The effects of heat stress, predation risk and parental investment on Malaysian plover nest return times following a human disturbance

Waders leave nests and conduct distractive displays when approached by people. The time taken for waders to return to nests depends on numerous factors that affect the costs and benefits of incubation and anti-predator behavior. Understanding this trade-off may help assess the reproductive consequences of different nest return times and identify variables to consider in breeding disturbance studies. We subjected 73 Malaysian plover (Charadrius peronii) nests to standardized human disturbances and an analysis of covariance was used to determine how weather, time of day, embryonic age, weeks into breeding season and nest attendance (proportion of time adults incubated nests) influence nest return times. Egg temperatures were estimated using a regression model that predicted the temperature inside unshaded eggs from air temperature, cloud cover and time of day (r2 = 0.88). We assessed the relationship between nest return times and hatch success. Plovers returned to nests faster at higher modeled egg temperature (P = 0.010), in the morning (P = 0.003), if they had younger clutches (P = 0.038), and if they had high nest attendance prior to the disturbance (P = 0.015). Pairs that returned to nests faster had lower hatch success (P = 0.021). This may be because pairs that spend more time distracting humans may also do so for predators. These results suggest that short nest return times may not indicate low fitness costs of disturbance. The thermal and predation environment in addition to nest return times should be taken into account when assessing the deleterious effects of human disturbance.