Capsaicin, the compound that gives chili peppers their heat, was tested as a potential deterrent for small mammal nest predators. In an initial trial using artificial nests and eggs, nests treated with capsaicin had lower depredation rates than control nests. However, subsequent trials found no differences between capsaicin-treated and control nests, possibly because predators learned cues about nest placement. Future experiments will test higher capsaicin concentrations and different application methods.

1. Abstract: Depredation of bird nests by small mammals represents a major fitness cost for temperate breeding songbirds and can be elevated by human alterations of
the habitat. Capsaicin is sold commercially as a small mammal deterrent (e.g. for crops), but little empirical evidence exists for its efficacy in deterring nest predators. We
used artificial nests, domesticated fowl eggs and liquid capsaicin to investigate the effects of capsaicin on nest depredation. In an initial trial, control nests had higher
rates of depredation than those treated with capsaicin. In subsequent trials, we did not see any differences between experimental and control treatments,
possibly because mammalian predators picked up on nest placement cues. These promising results will lead to future experiments in which the concentration of
capsaicin and area of application are increased.
Intro: Capsaicin, the
compound that gives chili
peppers their ‘heat’, could
serve as an irritant (and
deterrent) to small mammals,
while being benign to
songbirds. Previous research
has shown that chili pepper
flakes deterred predators but
also irritated the birds’ nasal
passages (Baylis et al 2012).
Here, we investigated the
utility of a capsaicin based
spray for deterring nest
predators.
Results: Trial 1 showed an insignificant
trend towards decreased depredation
rates in capsaicin treated nests
(independent samples t-test, P=0.25, Fig.
7-8). When we used t-tests to compare
depredation rates on any given day
(depredation = new nests
depredated/total nests available), day 7
showed the greatest difference (P=0.10,
Fig. 7). In trial two, nests were depredated
much more quickly and differences
between treatments were not evident
(P=0.79). Trials 3 and 4 (data not shown)
yielded similar results to trial 2.
Methods: We placed
artificial grass nests and brown
chicken eggs or quail eggs 30m
apart in honeysuckle thickets.
We treated the nests with
sprays of commercial
capsaicin repellent, water-
based capsaicin extract, or
control (water) and observed
them daily in three separate
trials over 12 days to simulate
the length of the incubation
period. We noted the various
levels of damage to the eggs
and removed the eggs from
the nest and surrounding area
upon noting depredation.
Discussion: While we found
promising results initially, subsequent
trials showed very high rates of
depredation and no differences between
treatments. This could be because our
capsaicin treatment was not an adequate
deterrent, and/or because small mammals
habituated to our nest placement (and/or
the capsaicin itself!). Our future research
will focus on using a GC mass spec to
quantify capsaicin content of our
treatments and experimenting with water
resistant methods of application. We plan
to conduct a large experiment involving
food removal rates at small mammal food
stations before re-attempting artificial
nest treatment.
Tiffany Dang, Heather Sprengel & Gabriel J. Colbeck
Figure 1: Map of study area, red dots show nests
Figure 2: Nest set up and treatment process
Figure 3: Chicken egg nest
Figure 4: Depredated chicken egg nest
Figure 5: Quail egg nest
Figure 6: Depredated quail egg nest
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Depredation
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Daily Depredation Rates
Non-capsaicin Depredation Rates
Capsaicin Depredation Rates
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TotalViableNests
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Nests Survived Over Time-Trial 1
Total Non-capsaicin Survival
Total Capsaicin Survival
P = 0.10