Each spring and fall, neotropical migrant birds fly thousands of miles between breeding areas in North America and wintering grounds in Central and South America, navigating by cues such as the sun and stars, visual landmarks, the earth's magnetic field, and gravity. These migrants include warblers, vireos, hummingbirds, shorebirds, and some birds of prey, and their populations reflect environmental health. Many have been declining because of habitat loss from forest destruction, wetland drainage, and urban growth in both North America and developing Latin American countries, as well as pollution, especially pesticides, human disturbance, and predators such as the common house cat. Growing attention to their plight has led to programs focused on these birds. Wildlife habitat can also be supported in yards and gardens by providing food, water, shelter, and space through trees, shrubs, flowers, feeders, and water sources. Berry-producing trees and a diversity of plants can attract a wider variety of birds and insects, while butterflies can be drawn by nectar-producing flowers and supported by host plants such as milkweed, which monarchs need for laying eggs and feeding their caterpillars.