Managing he abundance of bison in Yellowsone Naional Park winer 2012 Chris Geremia P. J. Whie and Rick Wallen Sepember 12 2011 EXECUTIVE SUMMARY Background Yellowsone Naional Park (YNP) developed a plan o manage he abundance of bison during he winer of 2012 using populaion daa modeled forecass of movemen and a suie of wildlife managemen ools consisen wih he 2000 Ineragency Bison Managemen Plan (IBMP) and subsequen adapive managemen plans. Specifically YNP is managing for an end-of-winer bison arge of 3000 while mainaining or progressing owards he following desired condiions: Bison abundance averages 3000-3500 per decade. Se raio of abou 50% males and 50% females and age srucure of abou 80% aduls and 20% juveniles a he conclusion of winer in he cenral and norhern breeding herds. Approimaely equal abundance in he cenral and norhern breeding herds. Mainain he processes of migraion and dispersal. More han 50% decrease in brucellosis prevalence in bison. In 2011 observers couned 3720 bison in YNP wih 2314 bison in he norhern breeding herd and 1406 in he cenral breeding herd. The se raio of bison observed in he cenral inerior is skewed owards males. This is he larges number of bison ever observed in norhern Yellowsone. Populaion and movemen models for bison were developed o eplore sraegies for reducing bison numbers owards an end-of-winer arge of 3000 while progressing owards equal abundance in each herd and se raios of 50% adul males and 50% adul females. Populaion and movemen models parameerized wih environmenal condiions such as average snow pack and forage values prediced wih high cerainy ha more han 750 bison will migrae o he norh boundary of YNP during he upcoming winer and more han 300 bison will migrae o he wes boundary. Model-generaed predicions of he number of bison surviving winer 2012 (November 2011-May 2012) wihou any huning or managemen removals averaged 3345 (95% confidence inervals = 2800-3969) including 2141 (1692-2686) in he norhern breeding herd and 1205 (928-1531) in he cenral herd. The cerainy of oal abundance being beween 2500 and 3500 bison was 0.71 wih an 88% chance of here being more han 3000 bison. Managemen Recommendaions Model resuls indicae ha approimaely 330 bison should be removed from he populaion during winer 2012. These effors will increase he cerainy of abundance being beween 2500 and 3500 a he end of winer o more han 90%. Managemen removals of 30 adul male bison from he cenral herd bison and 300 bison (200 adul females 50 yearlings and 50 calves) from he norhern herd should increase our cerainy of progressing owards desired condiions in erms of age herd and se srucure. In he cenral herd removal of 30 adul male bison could be accomplished hrough huner harves in Monana norh of Wes Yellowsone. The 200 adul female bison from he norhern herd could be removed hrough huner harves in Monana near Gardiner and he selecive culling of bison likely o be infecious a boundary capure faciliies. Fify calf and 50 yearling bison from he norhern herd could be removed hrough (1) huner harves (2) shipmen of seronegaive bison o operaional quaranine faciliies on ribal or oher lands (3) shipmen o research faciliies and (4) selecive culling of seroposiive individuals a boundary capure faciliies. Addiional bison (20-30) may be removed norh of he park during a lae-winer hun ha arges bulls resising effors o reurn hem o he park. 1
Inroducion The conservaion of Yellowsone bison from near eincion in he lae 19 h cenury o approimaely 3700 animals in summer 2011 has led o conflic regarding perceived overabundance he poenial for ransmission of brucellosis from bison o cale and safey and propery concerns when bison move ino Monana. Prior o 1969 bison spen winer wihin Yellowsone Naional Park because decades of culling reduced numbers o less han 500 bison and here was a lack of olerance for bison on winer ranges ouside he park (Plumb e al. 2009). However park managers ceased culling bison inside Yellowsone in 1969 and numbers increased o more han 2200 by he mid-1980s. As numbers increased seasonal migraions became he norm wih some bison moving from higher-elevaion summer ranges o lowerelevaions in and ouside he park during winer (Bruggeman e al. 2009). The numbers of bison migraing increased wih abundance snow deph and hardness and learning (Geremia e al. 2011). The Yellowsone bison populaion is infeced wih brucellosis which may induce aborions or he birh of non-viable calves and can be ransmied beween bison and cale (Rhyan e al. 2009). Thus he federal governmen and he Sae of Monana agreed o a bison managemen plan in 2000 ha esablished guidelines for cooperaively managing he risk of brucellosis ransmission from bison o cale. The plan emphasized conserving he bison populaion and allowing some bison o occupy winer ranges on public lands in Monana (U.S. Deparmen of he Inerior and U.S. Deparmen of Agriculure 2000). Due o risk managemen and oher concerns more han 3600 bison were removed from he populaion during 2001 o 2010 wih more han 1000 bison and 1700 bison being removed from he populaion during winers 2006 and 2008 respecively. These culls uninenionally removed more calf and female bison from he cenral breeding herd which if coninued over ime could resul in aleraions of he se and age srucure of he populaion and consequen changes in demographic processes ha could persis for decades (Whie e al. 2011). Also produciviy in he norhern breeding herd increased resuling in record abundance in 2011 wih