests containing hatchlings than nests containing eggs.  Dogs and coatis found nests at ALL stages of development.

For freshwater turtles, Congdon et al. (1987.  Reproduction and nesting ecology of snapping turtles (Chelydra serpentina) in southeastern Michigan.  Herpetologica 39-54.) found that foxes predated nests later than raccoons but most predation was still within the first 24 hours.

Recent nests are thought to be easier for predators to detect by scent.  If you do have mammalian nest predators in the area then why would they wait a month to go after the nests?  Have the predators recently moved into the area?  Has another food source been used up?  Is some sort of nest protection being used (predator exclusion, predator removal)?

Is it possible that your activity/scent in the area attracted the predators to the nests?

“Previous studies have found that turtle nest depredation is concentrated immediately post-oviposition, likely because cues alerting predators to nest presence are most obvious during this time. In Algonquin Provincial Park, Ontario, we examined the frequency of nest depredation during the incubation period for Snapping Turtles (…) and Midland Painted Turtles (…). Contrary to most past findings, nest depredation occurred throughout the incubation period for both species. In fact, 83% and 86% of depredation interactions with Snapping and Painted Turtle nests, respectively, occurred more than a week after oviposition at our study site. Peaks with ≥10% nest depredation) occurred late in incubation and may have coincided with hatching” (Riley, J.L. and J.D. Litzgus 2014. Cues used by predators to detect freshwater turtle nests may persist late into incubation. Canadian Field-Naturalist 128[2]: 179–188; attached).

Thank you for the comments and citations. This was partially just to see if others have seen these patterns as well. Much like Riley and Litzgus (2014), predation for my study species occurred over the entire incubation period. I would add that my study species was G. muhlenbergii, which tends to produce very shallow nests on the top of sedge tussocks.

In regards to human scent, I wore nitrile gloves whenever I moved through the sites to minimize human scent, and I was typically in hip boots on my way through the bog. Therefore, I do not necessarily think human scent is much of an issue. I typically checked nest status about once/week, which occasionally involved carefully removing the vegetational or substrate cover from the nests to check for insect predation. Keep in mind that most nests had less than a cm of cover over the eggs, so these are very exposed nests. 

My own observations have suggested insects and voles/ other subterranean mammals as the primary sources of nest depredation at my sites. My current thinking is that many of these predators would not necessarily use cues that mesopredators use for finding nests (such as scent) and may instead find the nests incidentally. Alternatively, rancid eggs in the nest locations may actually attract other nest predators to these sites later in the season. 

Other thoughts/discussion are appreciated!

In my case, working with Emys orbicularis in Northern Spain, the predation rate of turtles´ nests is very low (here soil is very hard and compact, so it can difficult the smell exit and the detection of nests by predators), and the only case I have registered was once the hatchlings borned into the nest. This nest was placed in the middle of a fox path, so I think that once the hatchlings borned the sound of their movements or the smell of open eggs could reveal the presence of the nest to the fox. It was other nest at only 2 meters from the predated nest but it had no problems with predators.

About reproductive parameters of Podocnemis unifilis in the Beni River, Bolivia. The neonate mortality was mainly caused by attacks of Diptera larvae.

In northeastern Brazil, Maranhão, eggs Kinosternon scorpioides are mainly attacked by agouti and Galea spixii.

I strongly suspect that different predators can detect turtle nests for different lenghts of time based on their olfactory capabilities.  For this, I believe the citation of Condgon et al. (1987), offered by John Orr (above in this thread), is among the best-quantified. For the background on probably why Walde et al. wood turtles experienced no predation, I'd suggest you contact him (there are likely reasons, but he is the best source for the details). The point raised by Riley and Litzgus (2014), is well-taken:  the late season nest depredation they observed is quite likely due to the presence of renewed nest location cues ... not really addressing the point you are interested in. With all due humility, you may find my recent paper of interest: A Test of Substrate Sweeping as a Strategy to Reduce Raccoon Predation of Freshwater Turtle Nests, with Insights from Supplemental Nests. Chelonian Consevation and Biology 14(1) 64-72.