3.3 The effect of male ornamental traits and temperature on parental investment during incubation.
We observed a high degree of consistency in both female and male incubation behavior across days (female: R = 0.621, confidence interval [CI]: 0.463, 0.741; male: R = 0.468, CI: 0.274, 0.626; Figure S5). This finding suggests that individual birds have a consistent incubation investment strategy.
Our results showed that the combined total incubation investment from both parents decreased with increasing ambient temperature (Estimate (95% CI) = -0.327 (-0.620, -0.047), z = -2.967, p = 0.003). This finding suggests that temperature is an important environmental factor that increases the overall incubation investment of plovers.
We observed that larger females invested more time in incubation compared to smaller females, as shown by a positive correlation between female incubation investment and individual tarsus length (Table 3). On the other hand, male ornamentation was found to play a role in their incubation strategy, as indicated by a significant interaction between male ornamentation and ambient temperature (Table 3, Figures 2a). Specifically, we found that more ornamented males decreased their incubation investment at warmer temperatures but increased it in colder temperatures (Table 3, Figures 2a, d, S6), suggesting that the effect of ornamentation on male incubation investment varies depending on the ambient temperature.