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Relationship to booming grounds

Movements of greater prairie chickens can best be described as occurring within and/or on the periphery of a distribution of booming grounds. This distribution of booming grounds and the area within 5 miles surrounding it delineates a prairie chicken population and its habitat. In other words, prairie chickens and their habitat will be found within sight of the booming grounds. Perhaps the most striking aspect of the relationship of prairie chickens to booming grounds can be seen during periods when individuals make major seasonal shifts. Even when individual radio-marked birds have moved 5-30 miles, they have always ended up within 2 miles and usually within 1 mile of a booming ground.

In central Wisconsin all radio locations (n= 8,000) and observations of prairie chickens (n=22,000) were within 4.5 miles of a booming ground, 92% were within 1.2 miles and the average distance was 0.6 miles. Hamerstrom and Hamerstrom (1973) stated, "With most of the known activities of birds within a range of 2-3 miles and almost all within 5 miles it follows that management practices should also be close together so that the annual requirements of the birds can be met within small compass."

All locations of radio-marked prairie chicken cocks in central Wisconsin were within 4 miles of their home booming ground and 75% were within 1.5 miles. The home booming ground is the one a cock displays on and the one nearest a hen's nest. Hens showed less of an association to their home booming ground than cocks with all locations within 8 miles and only 47% located within 1.5 miles.

The distance to the nearest booming ground varies with the season, sex, age, and distribution of habitat types relative to disturbance patterns as they relate to the height of the vegetation and its ability to conceal a bird. The seasonal changes in the distribution of prairie chickens is one of shifting to and from the grassland areas within 1 mile of the booming grounds. Prairie chickens are closest to the booming ground during the breeding season and farthest during winter when snow cover reduces the amount of food and cover. The main factors that control daily movement patterns are the distance from the booming ground and/or food source to night roosting cover.

Night roosting cover is critical as prairie chickens spend more than half their lives in this habitat. Toepfer (1988) and Toepfer and Eng (1988) found that prairie chickens do not use the same night roosting area on successive nights during the winter. The pattern of use was irregular and emphasizes the need for a large amount and good distribution of roosting cover. Night roosting and nesting cover are similar in form, hence many areas used for night roosting will also provide habitat for nesting. Most booming grounds are located within 0.25 miles of night roosting cover.

Booming grounds are not randomly located. Their location and habitat surrounding them must meet the daily, seasonal and year round needs of the cocks. During the period mid-September through April prairie chickens in the northern range typically make at least 1 flight per day of 0.25 to 1.25 miles from night roosting grassland cover to the booming ground or to agricultural fields to feed. We know of no radio-marked birds anywhere that have existed solely in the grassland habitat during the nonbreeding season.

Adult hens are rarely observed on or near the booming grounds and visit only to select a mate and/or breed. Hens have a loose bond to the area and habitat surrounding a specific booming ground, but not to the booming ground proper. Hens, unlike cocks, show no association to their nesting areas or home booming ground outside of the breeding season. This is in contrast with cocks that can be observed on the booming grounds on a regular basis every month of the year except during the peak of the flight feather molt during July and August. Cocks spend 10-15% of their lives on the booming grounds. This bond to the home booming ground is very strong especially in adults. Cocks have even been observed on the booming grounds on calm mornings in January and February when temperatures were 20-30 below zero.

Adult cocks will stay as close to their home booming ground as possible, but immature cocks are more likely to abandon their home booming grounds during winter and move to areas with better food conditions and/or less competition. They will, however, return when conditions improve or the breeding drive becomes too great.

Cocks start to abandon their booming grounds in mid-May. However, a majority continue to visit and display until the last week of June. Once cocks abandon the booming ground most spend the summer within 1-2 miles. It is at this time that the prairie chickens begin to molt their flight and body feathers. The replacement of flight feathers is not complete until October and the pinnae and body molt are not complete until mid-November. Prairie chickens are never flightless, but their ability to fly during summer becomes limited and their movements reduced to short low flights of 0.1 to 0.2 miles.

Summer home ranges for cocks in Wisconsin averaged 425 acres. Movements were limited with some individuals walking between feeding and night roosting cover. Many birds spent the summer along the edges of agricultural fields feeding in the crops and night roosting in the adjacent grassland cover.

