Non-Invasive Salivary Reproductive Endocrine Profiles in Gentoo Penguins

Reproductive endocrine monitoring in penguins is fundamental for improving reproductive management, conservation programs, and welfare assessment, but most studies use serum, which requires handling and blood collection. We hypothesized that saliva, which reflects the free fraction of circulating steroids and can be repeatedly collected with minimal disturbance, would be positively associated with serum concentrations, show hormone-specific reproductive temporal changes, and could be used as an alternative matrix for measuring steroid hormones in female gentoo penguins (Pygoscelis papua). Saliva from 21 females was collected every 3 days between 21 days before and 20 days after first egg-laying. Progesterone, 17β-estradiol, estrone sulfate, corticosterone, and testosterone were measured using competitive EIAs. Assay evaluation showed recoveries of 90.89–97.96% and intra- and inter-assay coefficients of variation <8%; paired serum–saliva analyses yielded r2 ≥ 0.858 for all hormones. Progesterone peaked in W−3 time window, 17β-estradiol in W−5, and estrone sulfate in W−4, with a decrease around egg-laying. These temporal patterns were consistent with endocrine changes associated with follicular growth, maturation, and oviposition. Saliva therefore appears to be a promising minimally invasive matrix for reproductive endocrine monitoring in female gentoo penguins, with potential future applications in welfare assessment and conservation breeding programs.