F33615-84-C-3404; University of Dayton Purchase Order No. R1-43007 issued February 5,
            1986Report issued on: issued February 5, 1986INHS Technical Report prepared for unspecified recipien

Bellrose, Frank Chapman

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Breeding Populations of Migratory Waterfowl

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ILLINOI SUNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGNPRODUCTION NOTEUniversity of Illinois atUrbana-Champaign LibraryLarge-scale Digitization Project, 2007.Si8ic 3LEN C. SANDE RSONILLINOIS- NATURAL HISTORYSURVNEYBREEDING POPULATIONS OF MIGRATORY WATERFOWLSection of Wildlife ResearchUniversity of Dayton Purchase Order No. RI-43007U.S. Government Contract F33615-84-C-3404BYFrank C. Bellrose5 February 1986eT I · I -r · I · · I I I-Nigh,IBreeding Waterfowl as Potential Hazards to Low Flying AircraftIntroductionFortunately, waterfowl do not constitute the hazard to lowflying aircraft from May to August within the contiguous 48states that they do at other times of the year. This isprimarily their breeding season, a period when 80-85% of theducks and over 97% of the geese are on their breeding grounds inAlaska and Canada.Not only are waterfowl populations at a minimum in thecontiguous states but their numbers are widely dispersed overavailable wetlands and adjacent uplands used for nesting.Moreover, their aerial activities are generally reduced as theypursue nesting and brood rearing which embrace about threemonths, followed by a flightless period of about one month (theflight feathers are molted and regained almost simultaneously).While the females are engaged in incubation that takes 3 to4 weeks and rearing the young to flight stage for an additional6-8 weeks, the males gather on the larger marshes for the bodyand wing molt.Flight BehaviorDuring the months of May-August, the flight activity ofducks may be broken down into five behavioral periods: l)pre-incubation; 2) incubation; 3) brood rearing; 4) wing molt; and5) postbreeding.Pre-Incubation Period: During the pre-incubation periodthere is considerable flight activity by males. At this timemales are engaged in "3-bird flights" pursuing the female of apair intruding his territorial area. In such 3-bird flights, thebirds may tower and gyrate up to 300 feet above ground level(AGL). The flights are most prevalent during the first hourafter sunrise, and again in the hour preceding sunset.The flight from the wetland waiting site (or core area) tosearch for nest sites usually in the uplands by dabbling ducksoccurs from mid-April through May. These flights are low,usually below 100 feet and in the early morning hours.The chronology of their nesting activities varies withspecies with the pintail and mallard being the earliest and theblue-winged teal and gadwall the latest. However, consideringall species through the month of May, ducks are in the air 2-5%of the daylight hours; most of this activity occurs in the first2 hours of the day. Between 1000-1500 hours flight activity isat its lowest.Incubation Period: For individuals of all species,incubation stretches from mid-April through mid-July; however,May through mid-June embraces the bulk of the incubationactivity. Females usually leave the nest early in the morningand late in the afternoon to fly 1/4 to 2 miles to a feedingarea. Such flights are seldom above 100 feet; an estimate oftime in flight/day is 15 minutes, 1-2% of the daylight hours.Shortly after females begin incubation, paired males leavetheir mates and begin to con6entrate on the larger marshes forthe wing molt, a period of one month when waterfowl are2flightless. Male pintails and mallards are the first species +0enter the wing molt early in July, but other species are only 1or 2 weeks later.Brood Rearing Period: Duck nests commence to hatch by mid-May and continue to do so for the next 60-90 days depending uponspecies and latitude. The mother accompanies her brood untilflight is approached or attained. Flight development varies withlatitude and the size of the species, but most young attainflight between the age of 6-8 weeks.After rearing her brood, the female enters the wing moltwhen she is flightless for about one month. Females unsuccessfulin nesting enter the wing molt earlier.Postbreeding Season: This is largely the month of August.The likelihood of an aircraft strike of a duck would increasesteadily through the month. The rise in the potential risk ofstrikes would increase for the following reasons:1. Males have regained their flight feathers and arebeginning to fly more over and around wetlands.2. Adult females regain flight throughout August,consequently by the end of the month a largeproportion are back on the wing.3. With each passing day more and more young enter theflight mode so that by the end of August, thepopulation of flying ducks is double that of May.Moreover, during August, waterfowl are flying considerablymore and higher than at any other time in the May to Septembertime frame. Birds are shifting about to find the most favorablefeeding sites. With the swathing of wheat and barley fields inthe Great Plains in late August, thousands of mallards andpintails begin flying out to these fields for waste grain. Thiscontinues to increase through September.The altitude of these flights to grain fields vary between100 and 500 feet AGL. There is the beginning of a