Adult cocks return to the booming grounds during the last week of September and will visit every morning weather permitting. Fall display is sporadic and if it is windy or raining the bird may not visit the booming ground proper or if they do they will just sit and not display. After visiting the booming ground cocks will fly to a feeding area then to a day roost or loafing area. During late afternoon they fly to feed and then make a flight to a night roosting area from where they return to the booming ground the next morning. This pattern continues through the fall and into early winter.

Fall display appears to occur more frequently on larger booming grounds (6 or more cocks) and less in populations of low density. In Illinois where the populations declined from 250 to 10 cocks, fall display was observed less and less and finally not at all (Westemeier personal commun.).

Adult hens without a brood follow a movement pattern similar to the cocks during fall except they seldom visit booming grounds. Immature cocks and hens will begin to visit booming grounds in mid-October. This coincides with the break-up of broods from first nests. The young cocks visit in an effort to obtain a territory. Young hens probably visit out of curiosity and/or due to the urge to become part of a flock. Once young cocks recruit to a booming ground they adopt the movement patterns of the local birds. Young hens localize their movements with flocks consisting of other hens and immature cocks that have not recruited to a booming ground. Fall home ranges in central Wisconsin averaged 265 acres and 1,575 acres for cocks and hens, respectively. Flight distances during the fall typically range from 0.25 to 0.5 miles.

Movements of both cocks and hens vary between areas and even between booming grounds within areas (Toepfer 1988). The distance moved is directly related to the distance between the different habitat types, especially the distance between feeding and night roosting areas. Snow has the greatest influence on daily movements as its presence and movement alters the form of cover and reduces the availability of food. Winter home ranges in central Wisconsin averaged 1,630 and 1,800 acres for cocks and hens respectively. On the SNG winter home ranges averaged 1,900 and 2,175 acres for cocks and hens respectively. Movements between feeding and night roosting areas during winter range from 0.5 to 1.0 miles.

Prairie chickens in Wisconsin, North Dakota and western Minnesota responded to long periods of sub-zero temperatures by reducing activity; by feeding only once a day and by remaining in snow burrows longer in the morning. Feeding activities were limited to once a day followed by a return to a night roosting area where the birds would make snow burrows earlier than at other times of the year (as early as 11:00 AM). At times, birds would night roost (snow burrow) in the fields they fed in during the day. Severe winter conditions, deep snow and cold temperatures also cause cocks to abandon their booming grounds for several days or for a month or more.

In winter, in both North Dakota and western Minnesota, prairie chickens can typically be found feeding in grain, soybean or sunflower fields where the wind has either reduced the amount of snow or blown it clear. In central Wisconsin, standing corn food plots are planted specifically to provide winter food for prairie chickens. Currently, the main agricultural crop in central Wisconsin is potatoes and there is little waste grain available for winter food.

Burger (1988) found prairie chickens in Missouri moved farther and covered larger areas in a grassland mosaic than in an area with large blocks of grassland cover. Toepfer (1988) found that annual home ranges in central Wisconsin were twice those of birds at Crex Meadows and reflected a closer juxtaposition to agricultural food plots and undisturbed grasslands for night roosting. Individual birds associated with booming grounds or areas with less undisturbed cover have to fly farther between feeding/day and night roosting cover and the booming ground to meet their daily and seasonal needs. However, smaller ranges may not indicate better habitat. At Crex Meadows, habitat conditions were ideal for adults but lacked enough upland grass habitat for nesting and brood rearing necessary to sustain the population.

Flocking

Prairie chickens are social birds. The exception is when hens often move alone during nest site selection and egg laying. Of 30,000 prairie chickens observed away from booming grounds in Wisconsin and North Dakota over 90% were in groups of 2 or more. The large flocks or packs observed during the winter in feeding areas are not social units but are concentrations of several smaller flocks using a common feeding area. It may be redundant but prairie chickens are attracted to prairie chickens. When immatures leave their brood mates and mother the first thing they attempt to do is try to join a local flock of prairie chickens. If they cannot recruit locally they will move until they find a flock they can join.

