Wildlife of Horicon Marsh Wildlife Area

It is commonly asked when the peak of migration is at Horicon Marsh. Of course, that depends on which group or species of birds are being referenced. The best migration time to see the greatest variety of birds is from mid-April to mid-May, and mid-September through October. However, there is no one time when you can see all the birds of the marsh. By the time one group of birds is at its peak, others may have already departed or might not yet have even arrived. Therefore, to see the greatest variety of birds it requires several trips throughout the season and throughout the year in order to get a true feel for the diversity and abundance of wildlife that is attracted to and supported by Horicon Marsh.

Over the years, approximately 300 species of birds have been sighted at Horicon Marsh. Among them are many common wetland and upland birds and some of Wisconsin's rarest bird sightings. On a single day in spring it is not unusual to find up to 100 species of birds on Horicon Marsh alone!

Each year a great number and variety of birds return to Horicon Marsh. This, in turn, attracts a great number of bird watchers who come to discover, observe and learn about our birds. Each year the same sequence of bird migration takes place. The birds return to our state in the same order, but the exact date depends on the progress of spring. Between warm and early spring seasons and late seasons, birds may be as much as three weeks apart from year to year.

Each group of birds, however, responds to a particular environmental condition that encourages them on their way. The geese arrive when the snow begins to melt and ducks cannot advance farther than the melting of ice and availability of open water. Woodcocks have to wait until frost is out of the ground so that their food of worms and insect grubs becomes available. Most songbirds have to wait until the weather is warm enough to assure a steady supply of insects. Therefore, the annual progress of spring determines the progression of the spring migration.

Horicon's phenology of birds

The geese of Horicon

Each fall, tens of thousands of Canada geese leave their Canadian breeding grounds and head for Horicon Marsh. Just as the geese flock to the marsh, so do the many visitors who come to hunt or just observe and thrill at this annual event. They come from all over the country and throughout the world to witness what is certainly one of the most amazing wildlife spectacles in the Midwest.

The geese that stop here in migration are part of the Mississippi Valley Population (MVP) of Canada geese. This is a mid-sized goose ranging from 7 to 10 pounds. In North America, there are several million Canada geese, consisting of 12 distinct subspecies. There are more than 1 million Canada geese in the MVP, with about 100,000 to 200,000 stopping at Horicon Marsh each fall. Another race, or subspecies, nests on the marsh and throughout Wisconsin, called the giant Canada goose.

Horicon Marsh is a migratory stop-over for the geese. In spring, they are on the marsh from late February or early March until mid-April. The marsh is a staging area that provides important spring food which will fuel their journey north and supply the energy for reproduction. Over the years, their average departure date from the marsh has been around April 21. It is the increasing daylight hours which stimulate the spring migration. From here, they migrate to their northerly breeding grounds, near Hudson Bay. They arrive on their breeding grounds around the end of April or beginning of May and begin to nest as soon as melting snow makes nesting sites available.

The Canada geese begin to breed when two to three years old. They will commonly mate for life, and will select a new partner if they should lose their mate. In the wild, the average life span for the Canada goose is about 6 to 8 years and has been known to live for more than 20 years. In captivity, they may live over 30 years. They come north to take advantage of large available nesting areas. Here, they can avoid most nest predators and take advantage of the abundant food supply and long daylight hours. They normally lay a clutch of five eggs, with older birds having larger broods. Eggs are incubated for 28 days, with most families hatching within a few days of each other. The young grow fast, being full grown within only two months. Before the end of the short arctic summer, they must grow their flight feathers, fatten up and condition themselves for the long journey ahead.

It is the changing season which signals the fall migration. With the oncoming cold weather and shorter days of fall, the flocks move south. They travel together as a family and the large flocks we see overhead are collective family groups and non-breeders. Loners, or single birds, are most likely sub-adults or non-breeding birds that have been at the marsh for some time and are not associating with family group. As the young follow their parents, they learn the migratory route from the experienced adults. The dramatic increase in the goose population at Horicon is the result of good management practices and due to successive generations of birds learning their way to the marsh.

When the large flocks are in flight, they travel in a typical V-formation. They apparently do this to reduce wind resistance and gain better visibility. On daily feeding flights, they fly from 100 to 500 feet high. In migration, they fly much higher, usually where they can find favorable winds. They average about 2,000 to 3,000 feet in altitude and have been observed at 9,000 to 11,000 feet.

