Sex-Specific Incubation and Body Orientation in the Black-Winged Stilt (Himantopus himantopus): Diel Patterns and Environmental Associations

Biparental cooperation during incubation is particularly important in harsh environments. We quantified sex-specific incubation contributions and body orientation in Black-winged Stilts (Himantopus himantopus) from one-minute images at 12 nests monitored for 24 h in Saudi Arabia. Incubation partitioning, environmental associations, and sex differences in body orientation relative to the sun and wind were evaluated using nest-level resampling and generalized linear mixed models, with Holm correction for environmental tests. Male incubation share averaged 50.72% (95% CI 47.21–54.35%), without clear evidence of deviation from 50% (p = 0.697). Male contributions varied among two-hour periods (cyclic-shift p = 0.042; parametric-bootstrap likelihood-ratio p = 0.004), whereas the daylight–night difference was inconclusive (p = 0.234). No environmental predictor of incubation partitioning was supported after correction. No clear sex difference was detected in solar-relative orientation (p = 0.154). Although the primary four-direction (p = 0.015) and exploratory eight-direction (p = 0.038) models yielded nominal sex-related differences in wind-relative orientation, these findings were not consistently corroborated by compass-preference-adjusted and episode-onset sensitivity analyses and therefore do not establish a sex-specific wind response. Sex-by-wind-speed interactions were inconclusive (p = 0.071 and 0.172). Overall, near-equal daily incubation contributions can mask temporal variation in parental duties across two-hour periods.