Editor’s Note: This is the first of a critically important and alarming four-part series examining in detail the broad scope of problems facing ducks, duck hunters and waterfowl managers. The author, Mickey Heitmeyer, one of the world’s leading authorities on mallards, provides unique and extraordinarily perceptive insights and solutions. We highly commend it to your attention. Because of its semi-technical nature, it is recommended that you first print the article, then read from the printed page. The remaining parts of this series will follow in weekly installments.

Variation among individuals is a basic fact of biological life. Biologists refer to this variation as heterogeneity, and it takes many forms - from obvious differences between species, sex and age-groups to more subtle, yet highly important, individual differences in genetic makeup, morphology (physical characteristics), behavior, and physiology. These variable traits influence whether an individual duck (or any living organism) survives, reproduces, adds offspring to the population and transfers genes to subsequent generations. Over time, natural selection causes traits of successful individuals to be retained, while discarding or reducing the frequency of those traits that are not. Consequently, how a duck looks, its behavior and food habits, and where it lives and moves throughout the year represents the accumulated adaptations of both a species and an individual to a changing environment.

If heterogeneity is so basic to our understanding of biology and ecology, why is it seldom incorporated into waterfowl management (with obvious exceptions such as variable bag limits for some species and hen restrictions for mallards)? Do waterfowl biologists not understand it? Is it difficult to incorporate into management programs? Do biologists simply disregard it? Does it really matter?

This four-part series asks these simple, yet hard, questions as they relate to contemporary waterfowl management. Specifically, questions are asked (and perspectives offered) about how changes in habitat type and availability, regional and continental land uses, and hunting regulations have changed the “playing field” for waterfowl. Do these basic adaptations and genetic makeup of birds still protect them from environmental and anthropogenic (man-made) factors? Or, are they potentially jeopardizing the future of species and populations?

Part I introduces the basic considerations of heterogeneity. Part II discusses how heterogeneity influences reproduction - the additions to the population. Part III discusses how heterogeneity affects variation in mortality and survival rates - the subtractions from a population. Finally, Part IV addresses issues related to effects, both intended and unintended, of current harvest regulations, including sources and directions of biases in population analyses, additive vs. compensatory mortality, and the thorny issues of spinning-wing decoys and expanded season lengths.

This series is deeply rooted in science. Despite heterogeneity’s relative lack of attention in contemporary waterfowl harvest and management programs, the subject is richly and widely represented in the scientific literature. Many of the descriptions of waterfowl heterogeneity in this series are simplified for sake of space and many exceptions to the generalizations exist. At the end of each part, I offer a few examples of scientific references to the reader who wishes to learn more about, or challenge, the scientific foundation of this series or my conclusions. Despite the semi-technical nature of these articles, I hope the average duck hunter will be able to relate to numerous examples from his or her own hunting experiences. Hopefully they will never look at another dead duck “in-the-pile” in the same way. Every hunter knows that not all ducks are the same - from the obvious differences in species, sex, and age to varying size and fatness, plumages and, importantly, their response (or lack thereof) to calls, decoys, and setups in various locations.

Species

Waterfowl are a wonderfully diverse group of species. Contemporary taxonomy recognizes 43 species that are native breeders in North America and another five-to-six species that are irregular visitors from Eurasia. These species have remarkable variation in morphology, behavior and social structure, physiology, and distribution - each trait an adaptation to the dynamic and widely distributed wetland resources they exploit. At the highest separating taxonomic level (subfamily) geese and swans have many obvious and distinct differences from most ducks. Geese and swans are large, slow to mature (first breeding typically does not occur until two to four years of age), mate for life, lay small clutches, do not renest, provide extended parental care, and have long life-spans. Geese and swans also are highly philopatric, i.e., they have strong traditions of use to specific geographical areas throughout the annual cycle. Generally, geese and swans can be considered “slow species” with more of what biologists call “K” reproduction strategies. This “slowness” to mature and reproduce, etc., is overcome by strategies designed to increase survival and production of young (e.g., strong philopatry, laying fewer eggs annually but over a greater number of years, producing larger eggs that result from large body sizes and stored nutrients, high incubation constancy, strong defense of nests and young, and extended parental care by both parents. Clearly, for these species, long-term stability and growth of populations requires high survival rates. By living a long time, geese and swans can “hedge-their-bets” against poor breeding success in any given year caused by bad weather, habitat changes and/or man-induced disturbance conditions.