Immature hens may initially try to join up with the flock of adult cocks on a nearby booming ground but they probably remain only temporarily because adult cocks almost always dominate hens. Hence young hens will continue to move until they can join a flock of adult hens/or immature cocks and hens. This is probably why young hens are so much more mobile than young cocks.

Where an individual bird is born, its sex and age, not necessarily habitat will play a dominant role in why, when and where individuals move. A young bird cannot go wherever it wants but has to work its way into an already existing social structure of cocks and hens. Therefore all habitats and areas are not available to young birds. Hence they tend to wander, especially the young hens, until they can establish themselves in a specific area and develop a familiar area. Habitat plays a role in these early movements but only as it relates to the presence and density of birds already in a given area. Once established these young inexperienced birds tend to adopt the movement patterns of the local birds they associate with. The establishment on a booming ground (cocks) or to a local area (hens) occurs for some in the fall and early winter but a portion do not become completely established until the following spring.

Relationship to booming ground - nests

All past and current studies indicate that the area immediately surrounding the booming grounds contains the habitat that is critical to reproduction and year round survival of prairie chickens. All nesting studies over the past 75 years indicate that most if not all nests are located within 2 miles of a booming ground with at least 75% located within 1 mile (Buhnerkempe et al. 1984, Newell 1987, Toepfer 1988, Toepfer unpub. data, Burger 1988, Schroeder and Braun 1992). There is little doubt that the area within 1-2 miles around the booming grounds should be the focal point of management activities for nesting habitat.

Home ranges

annual

Average annual home ranges for 21 radio-marked prairie chickens in central Wisconsin were 6.6 square miles and were larger for hens (11.1 sq. miles) than cocks (3.3 sq. miles). In northern Wisconsin at Crex Meadows average annual ranges for 9 radio-marked prairie chickens were approximately half those in central Wisconsin at 3.8 sq. miles and larger for hens (6.0 sq. miles) than cocks (2.1 sq. miles). Burger (1988) reported that the distribution of habitat also influenced annual home ranges of prairie chicken hens in Missouri where they were approximately 9.9 and 3.3 sq. miles, respectively for mosaic and large block grasslands. The smaller home ranges at Crex and Missouri reflect the close proximity of feeding and night roosting areas. However, all of these annual ranges are for adult birds and do not include the first 8 months of a birds' life or for birds followed for 3-5 years.

Recent work in western Minnesota indicated that the inclusion of movements during the first year of life results in much larger annual home ranges. Analysis is only beginning but some immature hens have first year ranges of 20-50 sq. miles and hens followed for 3-5 years have large lifetime ranges that exceed 70 sq. miles yet others have ranges of only 5-10 sq. miles in size. Our present concept of how large an area prairie chickens need and what constitutes a prairie chicken management area is too small.

breeding season

Movements of prairie chickens are closest to booming grounds during the spring. Cocks display on the booming grounds every day during both the morning and evening, and feed and night roost nearby. Adult hens shift from their wintering areas to their nesting areas (1-15 miles) during the last week of March or first week of April. Immatures shift from their wintering areas to nesting areas (1-30 miles) 1 to 3 weeks later than adults. Hens eventually localize their movements in the grasslands within 1-2 miles of the booming grounds where they will establish their egg laying ranges. Flight distances during this time range from 0.25 to 0.5 miles and decrease as the breeding season progresses. Breeding season home ranges averaged 650 acres for cocks and 1,400 acres for hens.

egg laying

During egg laying hens move alone or in small groups. The initial movement during this period is from the night roost to a feeding area by walking or flying 0.15 to 0.25 miles then walking to the nest site to lay an egg usually between 11: 00 AM and 1:30 PM with 1 egg laid per day. They fly or walk from the nest to a feeding area, then fly to a night roosting area. As egg laying progresses, the hen spends more and more time at the nest eventually remaining for the night, starting incubation. Hens often have an egg laying range that consists of a mix of agricultural fields and grassland cover. Hens utilize the former for feeding, but some hens do not visit agricultural fields to feed during this period and spend all of their time during egg laying in grassland cover. Average egg laying ranges vary in size from 77 to 160 acres and appear to be directly related to the amount of undisturbed grassland cover.

