Highlights

INTRODUCTION

What is waterfowl?

The term "waterfowl" refers to birds that at some point of their lives depend on wetlands. Waterfowl are usually called ducks but people with a better understanding of wildlife can tell the difference between swans, geese, ducks, grebes, mergansers and coots. The phylogenetic tree indicates that waterfowl evolved from swans and geese and that some birds from South America and Australia and related to swan and geese even though they may not look like true waterfowl.

Waterfowl are divided in three main families: (1) Anhimidae, (2) Anseranatidae, and (3) Anatidae.

The family Anhimidae is distributed in the South American rainforest in Venezuela, Colombia, Ecuador, Brazil and Peru. Horned Screamers are birds that belong to this family. They have semi-webbed feet, but their main characteristic is the horned in their heads and sharpie spurs in their wings that used for self-defense. The family Anseranatidae is best represented by the Magpie goose which is the only living species of this family. This bird is found in Australia and New Guinea. Additionally, most of the waterfowl known by men belongs to the family Anatidae. This family has been subdivided in tribes that usually tell something in particular about the groups: dendrocygnini (whistling ducks), anserini (geese), cygnini (swans), merganettini (torrent ducks), tadornini (shelducks & sheldgeese), anatini (dabbling ducks), aythyini (diving ducks), mergini (sea ducks), and oxyurini (stiff-tailed ducks).

Waterfowl and Man

The relationship between and waterfowl and men was initiated by the Native Americans and European centuries ago. Native had a different perspective about wildlife and nature in general; however, the overexploitation in the Americas began when the Europeans arrived to the new world. Back in the 1600s, people had an Anthropocentric view towards nature and all decisions were based on the benefits that humans will obtain from it. For this reason, many waterfowl species went extinct and some others were considered endangered for several years. Nowadays, waterfowl regulations and hunting seasons are monitored; however, the purpose of the conservation of waterfowl remains an anthropocentric idea because it mainly for the purpose of hunting rather than the intrinsic value of the individuals.

Waterfowl and Wetlands

Waterfowl have a very close link to wetlands therefore the conservation of waterfowl is closely related to the conservations of wetlands and suitable habitats that swan, geese and ducks. Men are directly related to climate change and the warmer/colder temperature affects their behavior such as migration timing, direction, breeding areas, suitable areas, and other components that directly affect their population growth and population dynamics.

FOOD AND FEEDING

Adaptive Radiation

Evolution is evident in waterfowl because species share some common characteristics but they also differ in some others too.These similarities and differences are observed in all species such is the case of geese in North America and Europe. The barnacle goose has short bill for quick pecking when they feed on grasslands whereas the Brent is found on saltmarshes and feed on eelgrass. Another example of speciation is the Hawaiian goose (Nene) who spends most of their time in land and rarely gets their feet in the water.

  Terrestrial vegetation:

    -short serrated bill for cutting grass blades (Ross' Goose, wigeon).

    -large gizzard for grinding up course vegetation.

    -long cacae to facilitate hind-gut fermentation of cell-wall fractions.

    -rapid ingesta throughput to facilitate high energy gain from low energy foodstuffs.

    -spend more time feeding.

Aquatic vegetation:

    -wider, spatulate bill (swans, Redheads)

    -large gizzard for grinding.

    -long intestines and cacae for digestion of large volumes of low energy food.

    -long necks (swans) or diving ability (Redheads, coots).

    -spend more time feeding (e.g. wintering Gadwalls feed 64% of the time; Mallards on waste grain feed 34%).

Tubers and rhizomes:

    -robust bill, head, and neck for digging (swans, Snow Geese, Canvasbacks).

    -long neck or diving ability (swans and Canvasbacks; aquatic tubers)

    -small gizzard and GI tract (high carbohydrate, soft, easy to digest).

Seeds:

    -dabbling type feeding method for windrowed seeds in shallow water

    -lamellae allow water and seeds to be taken in, seeds retained, water expelled

    -agile bills for picking up waste grain from fields.

    -relatively large gizzard to grind up seed husk (up to acorn in size)

Aquatic invertebrates:

    -lamellae for straining inverts from water.

    -dabbling ability (long necks) or diving ability (Ruddy Duck, Lesser Scaup).

    -minimal gizzard and GI tract needed (easy to digest)

Mollusks:

    -stout bill for ripping sessile mollusks from attached rocks (Eiders, Scoters)

    -strong, deep divers (Mergini use wings to dive, like Alcidae).

     Oldsquaws are deepest divers; gillnet captures at depths down to 240 feet!

    -big gizzard for breaking shells, small GI tract for easily digestible food.

Fish:

    -serrated bill for grabbing fish.

    -strong, fast, agile divers.

    -easy to digest, small gizzard and GI tract.

Note that bill and locomotory morphology are fixed; limiting a species dietary options.

