Partial Migration in a Population of Greater Prairie-Chickens in Northeastern Colorado

The Auk 110(1):21-28, 1993

PARTIAL MIGRATION IN A POPULATION OF GREATER PRAIRIE-CHICKENS IN NORTHEASTERN COLORADO

MICHAEL A. SCHROEDER 1'3AND CLAIT E. BRAUN 2 •Departmentof Fisheryand WildlifeBiology, Colorado State University, Fort Collins, Colorado 80523, USA; and 2ColoradoDivision of Wildlife,Wildlife Research Center, 317 WestProspect Road, Fort Collins,Colorado 80526, USA

ABSTRACT.--Seasonalmovements of radio-marked Greater Prairie-Chickens(Tympanuchus cupido)were examined in northeasternColorado during 1986-1989. Many birds migrated between breeding and winter areas; all appeared to display fidelity to both breeding and winter sites.The average date of migration from winter to breeding areaswas 20 February for malesand 27 March for females.The averagedate of migration from breeding to winter areas was 4 July for females and 28 July for males. Much of the variability in timing of migration from breeding areas for females was related to brood status;average date of migration was 10 June for females without broods and 26 August for females with broods. Average migration distance between winter and breeding ranges differed significantly by sex: 9.2 km for females and 2.7 km for males. When migration samples were expanded to include distances between breeding and late summer ranges (as suggestedby timing of movements),females migrated an averagedistance of 10.6 km, while malesmigrated 2.9 km. Seasonalmovements of Greater Prairie-Chickensappear to representa partial migration with both obligatory and facultative components.Received 3 June1991, accepted 23 February1992.

