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Mating season at hand for birds

PHOTO PROVIDED It is well known that when in captivity, closely-related species will readily crossbreed. For example, the mallard duck and the pintail duck will crossbreed in captivity. However, in the wild, they can be nesting side by side, in large numbers, and do not crossbreed.

Recently, I read a study had been done on the reproduction of bobcats. In 1991, 32 bobcats were placed on an isolated island, separated by open water which prevented the cats from returning to the mainland. Blood samples were taken from each cat before being released.

After the first litter of kittens was born, blood samples were also taken from them. Throughout the years, volunteers collected bobcat scat from which DNA was extracted and used it to monitor the genetic health of the population.

This study allowed scientists to identify individual bobcats, which enabled them to document the survival rates and levels of interbreeding. They were also able to document the loss of genetic diversity over a period of time affected the population.

Today, there are only 24 bobcats on the island. Researchers are predicting by 2040 the risk of extinction of bobcats on the island will be increased by 20%. Scientists could restore the loss in genetic diversity, simply by introducing bobcats from the mainland every four or five years.

After reading this study, I wondered what effect interbreeding has on birds and animals in the wild. When checking in my North American Encyclopedia of Birds of North America, I found birds in the wild do not interbreed in the wild and why not.

The Union of American Ornithologists officially recognizes 796 species of North American birds. A species is an interbreeding group of birds, animals or plants which does not, in nature, interbreed significantly (enough to break down species identity) with any other group.

A species is a kind of bird. For example, a robin, blue bird, wood thrush, blue jay and cardinal is each a member of a separate species. Although some species appear the same, they will not interbreed. There are five species of thrushes, which appear similar, which live, breed and nest within the same area. However, no hybrid birds have ever been seen.

Detailed scientific studies show that birds successfully mate with their own species to produce a continuing line of descendants. This is due to the species behavior toward the opposite sex.

Signs and signals which pass between two potential partners must be right for each species. The males of every species have specific courtships, or displays, to which (usually) only one female of the same species is receptive.

These behaviors are most important in keeping birds isolated in their species. Because each species has its own special courtship, interbreeding is prevented, and just as effective as if the two species, living side by side, were a thousand miles apart.

The special recognition of each species has caused males and females to come together. This can be done by songs, calls, special courtship flights, body posture and flashes of color.

Studies have shown that potential mates of different species, even in their very similar breeding rituals, will not interbreed. If interbreeding does occur, which is very rare, the male might not transfer sperm to the female. Even if two different species did manage to copulate and the male transferred sperm, the resulting egg might not hatch because the male sperm did not fertilize the female ova. Against all of these odds, and if the eggs did hatch, the hybrids might not be fertile or healthy enough to live.

It is interesting to note that the female makes the choice of mate by her acceptance of the male. In most species, the males establish their territories in the spring and then await the arrival of the females. In protecting his territory, the male will attack and drive away any invading males and even females. However, if the female chooses his breeding territory, she will remain in the area. The female will then submit to his aggressive tactics. Courtship begins, when this occurs, and now, the male begins to pursue the female.

At this point, the female could wander in and out of several territories before selecting a particular male. Within a few days, a bond is formed between the male and female.

Most birds have a preliminary period of courtship in selecting mates, followed by other rituals before mating occurs. This mating is frequently repeated during the breeding season, before and during the egg-laying period of the female. This ensures that the eggs will be fertile and also helps to maintain a bond between the male and female.

It is well known that when in captivity, closely related species will readily crossbreed. For example, the mallard duck and the pintail duck will crossbreed in captivity. However, in the wild, they can be nesting side by side in large numbers and do not crossbreed.

Well, the mating season for most birds is at hand. Perhaps there is no better time to study and enjoy our feathered friends than at this time. So, go outside and enjoy the songs, the flashing colors and the courtship flights.

Bill Bower is a retired Pennsylvania Game Commission Wildlife Officer. Read his blog and listen to his podcasts on the outdoors at www.onemaningreen.com.

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