Evaluation of caffeine and garlic oil as bird repellents
Wildlife Damage Management, Internet Center for
∗USDA, Wildlife Services, National Wildlife Research Center,
†USDA, Wildlife Services, National Wildlife Research Center,‡USDA, Wildlife Services, National Wildlife Research Center,
∗∗USDA, Wildlife Services, National Wildlife Research Center,
††USDA, Wildlife Services, National Wildlife Research Center,
This paper is posted at [email protected]
of Nebraska - Lincoln.
National Sunflower Association Research Forum 2007
Evaluation of Caffeine and Garlic Oil as Bird Repellents
George M. Linz1, H. Jeffrey Homan1, Linda B. Penry1, Thomas M. Primus2, and
1USDA, Wildlife Services, National Wildlife Research Center, Bismarck, ND
2USDA, Wildlife Services, National Wildlife Research Center, Fort Collins, CO
Ripening sunflower fields in the northern Great Plains provide blackbirds with easily
accessible sources of high-energy food. Blackbirds can be nearly impossible to
discourage from foraging in favored fields. Repellents sometimes can be effective
feeding deterrents, especially if alternative foraging sites are readily available.
Currently, there is one bird repellent (BirdShield®, a.i., methyl anthranilate) registered for
use on ripening sunflower. The cost-benefits of BirdShield are being questioned after
recent field trails showed no reduction in damage levels (Werner et al. 2005).
Both caffeine and garlic are potential taste repellents that have some promise of
reducing blackbird damage to field crops. Avery et al. (2005) conducted cage feeding
trials with red-winged blackbirds (RWBL) and brown-headed cowbirds and found that
caffeine used at a rate of 2,500 ppm on rice seed significantly reduced food
consumption. Trials with mixed species blackbird flocks in a flight pen and field trials in
Louisiana showed that caffeine reduced blackbird feeding to <10%. The authors
suggested, however, that changes in the formulation were needed to facilitate
agricultural spray applications. Mason and Linz (1997) and Hile et al. (2004) showed
that garlic-treated food consistently repels European starlings under laboratory
conditions. Field trials are still needed to test garlic on ripening grain.
In 2005, we tested the repellent properties of garlic oil and caffeine on caged RWBL.
We found that sunflower achenes treated with 4% and 12% w/w garlic oil reduced
feeding by 58% and 97%, respectively, compared to untreated achenes. Buoyed by
these results, we further explored garlic oil in a second series of experiments at reduced
concentrations. Treatments of 2%, 1%, and 0.5% w/w garlic oil reduced feeding by
80%, 40%, and 22%, respectively. In the experiments with caffeine, we found that
feeding was reduced by 17% at 0.25% w/w. No other tests were done with caffeine in
In the cage trials conducted in 2005, we used achenes that were fully coated with
repellent. Our current report explores the repellency effects of caffeine and garlic oil
when they are sprayed only on the exposed tips of the achenes on intact sunflower
heads. Additionally, we report the results of applying liquids to sunflower heads with a
Male RWBL were trapped and held in captivity in a roofed outdoor aviary at least 2
weeks prior to testing. During this time, they had free access to water and a mix of
grains. The feeding trials were conducted in cages (61 x 36 x 41 cm) that held single
individuals, visually isolated from the other test subjects. The birds were placed in
cages for a 4-day pretreatment period during which time maintenance food was
removed every morning before sunrise and a head of untreated sunflower supplied 1
After the pretreatment period, each bird was assigned to a treatment group or the
reference group. The bird with the highest average sunflower consumption during the
pretreatment period was randomly assigned a test group. The bird with the next highest
rate of consumption was assigned to the next group. This systematic process was
repeated until all birds had been assigned to a treatment group or to the reference
Each day during the 4-day treatment phase, maintenance food was removed before
sunrise and a treated sunflower head was placed in the cage 1 hour later. The exact
same conditions were held for the reference birds, except they received untreated
heads. The heads were withdrawn after 3 hours and maintenance food was provided
for the rest of the day and removed the following morning before light. Each day fresh
heads were used. Sunflower consumption was measured with a plastic template
consisting of 5-cm2 frames.