MIGRATIONhas been defined as "a regular gressive interactions, breeding success,and/or round trip within a life-span of the individual" heritability (Lack 1944,Biebach 1983, Smith and (Sinclair 1983:241),while patterns of migration Nilsson 1987). For example, Blue Grouse mi- have been categorized as "annual," "partial," gration has been attributed to elevational and/ or "differential" (Terrill and Able 1988). Species or seasonaldifferences in habitatselection (Wing of Tetraoninae are particularly variable with re- 1947, Mussehl 1960, Zwickel et al. 1968), and spect to migration patterns. While some species Spruce Grouse migration appears to be related such as Willow and Rock ptarmigan (Lagopus to fidelity to specificwinter and breeding areas, lagopusand L. mutus)may be annual migrants and to variability in dispersalmovements dur- in certain regions (Weeden 1964, Irving et al. ing their first spring (Herzog and Keppie 1980, 1967), most are consideredeither nonmigrants Schroeder 1985, 1988). Despite similarities in or partial migrants with only some individuals patterns of movement for Blue Grouse, Spruce migrating. However, extensive research on Grouse, White-tailed Ptarmigan, and Common movements of Blue Grouse (Dendragapusobscu- Capercaillie, possible explanations for move- rus; Wing 1947, Mussehl 1960, Zwickel et al. ment have not been thoroughly examined in 1968), SpruceGrouse (D. canadensis;Herzog and other speciesof Tetraoninae. Keppie 1980, Schroeder 1985), White-tailed Greater Prairie-Chickens (Tympanuchuscupi- Ptarmigan (Lagopusleucurus; Hoffman and Braun do) are among the most mobile of the species 1975), and Common Capercaillie (Tetraourogal- in the Tetraoninae, with seasonal movements lus;Rolstad 1989) indicate that patterns of par- up to 170 km (Hamerstrom and Hamerstrom tial migration may be the rule rather than the 1949).Early reportsindicated that Greater Prai- exception, particularly among females. rie-Chicken movements were particularly ex- Explanations for partial migration include tensive among females and typically related to seasonal and/or sexual differences in habitat seasonal differences in habitat selection selection, and dispersal differences due to ag- (Schmidt 1936, Hamerstrom and Hamerstrom 1949)and regional food availability, suchas the abundanceof acorns(Quercus spp.; Cooke 1888, 3 Present address: Washington Department of Gross 1930, Leopold 1931). However, Gross Wildlife, P.O. Box1077, Bridgeport, Washington 98813, (1930) suggested that introduction of corn USA. throughout the range of Greater Prairie-Chick- 21 22 SCHROEDERAND Bl•ora [Auk, Vol. 110 ens resulted in the elimination of their migra- (-<4 days between sightingsfor all birds) between 1 tory tendencies. Despite numerous anecdotal March and 15 August and weekly during other times reports about Greater Prairie-Chicken move- of year. There were three typesof exceptions:(1) birds ments, a thorough examination of their seasonal that movedlong distancesresulting in their departure from the study area; (2) birds that were dead with pattern of movement has not been undertaken. their transmitterstemporarily buried in soil and/or We examined patterns of movement in a pop- vegetation; and (3) birds that disappearedeither due ulation of Greater Prairie-Chickens in north- to movement, transmitter failure, or both. Aerial eastern Colorado during 1986-1989. The study searcheswere conductedtwo to three times each year area had both winter and breeding populations to locate missing transmitters. of prairie-chickensthroughout, and there was Locationsfor each sighting were obtained by visual no a priori reason to expect large movements observation(all nest sites) or by triangulation; three between winter and breeding ranges by mem- or more azimuths were obtained within 1.5 km of bers of the population. Seasonal movements target transmitters and at angles-of-incidencebe- tween 35 ø and 145 ø. All locations were recorded with were investigated with respect to three ques- Universal Transverse Mercator (UTM) coordinates tions: (1) Do Greater Prairie-Chickens migrate (Zone 13, nearest10-m interval). Ninety percent of between winter and breeding areas?(2) Do fe- locationsderived by triangulation were within 250 males migrate farther and more frequently than m of actual locations (Schroeder 1991). males?(3) Do movements occur in responseto We defined winter-breeding migration as move- habitat, weather, and nest failure? ment from winter to breeding areas and breeding- winter migration as movement from breeding to winter areas,regardless of specifictime. Migration METHODS distance was estimated as the distance between the breeding seasonlocation (lek for malesand nest for We selected a 301-km2 study area centered 10 km females) and mean X- and Y-coordinatesfor at least northeastof Eckley,Colorado (40ø11'N, 102ø22'W). The four locationsduring winter. Although 17 of 21 males areawas grasslanddominated by sandsagebrush (Ar- were observedon only one lek during the breeding temisiafilifolia) and small soapweed(Yucca glauca) in- season,the four exceptionswere observedon a single termixed with irrigated cropland, primarily corn lek at least 75% of the time (Schroeder and Braun (Schroeder and Braun 1992b). Forty-one to 47 leks 1992a);these "primary" leks were used as breeding were active (> 1 male) during each breeding season. season locations. Additional distances were estimated Trapping was concentratedin a core area of approx- using mean locations in late summer and autumn imately 75 km2. Trapping in winter at feeding sites seasonsas intermediatepoints betweenbreeding and with walk-in traps baited with corn and in spring at winter areas;this helped identify the specifictime of leks with walk-in traps and cannonnets resultedin migratory movements. capture of 243 Greater Prairie-Chickens(Schroeder Svedarsky(1988) attributed long movementsof and Braun 1991). GreaterPrairie-Chickens, particularly females, to their All capturedbirds were banded with a numbered previousnest failure and/or interactionswith pred- aluminumband and a unique combinationof three ators;he suggestedthat movementswere frequently coloredplastic bands. Birds were classifiedaccording nomadic in responseto disturbance.Consequently, to feather appearanceand wear (Ammann 1944)as: site fidelity between consecutiveyears was examined yearlings,5 to 17 monthsold (1 Novemberof first for both sexesto distinguishbetween regular migra- year to 31 Octoberof secondyear); and adults,greater tions and nomadic movements. Nomadic birds may than 17 months old (after 31 October of secondyear). not return to the same sites in consecutiveyears. Battery- and solar-powered radio transmitters were Dates were estimatedonly for distinct movements attachedto poncho-typemarkers (Amstrup 1980) and of at least5 km, clearly not part of the normal home placed on 111 female and 34 male GreaterPrairie- range. Since some migratory movementsmay be less Chickens. Radio masses were 1.8 to 2.3% of each bird's than 5 km, this procedurewas necessaryto estimate body massat the time of capture. time of migration, not the likelihood of migration. Seasonswere defined a priori as breeding (15 Feb- This procedureresulted in little ambiguity;birds of- ruary to 30 June),late summer(1 July to 15 August), ten moved from the study area (> 10 km) within 36 autumn (16 August to 31 October),and winter (1 No- h of being observedon or near their nest site, or on vember to 14 February)based on breeding behavior their winter area. In these cases, time of movement and daily movement (Robel et al. 1970). Breeding, was estimated based on search intensity (time be- nesting,and hatchingusually occur during the breed- tween searches).For example, if a telemetry search ing seasonand brood break-up during autumn. failed to result in detection of a bird later found off Radio-marked Greater Prairie-Chickens were lo- the study area, we assumedthe bird had migrated at catedusing a portablereceiver and three-elementYagi the midpointin timebetween the last successful search antenna. Observationsof each bird were made daily and the first unsuccessful search. January1993] GreaterPrairie-Chicken Migration 23

