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Nest tunnels: How many are enough?

A duckling prepares to make life's first big leap from a tunnel. 

The use of artificial nest structures to increase waterfowl production is not a new idea. Nest success in fragmented habitats often is too low to sustain local populations, and managers continually look for new tools and techniques to improve local production.

Past research on nest structures focused on determining which types of structures and site characteristics were preferred by mallards and other species and how structures influenced nest success and duckling survival.

Managers placed one to three structures in a wetland, because it was assumed that additional ones would not be used due to the territorial behavior of breeding mallard hens. However, the use of multiple structures in a wetland by mallard hens has been frequently recorded. By placing multiple structures per wetland, installation and maintenance time decreases, hence reducing cost while possibly increasing duckling production.

Recent research undertaken by Matt Chouinard, under the direction of Dr. Rick Kaminski at Mississippi State University, and funded by the Delta Waterfowl Foundation, has addressed a fundamental management question: How many nest tunnels should be installed per wetland to produce the greatest number of ducklings at the lowest cost?

This research was conducted on a 20-square-kilometer area near Minnedosa, Manitoba, in 2001 and 2002. This area in Prairie-Parkland Canada is known for abundant breeding mallards but low productivity of nesting ducks.

Wetlands in the study area were separated into two size classes of less than 0.4 hectare and 0.4 to 1.4 hectares. Larger wetlands were excluded because ice movement in these wetlands can damage nest structures. Ten wetlands in each size class were randomly selected to contain one, two, or four nest structures. This resulted in six treatment combinations, and a total of 140 structures were erected in March 2001.

Researchers monitored the use of tunnels, nest success, and the number of ducklings produced for each structure. Use of structures was 42% in 2001, and increased significantly to 75% in 2002.

Nest success was 98% in 2001, but dropped to 41% in 2002 due to egg depredation by corvids. However, nest success remained well above the 15% level believed necessary to sustain local populations.

In total, 967 ducklings successfully departed structures during the study period. Results indicated that one or two structures per wetland produced about the same number of ducklings (five ducklings per structure), but more than four structures per wetland produced less (three ducklings per structure).

Wetland size did not affect occupancy, nest success, or ducklings per structure.

Based on preliminary result, a current best management practice may be to erect two structures per wetland because of the increased duckling production and because installing, maintaining, and monitoring two structures per wetland is more cost effective.

Republished with permission of "Birdscapes: News from International Habitat Conservation Partnerships," a publication of the U.S. Fish and Wildlife's bird habitat conservation division. For more information or to subscribe, please visit their website at http://library.fws.gov/Birdscapes/birdindex.htm.