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Establishing hunting regulations and allowable harvest of mallards in the United States

As a major part of establishing hunting regulations each year in the United States, data for the mallard ( Anas platyrhynchos ) are examined extensively to estimate the effect of various harvest strategies on the breeding population the following spring. This requires estimates of the breeding-population level and of the production, harvest, and mortality rates. Predictions made at the time hunting regulations are established have been in general agreement with more reliable estimates made after the hunting season when data from banding, kill, and wing surveys are available.

Journal of Wildlife Management↗

Effect of restrictive hunting regulations on canvasbacks and redhead harvest rates and survival

Because of low population levels, there were especially restrictive hunting regulations between 1958-1965, including complete closures during the 1960-1963 seasons, for canvasback ( Aythya valimeria ) and redhead ( A. americana ) ducks. Banding data from 1952 through 1965 indicated that restrictive regulations reduced both harvest and annual mortality rates. During the period with very restrictive regulations, annual mortality-rate estimates ranged from 14 to 21 percent, much lower than before this period when estimates were 50 percent or higher.

Journal of Wildlife Management↗

A comparison of methods used to obtain age ratios of snow and Canada geese

The validity of group counts, cannon-net catches, and hunter-bag checks for estimating productivity of lesser snow geese ( Anser caerulescens caerulescens ) and small Canada geese ( Branta canadensis hutchinsii-parvipes complex) was studied at Sand Lake National Wildlife Refuge during the falls of 1965 and 1966. Age ratios of snow geese obtained from net-trapped samples were significantly higher (P < 0.01) than from group counts at the same site. Immature snow geese were shot in a significantly greater (P < 0.01) proportion than they existed in the population as determined by group counts. Cannon-net catches and hunter-bag checks of snow and Canada geese yielded age ratios which were biased because of behavioral characteristics of the geese. Immatures of both species were less wary of trap equipment and immature snow geese were more vulnerable to the gun than adults. It was believed that age ratios from group counts of snow geese were more representative of the population than those from net catches and hunter-bag checks. Sex ratios of net-trapped geese showed a preponderance of males for adult Canada and adult and immature snow geese, whereas females were predominant in the immature segment of Canada geese. Hunter selectivity of blue- or white-phase snow geese was not observed at Sand Lake Refuge. Differential vulnerability to hunting between snow and Canada geese resulted from differences m feeding-flight behavior.

South Dakota↗

Bursal depths of lesser snow and small Canada geese

Bursa of Fabricius depths of 88 lesser snow geese ( Anser c. caerulescens ) and 69 small Canada geese ( Branta canadensis hutchinsii/parvipes complex) were measured. Bursal depths were unreliable indicators of age-classes of lesser snow geese and small Canada geese; previously, the same had been found to be true for large Canada geese ( B. c. interior ). Regression in size or closure of the bursa first occurred at 17-20 months of age (yearlings) in lesser snow geese and small Canada geese, but at 29-32 months of age (2-year-olds) in large Canada geese.

South Dakota↗

A cable-chain device for locating duck nests

A cable-chain device towed between two vehicles was developed for locating occupied duck nests in brushy, herbaceous, and grassy cover types. Twenty-three of 29 previously located gadwall ( Anas strepera ) and blue-winged teal ( A. discors ) hens were flushed from their nests with the drag for an efficiency of 79 percent. Eighty acres of nesting cover can be searched in 4-6 hours by the method described.

