A new sexual signal in rutting male red deer: Age related chemical scent constituents in the belly black spot

Rutting behaviour of red deer stags (Cervus elaphus) includes an extensive repertoire of visual and acoustic signals directed either to rival males or to females. As in other mammals, olfactory communication is expected to play a central role in these rutting interactions too, but this has rarely been investigated. Only during the rutting season, red deer males show a conspicuous black spot area throughout most of their underbelly produced by the impregnation of substances with a strong scent. Here, we examined the origin of these compounds and their potential role as chemical signals. By using gas chromatography–mass spectrometry (GC–MS), we identified 67 compounds in the hair from the belly black spot of red deer stags, mainly heterocyclic aromatic organic compounds, such as m-cresol, benzoic acid, cyclohexanecarboxylic acid and ethylphenol, but we also found steroids, such as cholesterol and androstane-3,17-dione, carboxylic acids and their esters between n-C₆ and n-C₂₂, alcohols, squalene and other minor compounds. Many of these compounds are found in the belly black spot but not in other hair areas, and may have originated from several sources, such as the urine or the sebaceous glands of the skin, which impregnated the belly. Moreover, we found differences in chemical profiles depending on age, with older males having higher proportions of benzoic acid and androstane-3,17-dione, but lower proportions of m-cresol. Because most of these compounds are strongly odoriferous, and appear related to male characteristics, our data indicate that scent from the hairs forming the black spot of the belly may be regarded as an overlooked new sexual chemical signal in red deer in the context of competition for mates during the rutting season.