In order to determine some of the factors influencing waterfowl abundance in eastern Iowa, field studies were made of migrating ducks during the years 1940-1945. A study area was selected on the Mississippi River 20 miles north of Davenport, Iowa, and near the town of Princeton, Iowa. The study area, a low-land meadow and marsh, is 5 miles in length and 1½ miles in width. It is known locally as the Princeton Marsh. Additional observations were made at scattered points along the Mississippi from Dubuque south to Keokuk, Iowa; on the Wapsipinicon River for a few miles above its mouth; and on Rock River near Moline, Illinois

Morrissey, Thomas J.

English

University of Northern Iowa

Proceedings of the Iowa Academy of ScienceVolume 54 | Annual Issue Article 541947Some Factors Influencing the Abundance ofWaterfowl Along the Mississippi River in IowaThomas J. MorrisseySt. Ambrose CollegeCopyright © Copyright 1947 by the Iowa Academy of Science, Inc.Follow this and additional works at: https://scholarworks.uni.edu/piasThis Research is brought to you for free and open access by UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academyof Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu.Recommended CitationMorrissey, Thomas J. (1947) "Some Factors Influencing the Abundance of Waterfowl Along the Mississippi River in Iowa," Proceedingsof the Iowa Academy of Science: Vol. 54: No. 1 , Article 54.Available at: https://scholarworks.uni.edu/pias/vol54/iss1/54Some Factors Influencing the Abundance of Waterfowl Along the Mississippi River in Iowa THOMAS J. MORRISSEY In order to determine some of the factors influencing waterfowl abundance in eastern Iowa, field studies were made of migrating ducks during the years 1940-1945. A study area was selected on the Mississippi River 20 miles north of Davenport, Iowa, and near the town of Princeton, Iowa. The study area, a low-land meadow and marsh, is 5 miles in length and 1 ¥.! miles in width. It is known locally as the Princeton Marsh. Additional observations were made at scattered points along the Mississippi from Dubuque south to Keokuk, Iowa; on the Wapsipinicon River for a few miles above its mouth; and on Rock River near Moline, Illinois. Fourteen species of ducks were studied: mallard, gadwall, bald-pate, pintail, green-wing teal, blue-wing teal, shoveller, wood duck, redhead, ring-necked duck, canvas-back, lesser scaup, American golden-eye, and American merganser. Black duck, buffle-head, white-winged scoter, ruddy duck, red-breasted merganser, and hooded merganser were also studied but due to their small numbers and irregular occurence none of the factors affecting their abundance could be determined. As a result of field study it became apparent that the local abundance of any species of waterfowl is dependent upon a number of factors. Among these factors food, rest areas, water level, cover, and protection are the most important. The requirements of differ-ent species differ considerably, however, and ideal conditions for one species may not be at all suitable for another. Cover, food sup-ply, and protection may vary in amount from year to year or from l'!eason to season. Consequently various species of ducks show a sea-sonal or annual fluctuation in numbers. Counts were made of the waterfowl on the study area once each week from March 1 to May 15 and from September 1 to December 1 during the years 1940-1945. No counts were made in 1944. The numbers counted each week were totalled. Table 1 summarizes the data obtained. Mallards show the least seasonal and annual variation in numbers. (Table 1). While mallards show a definite preference in choice of feeding grounds-marshes, corn-fields, and sloughs, in about that order-they are so adaptable within these limits that such condi-tions as drought, high water, or failure of a food crop do not affect their numbers to the extent that other less adaptable species are affected. Moreover, their autumn food supply of corn is constant 345 1Morrissey: Some Factors Influencing the Abundance of Waterfowl Along the MisPublished by UNI ScholarWorks, 1947TABLE 1. Numbers of Ducks on Princeton Marsh and Adjacent Mississippi River H 0 I I ~ I 1940 1941 I 1942 I 1943 1945 > i I > I Spring I I i I I I I I ! 0 Fall > Fall \Spring I Fall I Spring 1 Fall / Spring II Fall I Spring/ tJ I I trJ ............. \ I I 78,000 I I I I I I ,-- ~ Mallard ..... -····································-········· 75,000 I 67,000 i 73,000 I 81.000 I 75,000 I 75,000 I 69,000 75,000 55,000 ~ Pintail •...... ............................... 12,000 2,000 13,000 I 3,000 15,000 2,000 I 15,000 I 3,000 10,000 2,000 0 Gad wall ·-···-······· ························· ......................... 1,000 . ................ I 1,500 I I 1,500 I 100 1,000 100 1,000 100 "'.l Baldpate ...... 5,000 50 i 6,000 ! 75 7,000 I 8,000 250 6,000 100 Ul .................. Green-wing Teal 2,000 200 2,500 I 150 I 2,500 I 100 1,500 100 1,500 100 0 H Blue-wing Teal ... ···············-······· :1 9,000 3,000 11,000 5,000 I 9,000 I 2,000 I 8,000 1,000 10,000 1,500 trJ Shoveller ........... ..................... 5,000 200 3,000 150 I 2,000 I 150 I 3,000 300 5,000 150 z Redhead ···························· .. 2,000 2,000 I 2,000 i . ................. I 3,000 2,000 50 0 Ring-necked Duck ..... .1 6,000 3,ooo / 6,000 4,000 I 7,000 I 6,000 I 7,000 5,000 5,000 3,000 trJ Canvas-back ............ ... 1 3,000 2,000 I 3,500 2,000 I 4,000 I 2,000 I 4,500 2,500 3,000 1,500 Lesser Scaup ...... . .................. ······-···· .1 30,000 25,000 I 30,000 ! 