The Canada goose can fly as fast as 60 mph, but usually prefers to go about 40 to 50 mph. They often leave with the passing of a cold front, so, with the aid of a strong tail wind, they can travel an easy 60 to 70 mph. At this rate, they can fly from Hudson Bay to Horicon, a distance of at least 850 miles, in about 15 hours. From here to their wintering grounds in southern Illinois, some 450 miles to the south, requires another seven to 10 hours.

The geese arrive on the marsh around mid-September. They stay for about four to eight weeks. The population peaks around late October to mid-November and departs by early to mid-December, as snow and ice cover the food supply and freeze open water resting areas. In most winters some geese remain in east-central Wisconsin, with the population size and distribution depending on open water, snow depth and weather conditions. While here, they feed on grass and grain and consume about a half pound of food per day. With so many geese in the Horicon area, crop damage to private lands is a constant concern. This is one of the many reasons for limiting the population size and distribution through regulated hunting.

The Canada goose has always been a part of Horicon, although the MVP geese did not stop here historically. The tremendous numbers the fall migration brings is a more recent event. After the restoration of Horicon Marsh, the first flocks arrived in the late 1940s. Through management and the establishment of food plots, they were attracted to the area. Since then, their numbers have increased dramatically.

Mississippi Valley Population

By the mid-1970s, the success of the program was beyond expectation, and the goose population at the marsh had become a matter of concern. Too many geese were stopping here! It became apparent that a potential disease epidemic would do tremendous damage to a large proportion of the entire MVP. Canada geese are susceptible to botulism, avian cholera, duck viral enteritis as well as other waterfowl diseases. Therefore, other marshes in east-central Wisconsin have been developed to accommodate Canada geese in fall, thereby spreading out the flock. In Wisconsin, the greatest number of geese still stop at Horicon, though others now also visit Theresa, Collins, Eldorado, Grand River, Pine Island and other state wildlife areas.

During their autumn visit, a close watch is kept on the Canada geese. A census of their numbers is regularly made by counting resting flocks from an airplane. Regulations and quotas are set each year to permit hunters to take about 25% of the population. Due to intensive research and management, the Canada goose has made a good comeback. From the very low population levels during the 1940s, it is probably more abundant today than it has ever been.

It is in the final analysis that we see the goose as a shared resource. It is managed regionally, with cooperation from the Canadian government, U.S. Fish and Wildlife Service, Wisconsin Department of Natural Resources and conservation agencies in surrounding states. It is also shared by various interested groups of people, ranging in activities from nature observation to sport hunting. Horicon provides many recreational opportunities for people and also resources and a rest stop for these wandering flocks of geese. It is only through continued management and public cooperation that we can ensure a healthy future for the Mississippi Valley Population of the Canada goose.

Fourmile and Cotton Island heron rookery

Within the marshland, interior are several narrow islands that rise above the surrounding marsh. Like huge ships moored in a sea of cattail, they align themselves with the length of the marsh. These islands are the emergent tops of buried drumlins; a common glacial feature that was formed by the advancing glaciers of the last Ice Age. These hills were piled up as the glacier over-rode this land and carved out the Horicon basin. As the ice retreated, it created a moraine at the south end of the marsh, which held back the waters and filled the marsh, inundating these hills. Over the centuries, sediment accumulation has filled the marsh, so that today only the crests of these drumlins rise above the marsh to form these islands.

The largest of these islands is Fourmile Island, one of our state natural areas. Natural areas, formerly called scientific areas, are unique areas that have been set aside for protection by the Natural Areas Preservation Council. They are selected from among the best remaining natural features in the state which contain nearly intact plant and animal communities or significant geological or archaeological features. Many natural areas contain features that remain essentially unchanged from presettlement conditions in Wisconsin. They are the last relics of what our state once looked like at the time when the earliest settlers arrived here.

While most natural areas are selected for their unique native vegetation, Fourmile Island and nearby Cotton Island have been chosen for their unique bird population. Until recently, these islands supported the largest heron and egret rookery, or nesting colony, in Wisconsin. As many as 1,000 pairs of herons and egrets nested here. There were four species of birds in this colony: the great blue heron, great egret, black-crowned night heron and the double-crested cormorant.

