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Integrated Management of the Greater Prairie Chicken and Livestock on the Sheyenne National Grassland

Brood Period


Early reports indicated that broods stayed in the vicinity of the nest for the first few weeks after hatching (Schwartz 1945, Hamerstrom and Hamerstrom 1949), and advanced the notion of "nest-brood habitat" (Hamerstrom, et al. 1957, Westemeier 1972, Kirsch 1974, Drobney and Sparrowe 1977). The mosaic of diverse habitats and smaller field sizes in the 1940's would have better facilitated chicks finding adequate brooding areas close to nests compared to current field sizes and the intensity of land use. The advent of radio-telemetry in the early 1960's (Marshall 1963) made it possible to unobtrusively document movements and habitat use by wildlife. This could not be done by following visually marked animals, particularly in the dense habitats which they often utilize, and greatly increased our knowledge of upland game bird ecology (Robel et al. 1970b).

Brood habitat and nesting habitat

"Nest-brood habitat" suggests that a given habitat is used for both purposes and, in some situations, for some species, this may be true. For prairie chickens, the term may be used in a general way. For example, in Minnesota "bluestem" might be termed "nest-brood habitat" but specifically, undisturbed bluestem was nesting habitat and recently (within 1 year) burned, grazed, or mowed bluestem was brood habitat (Svedarsky 1979).

Generally brood habitats differ from nesting habitats; not surprising because their functions are different. Brood habitat must accommodate chick movement at ground level; adequate amounts and kinds of insects are essential; cover to provide concealment from predators, protection from weather factors, yet openings for sun exposure, must be present; and it must be accessible from the nest site since chicks have to walk there. Nesting habitat has to be dense enough to conceal the female, provide for predator detection and escape, and can be widely separated from feeding areas due to the greater mobility of the female.

Perhaps Jones (1963:757) made one of the earlier descriptions of this difference: "Nesting took place in areas of exceptionally heavy cover. When hatching was completed, greater prairie chicken females moved their broods into areas where the vegetation had been disturbed: old fields, native shortgrass, or cultivated pastures." Disturbance seems to be a common denominator of good brood habitat so long there is adequate regrowth to provide cover from predators and weather factors. In all cases in a Minnesota study (Svedarsky 1979), broods moved directly from nests to areas disturbed by burning, grazing, or mowing; these habitats accounting for over 69% of 290 brood locations. Studies in other eastern portions of the range have noted similar patterns (Skinner 1977, Toepfer 1988, Westemeier et al. 1995, Burger 1988, Jones 1988). In the western parts of the prairie chicken range where grazing is the predominant land use, availability of disturbed areas may not be as limiting as areas containing adequate concealment cover and insect habitat.

Concealment cover

In a study on the Ft. Pierre National Grasslands in South Dakota, Rice and Carter (1982:18) pooled radio-tagged brood data for 13 prairie chickens, 9 sharptails, and 1 hybrid plus incidental observations and noted, "... sweet clover, snowberry, and good stands of western wheatgrass and green needlegrass were most commonly used for brooding habitat. Some use of vegetation associated with unmowed road ditches and stock dams was recorded. Birds were often located along drainages and on north-facing slopes." Quantitative data were not given but the implication was that the heaviest cover available was sought by broods, especially during the heat of the day. At the SNG, Newell (1988) found broods using vegetation taller than 25 cm an average of 80% of the time during the summer months.

In evaluating reported observations of brood habitat use, especially concealment cover, one should consider the method or circumstances of detection. An observer on foot without a dog would likely see more broods in more open covers where birds would be more apt to flush. Searching with 1 or 2 dogs, accompanied by various vocal commands, would likely alert broods at a greater distance and they could seek heavier cover, if available, before flushing. This could bias cover estimates toward denser cover. Incidental observations made while harvesting hay would obviously bias towards the use of hay fields. Judicious collecting of radio telemetry data is probably the most unbiased since it allows locating broods in some settings where incidental observations would be unlikely due to the reluctance of birds to flush in heavy cover or prejudging by the observer that a cover would not be a good place to find broods. Toepfer (1988:439), in following radio-tagged broods in Wisconsin, noted, "The consistent use of the taller grasses is probably the main reason why prairie chicken broods are rarely seen."

