Spicing It Up

Hot peppers

The Stoddard Bird Lab is collaborating with the Game Bird Lab in hopes of developing a new recipe for enhancing nesting success for ground-nesting birds.

Capsaicin is the active ingredient in hot peppers that can send human noses into to a sneezing conniption fit. Capsaicin has similar effects on other mammals, but it has virtually no such effect on birds. In fact, the pungency of capsaicin is thought to be linked to a strategy of deterring mammal consumption of pepper seeds in favor of bird consumption. As the theory goes, ground-bound mammals are not as effective as birds in dispersing seeds, and their sharp teeth and digestive systems also lower seed viability markedly compared to toothless birds.

Nesting success is one of the limiting factors for ground-nesting bird populations, including Northern Bobwhite and many species of sparrows. Nesting success for the critically endangered Florida Grasshopper Sparrows is extremely low — hovering in the range of 10-20% — and small mammals are thought to be major perpetrators.

Thanks to a grant from the U.S. Fish and Wildlife Service, we’ve been testing whether capsaicin can be used as an effective deterrent for mammalian nest robbers with an eye toward improving the outlook for the Florida Grasshopper Sparrow. Using off-the-shelf technology and quail as a surrogate, we developed a dispenser that sits a few feet above nests and sprays a small dose of concentrated pepper juice every 20 minutes. The spray gently coats the nest and surrounding vegetation, and is hoped to provide a chemical shield for eggs and adults alike.

Data are still being collected, but few nests treated with capsaicin have been taken by mammals. Instead, snakes have been the major threat, indicating that capsaicin is ineffective in deterring another major source of losses. It may also prove difficult to tease out a positive effect of the capsaicin treatment this year, because quail nesting success has been high across most of the property; but we’ll keep stirring the pot in an effort to find a recipe that works.


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