Nesting records for Fourmile Island go back to at least the early 1940s. Although it is an important site to all of the large birds that use this area, it has been a particularly important area for the great egret. The egret is a threatened species in Wisconsin. At one time, these birds were more widespread in our state. Today, barely 10 known nesting sites remain with most of these being located along the Mississippi River. Being sensitive to disturbance and habitat loss, many colonies have been abandoned. When we lose a rookery, we lose the entire local breeding population since these birds do not nest alone.

Despite our best intention to protect these birds, there have been problems for the birds on Fourmile and Cotton islands. This time, man is only indirectly responsible for their fate at Horicon. Due to our present dominating land use, we have left these birds few alternatives for nesting sites, confining them to the Horicon Marsh and a few similar, isolated sites. Yet, even in this large wetland, few islands are large enough or suitably located to offer nesting opportunities for such a large population. Due to their success over the years, nature itself began working against these magnificent birds. There have been so many birds on this 15-acre island for so long that they were having a serious effect on it. At the peak of their population, there were as many as 4,000 adults and young inhabiting the island. With a diet rich in fish and other aquatic food and so many birds nesting in so small an area, the accumulated guano, or droppings, was over-fertilizing the ground beneath. This resulted in changes to the soil chemistry which affected the trees where these birds nest.

Essentially, they were destroying the very habitat on which they depended. In addition to guano accumulation, tree diseases, such as Dutch elm disease and oak wilt, have destroyed many large trees. It is likely that the birds were stressing the health of the trees making them more susceptible to diseases. As a state natural area, it is the state's policy to monitor this site and the birds' progress. Annual surveys keep track of the population size and nesting success for each species. Surveys have also been conducted on the composition and health of the forest on Fourmile Island. Management aims to allow the birds to adjust to their own changing conditions while taking measures to maintain suitable nesting habitat.

Other steps have been taken to help these birds remain at Horicon. In the winter of 1992-93, wildlife biologists erected a series of artificial nesting platforms adjacent to Fourmile Island to provide additional nest sites and make up for the loss of trees on the island. During the following spring, birds were seen making use of some of these sites for building their nests.

Surprisingly, the birds seemed to sense the problems on Fourmile Island themselves and moved most of their colony onto nearby Cotton Island in the following spring. For several years, both Cotton and Fourmile Islands provided sufficient habitat to maintain this historical rookery. However, in spite of our best efforts to help the herons and egrets at Horicon Marsh, a natural disaster struck which ended their long-term tenure on these islands.

On May 31, 1998, a severe storm front swept across southern Wisconsin, creating winds of as much as 90 to 100 miles per hour. At the peak of the nesting season, these winds hit the islands broadside, toppling trees, tossing young from their nests and destroying most of the nests. An estimated 550 nesting pair of great blue herons and great egrets were nesting on Cotton Island. After the storm, nearly half of the trees were felled and almost all of the nests had been destroyed. With the loss of the trees and the catastrophic results of this storm, these birds abandoned Cotton Island.

Great blue herons still nest on Fourmile Island, both in the trees and artificial platforms erected for them, but not in the numbers that it once held. The great egrets seem to have moved to a colony outside of Oshkosh which grew in the following year.

The lesson learned from this experience is that in spite of our best efforts to manage wildlife, there is nothing we can do to avoid these periodic, catastrophic events. However, like putting all of your eggs in one basket, when we crowd our threatened or endangered species into the last remaining suitable habitat we risk these kinds of losses from natural events. While our goal is to maintain a breeding population of herons and egrets at Horicon Marsh, we also need to think regionally in order to maintain a series of healthy rookeries. Just in case another such natural disaster should ever strike a nesting colony, we will assure that other populations will be able to maintain the species. Of course, we cannot manage to avoid severe storms, but we cannot confine wildlife to only a few islands of habitat and expect that they will last forever in an ever-changing natural environment.

As a state natural area, public access to both of these islands is strictly prohibited during the nesting season, from April 1 to Sept. 15, to protect the remaining birds from disturbance. A good view of the island is possible from the DNR Service Center on Highway 28 or the overlook on North Palmatory Street. It can also be seen close-up by canoeing on the east branch of the Rock River. When using this approach, please keep in mind that access onto the island is strictly prohibited. It is our intention to keep the herons and egrets here and allow them to rebuild their numbers as an important part of our marshland resource.