We used multiresponse permutation procedures (MRPP; Zimmerman et al. 1985, Biondini et al. 1988) to statisticallycompare distributions of distancesand FEMALES dates. We compared variances with Fm•x-testsand BROOD FEMALES means with t-tests (SAS Institute 1985). Direction of •iMALESNONBROOD FEMALES movementwas examined with a chi-squaregoodness- of-fit testusing eight 45ø-categories(Cain 1989,Bergin BREEDING-WINTER MIGRATION 1991).

z 2 RESULTS

Sitefidelity.--Of six radio-markedmales mon- itored during at leasttwo consecutivebreeding seasons, all attended the same lek; the winter DATE(BEGINNING OF 2-WEEKPERIOD) area for one male was more than 5 km from its Fig. 1. Distribution of dates for distinct move- breeding area (returned to samelek three con- ments by Greater Prairie-Chickens in northeastern secutiveyears). An additional 10 banded males Colorado, 1986-1989. without radios were also observed on the same lek in consecutiveyears. Nest locations of individual hens between ing migration were earlier (MRPP-test, P = 0.002, consecutiveyears were an average of 0.83 km t = 4.518, P = 0.001) for males (œ= 20 February + SEof 0.19 km (n = 8) apart;two of thesehens + 4 days, n = 3) than females (œ= 27 March + wintered in areas that were more than 20 km 6 days,n = 13;Fig. 1). Datesof breeding-winter from their breeding areas.These distances were migration did not differ (MRPP-test, P = 0.520; not different (MRPP-test, P = 0.599) from dis- t = 0.792, P = 0.464) between males(œ = 28 July tances (œ = 0.81 _+ 0.11 kin, n = 10) between + 30 days, n = 5) and females(œ = 4 July _+ 10 first nests and second nests within the same days,n = 33). The tendencyfor malesto move year. Thus, distancesbetween consecutivenests early to their respectiveleks was expectedsince were the samestatistically for nestswithin years leks were frequently active by mid-February. as they were for nests between years. Breeding-wintermovements by femalesap- Distances between mean locations for con- peared to be bimodal (Fig. 1). Much of the vari- secutive winter ranges were relatively small (œ ability in movement was associatedwith their = 1.08 _+ 0.33 kin, n = 7 females and 2 males); brood status.The mean date of migration from five of these birds had moved more than 5 km breeding areas was 10 June _+ 9 days (n = 23) betweenwinter and breedingareas (four moved for females without broods and 26 August + >20 kin). Five of seven females returned to 19 days(n = 10) for femaleswith broods(MRPP- within 1 km of their previouslyoccupied winter test, P = 0.001; t = 3.693, P = 0.003). Similarly, area despitethe possibledisturbance of pred- 4 of 25 females(12%) migrating during May- atorsat their destroyednest sites (including two August,and 6 of 8 females(75%) migrating dur- females moving >20 kin). Overall, there were ing September-Octoberhad broods(X 2 = 9.989, no observationsof radio-markedbirds chang- P = 0.002). Exceptionsto the general pattern of ing (>5 km apart) either their winter or breed- female movement usually were females with ing sitesbetween consecutiveyears. late renesting attempts (late migration) or fe- One adult female that moved 26 km returned malesthat lost their broods relatively soonafter to the samewinter area she occupiedas a year- hatching (early migration). ling. This observationwas significantfor three Due to speed and distance of many move- reasons:(1) her first movement between winter ments, actual observations were difficult to ob- and nesting areas may have representeddis- tain. One female completeda 26-kin migration persal(marked as a yearling);(2) her subsequent between her depredated nest and her winter return to the same general winter area may in- range in a maximum of 71 h. Another female dicate that migration movementsmay retrace completeda 24-kin migration between her win- dispersal movements; and (3) she wintered in ter range and breeding area in a maximum of the same general area in which numerous fe- 137 h. males spent the breeding season. Many birds that apparently migrated died Timingof movement.--Datesof winter-breed- prior to being observedduring the winter or 24 SC,ROEDERAND BRAUN [Auk,Vol. 110

