Written by:
Abigail Holmes, Texas A&M University WFSC 19’ and Timothy Johnson, Texas A&M University WFSC
18’
Edited by Amanda Gobeli, Extension Associate and Dr. Dale Rollins, Statewide Coordinator, Quail Decline Initiative
It
is a fact that snakes prey upon adult quail, chicks, and eggs as part of their
diverse diet. Depredation, which literally means “to plunder or attack,” occurs
when predators steal, eat, or harm a nest full of eggs in any way. Snakes are
often assumed to be the culprits of nest depredation if there is no eggshell
evidence remaining in the area. This is because snakes consume their prey by
swallowing them whole (NWE contributors 2008), leaving almost no trace of their
presence other than an empty nest.
 |
| A bullsnake (Pituophis catenifer sayi) raiding a nest of mallard (Anas platyrhynchos) eggs. Photo courtesy of USFWS. |
Many researchers have questioned the accuracy of using
eggshell remains (or lack thereof) as the deciding factor in determining which
predator plundered a nest. Several animals other than snakes are capable of
removing eggs from the nest without leaving behind any evidence, including
Franklin’s ground squirrels (Poliocitellus
franklinii), gray foxes (Urocyon
cinereoargenteus), ravens (Corvus
spp.), gray jays (Perisoreus canadensis),
and even feral swine. Rats and mice have also been observed rolling eggs away from
nests without damaging the surrounding area (Marini and Melo 1998). The result
of this activity is an empty but otherwise intact nest bowl, which can lead to
overestimation of snakes as the culprits (Staller 2005).
On the other hand, some research suggests that
artificial (“dummy”)
nests, a tool often used to evaluate rates of nest
depredation, may actually underestimate
the influence of snakes. Snakes have an apparent distaste for fake nests and
avoid them altogether—they have never been recorded raiding a dummy nest and
refuse to consume quail eggs in captivity (Marini and Melo 1998). This aversion
may alter the results of a dummy nest study to favor mammals, birds, and other
predators as the culprits of nest predation (Davison 2000, Marini and Melo
1998, and Davison and Bollinger 2000).
 |
| As ground-nesting birds, quail nests are susceptible to a variety of predators. Photo by Dale Rollins. |
Ultimately, the only
foolproof way to determine which predator is responsible for the failure of a
nest—artificial or otherwise—is to capture the depredation event on
camera. One study conducted in Florida and Georgia used infrared
micro-video cameras to watch northern bobwhite (Colinus virginianus) nests and identify their predators. Before
looking at the video evidence, technicians tried to guess which animals raided the
nests using only diagnostic signs (e.g., egg shells, tracks) at the site.
Unsurprisingly, they overestimated the depredations caused by snakes, and they
could only identify 30% of mammal predators correctly when looking solely at the
remaining shell fragments. When they later viewed the evidence captured on
camera, they found that mammals actually caused about 59% of nest depredations
– snakes only caused around 29%, while ants
caused 12% of nest failures (Staller et al. 2005). Egg size also affects the
likelihood that shell evidence is left behind.
Hernandez et al. (1997) used both quail and chicken eggs in separate
experiments and found shells 91% of the time when using chicken eggs, but only 3% when using quail
eggs.
 |
| Eggshell evidence is one of several tools that wildlife researchers can use to identify nest predators. Photo by Jesse Wood. |
Cameras can take a lot of the guesswork out of
identifying nest predators, but they are not without disadvantages. Human
activity, scent and equipment may influence nest success by attracting or
deterring predators, or by altering the behavior of the nesting adults (Cutler
and Swan 1999). Another challenge is the considerable time and expense required
to maintain enough cameras to measure nest predation at the population level
(Hernandez et al. 1997). Several studies have successfully used game cameras to
record nest depredation events by snakes (Cox et al. 2012), although technician
error, false triggers, and improper camera positioning can prevent researchers
from positively identifying nest predators (Cox et al. 2012). When it comes to
quantifying the impacts of snakes and other quail nest predators, game
cameras—despite their shortcomings—are an invaluable tool that can be used
alongside eggshells and other evidence to piece together the fate of a nest.
Learn how to build a
simulated quail nest here.
Read more about trail cameras and their possible
uses for wildlife management here
or read our blog article: “Say
Cheese: The Role of Cameras in Wildlife Management”.
Literature Cited
- Cox, A.W., Pruett, S.M., Benson, T.J., Chiavacci, S.J., and F.R. Thompson III. 2012. Development of Camera Technology for Monitoring Nests. USGS Northern Prairie Wildlife Research Center. Paper 250.
- Cutler, T.L. and D.E. Swann. 1999. Using Remote Photography in Wildlife Ecology: A Review. Wildlife Society Bulletin 27(3): 571-581.
- Davison, W.B. and E. Bollinger. 2000. Predation rates on real and artificial nests of grassland birds. The Auk 117(1): 147-153.
- Hernandez, F., Rollins, D., and R. Cantu. 1997. Evaluating evidence to identify ground-nest predators in west Texas. Wildlife Society Bulletin (1973-2006) 25(4): 826-831.
- Marini, M.A. and C. Melo. 1998. Predators of quail eggs, and the evidence of the remains: implications for nest predation studies. The Condor 100(2): 395-399.
- New World Encyclopedia contributors. 2008. “Snake.” In New World Encyclopedia. Retrieved from http://www.newworldencyclopedia.org/p/index.php?title=Snake&oldid=771462.
- Rollins, D. and J.P. Carroll. 2001. Impacts of predation on northern bobwhite and scaled quail. Wildlife Society Bulletin 29(1): 39-51.
- Staller, E.L., Palmer, W.E., Carroll, J.P., Thornton, R.P., and D.C. Sisson. 2005. Identifying predators at northern bobwhite nests. Journal of Wildlife Management 69(1): 124-132.