Ducks in North America have an especially wide diversity of morphology, behavior, and life history strategies that range from species with many K-strategy traits similar to geese (e.g., Mergini, the sea ducks, have delayed maturity, large body size, reliance on stored nutrient reserves, low clutch sizes) to “fast species” that have what biologists call “R” reproductive strategies. These R-strategy species, such as blue-winged teal, have small body size, short life span, weak pair bonds, large clutch sizes, and tendencies to renest (sometimes many times). However, even within the common dabbling duck tribe (Anatini) huge differences exist among species in timing of pairing, migration, and reproduction (e.g., early for mallards vs. late for shovelers); propensity to renest and overall reproductive potential (e.g., high in mallard, low in pintail); nutrient reserve storage; and many other behavioral and physiological attributes.

Like a financial balance sheet, additions (recruitment of young) must equal, or exceed, subtractions (mortality) for the account (population) to remain in the “black.”

Consequently, variations in life history among waterfowl species affect their ability to accommodate different annual rates of mortality. In North America, management of geese generally has incorporated species differences better than for ducks, partly because there are fewer species and also because populations are better defined (see next section). Many species-specific regulations (e.g., variable bag limits) and some habitat management programs exist for ducks. However, management often generalizes among species and is highly influenced by trends in mid-continent mallard numbers, including current Adaptive Harvest Management (AHM) models. Certainly, there is value in simplifying regulations, but we have somewhat limited information for some species. The assumption that many duck species respond similarly to mallards in regard to management decisions is largely untested and probably incorrect.

Subspecies, Populations, and Genetic Variation

All waterfowl species are comprised of individuals of different genetic makeup. In some species, such as Canada geese, genetic differences are manifested as geographically distinct subspecies (e.g., the small Cackling Goose group of Dusky, Aleutian, Richardson, and Cackling subspecies). In other species, such as common eider, “races” are recognized (i.e., American, Northern, Hudson Bay and Pacific). Still others have defined “morphs”, [e.g., the mallard complex (see below)]. Finally, most species have at least some distinct “local populations” that share a single “gene pool” and have somewhat defined geographic ranges throughout their annual life cycle. In geese and swans (and probably some sea duck species) the identity of the “population” is maintained over time because young accompany parents to migration and wintering grounds and “learn” the routes and destinations, which become embedded traditions of use. Where these populations can be identified, they allow managers to implement specific habitat and harvest management actions. Examples of individually managed populations include the mid-sized Canada goose flocks – the Atlantic, Southern James Bay, Mississippi Valley, Eastern Prairie, Rocky Mountain, Hi-Line, and Pacific. For these populations, surveys are scheduled for known breeding, migration, and wintering locations and trends in recruitment and survival can be monitored annually.

In contrast to geese and swans, many ducks are more panmictic (mingled, with somewhat random mating) breeders and are not as segregated into distinct populations. Breeding philopatry (returning to the same area to nest in subsequent years) is female-based in ducks. That is, females determine the ultimate location of, and migration routes to, nesting areas and the male mate follows the female to the breeding site. Most ducks form new pair bonds each year. As an example, a male mallard pairs with a female mallard in December 2003 (say in central Arkansas) and follows her to a breeding area in Saskatchewan in the spring of 2004. The following year that same male returns to central Arkansas and pairs with a different female that eventually will nest in Wisconsin in 2005. Further, females typically abandon ducklings late in brood rearing (hens of some species such as pintails abandon the young much earlier than the norm), and juveniles separated from parents intermix with ducks from many clutches and breeding locations during fall. Juveniles then follow adults with varying traditional migration and wintering patterns to nonbreeding areas. It is common for brood-mates to have different migration and wintering locations depending on who they intermix with, and follow, during migration. Consequently, traditions of use are “learned” differently in ducks than in geese.