higher porions of females and calves in he herd. There is a need o reduce large culls of bison and heir poenial long-erm uninended demographic and geneic effecs by implemening smaller selecive culls ha dampen populaion growh (U.S. Deparmen of he Inerior e al. 2008). This plan provides a sraegy for mainaining Yellowsone bison numbers near a arge of 3000 while mainaining or progressing owards he following desired condiions: Bison abundance averages 3000-3500 per decade (which should mainain 90-95% of eising geneic diversiy over he ne 200 years; Pérez-Figueroa e al. 2010). Se raio of abou 50% males and 50% females and age srucure of abou 80% aduls and 20% juveniles a he conclusion of winer in he cenral and norhern breeding herds. Approimaely equal abundance in he cenral and norhern breeding herds. Mainain he processes of migraion and dispersal. More han 50% decrease in brucellosis prevalence in bison. We developed a populaion model using daa colleced from Yellowsone bison during 1970-2011 and esimaed he abundance composiion and rends of each breeding herd o evaluae he relaive impacs of harvess and oher ypes of managemen removals. We inegraed hese esimaes wih a model of bison migraion o predic he numbers of bison moving o he park boundary each winer. These ools combined long-erm monioring daa wih informaion gained from radio-collared bison o draw conclusions wih ariculaed cerainy abou fuure condiions of Yellowsone bison. We developed a decision-making process o advise he managemen of populaion abundance and ransboundary movemens of bison. During June and early July we conduced populaion couns and age and gender classificaions of each breeding herd. We hen used long-erm weaher forecass and he models described above o predic herd abundances and composiions a he end of he upcoming winer and he 2
magniude of numbers of bison migraing o park boundaries. We esablished annual removal objecives for bison based on abundance disease disribuion and demographic (age herd se) goals. During auumn 2011 we will updae he bison operaions plan o incorporae our removal objecives and oher possible managemen acions for he coming winer. As winer progresses monhly aerial couns snow model projecions for he park and revised long erm weaher forecass will be used o refine our predicions of he iming and magniude of rans-boundary movemens o suppor decision-making during winer operaions. A variey of managemen ools will be used o reduce bison numbers as necessary including (1) public and reay harvess in Monana (2) selecive culling (shipmen o slaugher) a boundary capure faciliies o reduce he proporion of infecious bison (3) selecive culling (shooing shipmen o slaugher) in Monana o preven brucellosis ransmission o nearby livesock or due o human safey or propery damage concerns (4) ransfer of bison o American Indian ribes or oher organizaions for quaranine and evenual release and (5) ransfer bison o research faciliies. We aended a meeing in Augus 2011 o discuss our removal objecives and harvess wih Monana Fish Wildlife and Parks and American Indian ribes wih recognized reay righs for bison on unoccupied federal lands ouside Yellowsone Naional Park in Monana. Pregnan bison will no be shipped o slaugher faciliies during heir hird rimeser (afer March 1 s ). During winer 2012 we will monior and documen acual huner harves winer-kill predaion off-ake and managemen culls. Mehods We refer o bison ha congregae during he breeding season in he Hayden valley as he cenral herd and hose ha gaher in he Lamar valley and associaed meadows as he norhern herd (Figure 1). During winer mos cenral herd animals evenually move wes from he Hayden and Pelican valleys ino he Firehole River drainage Madison River drainage and/or Hebgen basin in Monana. Also some cenral herd animals migrae o he norhern porion of Yellowsone and inerac wih he norhern herd during winer. While mos cenral herd migrans reurn o he Hayden valley during he subsequen breeding season some have dispersed ino he norhern herd in recen years (Geremia e al. 2011). Bison from he norhern herd ypically migrae wes during winer owards lower-elevaion areas near Mammoh Wyoming and Gardiner Monana. Dispersal from he norhern herd o he cenral herd has been negligible. We developed a populaion model ha esimaed he (1) annual size and composiion of Yellowsone bison herds during 1970-2011 (2) numbers of culls and harvess from each herd and (3) survival fecundiy and feal se raios. We combined esimaes of herd abundance composiion and survival wih informaion on seasonal disribuions o consruc a movemen model. We hen combined he populaion and movemen models o evaluae harves sraegies for he bison populaion during he upcoming winer. Specifically we used he movemen model o predic he magniude of ou-of-park movemens by bison during a winer wih below average average and ereme snow pack condiions. Ne we removed argeed numbers of bison from various demographic caegories (age se) and herds accouned for hose removals in he populaion model and prediced changes in herd sizes and composiions during he following summer. We also esimaed he cerainy wih which he bison populaion was likely o be wihin desired condiions for abundance and herd and gender srucure. Populaion model. We used a discree-ime sae-ransiion framework o consruc he populaion model (Caswell 2001). Five sages were used o porray demography in he cenral and norhern herds. The model updaed on an annual ime sep ha coincided wih he onse of he breeding season during July. This ime sep was chosen because we could differeniae beween herd membership based on spaial associaion during he breeding season. Bison reach reproducive mauriy a 2 years of age and we idenified sub-adul (1-2 years) and adul animals (greaer han 2 years). We defined he sages S 1 3
