California's Central Valley is one of the most important wintering areas forwaterfowl in North America, supporting about 60% of the Pacific Flyway'swaterfowl population. However, a substantial population of breeding ducks alsoexists in the Central Valley, primarily mallards, gadwall, and cinnamon teal.Although the Central Valley is primarily a wintering area, slight modificationsto wetland management practices can greatly improve habitat conditions forlocal ducks and a variety of resident wetland-dependent wildlife.
About 65% of the Central Valley's wetlands are in private ownership, managedprimarily for duck hunting. It is advantageous for landowners to increaseproduction of local ducks and other waterbirds through the provision of smallamounts of late spring and summer "brood water." However, spring and summerwater management should be conducted in a manner that does not negativelyimpact wintering waterfowl use or hunting success. For these reasons,landowners need to be informed of a variety of different management practicesthey can use to create valuable wetland habitat during the late spring andsummer.
"Spring/summer wetlands" should be flooded continuously from early spring(February or March) until late summer (mid-July or August) to provide duckswith suitable "pair water" and brood-rearing sites. In contrast, seasonalwetlands are kept dry throughout much of the summer to support seed-producingplants such as swamp timothy, watergrass, smartweed, and other "moist-soil"plants that provide the bulk of the natural food for waterfowl wintering in theCentral Valley. However, both of these objectives can be achieved on large(100+ acre) wetland properties. Smaller adjacent properties can work togetherto develop a "wetland complex" which includes seasonal wetlands andspring/summer wetlands.
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Figure 1.
The seasonal wetland flooding regime replicates natural winter flooding fromrainfall, whereas most types of spring/summer wetlands replicate historicalflooding from snowmelt, which occurred in May and June during most years.Permanent wetlands, one type of spring/summer wetland, traditionally werepresent in sloughs, oxbow lakes, and other deep depressions. Thus, seasonalwetlands and spring/summer wetlands both mimic historic Central Valley wetlandtypes.
Actual field experience by the California Department of Fish and Game (CDFG)and others has shown that the needs of local wildlife can be met through themanagement of relatively small spring and summer wetlands without sacrificingmeaningful amounts of seasonal wetland habitat. As a rule of thumb,spring/summer wetlands should comprise about 5% of the total wetland acreage ona property. Topography, water availability, low cost, and other factors maydictate that up to 20% of a property be maintained as spring/summer wetlands,but careful consideration should be given to increasing spring/summer wetlandacreage beyond the 5-10% range due to the need for seasonal wetlands andwintering waterfowl habitat in the Central Valley.
Spring/summer wetland management also can be extremely beneficial to pheasantpopulations, as was evidenced by a recent study at the Mendota Wildlife Area.Pheasant brood survival was related to the availability of feather-edged springand summer wetlands. These habitats supported good insect populations requiredby young pheasant chicks, as well as cool microclimates needed by pheasantsduring hot weather. The pheasant population quadrupled in two years at Mendotain response to spring/summer wetland management.
This technical bulletin summarizes current knowledge on the management ofspring/summer wetlands in the Central Valley. Important aspects ofspring/summer wetland management such as appropriate location, vegetationmanagement, and the timing, depth, and duration of flooding are discussed.Five specific types of spring/summer wetlands are presented. The managementpractices discussed below have been successfully used on CDFG wildlife areaswhere wintering waterfowl management and public duck hunting are highpriorities. An increasing number of duck club owners are also using thesepractices to enhance local duck production, which is thought by many to improveearly season hunting.
California's breeding duck population, which is much larger than originallybelieved to be, is currently estimated at 473,000 ducks. CDFG Breeding PairSurveys during 1994 estimated that the Central Valley contributes about 311,000of these ducks. Mallards are the predominate nester, however gadwall, cinnamonteal, and lesser numbers of shovelers, pintail, ruddy ducks, wood ducks, andredheads also nest in the Central Valley. The three primary habitats needed bydabbling ducks such as mallards for successful breeding are: "pair water",upland nesting areas, and "brood water."
