Sensitivity of Brown-Headed Cowbirds to Volatiles

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Abstract
We studied the ability of Brown-headed Cowbirds (Molothrus ater) to discriminate between two odors, ethyl butyrate and s-limonene, using a cardiac conditioning paradigm. Cowbirds not only learned to discriminate ethyl butyrate and s-limonene but they could also discriminate among concentrations of ethyl butyrate. Cowbirds could reliably discriminate the two odorants when vapor saturation was at least 0.6%. This suggests a discrimination sensitivity of at least 1.9 .times. 1013 molecules/ml or 0.76 ppm for ethyl butyrate. Despite the fact that passerines are presumed to have good olfactory ability, these values are within the same sensitivity range as found in nonpasserines that have more elaborately developed olfactory anatomies.