The Larger the Egg, the Safer the Nest: A Study on the Negative Correlation Between Nest Predation Rates and Egg Size of Two Tropical Phasianids in Hainan

ABSTRACT Nest predation is the principal cause of breeding failure, with ground nests facing greater predation pressure. Most phasianids are vulnerable to endangerment owing to their relatively large body size, low breeding rate, and tendency to build ground nests. However, research on the nest predation of phasianids largely overlooks egg size, a potential key factor, especially in tropical phasianid nest predation studies. We aimed to investigate the influence of egg size on the predation rate and predator combinations of two phasianids (red junglefowl Gallus gallus jabouillei and Chinese francolin Francolinus pintadeanus ), which exhibit significant differences in egg size. We installed 167 artificial nests in the sympatric distribution areas of the red junglefowl and Chinese francolin within the Chinese Datian and Bangxi Nature Reserves in Hainan Province between April and September 2023. Eggs of four sizes from artificially reared Japanese quails Coturnix japonica , Chinese francolins, domestic chickens, and domestic geese were placed in the nests and monitored with infrared cameras. The results showed that the predation rates for small eggs, medium‐small eggs, medium‐large eggs, and large eggs were 83.3% ± 5.8%, 65.1% ± 7.3%, 51.2% ± 7.8%, and 26.8% ± 6.9%, respectively, exhibiting a decreasing trend, indicating a negative correlation between egg size and nest predation rate. The infrared camera data revealed small‐ to medium‐sized mammals as the primary predators (70.00%: small Indian civet Viverricula indica , Asian palm civet Paradoxurus hermaphroditus , and wild boar Sus scrofa ), followed by birds (20.00%: Greater coucal Centropus sinensis and Eastern marsh harrier Circus spilonotus ) and snakes (10.00%). Small rodents exerted a weak influence on the nest predation of the two phasianids. Therefore, egg size may contribute to the higher nest predation rate of Chinese francolin than that of red junglefowl. We propose that using experimental eggs matched in size with those of natural eggs improves the accuracy of artificial nest simulation studies. This also provides important empirical evidence to advance our understanding of nest predation mechanisms in terrestrial tropical phasianids, and to inform the development of more effective conservation and management strategies for these species.