Temporal fluctuations in the sex ratio of a broad-snouted caiman (Caiman latirostris) population in a highly impacted Atlantic Forest of Brazil

Context The sex ratio of a population dictates intraspecific interactions, including agonistic behaviours and mating. Moreover, discrepancies in the male-to-female proportion may reduce reproductive processes and threaten population maintenance. Aims We estimated temporal changes in the sex ratio of a broad-snouted caiman (Caiman latirostris) population in northeastern Brazil. Methods From August 2013 to June 2022, we captured caimans in the Tapacurá Reservoir, a water source bordered by Atlantic Forest fragments in Pernambuco state. We made caiman captures manually or by snares, measured all individuals, determined their sex by cloacal inspection, and marked them by notching in caudal scutes and microchip subcutaneous implants. Key results We captured 455 caimans, including 45 recaptures. After excluding individuals for which we could not determine the sex (35.3%) and recaptures, we estimated the male/female ratio as 1.8 ± 0.8 across the years surveyed. Using generalized linear modelling, fast Fourier temporal transform, and Mann–Kendal analysis, we found no significant differences in sex ratio among years, between reproductive and non-reproductive seasons, or with varying rainfall levels. The higher proportion of males may be related to elevated temperatures, as sex of caimans is determined by temperature of incubation and higher temperatures produce male individuals (although temperatures over 34°C generally produce more females with reduced hatching success). The absence of temporal differences in the sex ratio may indicate that caimans are less likely to move across habitats and remain year-round in Tapacurá Reservoir. The dam wall in Tapacurá creates a physical barrier, minimising caiman dispersal and maintaining them within our target population. Moreover, we suspect no differential mortality between males and females, maintaining a stable sex ratio. Conclusions We highlight the importance of understanding the sex ratio of broad-snouted caimans in a little-known region from northeastern Brazil. Implications We encourage the continuation of surveys to estimate population sex structures across the broad-snouted caiman distribution, especially in regions with other latitudes, to improve conservation strategies of human-threatened caiman populations and their habitats.