The contraction of the spring home range into a small egg laying range in the vicinity of the nest suggests that this area is a critical aspect of nesting behavior and habitat use in prairie chickens. A hen must maintain herself in good physical condition for egg production, incubation and rearing of young chicks - a period of 70 days; much longer for renesting hens. Hence, a quality egg laying range may be as important to successful reproduction as the nest site itself and is an indicator of habitat quality. The small size of these ranges in several different study areas supports this hypothesis.

A comparison of egg laying ranges show they averaged 86, 91, 77 and 160 acres, respectively for central Wisconsin, Crex Meadows, western Minnesota and the Sheyenne National Grasslands study areas (Svedarsky 1979, Toepfer 1988, Newell 1987). The much larger egg laying ranges on the Sheyenne National Grasslands are thought to be the result of extensive areas of heavily grazed grasslands with short cover. The other areas have larger blocks of undisturbed grassland cover, consequently egg laying requirements of individual hens can be met in a smaller area.

Incubation

Incubating hens leave their nests twice a day to feed, once in the morning and once in the evening for 30-45 minutes. Some hens will walk from the nest and feed nearby, however, most make a flight of 0.1 to 0.25 miles to and from the nest. Many hens feed in agricultural fields on waste grain while off the nest, however there are hens that feed solely in native grassland cover. In 4 years of study in northwestern Minnesota we have documented no incubating hens feeding in CRP grasslands which are dominated by brome and alfalfa.

Renesting

Most adult hens renest but some immatures do not. This may be related to the condition of the hens as immatures are usually smaller than adults. The distance between first and second nest varies and appears to be related to the amount of nesting cover available. Where the quantity of nesting cover is limited, adult hens will remain relatively close to their first nest. This contrasts with immatures in that, if they renest, will nest farther away from the first nest. In areas with abundant nesting cover the distance between first and second nests is greater. This is probably because there are more potential nesting sites.

Brood Ranges

Hens with chicks move away from the nest right after the eggs hatch. Hens with broods move by walking until the chicks are 6-8 weeks old when some begin to make short flights between night roosting and feeding areas. Hens with chicks will remain within grassland cover until they are at least 6 weeks old at which time they may begin to feed in agricultural fields and return to night roost in grassland cover. Chicks from first nests remain with the hens until mid-October while chicks from renests stay until late October or early November. In the northern range chicks hatched after 15 July will have a difficult time surviving unless warm weather extends into November.

Brood ranges from nesting to fledging in Wisconsin averaged 625 acres and varied from 140 to 1,140 acres. Brood ranges on the Sheyenne National Grasslands ranges were 2-3 times larger than those in Wisconsin. This is thought to reflect the larger portion of that area which is heavily grazed or mowed during the summer. Grazing and mowing leave less taller cover making hens with broods cover larger areas to meet the needs of their chicks.

Non-brooding hens

Hens that have lost their brood or last nest exhibit movement patterns similar to that of cocks. However, their molt chronology can be 2-3 weeks behind that of cocks. Some hens will make major moves of 5-15 miles after they lose their last nest or young brood. Schroeder and Braun (1992) reported similar moves for prairie chickens in Colorado. Hens that lose older chicks probably cannot make such moves because they are in poorer condition and further into the molt. Hens and cocks, once into the primary molt, are probably not physically capable of making long sustained flights.

Dispersal

Preliminary information on dispersal of chicks from western Minnesota indicates that young of the year prairie chickens move farther and cover larger areas than previously thought. Hens captured as chicks that have been followed to their subsequent breeding areas ended up an average of 8 miles (n=11, range 3-30 miles) from where they were fledged. One hen nested 27 miles from where she was fledged, lost her nest and then returned the 27 miles to renest. Three sibling hens followed during the course of 1 year covered an area of over 1,000 square miles. Of 14 cocks followed from their fledging areas to booming grounds, all remained within 3 miles.

At this time there seem to be 2 strategies of dispersal and establishment in prairie chickens; hens wander away from their fledging area while cocks remain near their fledging sites. This means that the most of the cocks on a particular booming ground are coming from the habitat immediately surrounding the booming grounds.