NESTSITES FEMALES W NTERRANGES BROOD FEMALES 447O nO" WINTER-BREEDING BREEDING-WINTER MIGRATION • MIGRATION NONBROOD BROOD 446O r'• 3 FEM,ALES FEMALES MALES FEMALES

25FEB 35MAR 22APR 20MAy 17JUN 15JUL 12AUG 115EP DATE(BEGINNING OF 2-WEEKPERIOD)

Fig. 2. Distribution of disappearancedates in re- 442O lation to average date of migration (arrows) for Great- er Prairie-Chickens in northeastern Colorado, 1986- 1989. 4410 breeding seasons. Consequently, breeding- winter distanceswere divided into breeding- 710 720 late summer and late summer-winter compo- UTM (KM EAST) nents. Thesedistances were estimatedonly for Fig. 3. Straiõht-line distancesbetween estimated femalesfollowed throughoutall seasonsto pro- winter ranges (circles)and nest sites(asterisks) for 60 vide additional information on specifictiming female Greater Prairie-Chickenscaptured on study of movements. Of 38 distances recorded, all of area (dashed line) in northeastern Colorado, 1986- thosegreater than 10 km (n = 5) were observed 1989. Inset shows females with both winter ranges during the breeding-latesummer period. and nest siteson the study area. The three longest movements between late summer and winter areas (6-9 km) were re- cordedfor femaleswith broods.The only brood than adults for both males (3.52 vs. 2.48 km) female that moved a long distance early in and females (14.39 vs. 8.20 km), these differ- summer (23 km) lost her brood within two days ences were not significant (P = 0.501 for fe- of hatch (prior to movement).In general,move- males, P = 0.289 for males). With both ages ments between late summer and autumn ranges combined, movements of females were longer were relatively small (0-4 km) for all females. (P < 0.001) and more variable (P < 0.001) than However, the four longestmovements were by those of males. In addition, fewer male (0%) females with broods. than female(31.6%) migrations crossed the study We alsoexamined the datesof disappearance area boundary (X 2 = 4.986, P = 0.026). for radio-markedindividuals that, subsequent- Analysis of migration distanceswas conser- ly, were not found (Fig. 2). Although some of vative; only birds with known winter and theseradios may have becomedisabled follow- breeding areaswere included. Many birds that ing mortality, the synchrony of disappearance died prior to either the winter or breedingsea- dates with observedmigration dates indicates sons were not included in the analysis, even that many radios may have been on birds that though many had obviously made long migra- migrated but were not found. Thus, it is likely tory movements. Consequently, analysis of that estimatesof migration tendenciesand dis- movement data was expanded to include ad- tances were low. ditional birds based on locations between Distance of movement.--Distances between breeding and late summer areas. Females mi- winter and breeding areas ranged between 0.6 grated an averagedistance of 10.58 + 1.40 km and 40.0 km (•?= 9.18 + 1.73 km, n = 38) for (n = 60), while males migrated 2.86 + 0.76 km females, and between 1.0 and 6.1 km (œ= 2.74 (n = 22). Migration distancesof females(Fig. 3) + 0.44 km, n = 12) for males. Although there were longer (P < 0.001) and more variable (P was a suggestionthat yearlingsmoved farther < 0.001) than thoseof males(Fig. 4); both small January1993] GreaterPrairie-Chicken Migration 25