Despite the generalized panmictic nature of duck breeding, recent studies suggest stronger traditions of use patterns, especially during migration and winter, than previously assumed for many duck species. “Homing” to certain geographical migration and wintering areas is common for many ducks. Further, genetic investigations suggest that different population segments of ducks exist, at least for some species and locations. For example, relatively distinct populations occur for mallards that: 1) nest in eastern Canada and winter along the Atlantic Coast; 2) form the larger, mixed group of mallards present in the mid-continent region; and 3) breed in Washington, Oregon, and California and have short migration routes between Pacific Flyway wintering and breeding sites. In another example, recent satellite telemetry and biochemical “marker” information suggests some pintails are predisposed to breed in Alaska, others follow interior routes to prairie Canada, and still others vary migration and breeding site-selection depending on weather and habitat conditions. Other genetic and banding data suggest population segments for wigeon, green-winged teal, wood duck, canvasback, and lesser scaup (and probably many others). New technologies undoubtedly will refine information on “population” segments of each waterfowl species. With this information, managers can, and should, monitor and devise specific management programs for identifiable population segments.

An especially contentious management debate in North American concerns the mallard-mottled-Mexican-black duck species complex. Most likely, this group of “mallard-like” ducks was in varying stages of geographical and genetic isolation when European settlers arrived in North America. In a Holoarctic species such as the mallard, considerable “polymorphism” (phenotypic variation within an interbreeding population) exists and genetic variation apparently was advancing at the time of settlement toward a separation of the various morphs (mallard, black duck, Florida duck, mottled duck, Mexican duck) both in form (i.e., lack of sexual dimorphism in all except the mallard) and geography. Despite the apparent advancing divergence, the current genetic makeup of these morphs is very similar and probably is not deserving of species designation. In fact, more genetic variation exists within some populations of mallards (see above) than exists between mallards and black ducks. Black ducks and mallards interbreed freely and there may be more “hybrids” than “pure” black ducks in many locations. Controversy exists over the causes of increased hybridization of mallards and black ducks (and also between mottled, Florida, and Mexican ducks) and the capability, or willingness, to manage these morphs separately. It appears both high harvest rates and long-term habitat changes are to blame for declines in black ducks. In this extreme case of intra-specific heterogeneity, data on cause-and-effect are clouded and many critical management issues must be carefully addressed if the objective is to sustain the black duck morph.

Sex and Age

Probably the most recognizable groups (cohorts) within a waterfowl population are the sex- and age-classes of individuals. Demographic studies and management of any organism (whether mallard or mongoose) depends on understanding the differences between males and females, and also among age classes (at least juveniles vs. adults). In all waterfowl populations that have been studied for a long time, females have a higher annual mortality rate than males. Consequently more males exist in a population than females. This male-biased sex ratio causes females to be the limiting factor (as potential mates) of a population and increases competition among males for mates. Mate selection in waterfowl is “assortative” whereby females test (and make mate choices from) the potential fitness of males through assessment of their size, courtship displays, stamina, dominance, plumage, etc. These competitive forces have “selected” for the bright coloration of males (for showing off traits in courtship) vs. the complex relatively dull “browns” of females (for camouflage during nesting). Later parts of this series will discuss why the “quality” of the mate (either male or female) is so important to maximizing survival and reproduction, but for now we must acknowledge that not all females (or males) are of equal quality or have equal quality mates. These inequalities greatly impact reproductive potential and ultimate effects of differential mortality on one segment of the population vs. another. Further, and of obvious importance, managing (i.e., reducing) mortality factors for females is much more important than for males.

Investment of time and energy in annual events (e.g., incubation, egg-laying, brood rearing) varies among sexes and species of waterfowl. In geese, where extended parental care is the norm, both sexes contribute to rearing young, and timing of annual events such as migration are synchronized. In contrast, male ducks contribute less to recruitment and typically abandon female mates late in incubation. This separation causes asynchronous timing of subsequent events for male and female ducks and the sexes often become geographically separated for extended periods. As an example, male pintails leave females in mid-late incubation, depart prairie breeding grounds early in summer, and move to molting areas. Here, they complete wing and body molt and begin southern movements as early as August. In contrast, successfully nesting female pintails remain with broods into mid-late summer, and usually molt on, or near, breeding areas. Females and juveniles often leave breeding areas together in fall. Consequently, the first pintails arriving on wintering areas in the Central Valley of California are predominantly male; females and young do not begin arriving until one-to-two months later. In this case, depending on hunting season dates at various locations, harvest could potentially, and perhaps unknowingly, be differentially directed at a particular sex or age cohort.

