As the sun sets, many animals prepare to sleep for the night while others are just waking up, helping predators avoid competing with each other for food and space. Nighttime at the Slough is full of activity. Sunset signals the time for White Ibis to return to their rookery to roost. Night Herons have excellent night vision and feed in the evening so as not to compete with other wading birds. A single bat can gobble up to 3,000 insects in one night. Dragonflies spend their larval stage underwater, then crawl up a stem, shed their old skin, and emerge with wings, usually at night to avoid predators active during the day. Alligators mainly hunt and feed at night when the water temperature is above 73oF, and during cold spells they seldom eat. Male frogs call to set up territories and attract females. Owls' feathers have soft edges that help muffle the sound of their flight. Zebra Longwing butterflies gather in the late afternoon to roost for the night, sometimes in groups of up to 60 individuals. Many animals such as alligators, turtles, and raccoons move from pond areas to dry land using well-worn trails. Bobcats are shy and secretive, so their signs, such as scat, are more likely to be seen than the animals themselves. Moonflowers open at night and are white to attract attention in the dark, and moths such as Sphinx Moths use an extremely long proboscis to sip nectar found deep inside. Most birds perch to sleep at night and do not fall because special tendons in their legs lock their toes in place.