"Pair water" refers to habitats used by breeding ducks while establishingterritories and accumulating fat and protein reserves prior to nesting. Theseactivities occur between February and May. Aquatic invertebrates are believedto be the primary food source of pre-laying hens. "Pair water" typicallyconsists of shallow ponds adjacent to upland nesting fields, such as smallwetlands, ditches, or sloughs that have good invertebrate populations. Shallowwater (4-12 inches deep) is preferred because it provides ducks with betteropportunity to feed on invertebrates.
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Figure 2.
Nesting is the period of egg-laying and incubation for females, which occursbetween early March and mid-June. Hen mallards, for example, prefer to nest ingrass or legume-dominated upland areas where the vegetation is at least 18inches in height. Hen mallards generally lay one egg per day (the averageclutch size is 8) and incubate the eggs for 28 days, thus concealment of thehen and nest from predators is very important. Although hens rely primarily onbody reserves during nesting, they do take "nest breaks" to feed oninvertebrates. Drakes defend feeding territories, particularly during earlyincubation.
Upon successfully hatching a clutch, hen ducks rear their young to fledglingstage in typically 5-6 weeks. "Brood water" refers to habitats used forbrood-rearing, which usually occurs between May and August. During this time,invertebrates are the primary food of hens and their ducklings. Ducklings areparticularly dependent on aquatic and terrestrial invertebrates during theirperiod of rapid growth prior to fledging. Spring/summer wetlands with goodinvertebrate populations and relatively tall, dense "escape cover" are desiredby duck broods. The escape cover is required for protection from predators. Acomplex of wetlands exhibiting adequate cover and abundant food supplies arenecessary for optimal duck brood survival.
Ducks, even of the same species, enter specific annual cycle events (e.g.,nesting) at different times and the above chronology is generalized. Forexample, while some ducks are nesting, others may be preparing to nest (using"pair water") or may already have finished nesting (brood-rearing).
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Table 1.
Although there are several different methods of achieving good brood habitatfor ducks, at least three important habitat features must also be provided.All spring/summer wetlands must: 1) have sufficient quantity and availabilityof invertebrate food items, 2) contain vegetative cover that providesprotection from predators, and 3) be located in close proximity to suitableupland nesting habitat.
Invertebrates are the primary food item for ducks, shorebirds, and some wadingbirds during the spring and summer. In fact, more than 75% of the bird speciesthat use seasonal wetlands in California forage on invertebrates. Invertebratepopulations are usually greatest in ponds that are dry during a portion of theyear or in ponds managed in a way that results in high productivity. In thePrairie Pothole region of North America for example, invertebrate production ishighest in temporary or seasonal wetlands that remain flooded for only 2-6months of the year. The deeper, permanent wetlands are less productive and donot support abundant invertebrate populations.
Relatively tall wetland plants such as cattails, tules, and other bulrushesprovide cover for many species of wildlife, particularly young ducklings, whichneed to be able to escape predators. Research has shown that a 50:50 cover toopen water ratio is desired by breeding ducks. This wetland condition,referred to as a "hemi-marsh", provides ducks with an ideal mosaic of openwater feeding sites and vegetated escape cover (Fig. 1). Cattail and tulepatches provide cover for rails and may also serve as nest sites for colonialnesting waterbirds such as egrets, herons, ibis, and blackbirds.
Pond bottoms of uneven topography tend to develop an interspersion of emergentcover and open water. Shallow areas become vegetated over time, but portionsof ponds that are 24-36 inches deep generally remain open. Thus, most types ofspring/summer wetlands should have a pattern of channels, potholes, andpossibly small islands that create a mosaic of open water, dense emergentvegetation, and loafing sites. Potholes and channels should be interconnectedand sloped from the inlet to the outlet. The uneven pond-bottom allows for adiversity of vegetation and optimal foraging depths for various wetland birds.Shallow water (4-12 inches deep) is critical to waterbirds and shouldconstitute the majority of the wetland (Fig. 2). Although not essential,low-profile islands provide additional habitat diversity in spring/summerwetlands.
