Diversity, Migration, and Conservation of
Butterflies in Northern Costa Rica
William A. Haber and Robert D. Stevenson
MIGRATION CAN BE simply defined as a sustained, directional movement by an animal that takes it out of one habitat and into another (Dingle 1996), and this is the definition used here. It distinguishes migrating behavior from local movements within an animal's home range that tend to be nonlinear, of short duration, and confined to a single habitat (Dingle 1996). Seasonal migration typically involves a two-way trip between habitats, exemplified by the annual back-and-forth flights of Neotropical migrant songbirds between the North Temperate Zone and the tropics (Levey 1994; Martin and Finch 1995). Two-way migration by individual butterflies occurs in some longer-lived species such as the monarch in North America (Brower 1991, 1996) and the common Costa Rican migrant Manataria maculata (Satyrinae; Stevenson and Haber 2000a). However, the migration of most insects, relatively short-lived compared with vertebrates, is a one-way trip for a given individual, and members of a succeeding generation make the return trip (Haber 1993; Dingle 1996; chapter 7).
Migration behavior has been recognized in butterflies for centuries (Williams 1930; Johnson 1969; Baker 1978; Dingle 1996), although it has been studied in detail for only a few species, such as the monarch (Danaus plexippus) (Brower 1991, 1996) and the painted lady (Vanessa cardui) (Hansen 1997). Among butterflies, migrating individuals are generally easy to distinguish from nonmigrants. Migrants fly in a relatively straight line, usually 1–2 m above the ground, and rise over objects in their path, such as houses or forest patches, rather than flying around them. In contrast, active butterflies that are not migrating fly a crooked route, alighting often to bask or feed. Females stop frequently to check potential host plants, and males perch to watch for passing females. Their directed flights rarely take them more than 20 to 30 m in a given direction.