hrough S 5 o represen cenral herd members including S 1 as calves S 2 as sub-adul females S 3 as maure females S 4 as sub-adul males and S 5 as adul males. For norhern herd members we defined S 6 as calves S 7 as sub-adul females S 8 as maure females S 9 as sub-adul males and S 10 as adul males. Transiion probabiliies were defined for fecundiy (f) calf survival (s j ) adul survival (s a ) dispersal (i) and calf gender (g; Figures 2 and 3). We assumed ha sub-aduls and aduls had idenical survival bu calves had lower probabiliies (Meagher 1973). Empirical evidence suggess ha he survival of adul female bison varies across ime wih changes in annual snow condiions (Fuller e al. 2007 Geremia e al. 2009). Thus we represened adul survival as a funcion of accumulaed snow waer equivalens (SWE) which is he amoun of waer in a column of snow; Garro e al. 2003). Modeled values of daily SWE in meers were generaed across he bison range (Wason e al. 2006 Geremia e al. 2009) and summed during he snow-covered period (Ocober-April) o provide single annual merics of snow pack. Calf survival is undoubedly affeced by snow bu oo few years of calf survival observaions were available o model is influence. Therefore we porrayed calf survival as consan. Previous findings indicae ha brucellosis infecion decreases fecundiy bu i is oherwise relaively consan beween years (Fuller e al. 2007 Geremia e al. 2009). We used a single parameer (f) o esimae he probabiliy of birh and neonae survival. We did no differeniae moraliy occurring immediaely afer birh since annual calf couns occurred during June which is afer peak-calving (Jones e al. 2010). Dispersal of Yellowsone bison is largely unidirecional wih individuals moving from he cenral herd o he norhern herd beween breeding seasons (Whie e al. 2011). Thus we porrayed dispersal as consan across ime. Our analyical approach was o obain poserior disribuions of model parameers and numbers of bison in demographic sages across ime. We creaed a hierarchy in our model srucure by differeniaing beween rue and observed numbers of bison in each demographic sage. True numbers of bison were condiional on our model parameers (Figures 2 and 3) and process error (Clark 2007). Our observaions were condiional on rue saes and measuremen error (Clark 2007). We incorporaed he resuls of deailed sudies on Yellowsone bison as informaive prior disribuions for model parameers. We also incorporaed long-erm populaion couns and classificaion daa as likelihoods of rue saes condiional on parameers and observaions condiional on rue saes (Appendi I). Iniial numbers of bison in each demographic sage were esimaed. The bison populaion eperienced a prolonged period of selecive culling wihin he park o reduce brucellosis prevalence during 1950-1966. Females were preferenially removed which creaed a populaion biased owards males (Meagher 1973). We used composiions of harvess recorded during 1964-1966 (Meagher 1973) and aerial couns during 1970 (Taper e al. 2000) o esimae he iniial number of animals in each age and gender class. Bison eiing park boundaries were hisorically sho by agency personnel since animals were no allowed ouside of Yellowsone Naional Park due o hreas of brucellosis ransmission o livesock (Cheville e al. 1998). Fewer han 10 bison were culled during any winer unil 1984-1985 when 88 animals were removed ouside he norhern park boundary. Thereafer episodic removals of more han 500 migraing bison occurred during some winers as animals were eiher sho by sae huners or agency personnel or gahered and shipped o domesic slaugher faciliies by federal and sae personnel (Whie e al. 2011). We needed o aribue removals occurring o each herd o model he bison populaion. Cenral herd bison eclusively eied he wesern park boundary while boh cenral and norhern herd bison eied he norhern park boundary. Also while oal numbers of removals were known only parial informaion was available on composiion and herd membership. The annual composiion of bison removed near he wesern boundary of he park was esimaed from he subse of observed age and gender composiion. Similarly all norh boundary removals during 1970-1993 were aribued o he norhern herd. 4
Thereafer norh boundary removals were composed of members of each herd wih cenral herd size influencing he number of cenral herd animals removed (Geremia e al. 2011). Removals were subraced from model esimaes of he rue numbers of bison prior o updaing. The number of bison in each demographic sage was reaed as a lognormal random variable which is an appropriae error disribuion for a muliplicaive process such as populaion growh. Process model predicions were based on (1) a ransiion mari of survival birh and dispersal (2) he log of he number of bison in demographic sages adjused by removals and (3) process model variance on he log scale. We creaed several daa models o relae he likelihood of he iniial condiions (e.g. saring numbers of bison in each demographic sage during 1970) and process model predicions (e.g. unobserved number of bison in each demographic sage during 1971-2010) o our observaions during long-erm monioring effors. Aerial breeding season couns of Yellowsone bison herds were compleed