southwardmigration by teal and pintails in August, but numbers are small.Temporal Parameters of Duck Strike ProbabilityThese parameters are based upon judgment of behavioralactivities only, and would be subject to revision as more harddata become available.Assume: 1.0 = strike probability, May0.5 = strike probability, June0.75 = strike probability, July1.0 = strike probability, August 12.0 = strike probability, August 103.0 = strike probability, August 204.0 = strike probability, August 31MethodsMost of the breeding waterfowl in the contiguous 48 statesoccur on the northern Great Plains, and in the marshes andmeadows of the valleys and basins of the Rocky Mountains as wellas other mountain ranges of the West.The appraisal of breediig population numbers has beenderived in the West from surveys by state waterfowl biologists.4Many of these data have been obtained from the periodicallyissued Pacific Flyway Reports, collated and edited by Dr. JamesBartonek, U.S. Fish and Wildlife Service, Portland, Oregon.Other data have been obtained from direct contact with the stateconcerned. In Minnesota and Wisconsin data have been obtainedfrom the respective state publications.Data on breeding abundance of ducks in Montana, and Northand South Dakota have been obtained from aerial surveys madealong established transects each May by the U.S. Fish andWildlife Service. These have been conducted from 1955 to date,but we summarized the years 1965-1984 for this report.Maps have been prepared showing the level of abundance ofbreeding ducks in specific regions. For several reasons the mapsdo not show breeding numbers of ducks in extensive regions par-ticularly in the states east of the Mississippi River. In theseregions duck breeding numbers are relatively small, breedingbirds are dispersed along rivers and creeks, and in swamps. Mostof these ducks are wood ducks (Aix sponsa) that seldom fly abovetree height, negating their potential as a hazard to aircraft.To assist in evaluating the maps of breeding density, wediscuss the distribution on a state by state basis starting withCalifornia.CaliforniaBreeding numbers of ducks have ranged from 89,000 to309,000, 1976-1985, averaging 153,700. About 45% breed in theSacramento River Valley; 24% in the Klamath Basin; 17.3% in theHoney Lake region of the northeast; 9.8% in Suism, Napa, andother marshes in the Delta, east of San Pablo Bay; and 3.9% inthe San Joaquin grasslands between Los Banos and Mercede. Thisequates to the following numbers of breeding ducks/square mile(m2 ): Sacramento Valley (Sacramento to Willows) 864, KlamathBasin 392, Honey Lake 886, Delta marshes 485, and San Joaquingrasslands 55.0.OregonAbout 125,000 ducks breed in Oregon, largely east of theCascade Mountains. The principal breeding areas are extensivewetlands lying isolated in several basins/valleys: Upper KlamathLake marsh, Klamath Forest marsh, Summer Lake marsh, Lake Albertmarsh, and the marshes about Malheur and Harney lakes.These south-central wetlands cover 597 m2 and contain atleast 92% of the breeding ducks, 192/m 2 . The other 8% breed inthe Willamette River valley, Sauvies Island below Portland, andsmall, scattered wetlands elsewhere along the Columbia River.WashingtonAlmost two-thirds of the 194,000 ducks that breed inWashington occupy the dispersed wetlands of the Columbia Plateau,delineated by the loop of the Columbia River. The OkanoganHighlands, north of the Columbia Plateau, support about 24% ofthe breeders, the remainder (10%) are largely in the wetlandsadjacent to Puget Sound.Because of the dispersed nature of the wetlands, the densityof breeding ducks is prorated over the total regional area, and6not over the wetland acreage. On that basis there are about 13.7breeding ducks/m 2 in the Columbia Plateau and 39.7 ducks/m 2 inthe Okanogan Highlands.IdahoMountainous terrain in Idaho severely restricts the availa-bility of wetlands for breeding waterfowl. Of the 162 m ofwetlands, 76% (123 m2 ) occur in the southeast quarter. Scatteredwetlands adjacent to the Snake River in central Idaho constitute2.8%, in the area of Boise 10.2%, and the Panhandle region 16.0%of the breeding areas.The breeding grounds in the southeast are largely in theselocations: 30 m2 at the upper end of Bear Lake, 25 m2 Grays2Lake, 40 m  in the Camos-Mud Lake wetlands of Jefferson County.NevadaHistorically, waterfowl breeding grounds in Nevada havelargely been restricted to the marshes and meadows associatedwith the Carson Sink. In the last decade, these have been in ahigh state of flux as a result of drastic changes of the inflowof water from Pyramid Lake and from the Humboldt River. Areduction in flow from Pyramid Lake resulted in the marshes ofthe Carson Sink virtually disappearing in the late 1970's.However, unusually heavy snow pack in the Nevada Mountainsin the first of the 1980's resulted in exceptionally high dis-charges by the Humboldt River. Consequently the 105 m2 of wet-lands were restored in the Carson Sink, but these too, became7inundated by water too deep for breeding waterfowl by 1985. Atthat time there were about 12 ducks/m2Meadows along the Humboldt River and its tributaries providelimited breeding grounds for waterfowl.Although covering only about 25 m2 , the Ruby Lake marsh(on the Elko-White Pine county line) in eastern Nevada is thesingle most important duck breeding area in the state. About 52ducks/m 2 breed there. Outside