44•0* LEKSTES I ."'"...... '"', N i[•l• FEMALESMALES

Fig. 4. Straight-line distancesbetween estimated 0-2 4• 8-10 12-14 16-18 20-22 24-26 28•30 32•34 36•3• 40-42 44-46 winter ranges(circles) and lek sites(asterisks) for 22 DISTANCE (KM) male Greater Prairie-Chickenscaptured on study area (dashed line) in northeastern Colorado, 1986-1989. Fig. 5. Distributionsof migration distancesfor 60 female and 22 male Greater Prairie-Chickens in northeastern Colorado, 1986-1989. and large distances were common among females (Fig. 5). Twenty-one of 60 females (35.0%) Chickens have been observed making direc- and 1 of 22 (4.5%) males migrated farther than tional movements and/or were t•mporarily 5 km; this difference was significant (X 2= 8.230, present in areas with no acceptable habitat P = 0.004). (Gross 1930, Leopold 1931, Stempel and Rod- Directionof movement.--Therewas no obvious gers 1961). relationship between direction of movement We found that Greater Prairie-Chickens in and tendency to move north or south prior to northeastern Colorado are partial migrants. particular seasons.Directions of movement for Some individuals migrated substantialdistanc- birds between winter and breeding areas were es (up to 40 km) between seasonalranges, while not different from random (X 2 = 2.293, P = 0.942, others were resident on relatively small areas df = 7). Furthermore, many individuals occu- (<5 km between winter and breeding areas). pied winter or breeding areason the main study Similarly, banded individuals moved up to 170 area as the result of relatively large migratory km in Wisconsin (Hamerstrom and Hamer- movements(Fig. 3); femalesoften bypassedoc- strom 1949) and 30 km in Michigan (Ammann cupied habitatsduring the courseof their move- 1957), and radio-marked birds moved up to 12 ments. km in Minnesota (Svedarsky 1988); numerous marked individuals moved shorter distances in