during June-Augus from 1970-2010 wih beween one and hree annual surveys. Bison are highly visible during he breeding season as animals congregae in large groups in open areas for he ru (Hess 2002). However some unknown componen of he populaion was missed by aerial observers and we accouned for his uncerainy by eplicily modeling observaion error using replicaed couns. In addiion a single aerial coun was compleed during mos years a he conclusion of he birhing period which generally occurred in he beginning of June. Neonae calves were differeniaed from oher bison during couning. We also compleed annual composiion couns of he bison populaion during July 2002-2010. Effors began wih a comprehensive aerial survey where numbers of bison in mied gender and bachelor groups were couned. The presence of calves ha are brigh orange in color simplified idenificaion of mied gender groups. Ground observers subsequenly surveyed areas occupied by mied gender groups encounering more han 80% of herd members during single-day effors. Numbers of calves male and female sub-aduls and male and female aduls locaed in mied gender groups were recorded. Removal scenarios. We idenified several desired condiions supporive of long-erm conservaion and preservaion goals (Whie e al. 2011) and assessed he cerainy of he Yellowsone bison populaion eising wihin hese quanifiable ranges under alernae removal scenarios. Desired condiions included (1) a populaion beween 2500 and 3500 individuals (2) 1250-1750 individuals in each herd (3) a raio of males o females in each herd beween 0.90-1.10 and (4) a raio of juveniles o aduls in each herd beween 0.15-0.25. These crieria were assessed a he conclusion of he projeced 2012 winer and were adjused by proposed removals for ha year. Model forecass were made assuming average snow and forage condiions since curren long-erm forecass predic near normal precipiaion and emperaure during Augus 2011 hrough May 2012. Movemen model. Success in implemening he proposed removals will be influenced by he numbers and iming of bison movemens o boundary areas of Yellowsone Naional Park during winer. Thus we developed mechanisic nonlinear models o predic bison migraion o he park boundary and evaluae he likelihood of being able o mee he removal objecives (Appendi II; Geremia e al. 2011). We considered 142 aerial couns of bison compleed near he norhern and wesern boundaries of Yellowsone during Ocober-May 1990-2009. We couned all bison ha were ouside he park boundary or wihin a 5-km buffer inside he park boundary o accoun for animals ha had lef he park were poised o leave he park or had possibly been hazed back inside he park prior o couning. We summed hese couns wih he oal number of bison ha had migraed beyond he park boundary and were culled prior o couning o improve our measure of migraion. Culls included bison ha were harvesed by huners sho by agency personnel moved o ou-of-park research or quaranine faciliies sen o slaugher or held 5
in fenced paddocks unil release during spring. Culls were known for each year and aerial surveys provided accurae esimaes of numbers because bison are highly visible and ofen congregae in large groups in open areas (Hess 2002). We defined wo responses measuring migraion since herds differenially move owards each park boundary and are eposed o differen climae condiions. Y N where [19902009] was our observaion of migraion beyond he norhern boundary and was represened as he annual maima of couns of bison near he norhern boundary and culls occurring prior o couning. Y W was our observaion of migraion beyond he wesern boundary and defined as he annual maima of couns of bison near he wesern boundary and culls occurring prior o couning. Covariaes were defined for densiy snow pack severiy and above-ground dried biomass. We compleed annual breeding season couns of he norhern and cenral herds during July-Augus 1990-2009 as a surrogae for densiy. Bison locaed in he Madison Firehole Hayden and Pelican valleys were considered par of he cenral herd while bison on he Mirror Plaeau and in he upper Lamar River valley were included in he norhern herd. We defined cenral as he annual coun of cenral herd animals and norh as he annual coun of he norhern herd. We used a validaed snow pack simulaion model (Wason e al. 2006 2009) o esimae daily SWE by averaging values across all 28.5 28.5-meer piels wihin a 99% kernel of bison use. We summed daily model-generaed averages during Ocober 1 s hrough April 31 s and creaed single accumulaed annual values for he norhern range ( snown ) cenral inerior ( snowc ) and enire park ( snow ). We generaed above-ground dried biomass (grams per square meer) esimaes using modeled monhly ne primary produciviy from NASA's Carnegie-Sanford-Ames-Approach (CASA; Poer e al. 1993 2007). CASA a biophysical ecosysem model incorporaes emperaure precipiaion solar radiaion vegeaion cover and he normalized differenial vegeaion inde (NDVI) from Landsa saellie daa as inpus during he April o Ocober growing season (Crabree e al. 2009 Huang e al. 2010). We considered all piels wihin he 99% kernel of bison use ecep for foresed areas ha were clipped from analysis because bison are predominanly grazers. The resuling analysis area consised of approimaely 33 meadows greaer han 1 square kilomeer in size and disribued across he elevaion gradien of he norhern and cenral ranges. We censored areas affeced by cloud cover wihin years resuling in marginal differences in he size of he