Antler size decreases with increasing age: evidence of reproductive senescence in male Fallow Deer (Dama dama)

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Abstract Reproductive senescence, the decline in reproductive performance with increasing age, is extensively documented in females but much less investigated in males. However, senescence of secondary sexual traits in males, such as horns or antlers, has been reported across various vertebrate species. Our study investigates reproductive senescence in antler size, a conspicuous precopulatory trait in male deer, by taking advantage of detailed monitoring of a free-ranging population of Fallow Deer (Dama dama) living in a peri-urban area. We focused on 2 metrics utilizing noninvasive photogrammetry to measure antler length and palm width in 127 free-living males. Our results demonstrate clear evidence of reproductive senescence, with both antler length and palm width declining synchronously from approximately 7 years of age onwards. This decline matches previously reported decreases in male mating success from ages 6 to 7, suggesting that antler size may impact sexual competition and mating success. Males older than 7 years of age may experience reduced competitive abilities and diminished attractiveness to females. This study provides new evidence of senescence of antler size in cervids, enhancing our understanding of the eco-evolutionary factors driving male senescence and emphasizing the importance that antler size may have in the reproductive success of Fallow Deer.