Journal of Wildlife Management↗

Some effects of aldrin-treated rice on Gulf Coast wildlife

Wildlife casualties from aldrin-dieldrin poisoning are associated with the planting of aldrin-treated rice seed along the Texas Gulf Coast. The fulvous tree duck ( Dendrocygna bicolor ), which depends on the rice field habitats and is highly susceptible to aldrin-dieldrin poisoning, is suffering a serious population decline in that area. Dead waterfowl, shorebirds, and passerines were collected on study areas in Wharton, Brazoria, and Chambers counties, Texas, from 1967 through 1971. Residues of aldrin or dieldrin were found in all samples of bird casualties and in all eggs, scavengers, predators, fish, frogs, invertebrates, and soils. Fulvous tree ducks appeared to be less resistant to aldrin than other ducks. Dieldrin residues in brains of dead fulvous tree ducks were low, but whole-body residues were as high as 16 ppm. Brains of other dead ducks and geese averaged 10 ppm dieldrin. Some dead birds were exposed by eating treated rice seed, but many dead birds with high dieldrin residues were species that feed largely on invertebrates. Although soil residues were low, snails and crayfish contained enough aldrin and dieldrin (average 9.5 ppm) to account for deaths in birds that fed heavily on these invertebrates over a period of time. When fulvous tree ducks were penned for 3 days in fields aerially planted with treated seed, 3 of 10 birds died with brain residues of 2.5, 2.9, and 6.8 ppm dieldrin, and others were intoxicated. None of eight died, and some gained weight, when penned in fields planted with untreated seed. This study adds further evidence for the suspected lethal effects of aldrin-treated rice seed on wild birds and other wildlife in rice field habitats.

Texas↗

Lethal mobilization of DDT by cowbirds

This study is an experimental demonstration of lethal mobilization of DDT by brown-headed cowbirds ( Molothrus ater ) and the effects of food deprivation on the distribution and loss of DDT, DDD, and DDE. The principal experimental group consisted of 20 birds fed a dietary dosage of 100 ppm of DDT for 13 days. After 2 days of full rations of untreated food, they were subjected to food restriction. Food was reduced to 43 percent of normal. Seven of the 20 birds died within 4 days. No birds died in the three control groups, treated as follows: ( 1 ) 20 birds fed 100 ppm DDT for 13 days and full rations of untreated food thereafter, (2) 20 birds fed only untreated food but subjected to food restriction, and (3) 20 birds fed full rations of untreated food throughout. In a pilot study, birds were fed 100, 200, or 300 ppm of DDT and subjected to two periods of food restriction, the first of these immediately after dosage ceased and the second 4 months later. DDT-dosed birds from all dosage levels died in each period of food restriction. Before the weight loss that accompanied food restriction, the brains of DDT-dosed birds had concentrations of DDT and DDD that were far below the lethal range. Concentrations increased rapidly to lethal levels. In these birds, DDT in carcasses decreased while DDD increased. DDT-dosed birds that died during food restriction lost 16 percent of their total body burden of DDT + DDD + DDE, 21 percent of their weight, and 81 percent of their fat. The DDT-dosed birds that were subjected to food restriction but survived lost a significantly greater proportion of their body burden of residues than similarly dosed birds not subjected to weight loss. Brain levels of DDT and DDD in birds that died during food restriction soon after dosage did not differ significantly from brain levels of birds that died in a period of food restriction 4 months after dosage. Concentrations of DDE were significantly higher in the latter group, although they were lower than concentrations considered to be lethal. In contrast, carcass levels of DDT and DDD were significantly lower, and DDE was only slightly higher, in the birds that died in the second period of food restriction. It is concluded that stored DDT residues present a hazard to birds, which utilize stored fat during periods of stress due to reproduction, cold weather, disease, injury, limited food supply, or migration.

Journal of Wildlife Management↗

Observation of nighttime feeding behavior of ducks

A night vision scope was used during 1969-71 to study the nighttime feeding behavior of ducks on prairie wetlands of south-central North Dakota. Adult and immature ducks were observed feeding between 9:00 PM and 4:00 AM, predominantly on midges (Chironomidae) and mayflies (Ephemeroptera). The emergence pattern of these insects appeared to be a major factor influencing duck activity and feeding behavior at night.

North Dakota↗

Waterfowl breeding habitat in agricultural and nonagricultural land in Manitoba

Waterfowl populations and habitat characteristics were examined on 33 potholes in each of two 16-square-mile study areas of agricultural and nonagricultural land in southwestern Manitoba. The agricultural land potholes, lacking in or incompletely surrounded by trees, received greater use by lesser scaup ( Aythya affinis ), canvasback ( A. valisineria ), redhead ( A. americana ), coot ( Fulica americana ), and three species of grebes ( Podicipedidae ). The nonagricultural land potholes, completely surrounded by trees, were more attractive to blue-winged teal ( Anas discors ), and mallard ( A. platyrhynchos ), and over twice as many dabbler broods were censused there. Abundant, undisturbed nesting cover may have been the reason for greater dabbler use on the nonagricultural land potholes since chemical and biological properties suggest more fertile conditions in the agricultural land.