analysis area beween years. Due o his difference we summed values across available piels for each year and divided by he number of piels. We defined foragen for he norhern range foragec for he cenral inerior and forage for he enire park. The covariae does no eacly reflec annual plan biomass producion over he growing season or sanding biomass available for bison during winer due o herbivore off ake during April hrough Ocober. However our measuremen provides an ecellen assessmen of he qualiy of he growing season. Furher all covariaes were sandardized o indicae he percenage by which each was above or below 20-year averages. This faciliaed model convergence and allowed us o compare he relaive imporance of each conrol on numbers of migrans. Resuls Populaion model. The model-generaed average abundance of he Yellowsone bison populaion during July 2011 was 3654 (95% credible inerval = 3444-3866; Figure 4). There were an esimaed 2321 (2158-2482) bison in he norhern herd and 1333 (1199-1468) bison in he cenral herd (Figure 5). Male o female raios were 0.75 (0.62-0.95) in he norhern herd and 1.00 (0.81-1.20) in he cenral herd (Figure 6). The annual median of he probabiliy of bison being in bachelor groups ranged from 0.06-0.29 and he 2011 probabiliy was esimaed a 0.16 (0.11-0.23). However more animals han anicipaed (0.34) were observed in bachelor groups during he classificaion of he cenral herd in summer 2011 and he rue male o female raio was likely near he upper end of he credible inerval. The proporions of bison in each age class were 0.76 (0.65-0.80) aduls 0.12 (0.10-0.14) juveniles and 6
0.12 (0.11-0.13) calves in he cenral herd and 0.72 (0.70-0.74) aduls 0.11 (0.09-0.12) juveniles and 0.17 (0.16-0.19) calves in he norhern herd. We generaed produciviy esimaes as he raio of juvenile (calf and yearling bison) o adul animals (male and female; Skalski e al. 2005). Norhern herd produciviy (0.40; 0.35-0.43) was greaer han cenral herd produciviy (0.32; 0.28-0.36) indicaing he increased capaciy for fuure growh. We deeced differenial survival beween aduls and calves wih lower adul survival during years characerized by increased snow pack esablishmen (Table 1). For eample adul survival was 0.92 (0.90-0.95) when snow pack esablishmen was near he 42-year average 0.87 (0.79-0.93) when 50% above average and 0.80 (0.62-0.92) when 100% above average. Females produced 0.57 (0.53-0.61) calves each year afer reaching mauriy a 3 years of age (Table 1) wih a slighly higher probabiliy of male calves (0.53 0.51-0.56). While oal numbers of annual removals from he populaion were known (Whie e al. 2011) seasonal miing and inerchange of bison beween herds complicaed a simple analysis of aribuing removals occurring a he norhern park boundary o he norhern herd and aribuing removals occurring a he wesern park boundary o he cenral herd. Thus our modeling approach simulaneously esimaed wihin-year inerchange dispersal and herd-specific removals. Winer migraion of cenral herd bison o he norhern park boundary began during he mid-1990s and increased wih bison abundance in he cenral herd (p 0 = -1.78-2.70 - -0.87; p 1 = 4.80 2.98-6.69). Dispersal of cenral herd bison o he norhern breeding herd was 0.02 (0.01-0.03). Prior o implemenaion of he Ineragency Bison Managemen Plan (1971-1999) removals of bison from he cenral herd near he wesern park boundary consised of 548 (428-721) males 426 (321-601) females and 108 (57-197) calves (Figure 7). Removals near he norhern boundary of he park included 653 (531-801) males 490 (388-625) females and 142 (94-210) calves from he norhern herd and 336 (261-434) males 249 (192-330) females and 138 (101-186) calves from he cenral herd (Figure 8). During implemenaion of he Ineragency Bison Managemen Plan (2000-2011) removals of bison near he norhern boundary of he park were skewed owards females and calves from he cenral herd. These removals included 314 (219-435) males 428 (298-600) females and 173 (115-256) calves from he norhern herd and 595 (460-759) males 1075 (890-1280) females and 542 (453-637) calves from he cenral herd (Figure 8). Movemen model. Migraion beyond he norhern park boundary was affeced by herd size accumulaed SWE and above-ground dried biomass. There was greaer han a 95% probabiliy ha increases in cenral and norhern herd sizes and accumulaed SWE increased numbers of bison migraing beyond he norhern park boundary. There was also greaer han a 95% probabiliy ha fewer bison migraed wih increases in above-ground dried biomass. We found a greaer han 95% probabiliy of more bison moving beyond he wesern boundary wih increases in cenral herd size increases in accumulaed SWE and decreases in above-ground dried biomass. We ploed process predicions of he modified logisic model compared o observed couns and prediced rue saes and model performance decreased beginning around 2001. This finding suggess an imporan conrol on recen migraions (e.g. learning) was no included in he model. Modeling of fuure migraions indicaed ha large and episodic migraions of bison beyond he norhern and wesern boundaries of Yellowsone would occur during he ne decade. The Naional Oceanic and Amospheric Adminisraion (NOAA) emperaure and precipiaion forecasing models predic average emperaures and precipiaion during Augus 2011 hrough May 2012 (Table 2). Also field assessmens indicae here has been average o above-average forage producion during summer 2012. Thus he forecas for winer 2012 is average snow and forage condiions (100%) for more han 2000 bison in he norhern herd and less han 1500 bison in he cenral herd. Given his 7
