ornamental traits, female body size, and temperature
As female body size is correlated with female fecundity, larger females of both Kentish plover and white-faced plover tended to have larger egg sizes , which suggested a positive effect on offspring survival rate and fitness . In accordance with sexual selection theory, which suggests that more fecund females should mate with males with more elaborate ornaments, we investigated the effects of male ornament PC1 and PC2 values, male body size, ambient temperature, and their interactions on female body size using phylogenetic generalized linear mixed models (PGLMMs). In addition, we included laying date and incubation period as fixed effects, while population and year were included as random effects.
2.8 Modelling theeffect ofmale ornamental traits and temperature on parental investment during incubation
We classified incubation behavior as either female attendance, male attendance, or absence of both parents at the nest. Due to instances of nest predation, abandonment, or camera malfunctions, we only analyzed data from 71 nests with continuous recordings exceeding 24 hours. We first tested the effect of ambient temperature on total incubation time for each nest using a PGLMM. To control for the effect of ambient temperature on total incubation time (see results), we calculated the average daily incubation attendance of both parents and used the ratio of an individual parent’s attendance to the total incubation time as a measure of their investment. To investigate the effect of male and female ornamental traits, body size, and temperature on parental investment, we employed PGLMMs. Fixed factors included temperature and the interaction between temperature and individual traits (if significant).