DISCUSSION each population. In our study, females migrated farther and Askins (1913) suggestedthat Greater Prairie- more frequently than males. Similar tendencies Chickens were nonmigratory. In contrast, sev- were noted for Greater Prairie-Chickens in Wis- eral lines of evidence have been usedto suggest consin (Hamerstrom and Hamerstrom 1949) and that Greater Prairie-Chickens were historically North Dakota (Toepfer and Eng 1988). Differ- annual migrants in portions of their original ential movement biased toward females is con- and acquiredrange (Gross1930, Leopold 1931). sistent with patterns of migration and/or dis- Grange (1948:139) considered evidence for an- persalfor other grouseincluding SpruceGrouse nual migrations prior to 1850 as "indisputable." (Herzog and Keppie 1980,Schroeder 1985, 1986), First, seasonal increases and decreases in num- Blue Grouse (Hines 1986), Sharp-tailed Grouse bers were noted in both southern and northern (Tympanuchusphasianellus; Kobriger 1965), Sage parts of the range (Bogardus1874, Cooke 1888, Grouse (Centrocercusurophasianus; Beck 1977), Banta 1892, Judd 1905, Webster 1912, Leopold White-tailed Ptarmigan (Hoffman and Braun 1931,Schmidt 1936,Stempel and Rodgers1961, 1975), Rock Ptarmigan (Weeden 1964), Willow Spengler 1984). Second, evidence of biased sex Ptarmigan (Weeden 1964, Irving et al. 1967, ratios in resident and/or migratory populations Mossop 1988), and Black Grouse (Tetrao tetrix; has been used to demonstrate migratory ten- Willebrand 1988).Although reasonsfor female- dencies (Cooke 1888, Leopold 1931, Schmidt biased movement in Tetraoninae are not well 1936). Finally, large flocks of Greater Prairie- understood,factors may include sexual differ- 26 SCHROEDERANDBRAUtq [Auk,Vol. 110 encesin intraspecificcompetition (Herzog and Regional food availability (Cooke 1888, Gross Keppie 1980), habitat selection (Gross 1930, 1930, Leopold 1931, Lehmann 1939, Hamer- Schmidt 1936), and genetics (Keppie 1980, strom and Hamerstrom 1949, Mohler 1952, Am- Schroeder 1988). mann 1957, Toepfer and Eng 1988) and/or Timing of migration of Greater Prairie-Chick- weather (Leopold 1931,Hamerstrom and Ham- ens in northeastern Colorado was relatively erstrom 1949) have been suggestedas expla- complicatedas breeding-winter movementsoc- nations for migration of Greater Prairie-Chick- curredas early aslate May. Timing of breeding- ens. Data from our study indicated that habitat winter movements was bimodal; unsuccessful and weather could be ruled out as adequate females moved during June and brood females explanationsfor the observedmovements, par- typically moved during October-November. ticularly thosegreater than 10 km: (1) the prev- Although Greater Prairie-Chickens in other alence of early movements (most in midsum- regions were observedmoving as early as Au- mer) indicated that cold weather and/or snow gust (Leopold 1931),most movements were from were not major factors;(2) movementswere typ- October to November (Leopold 1931,Lehmann ically in randomdirections, with birdsas likely 1939, Hamerstrom and Hamerstrom 1949, Moh- to move north as southprior to winter; (3) birds ler 1952, Ammann 1957). often migrated to areasthat other birds vacated, The early timing of mostbreeding-winter mi- while others remained on the sameareas during grations by Greater Prairie-Chickensin north- both winter and breeding seasons;and (4) corn easternColorado was unusual. Most grousespe- (typical winter food) was available throughout cies migrate during late summer or autumn the region in both winter and breeding areas (Irving et al. 1967, Zwickel et al. 1968, Hoffman (Schroeder and Braun 1992b). and Braun 1975,Schroeder 1985, 1986). It is pos- Little information is available on migration sible the bimodality in timing of migration by prior to 1900. Migratory movementsmay have female Greater Prairie-Chickens (males showed been as long as 1,000 km before corn (typical a similar trend) may be due to molt of the flight winter food) was introduced throughout much remiges in summer. Females without broods of the Great Plains region (Cooke 1888); Ham- migrate prior to molting, and females with erstrom and Hamerstrom (1949) suggestedthe broodsmay wait until after the molt before un- tendency to migrate was reduced with in- dertakinglong movements.Similarly, the phys- creasedavailability of corn. However, planted iologicalcost of molting may force Lazuli Bun- food plots in Wisconsin failed to prevent birds tings (Passerinaamoena) to interrupt their fall from migrating from studyareas prior to winter migration (Young 1991). The molt period may (Schmidt 1936). be important for prairie-chickens since their One possible explanation for migration in movementsare often long, necessitatingat least Tetraoninae is that migratory movements mir- some flying. In contrast, Spruce Grouse have ror dispersalmovements of birds from their first been observedcompleting substantialportions winter area to their first breeding area. Birds of their migratory movements by walking may dispersebetween their place of hatch and (Schroeder 1985). breedingarea, while displayingfidelity to both Svedarsky (1988) suggestedthat many long their first winter and breeding areas (Herzog movements by female Greater Prairie-Chickens and Keppie 1980, Schroeder 1985, 1988, Hines may be due to disturbancesby predatorsat nest 1986). Whether this dispersaltendency reflects sites. In contrast, although migrations of fe- a genetic predisposition to disperseor environ- males in Colorado frequently occurred imme- mental pressure has not been determined diately following nest failure (Fig. 1), females (Greenwood and Harvey 1982). moved to their previouslyoccupied winter ar- Similarity between patterns of dispersaland eas and returned to the same nesting areas in migration in Greater Prairie-Chickensmay be following years, despite nest failure. Further- especially important given the context of his- more, femalesproducing broodsalso migrated, torical observationsof large-scalemigrations. even though their movements were later dur- Many observationsof migratory movements ing autumn or early winter. No females were were recorded during periods of rapid range observed renesting following migration after expansion (late 1800s).First, seasonalincreases the breeding-seasonloss of their nest or young and decreases in numbers were observed in brood. southern and northern parts of the range January1993] GreaterPrairie-Chicken Migration 27

