Incubation behavior of female western snowy plovers (Charadrius alexandrinus nivosus) on sandy beaches

In Western Snowy Plovers (Charadrius alexandrinus nivosus), both parents share incubation duties, with males typically incubating at night and females incubating during the day. Typically, plovers run off the nest at a long distance from potential nest predators, including humans. Thus, human disturbance in recreationally used beach areas may affect incubation behavior of female plovers incubating during the day. I studied Snowy Plovers nesting on two sites on Clam Beach, Humboldt County, California. I conducted focal observations on incubating females during mornings and recorded nest attentiveness, number and causes of off-bouts and counted human and natural disturbance within 100 m of nests. I further examined if female nest attentiveness varied with stage of incubation and level of experience. Females had markedly higher variation in nest attentiveness during early (days 0-10) than during middle (days 11-20) and late (days 20-hatch) incubation. Recesses tended to be shorter and less variable after the first ten days of incubation, while the number of off-bouts did not differ between early, middle and late incubation. Experienced females and birds nesting in areas of low human disturbance tended to have higher nest attentiveness and lower variation in incubation behavior than inexperienced females and birds exposed to high levels of human activity.