Broods and lowlands

Lowlands seem to be important to prairie grouse broods in grazed areas of the Northern Great Plains. Kobriger (1965), in Nebraska, noted sharptail broods to move into mowed wetland meadows during the day, using whatever shade that was available (trees, windrows, unmowed areas), and then moved into tall unmowed vegetation on the uplands as they began actively feeding in late afternoon. Grosz and Kirby (1986:23) followed radio-tagged sharptail broods near Streeter, North Dakota, and noted, by mid-July, broods had moved off the grazing treatments to the idle areas of the station and "were utilizing class I and II seasonal wetlands that had dried up by late June." Newell (1988:26) collected 921 locations from 36 prairie chicken broods on the SNG and found most in the lowland community "with the highest use occurring in June when lowland vegetation was much taller and denser than upland or midland vegetation." In all summer months, he found the portion of locations in lowlands over 44% with visual screening in excess of 2.5 dm. Svedarsky (1979) found lowland habitats ("willow", "sedge") to have positive preference ratings when burned or grazed but negative ratings when undisturbed; suggesting differences in openness at ground level and/or insect quantities.

Broods may use lowlands simply because of the taller cover which may be found there or there may be advantages in predator avoidance. Gratson (1988) suggested that small mammals tend to be less numerous in lowlands than uplands and this may be related to predators such as red fox hunting less in lowlands.

Along with all the other functions, brood cover must simultaneously function as secure roosting cover. Broods, especially young ones with mobility limitations, don't move to optimum roost habitats at the end of the day, they simply roost where they happen to be.

Brood food

Insects are the primary food source for young galliforms, especially during the critical first 2 weeks. In Oklahoma, Jones (1963) found insects (mostly beetles followed by orthropterans) comprised 97% of 14 prairie chicken brood droppings. Rumble, et al. (1988:51) found "arthropod parts" (mostly insects) comprised an average of 84.6% of 75 prairie chicken dropping collected over the 3 summer months at the SNG.

Forbs, in general, and legumes, in particular, are associated with insect quantities and brood habitats. Jones (1963:773) found, "counts of insects captured in the various habitat types revealed that the vegetation with the greater percentage of forbs consistently had more insects per unit area than did the other vegetational associations..." and that, "... the cultivated pasture association was the cover most frequently selected by birds with broods. This cover was dominated by low weeds and annual lespedeza." In Missouri, Drobney and Sparrowe (1977), noted legumes covered only 1% of their study area but accounted for 19% of all brood observations. Hollifield and Dimmick (1995) found nearly twice as many arthropods on logging roads seeded to clover in Tennessee than those seeded to timothy. Legumes may also be consumed directly by broods as Rumble et al. (1988) found alfalfa and sweet clover leaves comprised 7.4% of the June diet at the SNG; second to arthropod parts which made up 80.1%. Kobriger (1965) noted that one of the reasons why the wetland meadows were attractive to the grouse broods at Valentine Refuge in Nebraska was the clover and dandelions which grew there. Nova Silvy (personal commun.) in raising Attwater's prairie chickens noted that chicks can't develop properly on a pure diet of insects but "they need some greens."

Land management effects

Land management can also affect insect populations. Manske and Onsager (1996), in western North Dakota found the migratory grasshopper (Melanoplus sanguinipes) was reduced by 66-75% on twice-over compared to season-long grazed pastures. Apparently, the causative factor was the greater vegetation cover in the twice-over pasture and the resultant lower temperature and reduced access for egg laying. Bare, firm soil favors grasshoppers. Noetzel (1990:7) noted, "Grasshoppers usually prefer to oviposit in undisturbed (not tilled) sites such as roadsides, pasture, CRP and weedy fallow." "Weedy fallow is attractive to grasshopper egg laying, both because the weeds attract hoppers and the soil is firm."

Jones (1988) pointed out that haying could make insects more readily available for foraging by concentrating them near ground level. The trade-off, however, is the greater exposure to predators. Svedarsky (1979) observed a 30-day-old chick depredated by a female harrier in alfalfa hayfield regrowth, 25 cm high.