forecas we predic more han 750 bison will migrae o he norhern boundary of Yellowsone Naional Park and more han 300 bison will migrae o he wesern boundary during winer 2012 (Table 3). Managemen Implicaions Average produciviy (raio of juvenile o adul bison) in he cenral herd was high during 2002-2005 (2002: 0.42 + 0.02 SD; 2003: 0.37 + 0.02; 2004: 0.41 + 0.02; 2005: 0.42 + 0.02). Females ou-numbered males (Figure 6) and several winers of below-average snow condiions resuled in high survival which faciliaed growh. The cenral herd rapidly increased and reached record levels of abundance in 2005 (Figure 5) afer which repeaed large removals a he norhern and wesern park boundaries decreased he herd by more han 65% alered he gender raio and diminished produciviy o he lowes esimaed value (0.24 + 0.01) in he enire 42-year ime series. Concurrenly norhern herd produciviy consisenly increased from 0.27+ 0.01 in 2002 o 0.40 + 0.01 in 2011 as he herd subsanially increased o record abundance in 2011 and shifed owards a greaer proporion of females. We developed removals sraegies for he Yellowsone bison populaion o mee desired condiions for conservaion while moderaing large-scale aleraions o eiher breeding herd. Model-generaed predicions of he average number of bison surviving he 2012 winer wihou any huning or managemen removals were 3345 (2800-3969) including 2141 (1692-2686) bison in he norhern herd and 1205 (928-1531) in he cenral herd. The cerainy of oal abundance being beween 2500 and 3500 bison was 0.71 wih an 88% chance of here being more han 3000 bison. Huning or managemen removals of approimaely 330 bison during winer 2012 would increase he cerainy of abundance being beween 2500 and 3500 a he end of winer o more han 90% while providing equal cerainy (0.5) of here being more or less han 3000 bison. Disparae rends in produciviy and gender raios beween he cenral and norhern herds indicae ha removals should be argeed owards juvenile and adul female members of he norhern herd. Removals of 30 adul male bison from he cenral herd bison and 300 bison (200 adul females 50 yearlings and 50 calves) from he norhern herd would increase our cerainy of progressing owards desired condiions in erms of age herd and se srucure (Figure 9). Thiry adul male bison from he cenral herd could be removed hough huner harves in Monana norh of Wes Yellowsone. The 200 adul female bison from he norhern herd could be removed hrough huner harves in Monana near Gardiner and he selecive culling of bison likely o be infecious a boundary capure faciliies. Fify calf and 50 yearling bison from he norhern herd could be removed hrough (1) huner harves (2) shipmen of seronegaive bison o operaional quaranine faciliies on ribal or oher lands (3) shipmen o research faciliies and (4) selecive culling of seroposiive individuals a boundary capure faciliies. Success in implemening he proposed removals will be influenced by numbers of animals moving o boundary areas. The models predicing bison migraion o he boundaries of Yellowsone Naional Park sugges ha migraion should be sufficien o mee he removal objecives during winer 2012. Model forecass indicae hese removals would provide for 0.97 cerainy of fewer han 1500 surviving cenral herd bison wih an equal cerainy of a male o female raio above or below 1.0 and a juvenile o adul raio of 0.14 (Table 4). We do no recommend removal of any juvenile or adul female members from he cenral herd since such managemen would decrease he cerainy of meeing desired demographic condiions. The proposed removals from he norhern herd would increase he cerainy of meeing desired condiions (Table 4). However curren abundance and age and gender srucure will require removals of norhern herd animals for several years o aain desired condiions. 8
Lieraure Cied Bruggeman J. E. P. J. Whie R. A. Garro and F. G. R. Wason. 2009. Parial migraion in cenral herd bison. Pages 217-235 in R. A. Garro P. J. Whie and F. G. R. Wason ediors. The ecology of large mammals in cenral Yellowsone: sieen years of inegraed field sudies. Elsevier San Diego California. Caswell H. 2001. Mari populaion models: consrucion analysis and inerpreaion. Sinauer Associaes Sunderland Massachuses. Cheville N. F. D. R. McCullough and L. R. Paulson. 1998. Brucellosis in he greaer Yellowsone area. Naional Academy Press Washingon D.C. Clark J. 2007. Models for ecological daa. Princeon Universiy Press Princeon New Jersey. Crabree R. C. Poer R. Mullen J. Sheldon S. Huang e al. 2009. A modeling and spaio-emporal analysis framework for monioring environmenal change using NPP as an ecosysem indicaor. Remoe Sensing of Environmen 113:1486-1496. Fuller J. A. R. A. Garro P. J. Whie K. Aune T. Roffe e al. 2007. Reproducion and survival of Yellowsone Bison. Journal of Wildlife Managemen 71:2365-2372. Garro R. A. L. L. Eberhard P. J. Whie and J. Roella. 2003. Climae-induced variaion in vial raes of an unharvesed large-herbivore populaion. Canadian Journal of Zoology 81:33-45. Geremia C. P. J. Whie R. L. Wallen F. G. R. Wason J. J. Treanor J. Borkowski C. S. Poer and R. L. Crabree. 