Northern Prairie Wildlife Research Center
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
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.
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.
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.
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.
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
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.