Because seasonal wetlands supply most of the natural food for winteringwaterfowl, they should dominate the vast majority of Central Valley wetlands.However, the types of spring/summer wetlands described below offer alternativesfor brood water that can be used in small areas not highly suitable forproducing waterfowl food plants. These types are categorized as either"semi-permanent wetlands" (not flooded all year) or "permanent marshes"(flooded all year). Semi-permanent wetlands are thought to provide the bestduck brood habitat, but permanent wetlands also have value to many species ofwildlife. Habitat management strategies, wildlife benefits, advantages, anddisadvantages of the various types of spring/summer wetlands are describedbelow.
"Semi-permanent wetlands" are those wetlands that are flooded during the springand summer, but are dry during a portion of the year (Table 1). These wetlandsare generally more productive than permanent marshes because of the annualdrying process. Shallow water (6-12 inches deep) conditions, which arenecessary to allow ducks and other waterbirds access to foods, can bemaintained in these areas because the dry period in late summer or fallprovides a "window" for mechanical vegetation control, if needed, on a 2-4 yearcycle. The presence of deeper water (18-36 inches) in channels, potholes, andborrow areas also helps maintain open water conditions. Discing, mowing, andburning are methods that can be used to maintain semi-permanent wetlands in the50:50 "hemi-marsh" state (Valley Habitats Number 7). The four different typesof semi-permanent wetlands are discussed below.
This technique involves maintaining the low end, channel, or borrow area of aseasonal wetland in a flooded condition during the spring and summer while theremainder of the wetland unit experiences summer drying. These low areas are"sub-units" of larger wetland ponds; they are not isolated by levees or watercontrol structures (Fig. 3). Thus, the entire wetland unit consists of a large"seasonal wetland portion" and a small "summer wetland portion." The summerflooded portion of the pond, which can be as small as 2-5 acres, should beabout 5% of the entire pond. The water system must be capable of deliveringwater directly to the low summer wetland area without flooding the seasonalwetland area.
When seasonal wetlands are drained in the spring (e.g., April), water is leftin the lowest portion of the pond. Water is then added to the low area asneeded to maintain constant levels until late summer (July/August) or fallflooding (September/October). Some of the water required to maintain these lowsub-units can be captured during irrigation(s) of the seasonal wetland area.This practice results in nutrient exchange between the seasonal wetland andsummer wetland portions of the unit during drawdown, irrigation, and flooding.Invertebrates are concentrated in the low area during drawdown of the seasonalwetland in spring. During fall flooding, the low area can be a source ofinvertebrates for the seasonal wetland portion of the field, which may increaseinvertebrate colonization and production during the ensuing winter and spring.
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Figure 3.
The low areas that are flooded during the summer using this practice are oftenlong, narrow strips along the edges of ponds; these areas are not veryattractive to wintering waterfowl due to the proximity to levees or roads.Thus, the presence of summer water in these areas does not significantly reducewinter waterfowl use or hunting success. In fact, tule and cattail patchesoften develop in these brood areas and buffer the seasonal wetland fromdisturbances that occur along levees and roads.
An alternative of this system is to restore the site with a deeper (6-18 inch)channel meandering through the center of the pond. Remnant sloughs or swalesexist in some wetlands and are suitable low areas for this provision ofspring/summer water. Brood survival may be greater in these areas than alongthe edges of ponds due to reduced predation, however data do not exist from theCentral Valley to support or disprove this contention.
This practice was developed by the CDFG at the Mendota Wildlife Area and theU.S. Fish and Wildlife Service (USFWS) at the Sacramento National WildlifeRefuge Complex and is currently being employed on numerous State WildlifeAreas. CDFG staff is even constructing small brood areas in large wetlandcomplexes where they do not already occur. CDFG staff believes this practicehas the most potential of the five types discussed herein for use on privateduck club wetlands.
Reverse-cycle wetlands are flooded during the spring and summer (February/March- August), but are dry during the fall and winter. These predominately shallowwetlands are extremely productive duck brood habitats, yielding some of CDFG'shighest recorded duck brood densities.