2011. Predicing bison migraion ou of Yellowsone Naional Park using Bayesian models. PLoS ONE 6:e16848. Geremia C. P. J. Whie R. A. Garro R. Wallen K. E. Aune e al. 2009. Demography of cenral Yellowsone bison: effecs of climae densiy and disease. Pages 255-279 in R. A. Garro P. J. Whie and F. G. R. Wason ediors. The ecology of large mammals in cenral Yellowsone: sieen years of inegraed field sudies. Elsevier San Diego California. Hess S. C. 2002. Aerial survey mehodology for bison populaion esimaion in Yellowsone Naional Park. Disseraion Monana Sae Universiy Bozeman. Huang S. C. S. Poer R. L. Crabree S. Hager and P. Gross. 2010. Fusing opical and radar daa o esimae grass and sagebrush percen cover in non-foresed areas of Yellowsone. Remoe Sensing of Environmen 114:251-264. Jones J. D. J. J. Treanor R. L. Wallen and P. J. Whie. 2010. Timing of paruriion evens in Yellowsone bison implicaions for bison conservaion and brucellosis ransmission risk o cale. Wildlife Biology 16:333-339. Meagher M. 1973. The bison of Yellowsone Naional Park. Naional Park Service Scienific Monograph Series No. 1. Washingon D.C. Pac H. I. and K. Frey. 1990. Some populaion characerisics of he norhern Yellowsone bison herd during he winer of 1988 1989. Monana Deparmen of Fish Wildlife and Parks Bozeman. 9
Pérez-Figueroa A. R. Wallen T. Anao J. A. Coombs M. K. Schwarz F. W. Allendorf G. Luikar and P. J. Whie. 2010. Conserving geneic variaion in large mammals: effec of populaion flucuaions and male reproducive success on geneic variaion in Yellowsone bison. Universiy of Monana Missoula Monana. Plumb G. E. P. J. Whie M. B. Coughenour and R. L. Wallen. 2009. Carrying capaciy migraion and dispersal in Yellowsone bison. Biological Conservaion 142:2377-2387. Poer C. S. Klooser A. Huee and V. Genovese. 2007. Terresrial carbon sinks for he Unied Saes prediced from MODIS saellie daa and ecosysem modeling. Earh Ineracions 11:1-21. Poer C. S. J. T. Randerson C. B. Field P. A. Mason P. M. Viousek e al. 1993. Terresrial ecosysem producion: a process model based on global saellie and surface daa. Global Biogeochemical Cycles 7:811-841. Rhyan J. C. K. Aune T. Roffe D. Ewal S. Hennager e al. 2009. Pahogenesis and epidemiology of brucellosis in Yellowsone bison: serologic and culure resuls from adul females and heir progeny. Journal of Wildlife Diseases 45:729-739. Skalski J. R. K. E. Ryding and J. J. Millspaugh. 2005. Wildlife demography: analysis of se age and coun daa. Elsevier San Diego California. Taper M. L. M. Meagher and C. L. Jerde. 2000. The phenology of space: spaial aspecs of bison densiy dependence in Yellowsone Naional Park. U.S. Geological Service Biological Resources Division Bozeman Monana. U.S. Deparmen of he Inerior Naional Park Service and U.S. Deparmen of Agriculure Fores Service Animal and Plan Healh Inspecion Service. 2000. Final environmenal impac saemen for he ineragency bison managemen plan for he sae of Monana and Yellowsone Naional Park. Washingon D.C. U.S. Deparmen of he Inerior Naional Park Service and U.S. Deparmen of Agriculure Fores Service Animal and Plan Healh Inspecion Service and he Sae of Monana Deparmen of Fish Wildlife and Parks Deparmen of Livesock. 2008. Adapive adjusmens o he ineragency bison managemen plan. Copy on file a Yellowsone Naional Park Wyoming and a websie <ibmp.info>. Wason F. G. R. T. N. Anderson W. B. Newman S. S. Cornish and T. R. Thein. 2009. Pages 85-112 in R. A. Garro P. J. Whie and F. G. R. Wason ediors. The ecology of large mammals in cenral Yellowsone: sieen years of inegraed field sudies. Elsevier San Diego California. Wason F. G. R. W. B. Newman J. C. Coughlan and R. A. Garro. 2006. Tesing a disribued snowpack simulaion model agains spaial observaions. Journal of Hydrology 328:728-734. Whie P. J. R. L. Wallen C. Geremia J. J. Treanor and D. W. Blanon. 2011. Managemen of Yellowsone bison and brucellosis ransmission risk implicaions for conservaion and resoraion. Biological Conservaion 144:1322-1334. 10
Table 1. Poserior disribuions of parameers of a populaion model of Yellowsone bison herd during 1970-2011. Abbreviaions are sandard deviaion (SD) credible inerval (CI) logi ransformaion of adul female survival (s a1 ) logi ransformaion of he effec of snow on adul female survival (s a2 ) calf survival (s j ) fecundiy (f) feal gender (g) dispersal (i) process variance () logi ransformaion of he proporion of cenral herd animals included in norh boundary removals (p 0 ) logi ransformaion of he effec of cenral herd size on he proporion of cenral herd animals included in norh boundary removals (p 1 ) observaion error of replicaed aerial couns of bison ( obs ) and model deviance (deviance). Parameer Mean SD 2.5% CI 50.0% CI 96.5% CI s a1 2.48 0.19 2.15 2.46 2.87 s a2-1.09 0.31-1.66-1.10-0.43 s j 0.78 0.03 0.73 0.78 0.84 f 0.57 0.02 0.53 0.57 0.61 g 0.53 0.01 0.51 0.53 0.56 i 0.02 0.004 0.01 0.02 0.03 0.03 0.02 0.02 0.03 0.04 p 0-1.78 0.47-2.70-1.78-0.87 p 1 4.80 0.95 2.98 4.79 6.69 obs 144.01 10.83 124.45 143.58 166.97 deviance 3084 25.20 3037 3084 3136 Table 2. Predicions of he Naional Oceanic and Amospheric Adminisraion (NOAA) emperaure and precipiaion forecasing models a <hp://www.longrangeweaher.com/long-range-monhly-weaher- Forecass.hm>. Temperaure repored as deparure from average Precipiaion repored as deparure from average Augus 2011-1 o 2 Degrees + 10 % Sep 2011 Normal o - 1 + or 10 % Oc 2011 Normal o - 1 Normal o minus 10 % Nov 2011-1 Degrees Normal o + 10 % Dec 2011-1 o 2 Degrees + or 10 % Jan 2012-4 o 5 Degrees + 10 % Feb 2012-2 o 4 Degrees + 20 % Mar 2012-1 o 3 Degrees + 10 % Apr 2012 + 1 o 2 Degrees Normal o + 10 % May 2012 Normal o + 1 + 10 % 11
