The results of the U.S. Fish and Wildlife Service's 2009 Waterfowl Breeding Population and Habitat Survey are in, and the news is good.

The preliminary estimate of total ducks in North America was 42 million, up 13 percent from last year's estimate and 25 percent greater than the 1955-2008 average.

The survey samples more than 2 million square miles of waterfowl habitat across the United States (including Alaska) and Canada. It estimates the number of ducks on their primary nesting grounds and overall habitat conditions.

The key to waterfowl populations is habitat, measured as the number of ponds, the result of the previous year's snow melt and rainfall. The total pond estimate for the continent's "duck factory," the prairies provinces of Canada and northern prairie states of the U.S., was 6.4 million. This was 45 percent greater than the 2008 estimate of 4.4 million ponds and 31 percent above the long-term average of 4.9 million ponds.

Ducks require the nesting habitat surrounding ponds and the water itself to provide food and refuge. Simply stated, wet years result in more ducks; drought years cause duck numbers to plummet.

The vast majority of the continent's ducks nest around the potholes that dot the Dakotas, Minnesota, eastern Montana and Canada's prairie provinces. During drought years, however, potholes dry up and farmers cultivate these depressions in the landscape. This forces ducks to nest in increasingly fewer wetlands, making nests easier for predators to find. Drought imposes a double whammy on duck populations -- less habitat and higher predation rates.

The 1955-2008 averages of duck populations vary wildly, primarily based on the availability of nesting habitat in response to rainfall. Biologists are at the mercy of the independent and unpredictable powers of nature. Wildlife managers depend on wet years to help duck populations recover from dry years.

That's why the annual Waterfowl Breeding Population and Habitat Surveys are so important. Only by knowing where populations stand compared to past surveys can biologists intelligently manage North American duck populations, establishing frameworks used by the regional wildlife agencies that set duck hunter seasons and bag limits. The Pennsylvania Game Commission will announce seasons and bag limits next month.

During drought years bag limits are lowered, sometimes to zero, to protect species whose populations reach historic lows. In high-population years, such as this one, Pennsylvania and other states generally lengthen hunting seasons and increase bag limits to help control populations.

Mallards are widespread and abundant across the continent, so it's instructive to focus on them. As mallards go, so go other duck species.

This year the estimated mallard population was 8.5 million birds, 10 percent higher than last year and 13 percent more than the long-term average. But these numbers mean little without knowledge of historic extremes.

The best mallard years came in 1956 (10.4 million mallards), 1958 (11.2 million) and 1999 (10.8 million). The worst mallard years were 1965 (5.1 million), 1984 (5.4 million), and 1985 (5 million). So while this year's count of 8.5 million is nearly double the worst years' numbers, it is nearly 2 million birds below the highest counts.

Several other species are having banner years. Gadwalls (3.1 million) are up 73 percent over the long-term average. Blue-winged teal (7.4 million) and green-winged teal (3.4 million) are up 60 percent and 79 percent, respectively. Northern shovelers (4.4 million) are 92 percent above their long-term average.

Some species, on the other hand, are up for the year but still below their long-term averages. Northern pintails (3.2 million), for example, are up 23 percent this year, but down 20 percent from their long-term average.

The best way to guarantee healthy populations for the future is to protect more habitat. Hunters, birders and arm-chair conservationists can help by buying a duck stamp every year. Available at larger U.S. post offices and some outdoor stores, the Migratory Bird and Conservation Stamp costs $15 and is required by anyone who hunts waterfowl. A duck stamp also entitles its holder to free admission to national wildlife refuges.

The duck stamp funnels money into the Migratory Bird Conservation Fund. For every dollar raised, 98 cents is used to buy land for the National Wildlife Refuge System. Since 1934, the Federal Wildlife Service has collected more than $750 million and purchased or leased 5.3 million acres of waterfowl habitat.

The Pennsylvania Game Commission has invited hunters, representatives of waterfowl organizations and the general public to attend a briefing on the status of Atlantic Flyway waterfowl populations and proposed preliminary federal frameworks for the 2009-2010 waterfowl hunting seasons. The briefing starts at 1 p.m. Aug. 7 in the Stull Environmental Education Center at Presque Isle State Park, Erie County.