of Ruby Lake, waterfowl are notimportant during the breeding season in Nevada. The highestbreeding population in the state was 13,500 in 1981.UtahWaterfowl breeding grounds in Utah are in a highly unstablecondition because of excessive run-off from snow packs in theWasatch and Vinta Mountains, 1981-1985. The Great Salt Lake hasrisen to unprecedented historical highs, impacting the importantand formerly extensive marshes on the east and north side of thelake.For example, as late as 1982 there were still 770 m2 ofwetlands in Utah north of Salt Lake City. By 1985, the floodingof the lands left only 320 m2 . However, in Utah south of SaltLake City, breeding grounds for waterfowl have increased from 101m2 to 257 m2 . Nonetheless, wetlands for waterfowl have declined34%, 1982-1985. During the same period breeding ducks havedeclined 40% to 353,000.As of 1985, there were 287.2 ducks/m2 in wetlands along theeast and north side of Great Salt Lake and in the meadows alongthe Bear River. In Utah wetlands south of Salt Lake City, there2were 101.5 breeding ducks/m2ColoradoThe largest breeding area for waterfowl in Colorado embracesthe San Luis Valley of 4,000 m2 (with 1,783 m2 wetlands) in thesouth-central part of the state. Almost directly north are thewetlands of North Park, an area of 210 m2 embracing 52 m2 ofwetlands. In the High Plains east of the Front Range from Denverto Fort Collins and along the South Platte Valley is a region of3,900 m2 with wetlands of 205 m2These wetland regions of Colorado support a breeding popula-tion of 115,000 ducks. Prorated over the regional tracts, thisamounts to: 17.28/m 2 for San Luis Valley (37.5/m 2 wetland),84.3/m 2 for North Park (343.9/m 2 wetland), and 5.3/m 2 SouthPlatte-Front Range High Plains, (100.7/m2 wetland).MontanaMost of the waterfowl breeding grounds in Montana lie inthe Plains, especially north of the Missouri River. For the mostpart, wetlands are small and widely dispersed requiring the duckdensity to be based on total land area within the extensiveregion surveyed along aerial transects. North of the Missouri2River the duck density is 21.5 ducks/m2; south of the MissouriRiver it is 12.5 ducks/m2Large marshes with much higher breeding densities of ducksoccur at a few places. These are shown on the accompanying mapas distinct entities where breeding densities may be expected to9range from 200-500/m .WyomingWaterfowl breeding areas in Wyoming are small and widelydispersed over the rolling Great Plains covering the eastern halfof the state. Over the period, 1976-1985, the number of breedingwaterfowl has ranged from 276,000-585,000, a mean of 330,500.This equates to a density of about 6.7/m 2 . There is noparticular area of high density.North DakotaThe largest number of breeding ducks in the contiguousUnited States occurs in North Dakota. There has been a meanbreeding population of 3,177,000 ducks, 1965-1984. The highestdensity (100.2/m 2 ) is in the Missouri Couteau, east of theMissouri River. The Northeastern Drift Plain is next with90.6/m 2 , the Western Drift Plain 68.6/m 2 , the Western SlopeRegion, west of the Missouri River, 21/m , and the lowest occursin the Red River Plain (9.7/m2 ) of eastern North Dakota andwestern Minnesota.South DakotaSouth Dakota is second to North Dakota in number of breedingducks, with a mean 1965-1984 population of 2,030,000. West ofthe Missouri River the density is lowest (19.3 m2) because of thepaucity of small water areas. The Missouri Couteau, to the eastof the Missouri River, has 46 ducks/m2 . Farther east, thePrairie Couteau has 23.5 m2 . Other areas, as indicated on the10map, have lower densities.NebraskaBreeding populations of ducks in Nebraska are located in twodiverse regions: the Sandhills north of the Platte River and theRainwater Basins south of the Platte. Ponds and sloughs arescattered through the Sandhills, particularly west of 1010longitude. They are largely within that part of the Sandhillsshown on the map. The density of 11.0 ducks/m 2 is prorated overthe entire region depicted because of the land-wetland intersper-sion.The Rainwater Basins have a breeding density of 7.0 ducks/m2in the east and 5.0/m 2 in the west.MinnesotaMinnesota's average 664,000 breeding ducks, 1976-1985, varygreatly in density with the wide variety of ecosystems prevalentin that state. The prairie-parkland landscapes in the west-central part of the state have the highest breeding densities.The northern bogs and the coniferous forest region of thenortheast have low densities of breeding ducks. The driftlessregion in southeastern Minnesota is almost devoid of breedingducks because of its mature drainage.WisconsinWisconsin's average 289,000 breeding ducks are largelyconcentrated in a broad arc stretching across the state from thesoutheast to the northwest. The driftless areas of the11southwestern part of the state are almost devoid of breedingducks, as it is in Minnesota. The breeding density declines to2/m2 in the coniferous forest region of the north and northeast2/m n h ou  o h .12PREPARED BY:Frank C. Bellrose, Principal ScientistSection of Wildlife ResearchIllinois Natural History SurveyChampaign, Illinois 61820Date: 5 February 1986APPROVED BY:G1en C. Sanderson, HeadSection of Wildlife ResearchIllinois Natural History SurveyChampaign, Illinois 6182013

Breeding Populations of Migratory Waterfowl

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