Burning significantly increased numbers of Hemiptera and Homoptera on a central Missouri prairie (Cancelado and Yonke 1970), Orthoptera and other herbivorous insects on a Mississippi right-of-way (Hurst 1970) and certain families of Coleoptera, Diptera and Homoptera on a Minnesota prairie (Van Amburg et al. 1978). However, Halvorsen and Anderson (1979) found greater densities (28,500/acre) in unburned control plots than burned plots (18,000/acre) in Wisconsin. Hemiptera, Coleoptera and Homoptera represented 70% of all insects samples. Factors such as timing, intensity, fuel loads, and moisture probably all influence fire effects on insects and furthermore, different taxonomic groups may be affected differently.

Weather effects and insects

Weather conditions are closely tied to early brood survival as it relates to insects and/or direct chick mortality. A certain amount of heat units are required for the emergence and development of insects. Being cold-blooded, the activity level of insects is related to temperature and chicks feed mostly on moving insects. Also, young chicks are brooded more by the hen during cool and damp weather, thus restricting the amount of time which can be spent foraging. Though weather factors are very important to upland game birds, they cannot be directly managed; only habitats can be manipulated to an extent to make birds less vulnerable to weather extremes.

In Britain, Southwood and Cross (1969) found most of the mortality of gray partridge (Perdix perdix) populations is that of young chicks. Young chicks feed largely on insects and require about 2 g dry weight per day by the 10th day of age but their resistance to chilling is increased if they consume about 3 g/day (Cross 1966). Southwood and Cross (1969) found the annual breeding success (young to old ratio) to be highly correlated (r = .95, P<0.001) with general insect abundance in June. The variables of June insect abundance and hours of sunshine, considered together, accounted for 92% of the variation in breeding success. In Illinois, Shelford and Yeatter (1955) were unable to demonstrate a clear relationship between June rainfall and temperature and prairie chicken booming ground counts the following spring; however, they did not determine insect quantities. They believed the variability was explained by nesting cover. John Toepfer (personal commun.) believes that most of the first hatch can be wiped out within 2 days depending on chick age, rainfall amounts and duration, and associated temperatures. This emphasizes the importance of weather extremes. Scott et al. (1955) found that pheasant chick resistance to chilling rains was substantially increased when dietary protein was increased from 28 to 34% by the addition of either liver or casein. It was unknown if the improvement was due to the increased protein per se or some unknown nutrient in the supplements.

Enck (1987) studied the effect of insect abundance on gray partridge chick survival in New York and found them to be positively correlated. He recommended that first nests be secured by providing better nesting cover, reducing pesticides, promoting unsprayed buffer strips around field edges, and "undersow" small grain with forbs to maintain insects. Carroll, et al. (1990) estimated partridge brood survival to 3-4 weeks in Pierce County, ND in 1985-1987 as 75.8% for unmarked broods and 57.4% for marked broods and believed that nesting cover was more important than chick survival. They found most first nests were initiated during the last 2 weeks in May. They concluded that greater brood survival in their study area, compared to others, may have been due to greater acreage of cereal grains, lower rates of pesticide use, and high insect populations (although quantitative data were not given). For Minnesota, Kurt Haroldson (personal commun.) indicates that gray partridge peaked during the drought years and have been going down ever since. He believes that spring and summer weather are key factors. In feeding trials with imprinted birds, they found the best feeding rates (on insects) in forb/grass fields that were not too dense.

Southwood and Cross (1969) evaluated insect quantities in different habitats and related these to the needs of growing partridge chicks. The minimum daily distances needed to obtain sufficient insects in different habitats by 7-day-old partridges were estimated as follows:

Downland (wild grassland) -- 101 m
Unsprayed (weedy) barley field -- 163 m
Uncut grass (hayfield) -- 174 m
Grass/clover ley  -- 254 m
Herbicide treated barley field -- 557 m

These values are for a different species and area than prairie chickens in the Northern Great Plains, but the concept is applicable and required movements in different habitats are of interest since movements require energy and increase exposure to predation. Note that reduction of weeds (presumably mostly forbs) by herbicide use in barley fields, decreased insects by more than 3-fold.

In Texas, Griffin and Silvy (1995) evaluated the insect demands of growing Attwater's prairie chicken chicks relative to insect quantities in the brood habitats and concluded that there were not adequate amounts of insects present. Low insect numbers in their study area may be due to recent increases in cattle egrets and fire ants.

