The Zebra Finch
In an article by Dave R. Vos, the role of sexual imprinting for sex recognition in zebra finches was studied by painting the bird’s beaks with nail polish. The white zebra finches were specifically used, and the researcher painted the bills of either parent orange and red, or red and orange, respectively. The sexual preference of the offspring, who were being reared by parents with painted bills, was then estimated through a series of tests with all combinations of stimulus birds of both sexes and bill colors (Vos, 1994).
Once the offspring were 120 days old, the testing began. Six males and five females were used as stimulus birds, which were reared by white parents with nail polish on their beaks. All birds were tested six times in a central cage with smaller cages inside on both sides. Each test lasted 20 minutes. For males, the number of song strophes was measured, as well as the amount of time spent in front of a stimulus bird. The female’s behavior that was worth observing was how long she spent in front of a stimulus bird (Vos, 1994). |
After these tests, results were analyzed in terms of males and females. Females proved to have no preference over bill color, and instead only had preference for males and males only. Males, on the other hand, showed a significant preference for a mate that had the same bill color as his mother. That being said, they did also show a preference for females over males (Vos, 1994).
These results provide good evidence to support that these preferences are critically dependent early experiences with the offspring’s parents. Males prove to only learn to respond to the sexual features of their mother and not their father at a young age. Because females didn’t seem to have preference over bill color, they have preference over the individual being male by exhibiting courtship behaviors. Females used differences in behavior of the stimulus birds to identify which individuals were males. These different behaviors demonstrated by each sex may have evolutionary consequences later on for the zebra finch (Vos, 1994). |
In
an article by Bischof and Rollenhagen, there is much emphasis placed on the
idea that sexual imprinting actually occurs in two stages. The first, called the acquisition period,
includes the birds learning about their social environment. The second, called consolidation or
stabilization process, incudes the birds’ sexual preferences once they are
sexually mature. The discovery of the
consolidation process is relatively new, and has raised the opportunity for the
physiological events that occur alongside imprinting to be investigated (Bischof, Rollenhagen, 1999).
A huge part of understanding sexual imprinting is understanding what areas of the brain go hand-in-hand with this process. While being exposed to females for approximately one hour, there were four parts of the forebrain that were significantly activated in male zebra finches. The first was the hyperstriatum accessorium and dorsale (HAD). The second area, called the lateral neo/hyperstriatum (LNH), receives visual projections. The third part is the archi-neostriatum caudale (ANC), which receives projections from sensory and brainstem areas. The fourth is the medial neo/hyperstriatum (MNH). All four of these forebrain areas light up during first courtship (Bischof, Rollenhagen, 1999). It is not exactly clear which physiological variables are important to understanding sexual imprinting entirely; however, understanding and observing which brain areas are activated during the stabilization process is the key to fully understanding this topic. Imprinting is a special case of learning, essentially, because it is a process of shaping neuronal networks to the environmental needs during development. Without sexual imprinting, the zebra finch would be unable to survive and reproduce (Bischof, Rollenhagen, 1999). |