Immature and mature sperm morphometry in fresh and frozen-thawed falcon ejaculates (Villaverde-Morcillo et al., 2017)

Sperm morphometry can help predict fertility and sperm freezability in various species. Understanding the ejaculate`s sperm characteristics and morphometric descriptors is crucial for effective sperm cryopreservation. This study aimed to describe the sperm of two falcon species (Peregrine Falcon Falco peregrinus peregrinus/brookei and Gyrfalcon Falco rusticolus), including immature sperm, sperm head morphometry, and the presence of subpopulations of mature sperm. Semen samples were collected via massage and voluntary false copulation, diluted with Lake and Ravie medium, and analyzed through morphological and computerized morphometric techniques, measuring sperm head length, width, area, and perimeter. In the Gyrfalcon, pooled semen was frozen using DMA as a cryoprotectant, and analyses were repeated after thawing. The study found similarly high percentages of immature sperm in all species/subspecies: 55.5% in Brookei Peregrine Falcons, 65.5% in European Peregrine Falcons, and 64.7% in Gyrfalcons. Four distinct subpopulations of mature spermatozoa were identified, with different morphometric characteristics, although their relative proportions were consistent across species. The thawed Gyrfalcon samples showed significantly lower morphometric values compared to fresh samples. These findings support the notion of pleiomorphy in raptor sperm and suggest that identifying different sperm subpopulations may play a critical role in developing future cryopreservation protocols for falcons.