Movements

Svedarsky (1979) recorded average minimum movements of about 1.25 miles (2 km, n = 9) for prairie chicken broods during their first week. Newell (1988) recorded average moves of 0.3 mile (0.47 km, n = 20) from nests to the first intensive use areas by prairie chicken broods at the SNG. In Kansas, Silvy (1968) and Viers (1967) each recorded a prairie chicken brood to move 2 miles (3.2 km) from the nest in 6 and 7 days, respectively. Newell (1987) found a 12-day-old brood to move 6.4 miles (10.3 km) in 8 days. Both Svedarsky (1979) and Newell (1987) documented extensive early movements and high brood mortality, prompting them to suggest that brood-rearing habitat, or at least the brood-rearing period, is a very important limiting factor.

Rice and Carter (1982:18) related movements to cover height: "During the severe drought of 1976, movement up to 1 mile in a 24-hour period was not uncommon. In 1978, when vegetation conditions were good, movement by hens was considerably less than previous years as birds were never recorded more than ¼ mile from nest sites."

Burger (1988) studied the movements and range of female prairie chickens in 2 study areas in Missouri; one, a mosaic of prairie tracts and other land uses, the other having a larger, contiguous tract of prairie. He believed the longer movements of broods in the mosiac area contributed to the steady decline in recent years of prairie chickens there as compared to the large block of prairie where populations have remained stable.

Disturbances

The most sensitive period for disturbance effects on broods is the first 2-3 weeks after hatching; chicks are small and potential prey for many predators, they are unable to fly far and need regular brooding by the female, especially at night. Brood females should select those habitats where the likelihood of disturbance (predators, dogs, humans, cows) is minimized while still meeting the food and cover needs of the chicks. When an encounter does occur, it is apparently adaptive for brood females to make long movements with broods, presumably to reduce the odds of a return encounter. Svedarsky (1979) and Newell (1987) both observed instances where predator encounters stimulated long moves by hens and their broods.

Newell (1987) found 74% of all brood locations in areas without cows suggesting a preference for the absence of cattle during use of a habitat; however, grazing before brood use could increase the ease of chick mobility. Newell observed 1 brood female who spent 32 days in an intensive use area but left 3 days after cattle were introduced. He found 11 of 13 renests in pastures without cattle. Obviously, prairie chickens evolved with large ungulates but young chicks and nests could be vulnerable to trampling if heavy stocking rates occurred. Ordal (1962) reported 5 of 8 teal nests in a heavily stocked Minnesota pasture were trampled and Sisson (1976) reported 2 prairie grouse nests trampled in Nebraska. Newell (1987) did not indicate if stocking rates seem to affect prairie chicken behavior. Gross (1930:93) observed prairie chicken nests at hatching, from a blind, and noted one instance where 2 chicks fell into a deep horse track as the female was leading them away from the nest and; "These two young would have perished without my intervention."

Haying operations are known to be a source of mortality (Burger 1988) and caused broods to shift movements at the SNG (Newell 1987). Grain harvesting can cause some chick mortality (John Toepfer, personal commun.). Dogs could also be a disruption to a brood, particularly if it is young. They and other predators could scatter a brood to the extent that some might get lost, and even kill younger chicks (Rick Baydack, personal commun.)

Nutrition of brood hens and brood survival

Brood survival may be affected by prehatching influences as evidenced by blue grouse chicks reared in captivity from wild-collected eggs having similar mortality patterns as same year chicks reared in the wild (Zwickel and Bendell 1967). They found no evidence however, that this reflected the nutritional state of the hen but having access to high protein food resources during the prelaying and laying periods would seem to be as important to grouse as has been documented for waterfowl (Krapu 1974, Swanson et al. 1974). The spring and early summer nutritional requirements of female prairie grouse are not as well known as waterfowl but should share some physiological similarities since they nest about the same time, are of similar body size, lay similar sized-eggs, have precocial young, and are persistent renesters.

