The black-headed duck of South America is an odd duck because it is an obligate parasite, meaning that it lays its eggs only in the nests of other species, including other ducks, gulls, and coots. The ducklings mature independently, requiring only a few days of care by the unsuspecting parent. Black-headed ducklings rely entirely on their genetic heritage to respond to calls and displays of their own species when it comes time to pair as adults.
Migration is another complex activity in birds, which exhibit two behaviors when preparing to migrate: pre-migratory fattening and restless nocturnal activities. Both behaviors are genetically programmed, as they are observed across all types of experimental protocol including birds raised in complete isolation. Migratory birds predictably exhibit Zugunruhe, a word of German origin meaning “migratory restlessness,” right before they migrate. If birds can see the sun, they orient this restlessness in the direction of the migration they are about to undertake. Pre-migratory fattening is also genetically programmed to ensure that long-distance migrants, such as waterfowl, have enough fuel deposited to aid the trip.
Once birds physiologically commit to the journey, they use navigation to chart their course during migration. The navigational ability of birds is the result of dual influences from nature and nurture. Orienting, the first step in navigation, is a genetically programmed ability to adjust direction based on the earth’s geomagnetic field. Use of the earth’s magnetic fields, however, cannot get a bird precisely to its destination. Precision in navigation is a learned behavior and generally based on early experience with prominent landscape features, such as river systems and mountain ranges. Birds also learn to use the sun as a solar compass. Because experience is required to fine-tune migratory pathways, immature birds get lost from time to time and end up in odd places.
Scientists now know that the variation of behaviors that exist within or across species is shaped by the interaction between nature and nurture. Those behaviors we observe in waterfowl are no different. But the nature versus nurture debate is still rather healthy when it comes to human behavior.
Dr. Tina Yerkes is director of conservation planning at DU’s Great Lakes/Atlantic office in Ann Arbor, Michigan.