Waterfowl biologists with the North Carolina Wildlife Resources Commission are studying the broad-scale movements of American wigeon from wintering areas in North Carolina to their breeding areas in Canada using transmitters that can be tracked by polar-orbiting satellites. Specifically, Commission biologists hope to better understand their seasonal distributions by examining the timing of migration, migration pathways to and from wintering and breeding areas, and important staging and stopover sites during their migration. Additionally, the research should help to gain a better understanding of the breeding ground affiliations of wigeon wintering in North Carolina.
In February of 2006, 3 male and 2 female wigeon were fitted with 20-g satellite transmitters. As a trial, 2 additional hens were fitted with a new solar-powered and lighter 12-g transmitter. Based upon the results of 2006, Commission biologists fitted 7 additional hens with a somewhat sturdier 18-g solar satellite transmitter in February of 2007, and 10 hens in February, 2008.
Characterized by a haunting whistle and contrasting plumage, the American wigeon (Anas americana) is one of North America’s most distinguishable ducks. Its whistle, coloration and low abundance relative to other ducks (e.g. mallards, gadwall, blue-winged teal, pintails) makes wigeon a welcomed addition in hunters’ bags.
Although many species of waterfowl are more abundant than wigeon, the species is widely distributed. It nests farther north than any other dabbling duck except pintails and wigeon can be found both nesting and wintering across all four flyways. Wigeon populations have been dynamic over time. However, in many portions of its range, the species is currently below its long-term breeding average and the trend is strikingly similar to other species of recent concern, namely scaup and pintails. Wigeon were once fairly common within the Atlantic flyway (AF). While wintering numbers did rebound slightly with excellent habitat conditions during the late 1990s, their numbers did not approach the estimates recorded in the early 1970s and current figures are similar to lows reached during the 1980s.
In the AF, numbers of wigeon observed during the annual midwinter waterfowl survey routinely approached or exceeded 100,000 birds until 1969 (Figure 1). Estimates averaged 133,000 for 1955-1960, 109,000 for 1961-1965, and 104,000 for 1966-1970. By the early 1980s, midwinter estimates had fallen below 70,000 birds, and have remained low. While some AF states (i.e. Florida) have eliminated midwinter waterfowl surveys, estimates from the last complete flyway surveys (1999) were around 40,000 wigeon.
|Figure 1. Average number of wigeon observed during 5-year intervals during the annual mid-winter waterfowl survey in the Atlantic Flyway, 1955-2005. (Data for Florida, 2001-2005, are incomplete or estimates from previous years).
AF midwinter waterfowl survey estimates for wigeon have fluctuated by state and across years. However, approximately 78 percent of the wigeon observed during the midwinter waterfowl survey occurred in North Carolina (22 percent), South Carolina (33 percent), and Florida (23 percent) from 1960-2000 (Figure 2). Since 2000, midwinter estimates for wigeon in Florida, an historically important wintering area in the AF, are incomplete or absent (i.e. discontinued in 2004). Therefore, interpretation of trends in the midwinter estimate for wigeon since that time is difficult.
|Figure 2. Total number of wigeon observed in the Atlantic Flyway and total number of wigeon observed in North Carolina, South Carolina, and Florida during the annual midwinter survey in the Atlantic Flyway, 1955-2005. (Data for Florida, 2001-2005, are incomplete or estimates from previous years).
The 2006 estimated abundance of wigeon in the traditional continental survey area was 2.2 million birds, which was 2 percent below the 2005 estimate and 17 percent below the long-term average (Figure 3). Pintails and scaup are currently 18 and 37 percent, respectively, below their long-term averages. Every region within the traditional survey area was below its long-term average for wigeon, except for Alaska-Yukon Territory-Old Crow Flats (+61 percent), Montana and Western Dakotas (+10 percent), and Eastern Dakotas (+39 percent). Breeding estimates in N. Alberta-Northwest Territories (-38 percent), N. Saskatchewan-N. Manitoba-W. Ontario (-58 percent), S. Alberta (-36 percent), S. Saskatchewan (-34 percent), and S. Manitoba (-74 percent) are significantly (P <0.001) below the long-term average. Based on direct recoveries of preseason-banded wigeon from 1960-2005, southern Saskatchewan and Manitoba were the most important breeding areas to the AF outside of eastern Canada. The 2006 estimated abundance of wigeon in the eastern survey area was 7,900 birds, which was 51 percent below the 2005 estimate and 28 percent below the long-term average of 11,000 birds (Figure 4).