25,000 I 35,000 25,000 I 35,000 25,000 30,000 20,000 2Proceedings of the Iowa Academy of Science, Vol. 54 [1947], No. 1, Art. 54https://scholarworks.uni.edu/pias/vol54/iss1/541947] FACTORS INFLUENCING WATERFOWL 347 and their habit of feeding in cornfields in early morning and late evening affords them considerable protection. The abundance of wood ducks in this area is largely dependent upon available cover since the food supply (duck weed, acorns, in-sect larvae, etc.) remains fairly constant. Closely connected with its cover requirements, is this specie!!lmeed for protection during the migratory season. Only a very small proportion of the Princeton Marsh is heavily wooded swamp and therefore good cover for wood ducks. Prior to 1943 about 600 wood ducks were counted each fall on the study area and about 300 were counted there each spring, the lesser number probably being due to a wider dispersion of the birds in connection with the spring floods. In 1943 hunting regulations which had given complete protection to the wood duck were relaxed to permit the inclusion of one duck of this species in the bag limit. Nearly all hunters made an effort to get the one bird allowed them. In the fall of 1943 only 75 wood ducks were counted on the Prince-ton Marsh although the numbers of this species in the spring of 1943 and the following spring of 1944 were normal. The combination of heavy hunting pressure and lack of adequate cover drove most of the birds from this area. In other areas having a greater acre-age of flooded woodland, numbers of wood ducks remained the same despite hunting. Baldpate, pintail, gadwall, green-wing teal, blue-wing teal, and shoveller show a great seasonal variation in numbers. (Table 1). On the Princeton Mari1h the chief food of these species is smartweed and includes the species Polygonum pennsylvanicum, P. hydropipero-ides and P. Muhlenbergi. Bellrose and Anderson (1943) give these plants a fairly high preferential rating as duck food in the Illinois River Valley and they are of even greater importance in this area where other desirable food plants are absent. Smartweeds grow up quickly on any recently flooded land and form dense beds many acres in extent. In August and September the plants produce abun-dant hard seeds. This source of food is not available to ducks, however, unless the beds of Polygonum are shallowly flooded. From 6 to 24 inches of water seems to be the optimum depth of flooding but as little as 1 inch is sufficient to attract many ducks. On the Princeton March, spring floods made ideal feeding grounds. In autumn, however, water levels ar stabilized by dame at Clinton and Leclaire, Iowa. Conse-quently the beds of smartweed are not suitable for feeding purposes until the high water of the following spring and the 6 species of ducks which are almost entirely dependent on this source of food are cor-respondingly uncommon in fall anad common in spring. Control of water levels to provide shallow flooding of marshes during the autumn migratory season as recommended by Bellrose (1941) would increase considerably the fall numbers of pintail, bald-pate, gadwall, green-wing teal, blue-wing teal, and shoveller. Redhead, ring-necked duck, canvas-back, and lesser scaup show 3Morrissey: Some Factors Influencing the Abundance of Waterfowl Along the MisPublished by UNI ScholarWorks, 1947• 348 IOWA ACADEMY OF SCIENCE [VOL. 54 a seasonal variation in numbers which, except in the case of the readhead, is more apparent than real. In spring migration these 11pecies are abundant and conspicuous due to their habit of forming in large "rafts" on favorite feeding grounds. During fall migration large flocks are soon dispersed by hunters. Small flocks of these species are naturally less colll(>icuous and because of hunting, the ducks are more retiring. The factors combine to produce the im-pression of an abundance of these diving ducks in spring and a sharp reduction in their fall numbers. Actually the number of birds in small, widely di11persed flocks is about equal to that of the large spring concentrations (Table 1) . The increased steam boat traffic on the Mississippi River also prevents any fall concentrations. Prior to 1942 very large flocks could be found above the dams at Daven-port, Muscatine, and Keokuk where the ducks were safe from hunt-ers but recently traffic has increased to such an extent that any large flocks are soon driven away. Redheads show a seasonal variation in numbers which the pres-ent studies were unable to explain. (Table 1). It has been sug-gested that a large proportion of the migrants of this species which use the Mississippi Valley route in spring migrate via the Missouri Valley or routes farther west in fall. American golden-eye and American mergansers are important chiefly as winter residents, although the two species occur from No-vember to April. Their abundance is determined by the amount of open water on the Mississippi during the time the river is largely ice-bound. Unlike the lesser scaup and canvas-back which are oc-casional winter residents, golden-eye and merganser are intolerant of crowding on their feeding and resting grounds. A pool which may support 100 lesser scaup through the winter will usually support only 1h to % that number American golden-eye and even fewer American mergansers although these species may be much com-moner in the area than the scaup. However, no competition has been observed between these species for the limited amount of open water. ST. AMBROSE COLLEGE, DAVENPORT, IOWA. Literature Cited Bellrose, Frank C. 1941. Duck Food Plants of the Illinois River Val-ley. Natural History Survey Bulletin. Vol. 21, Article 8, p. 274. Bellrose, Frank C. and Harry G. Anderson 1943. Preferential Rating of Duck Food Plants. Natural History Survey Bulletin. Vol. 22, Article 5, p. 424. 4Proceedings of the Iowa Academy of Science, Vol. 54 [1947], No. 1, Art. 54https://scholarworks.uni.edu/pias/vol54/iss1/54

Some Factors Influencing the Abundance of Waterfowl Along the Mississippi River in Iowa

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Some Factors Influencing the Abundance of Waterfowl Along the Mississippi River in Iowa

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