Caffeine concentrations were analyzed at the National Wildlife Research Center, Fort
Three helicopter sprays with water and a caffeine solution were done on ~0.81 ha of
sunflower in September 2006. Results and Discussion
–The caffeine-treated heads had less damage (cm2/bird) than reference (untreated) heads; whereas, no difference in consumption was detected between garlic-treated heads and untreated heads (Fig. 1). Average consumption of sunflower was less for the caffeine solution (2826 ug/ml) than the garlic oil (0.02 g/ml, P =
0.02). We also directly compared 2 different concentrations of caffeine, 2 ml (2212 ug/ml) and 3 ml
(4747 ug/ml) per head. Overall, mean consumption (cm2/bird) differed among treatments (P =
0.10), with the birds fed the highest concentration (3 ml/head) eating less than the other two treatment groups (Fig. 2).
Figure 1. Consumption of sunflower (cm2) by individually caged male (n=5) red-winged
blackbirds after treatment with garlic oil or caffeine. Each bird was given 1 sunflower head
for 3 h on each of 4 treatment days. Capped vertical bars denote 1 SE.
Figure 2. Consumption of sunflower (cm2) by individually caged male (n=5) red-winged
blackbirds after treatment with 2 ml or 3 ml of an aqueous caffeine solution. Each bird was
given 1 sunflower head for 3 h on each of 4 treatment days. Capped vertical bars denote 1 SE.
In this study, garlic oil had no effect on sunflower consumption. In tests conducted in
2005, where the entire achenes were coated with 2%, 1%, and 0.5% w/w, feeding was
reduced 80%, 40%, and 22%, respectively, compared to consumption of untreated
sunflower heads. Perhaps treating only the exposed portion of the achenes was not
sufficient to deter feeding, particularly when the birds no access to alternate foods. On
the other hand, free-ranging birds might be deterred by low levels of garlic oil if
alternative foods are available. Helicopter Trial
– Under the conditions of our experiment, the aerial application by
helicopter was not capable of contacting the achenes with the spray. Despite 3 flights
that involved flying at different altitudes and speeds, very little spray contacted the face
of the heads (i.e., achene surface) because of the heads’ horizontal position to the
ground. The problem of applying repellent treatments that will reach the achene surface
of horizontally orientated heads remains a vexing problem.
Our study adds to the growing body of evidence that caffeine treatment can reduce
blackbird feeding (Avery et al. 2005). In comparison, it appears higher concentrations
of garlic will be needed to repel blackbirds from sunflower. If achieving adequate spray
coverage on the achenes is overcome in field settings, caffeine and perhaps other bird
repellents might be an effective management option. Literature Cited
Avery. M. L., S. J. Werner, J. L. Cummings, J. S. Humphrey, M. P. Milleson, J. C.
Carlson, T. M. Primus, and M. J. Goodall. 2005. Caffeine for reducing bird damage
to newly seeded rice. Crop Protection 24:651–657.
Hile, A. G., S. Zhixing, S. Z. Zhang, and E. Block. 2004. Aversion of European
starlings (Sturnus vulgaris) to garlic oil treated granules: Garlic oil as an avian repellent.
Garlic oil analysis by nuclear magnetic resonance spectroscopy. J. Agric. Food Chem.
Mason, J. R., and G. Linz. 1997. Repellency of garlic extract to European starlings.
Crop Protection 16:10-108.
Werner, S. J., H. J. Homan, M. L. Avery, G. M. Linz, E. A. Tillman, A. A. Slowik, R. W.
Byrd, T. M. Primus, and M. J. Goodall. 2005. Evaluation of Bird Shield as a blackbird
repellent in ripening rice and sunflower fields. Wildlife Society Bulletin 33:251-257.
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Wildlife Damage Management, Internet Center for∗USDA, Wildlife Services, National Wildlife Research Center,†USDA, Wildlife Services, National Wildlife Research Center,‡USDA, Wildlife Services, National Wildlife Research Center,∗∗USDA, Wildlife Services, National Wildlife Research Center,††USDA, Wildlife Services, National Wildlife Research Center,This paper is posted at DigitalC