|Figure 3. Breeding population estimate and long-term average for wigeon in the traditional survey area (strata 1-18, 20-50, 75-77).
|Figure 4. Breeding population estimate for wigeon in the eastern survey area (strata 51, 52, 63, 64, 66-68, 70-72).
Wigeon harvest in the United States has ranged from 272,000 birds in 1988 to 1,053,574 in 1978. The Pacific flyway annually accounts for about 50 percent of the United States harvest, followed by the Mississippi (29 percent), Central (17 percent), and Atlantic (3 percent) flyways. The wigeon harvest in Canada has declined from a high of 158,677 birds in 1975 to less than 50,000 birds in 2005. About 90 percent of the harvest occurs in British Columbia, Alberta, Saskatchewan, Manitoba, and Ontario combined. California, Texas, and Arkansas and Louisiana are the top harvest states in the Pacific, Central, and Mississippi flyways, respectively. Wigeon harvest in the AF varies between states annually but is normally greatest from the Mid-Atlantic region southward, with North Carolina perennially at the top. Little harvest occurs in the Northeast, with the exception of New York.
Based upon the annual mid-winter waterfowl survey in North Carolina, the highest concentrations of wigeon are located in coastal areas in Hyde, Dare, Pamlico, and Beaufort counties. All wigeon were captured on private lands adjacent to Lake Mattamuskeet and on Mattamuskeet NWR utilizing rocket nets. Adult hens were chosen to be fitted with transmitters because they are likely to return to where they were hatched or raised broods in previous years. Adult hens were identified by molt and wear patterns on wing feathers. All other wigeon and non-target ducks were leg-banded and released on site.
The satellite transmitters (called PTT's or Platform Transmitter Terminals) are manufactured by Microwave Telemetry, Inc. and weigh 18g. The weight of the transmitter is critical as the overall weight of the transmitter/harness package should not exceed approximately 3-4% of the weight of the bird. Therefore, only hens weighing >775g were chosen. The battery within the transmitter is charged by a solar-cell on the top of transmitter which allows for operation up to 3 years. Until very recently, technology did not exist that allowed for such a lightweight package with an extended battery life. The transmitter rests on the back of the bird and is attached with a Teflon ribbon harness. After wigeon were fitted with transmitters, they were kept in holding pens up to 2 days to ensure each bird adapted well to the transmitter package before being released at the capture site.
Transmitters may be programmed an infinite number of ways, depending upon study objectives. In 2006 and 2007, the solar satellite transmitters were programmed to send a signal every 65 seconds for ten hours during a 72-hour period. This routine ensured the solar cell was able to sufficiently recharge the battery and allow us to track the broad-scale movements of wigeon through spring migration, breeding, and the following fall migration. In 2008, we adjusted the duty cycle to send a signal every 65 seconds for ten hours during a 36-hour period.
Signals are picked up by an ARGOS tracking system receiver attached to several NOAA polar-orbiting weather satellites. SERVICE ARGOS is a cooperative venture under the joint management of France's Center of National Space Studies, and the United States of America's National Oceanic and Atmospheric Administration (NOAA) and the National Aeronautics and Space Administration (NASA). The purpose of ARGOS is to allow researchers to remotely collect environmental data on a wide range of subjects, including: meteorology, oceanography, and animal ecology. The data is then relayed down to earth where locations are determined by ARGOS and then sent directly to Commission waterfowl biologists.