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Wed November 14, 2012
Dr. Walter Piper, Chapman University – Loons and Deadly Combat
In today’s Academic Minute, Walter Piper of Chapman University explains why territorial disputes among loons can become a battle to the death.
Walter Piper is a professor of biology at Chapman University in Orange, California. He has studied the territoriality of Common Loons since 1993 in Oneida County, Wisconsin. His Loon Project seeks to understand how young animals acquire a breeding territory and how older, established breeders hold onto their territories for as long as possible. He earned his Ph.D. at the University of North Carolina at Chapel Hill.
Dr. Walter Piper – Loons and Deadly Combat
Fights to the death are rare in animals. Premature death is evolutionarily disadvantageous, because it limits the number of offspring an animal can produce. Indeed, lethal battles occur chiefly in animals like fig wasps and spiders, which live fleeting lives and have only one chance to breed.
Common loons, large aquatic birds of the far north, are different. They often live into their 20s and have many potential years of breeding. A loon that dies in battle cuts short its reproductive life. Our 20-year study of loons in Wisconsin has revealed that, while both sexes engage in battles over territories, only resident males die during such contests. Why do male loons fight so desperately to retain territories? Could they benefit from residency in a way that females do not?
In fact, they do. You see: male loons, not females, decide where to place the nest. We know this because pairs in which a new male has replaced the old one fail to reuse the nestsite where the pair hatched chicks the previous year, while pairs that have lost the female breeder continue to use good sites. Since males control nest placement, only males show increased reproductive success on familiar territories. This no doubt helps explain why males would risk more than females to hold onto a breeding lake.
Still, continued ownership of a familiar lake seems an insufficient reward for a brush with death, considering that there are always vacant lakes available where displaced males could breed. At present, we are testing the hypothesis that male loons can become geriatric desperados -- birds so old and with so little expectation for the future that they put it all on the line in hopes of one more breeding attempt on a familiar lake.