The dry period during the fall and winter allows annual grasses and otherupland vegetation to develop. Annual upland grasses, unlike cattails or tules,decompose rapidly when flooded during the growing season. The decayingvegetation provides optimal conditions for invertebrate production. Thesewetlands are used heavily by ducks throughout the breeding season, presumablybecause of high invertebrate populations. As the growing season progresses,cattails and tules become prevalent and provide ducks and other marsh birdswith suitable escape cover.
Reverse-cycle wetlands are best suited for small areas, typically less than 20acres. Ideally, they are developed adjacent to upland nesting fields in areasthat would not likely receive heavy use by wintering waterfowl even if theywere flooded during the fall and winter. Although these wetlands do notprovide habitat for wintering waterfowl or offer duck hunting opportunities,they can provide outstanding habitat for pheasants. If reverse-cycle wetlandsare near upland nesting fields, pheasant broods often use the edges of theponds to forage for insects. During the fall and winter, the dry ponds provideexcellent pheasant cover and are ideal pheasant hunting sites.
This practice has proven very successful for providing duck brood habitat whenimplemented one year at a time on an individual site. Repeating the processfor several years on the same wetland field has resulted in "climax" stands ofcattails and tules which are desired by other species of wetland wildlife suchas black-crowned night herons, white-faced ibis, and red-winged and tricoloredblackbirds. If used for more than one year on a particular field, discing isnecessary in the fall to "open up" lanes, potholes, and channels for thefollowing spring, which keeps the wetland relatively attractive to breedingducks. Although it is probably best to rotate the location of reverse-cyclewetlands annually, landowners interested in providing habitat for a widevariety of wildlife can maintain reverse-cycle wetlands on the same site for upto 5 years.
This practice involves the constant flooding of the low portion of an uplandnesting field during the spring and summer (February/March - August). Likereverse-cycle wetlands, these areas are kept dry during the fall and winter.These habitats are used heavily by ducks, pheasants, and shorebirds as feedingand brood-rearing sites. This technique has resulted in increased duck nestingeffort in a number of irrigated upland fields on CDFG Wildlife Areas,presumably because "pair water" sites are provided adjacent to nesting habitat(Fig. 4). Although the "periodic" irrigations used in 1993 on Los BanosWildlife Area provided suitable nesting habitat, nest densities doubled in 1994when "constant water" was maintained in the low end of the upland in additionto the periodic irrigations.
Flooded uplands are usually most productive the first year they are flooded.Cattails and tules develop rapidly and can lead to decreased productivity afterseveral years. For these reasons, alternating the location of summer floodeduplands every two years is recommended.
To create this type of habitat, the water system must be capable of deliveringwater directly to the low portion of the upland, such that the flooded area canbe maintained at constant levels throughout the spring and summer withoutflooding the nesting habitat. However, cattle ranchers often create summerflooded uplands at the low ends of irrigated pastures where irrigationtailwater collects. This type of management especially is conducive toirrigated upland or pasture habitats.
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Figure 4.
"Summer water" ponds are the most common spring/summer wetlands. Thesewetlands are flooded most of the year, from fall through the following summer,and often are used conjunctively as duck hunting sites and livestock wateringholes. The brief drawdown period in late summer allows for vegetation control,maintenance, and some nutrient recycling.
Most summer water ponds, unless heavily grazed, provide habitat for a widediversity of wetland wildlife. However, long-term use of this floodingschedule on a particular wetland unit can lead to excessive cattail or tulegrowth and decrease productivity. Although ample cover is provided,invertebrate production is thought to be only moderate since stable waterlevels exist for 9-10 months per year. Other flooding schedules(reverse-cycle, seasonal wetland - summer water combination, etc.) have beendeveloped to provide more productive duck brood habitat.
Permanent marshes are flooded throughout the year, contain primarily deepwater, and are characterized by cattails, tules, submerged aquatic vegetation,and a few scattered islands. Invertebrate populations are usually diverse, butnot abundant, because of low primary productivity associated with stable waterlevels. Fish commonly become established in permanent marshes. Therefore,permanent marshes provide valuable habitat for egrets, herons, and otherfish-eating waterbirds, but are not usually the best "brood ponds" for ducks.