Manitoba↗

Correction of bias in belt transect studies of immotile objects

Unless a correction is made, population estimates derived from a sample of belt transects will be biased if a fraction of, the individuals on the sample transects are not counted. An approach, useful for correcting this bias when sampling immotile populations using transects of a fixed width, is presented. The method assumes that a searcher's ability to find objects near the center of the transect is nearly perfect. The method utilizes a mathematical equation, estimated from the data, to represent the searcher's inability to find all objects at increasing distances from the center of the transect. An example of the analysis of data, formation of the equation, and application is presented using waterfowl nesting data collected in Colorado.

Colorado↗

Soil-food chain-pesticide wildlife relationships in aldrin-treated fields

Soil-food-chain-pesticide wildlife relationships were investigated to learn the concentration of pesticide residues present in soils, macro-invertebrates, vertebrates, and seeds as a result of annual applications of aldrin at recommended rates for pest control. Two central Missouri cornfields treated with aldrin at 1 lb/acre, for 16 and 15 of the past 17 years, were selected for study during 1965-67. Primary samples collected for residue analyses included soils, earthworms (Lumbricidae), crickets (Gryllidae), and two kinds of ground beetles (Carabidae) obtained during early April, June, August, and October. Vertebrates and plant seeds collected during 1967 included white-footed mice ( Peromyscus maniculatus ), toads ( Bufo americanus ), snakes ( Thamnophis sirtalis and Pituophis sayi ), corn ( Zea Mays ), foxtail ( Setaria Faberii ), and annual sunflower ( Helianthus annuus ). Pesticide residues consisted primarily of dieldrin, the degradation product of aldrin. Combined aldrin and dieldrin residues, as two field all-season averages, wet weight basis, were: soils, 0.31 ppm; earthworms, 1.49 ppm; crickets, 0.23 ppm; Harpalus ground beetles, 1.10 ppm; Poecilus ground beetles, 9.67 ppm; white-footed mice, 0.98 ppm; toads, 3.53 ppm; garter snakes, 12.35 ppm; and corn, foxtail, and sunflower seeds less than 0.02 ppm each. Unusually high average residues (37.48 ppm) in Poecilus beetles during June, 1967, were attributed to abnormally high soil moisture and predacious feeding habits of these insects.

Missouri↗

Mortality among bobwhites confined to a heptachlor contaminated environment

The lethal effects of heptachlor on bobwhites ( Colinus virginianus ) were studied at the Patuxent Wildlife Research Center during 1962 and 1963. A pair of adult birds was placed in each of 32 wire-covered field pens (20 x 50 x 61/2 ft) in May, 1962, and in 36 additional pens in May, 1963. Heptachlor (technical grade on clay granules) was spread in the pens at rates of1/8, 1/4, 1 1/4 and 2 lb/acre. In 1963 the treated pens were thoroughly soaked with a hose before birds were introduced to avoid the possibility of birds pecking granules. Heptachlor at 1 1/4 and 2 lb/acre caused severe mortality among birds introduced successively during the first 15 days after application. Mortality declined rapidly among birds placed in these same pens thereafter and was undetectable after 45 days. Mortality at 1/4 lb/acre was significant only during the first 15 days of the 1962 test. There was no detectable difference in mortality of the sexes. Water applied to the pens followed by fairly heavy rain did not significantly affect mortality.

Alabama↗

A new stratification of mourning dove call-count routes

The mourning dove ( Zenaidura macroura ) call-count survey is a nationwide audio-census of breeding mourning doves. Recent analyses of the call-count routes have utilized a stratification based upon physiographic regions of the United States. An analysis of 5 years of call-count data, based upon stratification using potential natural vegetation, has demonstrated that this uew stratification results in strata with greater homogeneity than the physiographic strata, provides lower error variance, and hence generates greatet precision in the analysis without an increase in call-count routes. Error variance was reduced approximately 30 percent for the contiguous United States. This indicates that future analysis based upon the new stratification will result in an increased ability to detect significant year-to-year changes.