Notes from Todd Arnold

Exploitation of habitats

Waterfowl species take advantages of their unique characteristics to exploit their habitats effectively. Swans have a very long neck that allow them to reach over one meter under water, whereas geese and sheldgeese spend most of their time on land but always near water to protect themselves from predators.  Some geese like the white-fronted goose feed 95% of the time during daylight. Most dabbling ducks and diving ducls feed at night and are difficult to observe with some exception like the Bufflehead who also feed during the day (Personal observation).

Food selection and energy cycle

As in any other animal, food selection does not occur randomly in waterfowl. They intensity in which they feed in also determine by the time of the year because breeding season plays a critical role in the feeding behavior of waterfowl. The following is an example of how some species gain and lose weigh in a short period f time:

Female 110-200 lbs in 2 months then drop back to 100 lbs in a month

Male 130 to 190 lbs to 150 lbs

Juveniles 10 to 150 lbs in 2.5 months

Geese evolved vegetarian but their digestive system is poor at absorbing nutrients therefore they need to eat a lot to be in good shape. Waterfowl species can be endogenous or exogenous. The first one means that some species lay their eggs based on the fat (energy) stored in their bodies, the fatter, the better. Exogenous means females lay their eggs based on the food (energy) available in the area at that particular time.

BREEDING BIOLOGY

Timing pair formation

Mating in waterfowl is different from other birds because they start pairing during the winter, months before breeding season. There are several reasons why waterfowl choose their mates months before the breeding season. First, females need to store energy by gaining weight for the egg laying and incubation period. In order for females to feed constantly, males need to be vigilant if a predator is approaching. Also early mating is beneficial because they can explore together the area for the best place to build their nest and the pair supports each other if intraspecific competition takes place. 

The timing of nesting and nest sites

The time when females start laying and incubation their eggs is not a random event. For example, ducks in northern Swedish lake synchronize the hatching event of their eggs with the time in which local bugs density are very high and more abundant. Additionally, geese nesting period varies with latitude and distance from the equator. In the tropics, there is little variation in the daylength, precipitation and weather in general; therefore, suitable habitat is available all year around. The nest site of ducks, swans and geese are related to their needs for nesting and foods (e.g. Mandarin and wood duck). It is not that all the individuals of a species migrate south/north to nest but they migrate where they know that food and nesting conditions are fulfilled. Once they migrate to a place, then individuals have to look for the best available site to lay their egg and this depends on how safe their eggs are going to be from predators. Nests location varies in waterfowl and this variation can be in cliffs for brant and smaller species, nearby ponds for mallards and most ducks and forests for wood ducks and buffleheads.

Egg, clutch size and incubation

The clutch size (number of eggs laid by females) is usually correlated with the size of the species and because the bigger the egg and the more energy will be invested per egg usually results in the smaller the clutch size. It is important to remember that waterfowl chicks, compared to passerines, are precocials which means that they hatch from egg sufficiently developed to leave the nest almost immediately and get food on their own.
The following table shows the egg weight, clutch size, and clutch weight in relation to the body weight of the female.

In addition, clutch size depends on several factors such as the experience of the female, food availability, population size, energy reserves and the time when the first egg was laid (proximity to the end of the breeding season). Besides, incubation periods last for up to a month in most species with most eggs hatching in the third and fourth week. This process has evolved and is different in swans, geese and ducks. In swans, the process of incubation involves both male and females, in geese this process involves mostly males, whereas in most duck incubation is a unique duty for females. Some species pluck down feathers leaving expose what is called “the brood patch” and some species like the Emperor goose do not pluck their down feather and their nests are composed of 99% of vegetation. The time that the female spends incubating her eggs (non-stopping) varies from 20 hours a day in the blue-winged teal to 48 consecutive hours in the Emperor goose.

Renesting

The process of renesting under the loss of their nest depends on the proximity to the end of the breeding season and the study provided by Arnold, Devries and Howeter shows the renesting process on Mallards. The study and data collection took place in 27 study sites throughout the Canadian Prairie Parklands. Approximately 135 female Mallards were radiomarked at each study site. Investigators took several bearings of nesting females and returned to the nesting location later that day when the female was absent and came back to determine clutch size when the nest failed (abandoned or destroyed) or until 18 days of incubation. Renesting propensity was the proportion of failed nests followed by a renesting attempt, whereas renesting interval is the number of days between nest destruction and laying the next nest. Nests were revised when females were absent to observe their fate. Renesting was considered when a female laid more eggs after her previous nest was destroyed or abandoned. The paper showed that 44% of Mallards that lost their eggs during the laying process, re-nested within four days. On the other hand, only 2% of Mallards re-nested within four days when the loss of their eggs occurred after clutch completion. The renesting chance was high in the beginning of the breeding season in April and very low at the end of the breeding season in June. Most clutch sizes were 9 eggs for first and second attempts and 8 eggs for third and following attempts.