Permanent marshes are most productive during the first 1-2 years they areflooded. Because nutrients accumulate in the standing vegetation after acouple years, permanent marshes need periodic draining and vegetationmanagement to remain productive. If a property contains several sites suitablefor permanent marsh management, the best method is to alternate permanent marshlocations every 2-3 years. Otherwise, they should be dewatered and rejuvenatedon a 3-5 year basis.
Because permanent marshes provide excellent escape cover, they are highlydesired by ducks during the mid-summer flightless molting period. Mostmallards that breed in the Central Valley are believed to migrate northward tomolt in the vast permanent tule marshes of the Klamath Basin and southernOregon, probably due to the lack of permanent marshes in the Central Valley.Permanent marshes in the Central Valley are not used heavily by winteringwaterfowl, although they can be good loafing sites for ducks on cold or windydays.
Spring/summer wetlands are an integral part of a wetland complex and should bedeveloped, whenever feasible, to improve habitat conditions for breeding ducksand other resident wetland wildlife in the Central Valley. Spring/summerwetlands should comprise about 5% of the wetland acreage on a property orcomplex of wetlands. The methods presented herein provide landowners withvarious options for spring/summer wetland management. Plans for providingspring and summer water on managed wetlands should first consider potentialimpacts on non-wetland wildlife, endangered species, or water diversions thatmight impact native fishes. Aspects of water sources, water rights, and waterquality must also be weighed prior to implementing these management strategies.Consultation with wetland biologists from CDFG, USFWS, Ducks Unlimited, and theCalifornia Waterfowl Association is recommended.
REFERENCES:
Euliss, Jr., N. H. and G. Grodhaus. 1987. Management of midges and otherinvertebrates for waterfowl wintering in California. Calif. Fish and Game.73(4):238-243.
Fredrickson, L.H. and F. A. Reid. 1990. Impacts of hydrologic alteration onmanagement of freshwater wetlands. Pages 72-90 in J. M. Sweeney, ed.Management of Dynamic Ecosystems. Proc. symp. N. Cent. Sect., the Wildl. Soc.,Springfield, Ill.
Fredrickson, L. H. and T. S. Taylor. 1982. Management of seasonally floodedimpoundments for wildlife. U.S. Dept. of the Interior. Fish and Wildl. Serv.Resour. Publ. 148. 29 pp.
Heitmeyer, M. E., D. P. Connelly, and R. L. Pederson. 1989. The Central,Imperial and Coachella Valleys in California. In L. Smith, R. Pederson, and R.Kaminski, eds. Habitat management for migrating and wintering waterfowl inNorth America. Texas Tech Univ. Lubbock. pp. 475-505.
Kaminski, R. M. and H. H. Prince. 1981. Dabbling duck and aquaticmacroinvertebrate responses to manipulated wetlands habitat. J. Wildl. Manage.45(1):1-15.
Reid, F. A. 1993. Managing wetlands for waterbirds. Trans. 58th N.A. Wildl.& Nat. Res. Conf. pp. 345-350.
Yarris, G. S., M. R. McLandress and A. E. H. Perkins. 1994. Molt migration ofpost-breeding female mallards from Suisun Marsh, California. Condor.96:36-45.
The National Fish and Wildlife Foundation, Hofmann Foundation, and WildlifeConservation Board provided the generous funding for this issue of ValleyHabitats.
Valley Habitats is produced by Ducks Unlimited's Western Regional Office.Items contained herein may be reproduced with permission. Copyright, DucksUnlimited, Inc., 1995.
Valley Habitats is published as part of Ducks Unlimited's VALLEY CARE Programto provide information to private land managers who wish to integrate wildlifemanagement into their existing operations.
Prepared by: W. David Smith, California Department of Fish and Game, WildlifeManagement Division, Sacramento, California.
For more information regarding conservation related land management practicescontact: Ducks Unlimited, Western Regional Office, 9823 Old Winery Place, #16Sacramento, CA 95827 TELEPHONE: (916) 363-8257 FAX: (916) 363-9849