Study Prompts Uncertainty About Habitat Management
by Thomas Hutchens

Put on your thinking caps and see if you can identify the source of the following quote: “with the exception of nest structures, nest success was low in all habitats. Predation negatively influenced production at all sites...”

How about this one? “they (nest success results) imply greater uncertainty about habitat management prescriptions...”

Most readers would probably guess those quote came from one of Delta Waterfowl’s student research projects on predator management.

They did not.

The above quotes were excerpted from an ambitious nine-year research project that should have left waterfowl management in a state of shock: The Prairie Habitat Joint Venture (PHJV) Assessment Study conducted by Ducks Unlimited’s Institute for Wetland and Waterfowl Research (IWWR).

From 1993 to 2000, IWWR scientists monitored nest success on 27 low-, medium- and high-treatment sites across Manitoba, Alberta and Saskatchewan, and what they discovered shakes the sacrosanct assumption that habitat alone is the key to sustaining healthy duck populations.

Scientists say that for mallards to sustain their existing population, nesting hens must achieve about 18 percent nest success. In the eight-year IWWR study, mallards surpassed 18 percent at only three of the 27 sites—Mayfield success of 21 percent, 23 percent and 36 percent were recorded at three high-treatment sites. The other six high-treatment sites recorded nest success ranging from one to nine percent.

At five of the nine sites, the percentage of hens that died during the nesting season exceeded the number of hens that successfully hatched an egg.

If the reader is not floored by these findings, I’d suggest the foregoing should be re-read. Does this represent the best habitat manipulation can produce?

Statistically, treated landscapes did better than untreated landscapes. Nest success at four of the nine high-treatment sites and four of the medium-treatment sites were statistically better than nest success on control sites. The bottom line for duck hunters: Mallard nest success still fell below population-sustaining levels at all but one of those sites.

The fact that the PHJV study was conducted between 1993 and 2000, a time when the continental duck population was soaring thanks to one of the most prolonged wet cycles of the 20th century, should be of grave concern to waterfowl managers everywhere.

It should be of concern, but it shouldn’t come as a surprise.

Scientific research published since the PHJV study was undertaken explains the pathetic results. One of those research projects shows that unless 40 percent of the landscape has grass cover, ducks typically don’t achieve population-expanding nest success, regardless of how many dollars were spent on small-scale habitat manipulation.

At Delta Waterfowl, we believe two approaches are necessary to produce ducks. First, when it comes to habitat—go big (40 percent grass cover). Second, in areas where duck hunters will never have the dollars to put 40 percent of the landscape into grass, management tools like predator removal and artificial nest structures (Hen Houses) must be incorporated.

We encourage DU and everyone else involved in the critically important job of securing habitat to re-evaluate their approach to the former, and allow Delta Waterfowl to focus on the latter.

If the PHJV Assessment study proves scattered habitat projects aren’t always enough to increase duck production, it also confirms the wisdom and prescience of the early-on observation made by one of the preeminent duck biologists of recent times, who in 1994 wrote, “The single most important factor depressing current waterfowl populations is the low success rate of nesting hens that is the result of severe predation rates on the prairies. In many areas of Canada, this factor is thought to be even more significant than the historical loss of wetlands.”

Who said that? Dr. Bruce Batt, Ducks Unlimited’s chief biologist.