Hatching, growth and development

Hatching is a synchronized event in which communication of the chicks (while still in the egg) is important so that they can all hatch almost at the same time. This is critical for the survival of the young because if a chick hatches too late he/she will be left behind. Ducklings leave the nest the same day after hatching by following their mother to the nearest wetland where they are safer from predation. Parents play an important role in the development of the young and some parents carry their chicks on their backs to protect them from predators whereas other species mix their chick forming big families. Ducklings take 2 months until they can fly and cygnets a little longer for up to 5 months.

Age and reproductive success

The age in which some species start breeding is important for the success of the brood. For example, Mute swans show a positive correlation between age of the male and the number of young fledged. The fact that older individuals (with more experienced) have a higher reproductive success lead to the protection preference of population to be biased towards older members since they population growth depends mainly on them. This is not only the case of waterfowl but it also occurs on other birds like the Snowy Plover which is a endangered species in the coast of California that is struggling for survival and all hopes are placed on the older males (M. Colwell personal communication).

Flightless moult

Waterfowl species go under a period of moult in which all birds lose their primary and secondary feathers, also known as flight feathers, becoming flightless for a couple of weeks. This moulting process is synchronized with the hatching of their chicks so that the whole family is able to fly after a month in most ducks or two months in swans. In some cases this process is synchronized with the other parent like in Mute swans where at least one parent can always fly and protect the cygnets. This process is stressful for the birds, they lose weight because they are very vulnerable to predators and therefore they go under the process of moulting always nearby wetlands where they can run into if they feel that in danger

SOCIAL AND SEXUAL BEHAVIOR

Mating systems

Waterfowl does not follow a unique and standard mating system; however, most species practice monogamy. Most waterfowl are monogamous but this system varies considerably if we compare ducks and swans. Northern swans and geese form strong bonds that can last for many years and where the partners are together 24 hours a day the entire year. On the other side, ducks are seasonally monogamous because their bonding only last for the breeding season and some males even leave as soon as the female lay their eggs. Copulation usually occurs before they arrive to the breeding grounds and males protect their partners so that females can store the right amount of energy for the incubation period. In long-term monogamous species, males perform some others duties not observed in ducks. Geese and swan males raise their young and provide protection during their early lives. In Bewick’s Swans, the mean number of cygnets raised in a year was significantly correlated with pair-bond duration. On the other side, only three species from the tropics are known to be polygamous, the Magpie Goose, the African Comb Duck and the Maccoa Duck.

Other strategies

Parasitism is somewhat common in waterfowl. For example, female Wood Ducks and Lesser Snow Geese dump their eggs on other females’ nests due to the lack of experience and fail to obtain a territory. Nevertheless, the South American Black-headed duck is the only true parasite and it is well adapted to this strategy because the just-born chick is observed to leave the nest right after hatching. Additionally, some species like the Australian Magpie Geese cooperate in the incubation process by sharing the same nest and taking turns during the incubation period.

Family and flock behavior

According to Black and Owen, Barnacle geese have shown that dense flocks was the most important predictor of success. Family and flock behavior has been studied extensively especially in geese and swans. There was a study focused focused on the social support of primary families (parents raised concurrent young) and secondary families (parents did not raise concurrent young) of greylag goose by observing agonistics encounters and the extraction of corticosterone (CORT) in feces.

Data collection took place in River Alm, Upper Austria, Austria. 45 individuals from a 150 non-migratory greylag goose flock were used in the study: 10 adult males, 10 adult females, and 25 subadults which were surviving offspring from the primary family units of the previous year. Behavioral protocols and fecal samples were collected during Aug’04-Feb’05 and Aug’05-Feb’06. The family was observed for 1 hour and all agonistic interactions were recorded whereas feces were collected from all the individuals within the family for 3 hours. Results indicated that primary family groups (PF) were more common than secondary families (SF). Active social support was 38% of 4474 interactions in PF and 1.5% of 965 interactions in SF. Additionally, subadult males were more likely to win agonistic encounters than subadult females. Adult females in SF excreted less CORT than females whose young had not rejoined. Subadult females excreted less CORT during social density stress when rejoining their parents; yet this passive social support was neither detectable in adult nor in subadult males. This paper is important to understand the importance of primary and secondary families; and how social support helps inexperience young adults to establish themselves in the area (Scheiber et al. 2009).

Territoriality and Interspecific Interactions

The Golden Barrow’s Goldeneye is the only waterfowl species where both the male and female have been seen to defend their territories in summer and winter. In some places, the range of different species overlap and evolution has provided specializations of behavior and morphological adaptations which minimize the competition among two or more species. One of the most territorial and violent waterfowl is the Flying Steamer Duck. In1985, Neuchterlein and Storer saw male F. Steamer ducks killing Red shovelers and this behavior may be expressed not only due to the competition of food but also to show females their fighting abilities.

MOVEMENTS AND MIGRATION
Monitoring migration
Monitoring migratory birds has been a challenge achieved thanks to technology. Nowadays, biologist can track waterfowl not only in North America but around the world.