(Grange1948). These changes in numberswould BIONDINI, M. E., P. W. MIELKE, JR., AND E. F. REDENTE. be expected if Greater Prairie-Chickens were 1988. Permutation techniques based on Euclid- dispersing into previously unoccupied areas, ean analysisspaces: A new and powerful statis- particularly in the northern and western por- tical method for ecological research.Coenoses 3:155-174. tions of their distribution. Second, evidence of BOGARDUS,A.H. 1874. Field, cover,and trap shoot- biased sex ratios in resident and/or migratory ing. J. B. Ford and Co., New York. populations has been used to demonstrate past C,MN,M. 1989. The analysisof angulardata in eco- migratory tendencies (Grange 1948). Dispersal logical field studies.Ecology 70:1540-1543. into previouslyunoccupied range (during range COOKE,W.W. 1888. Reporton bird migrationin the expansion)would be observedas a female-bi- MississippiValley in the years 1884 and 1885. ased pattern of movement, particularly since U.S. Dep. Agric., Div. Econ. Ornithol., Bull. dispersalmovements are female-biased(Ham- No. 2. erstromand Hamerstrom 1949). Consequently, GRANGE,W. B. 1948. Wisconsin grouse problems. it may be possible that historical "migrations" WisconsinConservation Department, Madison. of Greater Prairie-Chickens consisted of little GREENWOOD,P. J., AND P. H. HARVEY. 1982. Natal and breeding dispersalin birds.Annu. Rev. Ecol. more than localmovements in responseto hab- Syst. 13:1-21. itat availability (<5 km movements) in com- GROSS,A.O. 1930. Progressreport of the Wisconsin bination with dispersaltendencies and fidelity Prairie Chicken investigation. Wisconsin Con- to winter/breeding sites. servation Commission, Madison. HAMERSTROM,F. N., JR., AND F. HAMERSTROM. 1949.

ACKNOWLEDGMENTS Daily and seasonal movements of Wisconsin Prairie Chickens. Auk 66:313-337. M. E. Rasmussen and L. A. Robb assisted with field HERZOG,P. W., AND D. M. KEPPIE.1980. Migration work. R. E. Bennetts,G. G6ransson,J. W. Hupp, R. L. in a local population of SpruceGrouse. Condor Knight, H. Landel,K. Martin, O. B. Myers, L. A. Robb, 82:366-372. J. A. Schmutz, B. Van Horne, and G. C. White pro- HINES,J.E. 1986. Recruitmentof young in a declin- vided helpful discussionsduring the research.S. J. ing population of Blue Grouse.Ph.D. disserta- Harmon, D. M. Keppie,R. L. Knight, J. T. Ratti, L. A. tion, Univ. Alberta, Edmonton. Robb, B. Van Horne, and G. C. White reviewed earlier HOFFMAN,R. W., ANDC. E. BRAUN. 1975. Migration drafts of the paper. This work was supportedby the of a wintering population of White-tailed Ptar- Colorado Division of Wildlife through Federal Aid migan in Colorado.J. Wildl. Manage. 39:485-490. in Wildlife RestorationProject W-152-R and the Non- IRVING, L., G. C. WEST,L. J. PEYTON,AND S. PANEAK. game CheckoffFund. 1967. Migration of Willow Ptarmigan in arctic Alaska. Arctic 20:77-85.

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