Posted by tags: researchblogging.org, evolutionary behavior, sociobiology, ornithology, birds, avian, evolution, William Dilger, Agapornis roseicollis, Agapornis fischeri, lovebirds
Peach-faced lovebirds, Agapornis roseicollis (left)
and Fischer’s lovebirds, Agapornis fischeri (right),
can interbreed to produce sterile offspring.
Images: LoveBirds New Zealand.
Is behavior genetically “programmed” or is it the result of learning? Or is it instead a little bit of both? This is the old “nature versus nurture” argument that has occupied behavioral and evolutionary scientists, psychologists and even the general public for decades. Interestingly, nearly 50 years ago, a series of elegant experiments by an ornithologist and aviculturist revealed that, in lovebirds, at least, nest-building behavior has a very strong genetic component combined with surprisingly little experiential modification.
William Dilger, a professor of ornithology at Cornell University, studied lovebirds for many years as he sought to learn more about the evolution of breeding and social behaviors, especially to understand which components of these behaviors are inherited and which are learned. Further, he determined the evolutionary relationships between these birds based on the complexity of their behaviors.
His subjects, the lovebirds, are a group of small short-tailed parrots in the genus Agapornis that are endemic to Africa and the island of Madagascar. Lovebirds were so named because breeding pairs typically feed each other to re-establish their pair bonds after experiencing separation or stress. This feeding behavior, where one bird transfers food from its mouth to that of its mate, resembles kissing in humans, thus earning them their name. Fortunately, several species of lovebirds have been and continue to be popular pets and breeding subjects for aviculturists throughout America and Europe, so they are easy to propogate and to study in captivity.
During the course of his many studies, Dilger noted that even though lovebirds are closely related, different species use different strategies to collect materials and carry them to a pre-selected tree hole where they then constructed their nests. For example, Fisher’s lovebirds, Agapornis fischeri, carry single strips of tree bark in their beaks whereas peach-faced lovebirds, Agapornis roseicollis, tuck many pieces of tree bark into their flank and rump feathers before carrying them to their nest hole. Because the peach-faced lovebird’s behaviors are more complex, Dilger deemed this species’ behavior to be ancestral to that of the Fischer’s lovebird.
To determine whether this particular behavior was genetic or learned, Dilger hybridized Fischer’s lovebirds with peach-faced lovebirds. Even though the resulting hybrids were sterile, the lovebird hybrids still showed breeding behavior and surprisingly, they displayed nesting behaviors that are intermediate between the two parental species.
In short, Dilger found that the hybrid lovebirds demonstrated a confused combination of the two nest material carrying strategies: initially, the young birds tucked the nest material (strips that they had chewed from a larger piece of paper) into their flank and rump feathers but failed to let go, so they pulled them out again and again, repeating this pattern many times. As the birds matured and gained experience over a period of three years, they eventually settled on carrying nest materials in their beaks, like their Fischer’s lovebird parent. However, they still maintained a peculiar ritual associated with the tucking of nest materials, like that of their peach-faced lovebird parent, prior to flying off with the paper in their beaks. Typically, they would turn their heads toward their rumps but would not tuck the nest materials among their feathers, although occasionally they still tried to tuck the paper strips into their rump feathers. It is interesting to note that the hybrid birds eventually adopted the least complex (and most derived) behavior among those available to them.
Since lovebirds can breed at six months of age, even if these hybrid birds were fertile, they would have not lasted long in the wild (nor, probably in captivity) because they would not have been able to produce many (or any) offspring in their lifetimes due to the length of time required for them to learn how to circumvent a seemingly simple yet genetically programmed behavior, such as carrying nest materials to their nest hole. This research concisely demonstrates the difficulties involved with learning to use one innate behavior at the expense of another.
Because the hybrid lovebirds were sterile and thus, could not breed with either parental species nor with each other, Dilger was never able to determine whether this behavior was the result of a single gene or several. But Dilger’s studies were so elegant that they helped to define this new field of evolutionary behavior.
Sources
Dilger, William. The Behavior of Lovebirds. Scientific American 206 (1), 89-98 (January 1962) [PDF]
Alcock, John. Animal Behavior: An Evolutionary Approach, 3rd Edition. (Sunderland, Mass.: Sinauer Associates; 1984) pp 32-33.
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