As shown in the above example, different age cohorts (within and between sexes) may have different distribution, timing, and behavioral patterns. As with most animals, waterfowl young of the year [known to biologists as hatch-year (HY) birds] typically are smaller, have delayed and less defined coloration, unrefined courtship displays, slower succession of annual events, higher mortality, and lower recruitment rates than adult after-hatch-year (AHY) birds. A further age complication occurs for species with delayed maturation such as geese, where the “adolescent” or “subadult” period may last two-tothree years before pairing and first breeding occurs. Plumage characteristics (including feather patterns on the wing) often enable biologists to determine whether a bird is HY, subadult, or AHY. Many population analyses attempt to determine differences in survival/harvest rates of these age classes. Other species have additional unique morphological features that allow age determination for several years (e.g., eye color of lesser scaup is different from age one to age five or six). Finally, banding and color marking (including neck collars, nasal saddles, and patagial or wing markers) have been employed to determine exact ages of birds in some species and populations. Despite the obvious differences in age classes of waterfowl, the significant efforts to determine age-classes of species, and the differential contribution to changes in population size and distribution, it is disappointing to find them lumped together in certain population analyses such as Adaptive Harvest Management and in studies of distribution dynamics.

It is important to recognize that certain traits of waterfowl, whether they be population-, sex-, or age-related, are inherent (nature) and genetically programmed. Others are a product of the environment, a duck’s experiences and its ability to “learn” successful survival and reproductive tactics (nurture). Collectively, these factors create heterogeneity - and they create inequality or differential success in reproduction and survival among individuals. The key to enlightened and progressive management of waterfowl is understanding which individuals are the most reproductively successful (“super hens”) and which hens are less consequential to population changes. In the second part of this series I will discuss characteristics of the “super hens,” explain why they produce most of the young each year, and why management actions are needed to enlarge this population segment.

Selected References

Anderson, M.G., J.M. Rhymer, and F.C. Rohwer. 1992. Philopatry, dispersal, and genetic structure of waterfowl populations. Pages 365-395 in B.D.J. Batt, A.D. Afton, M.G. Anderson, C.D. Ankney,

D.H. Johnson, J.A. Kadlec, and G.L. Krapu, editors, Ecology and management of breeding waterfowl. University of Minnesota Press, Minneapolis.

Bellrose, F.C. 1980. Ducks, geese, and swans of North America, 3rd edition. Stackpole Books, Harrisburg, PA. 540pp.

Bellrose, F.C., T.G. Scott, A.S. Hawkins, and J.B. Low. 1961. Sex ratios and age ratios in North American ducks. Illinois Natural History Survey Bulletin 27:391-474.

Miller, M., J. Takekawa, J. Fleskes, D. Orthmeyer, M. Casazza, and W. Perry. 2005. Spring migration of

northern pintails from California’s Central Valley wintering are tracked with satellite telemetry:

routes, timing, and destinations. Canadian Journal of Zoology 83: 1314-1332.

Martinson, R.K., and A.S. Hawkins. 1968. Lack of association among duck broodmates during migration and wintering. Auk 85:684-686.

Ranson, D., Jr., R.L. Honeycutt, and R.D. Slack. 2001. Population genetics of southeastern wood ducks. Journal of Wildlife Management 65:745-754.

Raveling, D.G. 2004. Waterfowl of the world - a comparative perspective. Special Publication No. 9. Gaylord Memorial Laboratory, University of Missouri-Columbia. 180p

Dr. Mickey Heitmeyer has investigated waterfowl and wetlands for nearly 30 years, and is widely recognized as one of the world’s leading experts on the biology of mallards. His professional background includes: technician and wetland manager for the Missouri Department of Conservation, research biologist for the University of California-Davis, Director of Research and Outreach for the California Waterfowl Association; Group Manager of Conservation Programs and Director of the Institute for Wetland and Waterfowl Research for Ducks Unlimited, Inc. and Ducks Unlimited, Canada. He is currently a Research Associate with the Gaylord Memorial Laboratory at The University of Missouri. He is an avid duck hunter and is owner of Dark Cypress Farms and co-owner of Cato Slough LLC. Both are conservation properties in southeast Missouri that offer wetland management services and limited high-quality sporting opportunities. He and several other wetland scientists and managers currently are forming a nonprofit entity and a consulting LLC to provide wetland ecosystem services (including waterfowl research, continuing education and habitat management ) rarely or never provided by traditional agency, academic and nongovernmental organizations. He can be contacted by e-mail at: mheitneyer@earthlink.net