Krapu (1974) described the importance to early nesting pintails of subcutaneous and visceral fat reserves as well as having access to protein-rich invertebrates in shallow potholes. Reduction in clutch size per nesting attempt (as occurs in prairie chickens as well) may be in response to the loss of fat reserves during early nesting attempts. "Presumably reduction of clutch size is more advantageous to the species than reduction of stored energy reserves in each egg because of greater survival of the young when provided the additional energy" (Krapu 1974:287). Pintails often nest a considerable distance from water and fat reserves may be a particular advantage in young being able to move to feeding areas. Krapu found pintail ducklings given no food after hatching survived an average of 5 days. Are young prairie chickens as well equipped as pintails to make long early movements to feeding areas or must they begin feeding soon after hatching? Could this preparation be affected by the nutritional status of the nesting hen? Svedarsky (1979) recorded 1 female who renested twice and laid a total of 35 eggs consisting of 84% of her body weight, demonstrating that the nutritional demands of nesting females can be significant. This female clearly needed to access nutritious food resources during renesting and fed mostly in cropland. He found 10 of 17 females to use cropland at least once during the preincubation period. In Colorado, Schroeder and Braun (1992) observed 11 different incubating female prairie chickens to forage 24 of 27 occasions in cornfields. Renesting and the associated nutritional demands can be common as Newell (1987) found 36% of the chicks produced at the SNG from 1983-85 came from renests. The young in these broods will be smaller in the fall and smaller females may have reduced reproductive success the following spring.

Though more definitive research is needed, food plots and agricultural crops may have critical but generally unrecognized importance to egg-laying females as well as broods. What Hamerstrom (1963:793) pointed out for sharptail broods in Wisconsin may be even more true for prairie chicken hens and broods in the northern prairies: "... food patches may have an unappreciated value for summer food. The greens and insects which accompany cultivation may be even more important than the grains which have been planted." Brood habitat values of early agriculture on the northern prairies (small pastures, weedy cropland, abundant field edges, poor drainage preventing replanting of some cropland) may have been as important as winter values of waste and field-stored grains (bundles, shocks) in moving the greater prairie chicken north and west in the settlement of the prairies.

The brood period represents an excellent example of the interaction of ecological factors. The early-season nutrition of the female may have prelaying influences on chick survival, chicks must find adequate amounts and kinds of insect food, temperature and precipitation can determine insect availability as well as foraging opportunities of chicks. Chicks must be able to move through foraging habitats which provide cover from weather and predators; for them as well as the brood hen. Land management activities, such as haying, grazing, and grain harvesting, can add direct effects such as injuries from harvesting equipment or indirect effects such as added predation resulting from induced movements. There can be many weak links in this system. Svedarsky (1979) felt that brood-rearing habitat and associated conditions was a greater limiting factor in Minnesota than nesting cover due to extremely low brood survival. Newell et al. (1988b:30) found, "Mortality of chicks was very high, with only 28.4% of the chicks surviving to the end of the summer" and suggested that the population declines at the SNG may be, in part, due to poor brood survival.

While nesting cover is obviously fundamental to prairie chicken reproduction, brood-rearing habitat is equally important but generally different (Svedarsky 1979, Newell 1987, Jones 1988). If there is 100% apparent nest success, but low brood survival, a population will decline. Prose (1985:10) developed a Habitat Suitability Index Model for the greater prairie chicken in which he identified nesting cover and winter food as limiting, "life requisites" but not brood rearing habitat. This model served as the basis for a recent habitat monitoring report (McCarthy et al. 1995a) for the SNG which accordingly placed little specific attention on the highly vulnerable, brood-rearing period and its supporting habitat.

Summary

  1. Brood habitats are generally different from nesting cover; the former requiring some type of disturbance, the latter, generally undisturbed for one or two growing seasons.

  2. Brood habitats should be close to nesting cover; provide physical protection from weather and predators; facilitate chick and hen movement at ground level; support abundant insects of the types that chicks eat; contain forbs, especially legumes, for insect diversity and as a direct food source; and provide openings for loafing and dusting.

  3. In some areas, the brood-rearing period and/or habitat may be as limiting to prairie chicken populations as nesting habitat.

  4. If not excessively wet, lowlands at the SNG may be critical brood habitat because of their accessibility and dense cover which they can provide, but they need to be disturbed the previous year and then undisturbed during brood use. Alfalfa hayfields and unplanted cropland may be very important as brood habitat.

  5. Long, early brood movements are probably related to lack of appropriate brood habitats and/or disturbance by livestock, predators, and mowing activities and likely contributes to mortality.

  6. Weather could affect broods through direct mortality, but also via indirect means; influencing insect abundance (and activity levels, thus chick detection) and the time that chicks can forage without having to be brooded by the hen.

  7. Winter food plots could have an unappreciated value to nesting females in the spring and broods in the summer, particularly if a portion is left untilled for an additional growing season.

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