Breeding Ecology of the Redhead Duck in Western Montana

Abstract

The habits of the redhead duck (Aythya americana) were studied in the Flathead Valley of western Montana in 1960 and 1961 to determine their habitat preferences in this pothole breeding ground. The 2,600-acre study area, surrounding the Ninepipe Reservoir, contained 686 potholes. Redheads usually were paired by the time they arrived on the study area in March. The average density of redhead breeding pairs was 25 pairs per square mile. For all spring activities except nesting, the birds used large, deep, open potholes or breeding-pair potholes. The several breeding-pair potholes and the nesting pothole utilized by the pair comprised their home range. Starting in late April, the pairs moved about the home range as the hens selected nesting sites, usually in the dense emergent vegetation of small, shallow potholes. Hard-stem bulrush (Scirpus acutus) and cat-tail (Typha latifolia) were preferred nesting cover. Redhead nesting success was only 15 percent, a low rate apparently caused by degenerate nesting behavior complicated by high redhead density, a lack of suitable nest hosts, and certain habitat deficiencies. By late June most drakes and unsuccessful hens had moved from the potholes to nearby reservoirs. All successful hens led their newly hatched broods from the nesting potholes to larger brood potholes and many eventually moved to the reservoir. By mid-July virtually all redheads had moved from the potholes to the reservoirs, where they remained until fall migration. 1A contribution from the Montana Cooperative Wildlife Research Unit (U. S. Fish and Wildlife Service, Montana Fish and Game Department, University of Montana, and Wildlife Management Institute cooperating). 2 Present address: Northern Prairie Wildlife Research Center, Jamestown, North Dakota. The redhead duck is an important nesting species in the Flathead Valley of western Montana. A study of redhead habits was conducted in 1960 and 1961 to determine breeding behavior, habitat preferences, and This content downloaded from 207.46.13.129 on Wed, 29 Jun 2016 04:41:10 UTC All use subject to http://about.jstor.org/terms BREEDING ECOLOGY OF REDHEAD * Lokemoen 669 nesting success. Ecological information was gathered on each pothole in the study area and then correlated with redhead use to determine habitat preferences. Nesting success and production, as affected by habitat conditions, redhead parasitism, weather, and other environmental factors were included as major features of the study. Williams and Marshall (1938:46) who studied a large number of redhead nests at Bear River, Utah, noted a 62 percent nesting success but only a 26 percent hatching success. Many eggs were lost from unknown causes, plus flooding, predation, desertion, or being knocked from the nest. Redheads preferred to nest in hard-stem bulrush, phragmites (Phragmites communis), and cat-tails, in that order. Nests were generally located over shallow water, in dense emergent vegetation, and near an opening. To improve the Bear River marshes for nesting redheads, C. S. Williams and M. C. Nelson (Unpublished report, 1943. Management of the redhead duck in Utah. Filed with U. S. Fish and Wildl. Serv., Washington, D. C. 85pp.) suggested stable water levels, predator control, and good interspersion of nesting cover with open