Research

Mallard Hen Survival in the Canadian Aspen Parklands
by Jim Devries, Institute for Wetland and Waterfowl Research

Editor: This is the fourth in a series of articles on the findings of the 8-year Prairie Habitat Joint Venture Assessment Project.

The breeding season is a dangerous time for mallard hens. Hens attending nests are particularly vulnerable to a suite of avian and mammalian predators. Analyses of banding data have inferred relatively low survival during this period, and the few studies conducted to measure survival rates support this conclusion.

The Prairie Habitat Joint Venture Assessment Project determined the response of waterfowl to an array of upland habitat programs. It also explored female mallard breeding season survival in unprecedented detail. The study was conducted on 27 sites in the parklands of Prairie Canada from 1993-2000. During that time, about 3,600 mallard hens were equipped with radio transmitters and tracked throughout the nesting season. Analyses of survival rates and factors that affect those rates have uncovered new and, in some cases, surprising findings.

To date, relationships between hen survival and geographic location, habitat composition, predator abundance, nesting activity, age, population density, and level of joint venture habitat treatment have been examined. Hen survival from mid-April to mid-July varied between 60% and 85% and averaged 76%. Unexpectedly, survival rates tended to be lower in the western parklands, where coyote and red-tailed hawks are dominant predators, and highest in eastern parklands, where fox and mink are dominant. Fox and mink were considered to be the main predators of breeding females. Survival also depended on the wetland and grassland composition of study sites. At sites with little grassland, survival decreased with the percentage of wetland habitat. At high grassland sites, survival increased as wetland habitat increased. The influence of wetlands and grasslands on predator foraging patterns and east-west gradients in predator communities may be driving these results.

Hen survival was particularly low during the middle of the season when nesting activity was most intense. Many females were found dead on or near known nests. However, contrary to conclusions from banding analyses, which indicate lower survival of older females during the April-September period, no difference in survival was detected between age classes. This indicates that age differences arise during late summer. Hen survival was not affected by population density nor by the amount of joint venture habitat treatments on the sites.

These results provide important new information. A previous analysis of assessment data indicated that female survival and nest success have the greatest impact on mallard population growth rates (Birdscapes, Fall 2003). While habitat programs designed to improve nest success were expected to improve hen survival, this was not the case. Nevertheless, this analysis provides another piece of the puzzle in understanding the interplay of habitat and waterfowl productivity. Wetlands influence several aspects of waterfowl productivity. Previous analyses have identified wetland habitat impacts on duckling survival, nest success, and now hen survival. Finally, the magnitude and variation in breeding season survival estimates observed during this study provide essential information for those tasked with managing mid-continent mallard populations.

For more information, contact Michael Anderson, Director, Institute for Wetland and Waterfowl Research, Ducks Unlimited Canada, (204) 467-3231, m_anderson@ducks.ca.

Pintails in the Playas
by Jena Moon and David Haukos, U.S. Fish and Wildlife Service

Northern pintail population estimates have been declining in the traditional survey area since the late 1970’s, from over 5 million birds to an all-time low of 1.8 million birds in 2002. Researchers have hypothesized that declining habitat conditions in migrating and wintering areas in combination with low nest success, disease, low survival rates, and high harvest rates have kept pintail populations depressed. Managers need information from all aspects of pintail ecology, especially wintering ecology, to create a population model and to better develop management recommendations.

To enhance the information base, we initiated a radio telemetry study on female northern pintails in the Playa Lakes Region of Texas, which provides important migration and wintering habitat for these birds. Using baited swim-in traps and rocket nets, we captured 158 females in fall 2002, and 168 in fall 2003. Each year, we fitted all the birds with a radio transmitter and monitored them from October 10 through February 18, or until they left the region.

The estimated survival rate for the 2002-2003 field season was 92.6%. Mortality factors included predation (38%), hunting (24%), and unknown causes (38%). All but one case of mortality occurred between December 12 and January 19, the pintail hunting season. Data are currently being collected, compiled, and analyzed for the 2003-2004 season. The final report will be available in August 2004.

We collected habitat-use and movement data three times a week during four daily time periods. The 1,251 habitat observations made in 2002-2003 revealed that habitat use differed by time of day and by month throughout the study. Female pintails used more heavily vegetated wetlands during crepuscular hours and in late winter (January and February).

Based on 361 observations, we determined the birds’ 24-hour movements for the entire length of the study. One-way, daily-movement distances increased by 60% with the onset of the pintail hunting season and the initiation of field-feeding, both of which occurred during the same week. We noted a subsequent 40% drop in daily-movement distance at the end of the hunting season; however, birds continued to field-feed.

During the 2002-2003 field season, the Playa Lakes Region of Texas experienced mild temperatures and had exceptional habitat quality for wintering waterfowl, which led to high survival rates. An estimated 22% of the approximately 25,000 playa wetlands were available to wintering waterfowl during 2002-2003. Habitat conditions in the 2003-2004 field season differed drastically, with precipitation being the lowest since 1917. The Playa Lakes Region received only 8 to 11 inches of rain, less than half the long-term average. Under these conditions, less than 1% of total playa wetlands were available to wintering waterfowl. Preliminary data from the 2003-2004 field season indicate a much lower survival rate than for the previous field season.

Researchers in California, New Mexico, Nebraska, and on the Texas Coast are collecting pintail data complementary to ours. Combined, these data will provide insight into the potential causes of the downward continental-population trend. Ultimately, the collective data will be used to evaluate cross-seasonal effects on pintails’ spring-migration-habitat use, survival, and movements.

For more information, contact Jena Moon, Research Assistant, or David Haukos, Regional Migratory Bird Management Specialist, U.S. Fish and Wildlife Service, Department of Range, Wildlife and Fisheries Management, Texas Tech University, P.O. Box 4169, Lubbock, Texas 79409, (806) 742-2843, jena_moon@hotmail.com or david_haukos@fws.gov.

Northern Pintail Study Partners

U.S. Fish and Wildlife Service - Region 2
Northern Prairie Wildlife Research Center
Texas Tech University
Playa Lakes Joint Venture
Texas A&M Kingsville
Canadian Wildlife Service