By Tina Yerkes, Ph.D.
The apple doesn't fall far from the tree. Unfortunately, I hear this all too often when my kids are misbehaving in public. Of course, I immediately attempt to blame their behavior on my husband's side of the family.
In general, behavior develops because of the interaction between genetic and environmental influences, often referred to as the nature versus nurture debate. Genetically programmed, or instinctive, behavior is often associated with survival. For example, sucking is an instinctive behavior for a newborn baby and necessary for the child to survive.
On the other hand, some behaviors are learned, such as typing on a computer keyboard. Much research into the nature versus nurture debate has been conducted, including studies involving human twins, and scientists now accept that nature and nurture interact, which ruins my ability to blame my kids' behavior on my husband's family.
Imprinting is a good example of how both nature and nurture influence waterfowl behavior. Upon hatching, many waterfowl are genetically programmed to recognize and follow movement of any kind. During a short window of time, they are also capable of learning to recognize the first moving object they see and will become socially attached to it. This object is usually their mother. However, geese hatched in captivity will imprint on humans, dogs, or other animals they first encounter. Researchers who raise goslings from the time they hatch often find themselves courted by the males when they become adults—an unfortunate side effect of imprinting.
Knowledge of the imprinting process has come in handy by allowing conservation organizations to teach migratory patterns to endangered birds. Whooping cranes were reintroduced to Wisconsin by imprinting captive-reared chicks on an ultralight aircraft made to look and sound like an adult crane. The whooping cranes flew behind the aircraft to establish a pathway between their wintering grounds in Florida and their breeding grounds in Wisconsin, thus reestablishing an eastern migratory population of whooping cranes.
Imprinting also serves an important reproductive function. In some cases, early imprinting determines preference for future pairing. This specialized form of imprinting, called sexual imprinting, enables birds to learn the characteristics of their siblings, which later influences their mating preferences as adults. Experiments with mallards and black ducks have demonstrated that females preferred males of the type they were raised with, even when ducklings were raised by parents of another species.
Lesser snow geese, which have both blue and white color phases, choose mates based on their experience with siblings and parents. Therefore, a blue-phase gosling raised with blue-phase siblings and parents will later choose a blue-phase partner most of the time. Ultimately, female choice is an interaction of "like-self" learning and the existence of the appropriate male courtship displays for that species.
Luckily, "like-self" pairing does not occur in waterfowl species that exhibit parasitic nesting behavior. One clear case of genetic hard-wiring occurs in waterfowl species that lay their eggs in the nests of other species. In North America, hen redheads often lay eggs in canvasback nests, and subsequently the redhead ducklings are raised by canvasbacks. But being a redhead is hard-wired, because redheads do not pair with canvasbacks later in life.
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.