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Where Have All the Females Gone? Experts on Canvasbacks Worried


It's hard to imagine what the world would be like with three men to every woman. No doubt, the male ego would be thrown into overdrive and the battle of the sexes would take on a whole new meaning. Fortunately for the human race, the sexes are fairly evenly matched, with men and women each representing about 50 percent of the population.

For canvasback ducks, on the other hand, the sex ratio is decidedly skewed in favor of the males. According to an aerial survey conducted by the U.S. Fish and Wildlife Service in 1981, male canvasbacks outnumber females by a ratio of nearly 3-to-1. This imbalance represents the most disparate sex ratio of all North American ducks and has raised concern among biologists about the future success of the species.

Particularly troubling to some scientists was the Fish and Wildlife Service's decision to open a hunting season on canvasbacks this year. For many areas, the 1994-'95 season on canvasbacks was the first in nearly a decade and the first in 22 years that did not in some way restrict the harvest of females. The Fish and Wildlife Service authorized a one-month period to hunt canvasbacks with a bird-a-day bag limit. The regulations did not specify gender; thus, either sex could be taken to satisfy the limit.

States may narrow hunting seasons and bag limits proposed by the federal wildlife service. Maryland chose to shorten the one-month season to one week, which started on Jan. 7. The Maryland season retained the one-bird-a-day bag limit and did not add any further restrictions based on sex. Virginia is allowing a full one-month season which began on Dec. 20, 1994, and closed on Jan. 20, 1995. Virginia also is enforcing the one-bird-per-day limit.

The decision to open a season on canvasbacks was based on improved breeding conditions and successful recruitment of the species in recent years. The problem, according to Matthew Perry, a biologist at the wildlife service, is that "the species isn't ready for a hunting season, especially the females. People forgot that one hen killed today is one not producing eggs in the spring." In past experimental seasons, the wildlife service has controlled three male birds and one female per day during a six-day season. Scientists and conservationists are concerned that the lack of such safeguards in this year's season may detrimentally affect the canvasback population.

Canvasbacks are the largest member of the diving duck family and slightly outweigh the mallard and American black duck.

The white plumage of the drake and its fabric-like appearance on the water appear to account for the duck's name. Others believe the name derives from a system of transporting hunted ducks in bags marked "canvas-back."

In air, not on ground

Canvasbacks are extremely capable fliers. Traveling at speeds in excess of 80 mph, they are the fastest of all the duck species. Despite their prowess in the air, however, they are extremely awkward on land, and therefore, rarely come ashore.

Each year, the ducks arrive in mid-December and stay on the bay until early spring, when they depart for their breeding grounds on the northern prairie. Like crabs and oysters, the canvasback has played an important role in the history and economy of the bay. Through the 1800s and most of the 1900s, the canvasback has been hunted for sport and for food. From 1966 to 1970 an average of about 15,000 canvasbacks per year were killed in Maryland and 8,000 per year in Virginia.

There is no telling how many ducks were taken before official records were kept, but it is clear that the canvasback was hunted aggressively and without restraint. Everything from boat-mounted cannons to heavy-bore shotguns and punt guns was used against the big flocks. These unregulated takings eventually depleted the enormous population of canvasbacks that wintered on the Chesapeake Bay. As recently as 1954, there were an estimated 420,000 canvasbacks on the bay. Today, surveys indicate that there are about 51,000.

In 1972, the wildlife service banned all hunting of canvasbacks on the Chesapeake Bay. In 1983-'85 there was an experimental season along portions of the Atlantic flyway including the bay. An estimated 15,850 canvasbacks taken in those three years, or 71 percent of the canvasback harvest, came from the bay region.

Why no rebound?

Even though canvasback hunting has been prohibited or strictly controlled for more than 20 years, the species has not fully rebounded in the Chesapeake Bay area. Some experts speculate as to why the ducks have not made a better comeback on the bay, but to others the answer is painfully clear.

"The canvasbacks simply could not get the food they needed to survive anymore," explains Dr. Kent Mountford, a senior scientist with the EPA's Chesapeake Bay Program. "Water disturbance and contamination caused the depletion of a large amount of submerged aquatic vegetation which is a key food source for the canvasback. The loss of the [vegetation] seemed to be what drove away the ducks."

While habitat degradation is one problem the species still faces, scientists also are concerned about the mysterious imbalance between male and female birds. With almost three times as many male birds, the breeding potential of the species is severely limited.

Wildlife biologists are not sure what causes the disparate sex ratio in canvasbacks. The most probable theory is that females are more susceptible to predation during the breeding season due to their role of guarding the nest. Another theory, supported by a study conducted by the wildlife service in 1986, is that males simply out-survive the females because of the greater body weight and food dominance. The study indicates that a mature male canvasback usually outweighs the adult female by at least a couple of ounces. The additional body weight, according to the study, directly correlates to better endurance and winter survival.

Because the female canvasback tends to wander from the safety of the flock, she is vulnerable to inadvertent hunting. Maryland game officials report incidents of female canvasbacks being killed by hunters who believe that they are shooting at a different species.

Picking out males

Opponents of the current canvasback season argue that it would have been feasible for the wildlife service to require hunters to shoot only the male canvasbacks. Unlike the female, they argue, the male canvasback is easily distinguishable from the female and from other duck species.

Advocates of a "males only" season point to existing wildfowl regulations which require hunters to distinguish between similar-looking species of ducks. These regulations, they claim, force hunters to make finer distinctions than would be required in a selective season on male canvasbacks.

The wildlife service believes that a "males only" season places too much of a burden on hunters trying to distinguish between the sexes. "Telling the difference between males and females can be extremely difficult in early morning light," remarked one official.

Educating hunters

Mr. Perry, the wildlife service biologist, believes the restriction would not be too burdensome if hunters were properly educated about wildfowl.

Protecting the canvasback duck is as much about preserving heritage and tradition as it is saving wildlife. For many residents along the Bay, the canvasback has become a symbol of the Chesapeake and a bygone way of life. For these people, ensuring a successful future for the canvasback is like protecting a valuable family heirloom.


Blaine T. Phillips is a free-lance writer who lives in Delaware.

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