Hot off the Press: Turtle Nest Predation Occurs Late in Incubation too!
Turtle nests are targeted by many predator species (mammals, birds, reptiles, and even humans) as a delicious and nutritious snack! This relationship has exisited for many years, yet as predator presence on the landscape increases due to human subsidization the rate of nest predation also increases to unsustainable levels. In some turtle populations, high rates of nest predation is attributing to population declines. During my work in Algonquin Provincial Park, myself and the other researchers noticed that nest predation seemed to occur throughout incubation and even was happening as turtles were emerging from the nests in the fall! This was contrary to what was reported in the scientific literature most commonly - that nest predators targeted turtle nests immediately after they were laid during turtle nesting season. So, myself and colleagues decided to take a closer look.
We found that in Algonquin Provincial Park, over 80% over nest predation occurred more than a week after the nest was laid. Also, later peaks in predation may have coincided with turtle hatching out of the eggs within the nest cavity. Also, the presence of predators at the nesting sites increased in the fall - especially the presence of canid nest predators (foxes and wolves).
In order to fully understand how nest predation effects turtle populations, it is important to study how nest predation occurs over time at each study site. Our study highlighted that it can be different than what is traditionally expected! Also, in recovery plans that protect turtle nests from predators using nest cages, it may be important to keep the nests covered throughout the incubation period until the hatchling emerge (learn more about nest caging here). Overall, when studying a new population of turtles and taking actions to conserve it - knowing as much as possible about the nest predators in the area will help to garner the recovery plan to maximize success!
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 (Chelydra serpentina [Linnaeus, 1758]) and Midland Painted Turtles (Chrysemys picta marginata [Agassiz, 1857]). 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 in nest depredation (weeks with ≥10% nest depredation) occurred late in incubation and may have coincided with hatching. Trail cameras deployed at four nesting sites revealed six predator species interacting with nests. The presence of predators at nest sites increased late in the incubation period indicating a persistence or renewal (from hatching) of cues; additional research is necessary to determine the nature of these cues. These findings have implications for both research and turtle conservation. Further research should examine the relationship between temporal changes in predator species’ density and patterns of nest depredation. additionally, in areas where protective nest caging is used as a species recovery action, it may be important to ensure that cages remain in place throughout the incubation period until emergence of hatchlings.
Riley, J. L. and Litzgus, J. D. 2014. Cues used by predators to detect freshwater turtle nests may persist late into incubation. Canadian Field Naturalist 128(2): 179-188.
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