conterminous United States↗

Aging small Canada geese by neck plumage

The neck plumage method, a new technique for separating immature from adult Canada geese ( Branta canadensis ) in the hand, was evaluated by comparison with the notched tail feather and cloacal examination methods. Two (1.4 percent) of 141 geese examined were misaged, resulting in a 6 percent error in the immature-adult ratio obtained by the neck plumage method. The neck plumage method is a rapid aging method and reasonable accuracy (94 percent) can be obtained. It can also be used to differentiate immatures from adults on the ground at distances up to 175 yards, but was almost impossible to use when geese were in flight. As yet, the neck plumage method has only been tested on the subspecies ( B. c. hutchinsii-parvipes complex) in the Tall-Grass Prairie population of small Canada geese.

South Dakota↗

Disappearance and persistence of aldrin after five annual applications

Investigation was initiated in 1965 to ascertain the disappearance rate of aldrin applied on loam soils at the recommended level of 1.5 lb per acre from 1960 through 1964. There was no further application of pesticides. Sampling began in 1965 and extended into 1970. Data from gas chromatographic analyses of soil and earthworm samples, collected spring and fall, showed that more than 95 percent of the pesticide had disappeared before the study began. There was no significant (P > 0.05) reduction in aldrin plus dieldrin residues throughout 6 years of study. Similarly, residues in earthworms ( Allolobophora caligimosa ) failed to decline during the 6 years. Average combined residues for 11 semi-annual collection periods was 0.11 ppm in soils, 0.61 ppm in earthworms, wet-weight bases. Results showed that high levels of pesticide did not accumulate and remain in the soil as a result of annual applications and that a large part of applied aldrin had disappeared within 1 year. Earthworms contained 4 to 15 times (average 5.6) as much aldrin plus dieldrin as was found in soils.

Missouri↗

Eggshell thickness in mourning dove populations

Eggs ( n = 452) of the mourning dove ( Zenaidura macroura ) were collected from 9 states in 1969 and 11 states in 1970, and shell thickness was compared with that of eggs ( n = 97) collected from 24 states during the years 1861 to 1935. Mean shell thickness did not differ significantly in the test groups.

conterminous United States↗

Influence of radio packs on captive mallards and blue-winged teal

Back-mounted radio packs of three weights were attached to 30 captive mallards (Anas platyrhynchos) and 30 blue-winged teal (A. discors), and physical condition of the birds was evaluated for 12 weeks. All groups with radio packs lost more weight than did control groups. Feather wear often followed by skin irritation occurred in the axillary region of the wings on 90 percent of the treated birds within 1 week, and on the backs of 55 percent of the treated birds within 4 weeks after the radio packs were attached. The treated birds appeared preoccupied with the radio packs and exhibited a partial aversion to swimming.

Journal of Wildlife Management↗

Waterfowl nesting on interstate highway right-of-way in North Dakota

We studied 630 acres of roadside along 23 miles of Interstate 94 in Stutsman County, North Dakota, to assess wildlife values of highway rights-of-way. We found 422 duck nests that had an overall success of 57 percent in 1968, 1969, and 1970. Mammalian predators were responsible for 85 percent of the destroyed nests. To test the effect of mowing on duck nest initiation and success, alternate 1-mile blocks of the study area were not mowed in the fall of 1968. In 1969 and 1970, significantly more ducks chose unmowed vegetation in preference to mowed vegetation for nest sites. Mallards ( Anas platyrhynchos ), pintails ( A. acuta ), and gadwalls ( A. strepera ) were especially responsive to unmowed vegetation. Success of duck nests in unmowed vegetation was 62 percent compared with 51 percent in mowed vegetation. Sixteen percent of the nests were unhatched by July 5, the beginning mowing date previously recommended by the North Dakota Highway Department. Wildlife killed by traffic did not increase when half the mile blocks were unmowed, and no significant difference was observed in buildup of snow between mowed and unmowed blocks in the winter of 1968-69. Of 182 motorists interviewed in the study area, 82 percent had not noticed the unmowed rights-of-way. We strongly recommend no mowing of ditch bottoms or back slopes, minimal mowing of inslopes, and no mowing before July 20 to enhance waterfowl nesting and to reduce maintenance costs of highway rights-of-way in duck-producing regions.

North Dakota↗