A summary of 847 dispersal movements from winter to first spring for banded birds in central Wisconsin showed that only 60% of adult and 26% of immature hens moved 3 miles or less from winter to spring while 87% and 76% of the adult and immature cocks respectively, moved less than 3 miles or less from winter to spring; 28% of the immature hens moved from 6 to 15 miles from winter to spring. They also found that when birds moved long distances they moved to areas where birds were known to be present. On the SNG, radio-marked hens moved an average of 4 miles from winter to spring while cocks moved an average of only 2 miles (Toepfer and Eng 1988). These movements do not appear to be related to food or habitat. Based on data collected in western Minnesota these movements appear to be a return to a familiar area (adults) or in immatures an effort to establish a nesting area or recruit to a booming ground.

Migration

Historically, greater prairie chickens were thought to be migratory (Hamerstrom et al. 1973, Amman 1957, Grange 1948, Gross 1930). Cooke (1888) said they migrated as regularly as Canada geese. The distance of the migration south was believed to vary depending upon the severity of the winter. It was thought that hens were more migratory and left the cocks behind (Gross 1930). The need for migratory movements were thought to have been reduced with the introduction of agriculture especially standing corn (Leopold 1931).

In western Minnesota, radio-marked birds have moved up to 30 miles as have banded prairie chickens in Wisconsin (Hamerstrom and Hamerstrom 1973). In western Minnesota we have had birds move 3-15 miles to winter and then return for the breeding season. Fredrickson (1987) in South Dakota had 4 radio-marked birds abandon their grassland areas during the winter and move 4-27 miles to areas with standing corn along the Missouri river. All 4 returned ("migrated") back to the areas they used the previous fall.

The question of whether prairie chicken migrate or not is moot as they do move large distances, especially young hens during dispersal. They also make relatively large moves from fall to winter and winter to spring (Hamerstrom and Hamerstrom 1973). The dispersal movements probably cannot be limited nor should they because they are probably necessary for the exchange of genes to prevent inbreeding.

All agree that the seasonal shifts appear to be movements to winter food. In an agriculture community there are usually great quantities of waste grain in fields during the fall. However, there are 2 major factors that influence the availability of food and hence movements and survival of prairie chickens. One is snow cover but in most years the wind blows sizable portions of fields open allowing access to waste grains. The second factor is fall plowing. This practice greatly reduces the quantity of food available to birds. The placement of windbreaks can prevent wind from exposing waste grain. If it is deemed necessary to reduce these long moves from fall to winter and to spring it could best be accomplished by providing winter food plots or scraping snow from agricultural fields to expose waste grain.

In western Minnesota we are beginning to accumulate data that suggest that winter food may not be as limiting as previously thought. In the winter of 1995-96 in western Minnesota, one of the toughest winters on record, only 2 birds moved distances of 6-8 miles. Yet during the winter of 1993-94 at least 10 birds, mostly hens, moved 10-15 miles between their fall and winter areas. One hen moved 27 miles in less than 10 days. This suggests that what we may perceive as difficult winter conditions may not be as hard on the birds as we think. Winter survival in western Minnesota the past 4 winters has averaged 76% for 209 radio-marked birds and ranged from 58% to 90%.

Birds translocated to the Bry area in North Dakota (west of Grand Forks) have for the past 4 winters, shifted 5-13 miles to find winter food. However, the areas used 1 year have not been the same as those used in previous years, and appear related to the presence of standing corn or sunflowers in proximity to winter night roosting habitat. Standing corn or winter food may not be available to the birds if it is not within flying distance (1-2 miles) of night roosting cover.

Prairie chickens are mobile birds with large home ranges and this aspect of their ecology needs to be addressed in any management scenario. Long migratory movements do not appear to be a regular occurrence today but birds do make seasonal shifts of several miles and up to 35 miles.

Tradition

Tradition is important in prairie chickens as indicated by the use of certain booming grounds for over 50 years. Hens show fidelity to nesting areas at least for the first 2 years. However, evidence currently being collected suggests that fidelity to previous nest sites may not be as strong in 3-year-old or older hens. Booming ground locations shift or move generally because the cover on the booming ground proper changes (i.e. gets too high or rank so birds cannot be seen) or not enough young birds are recruited to the area to maintain numbers. Once established, cock prairie chickens maintain a strong fidelity to a particular booming ground; 84% of the banded cocks in central Wisconsin remained on the booming ground on which they displayed the previous spring.