Table 3. Prediced annual maima of bison migraing beyond he norhern and wesern boundaries of Yellowsone Naional Park generaed using a modified logisic process equaion ha incorporaes he effecs of cenral herd and norhern herd size accumulaed SWE aboveground dried biomass and an ineracion beween herd size and accumulaed SWE. Table values indicae approimae maima abundances wih 95% probabiliy e.g. he probabiliy ha here will be no more han he lised number of bison ouside of he park is 0.95 given cenral and norhern herd sizes and accumulaed SWE (snow) and aboveground dry biomass (forage) as percenages of 20-year averages. NORTH BOUNDARY Cenral Norhern Snow 60% 60% 100% 100% 100% 130% 130% 130% Forage 100% 60% 130% 100% 60% 130% 100% 60% 1000 1000 -- 135 185 210 275 360 390 500 635 1500 1000 -- 175 240 250 335 440 460 580 740 2000 1000 -- 215 285 305 400 525 550 700 890 1000 1500 -- 255 340 320 415 535 510 630 785 1500 1500 -- 330 445 410 520 675 605 765 960 2000 1500 -- 400 530 485 625 810 725 915 1150 1000 2000 -- 470 600 510 645 810 690 860 1040 1500 2000 -- 620 790 650 830 1040 870 1070 1300 2000 2000 -- 740 950 785 1000 1250 1040 1290 1560 WEST BOUNDARY Cenral Norhern Snow 60% 60% 100% 100% 100% 130% 130% 130% Forage 100% 60% 130% 100% 60% 130% 100% 60% 1000 -- -- 150 170 140 160 185 155 180 205 1500 -- -- 235 270 255 295 335 315 360 415 2000 -- -- 260 300 260 300 345 295 340 390 Table 4. Model-generaed cerainies of meeing desired condiions of age gender and herd srucure of Yellowsone bison a he conclusion of he 2011-2012 winer comparing no removals and our recommended removal (i.e. culls and harvess) of 330 bison. Desired condiions measured a he end of winer include mainaining or progressing owards (1) a populaion beween 2500 and 3500 individuals (2) 1250-1750 individuals in each herd (3) a raio of males o females in each herd beween 0.90-1.10 and (4) a raio of juveniles o aduls in each herd beween 0.15-0.25. Desired Condiion Disribuion No Removals Remove 300 Bison 2500-3500 bison park-wide 0.71 0.91 1250-1750 cenral 0.32 0.27 norhern <0.01 0.07 0.90-1.10 cenral 0.32 0.31 male:female norhern 0.23 0.29 0.15-0.25 cenral 0.02 0.14 juvenile:adul norhern <0.01 0.69 12
Figure 1. Major use areas of bison in Yellowsone Naional Park including bison managemen zones idenified in he Ineragency Bison Managemen Plan beyond which bison were rarely observed during 1990-2009. 13
Figure 2. A concepual model of he life cycle of calf and female Yellowsone bison. Sages S 1 hrough S 3 represen cenral herd bison while sages S 6 hrough S 8 represen norhern herd bison. Sages S 1 and S 6 represen calves sages S 2 and S 7 represen sub-adul females and sages S 3 and S 8 represen adul females. Parameers for ransiion probabiliies were fecundiy (f) calf survival (s j ) adul survival (s a ) calf gender raio (g) and dispersal o he norhern herd (i). f s a i f s a (1-i) s j (1-g) (1-i) s S 1 S a (1-i) 2 S 3 s a (1-i) s a i s a i s j (1-g) i s a s a S 8 S 6 S 7 s j (1-g) f s a 14
Figure 3. A concepual model of he life cycle of calf and male Yellowsone bison. Sages S 1 S 4 and S 5 represen cenral herd bison while sages S 6 S 9 and S 10 represen norhern herd bison. Sages S 1 and S 6 represen calves sages S 4 and S 9 represen sub-adul males and sages S 6 and S 10 represen adul males. Parameers for ransiion probabiliies were calf survival (s j ) adul survival (s a ) calf gender raio (g) and dispersal o he norhern herd (i). s j g)(1-i) s S 1 S a (1-i) 4 S 5 s a (1-i) s a i s a i s j g i s a s a S 10 S 6 S 9 s j g 15
Figure 4. Model generaed predicions of he abundance of bison (ecluding new-born calves) in July during 1970-2014. The solid line depics he prediced average populaion size while he doed lines depic he inerval of 95% credibiliy. Open circles indicae he highes annual aerial couns compleed each year. 16
Figure 5. Model generaed predicions of bison abundance (ecluding new-born calves) in he cenral and norhern breeding herds in July during 1970-2014. Solid lines depic he prediced average herd sizes while doed lines depic he inervals of 95% credibiliy. Open circles indicae he highes annual aerial couns compleed each year. 17
Figure 6. Model generaed predicions of he raios of males o females in he cenral and norhern breeding herds during July from 2000-2011. Solid lines depic he prediced average raios while doed lines represen he inervals of 95% credibiliy. 18
Figure 7. Model generaed predicions of bison removals (harvess managemen culls) from he cenral herd near he wesern boundary of Yellowsone Naional Park before (1971-1999) and afer (2000-2011) implemenaion of he Ineragency Bison Managemen Plan. Circles depic he prediced averages while lines represen he inervals of 95% credibiliy. 19
Figure 8. Model generaed predicions of bison removals (harvess managemen culls) near he norhern boundary of Yellowsone Naional Park before (1971-1999) and afer (2000-2011) implemenaion of he Ineragency Bison Managemen Plan. Circles depic he prediced averages while lines represen he inervals of 95% credibiliy. 20
Figure 9. Model generaed predicions of abundance for he cenral and norhern breeding herds in Yellowsone Naional Park during July from 2000-2012. Solid lines depic he prediced average herd sizes while doed lines depic he inervals of 95% credibiliy. Red solid and doed lines represen prediced herd sizes (including new-born calves) provided he recommended removals of 330 bison are implemened during winer 2011-12. The recommended removals are 30 adul males from he cenral herd and 200 adul females 25 juvenile females 25 juvenile males and 50 calves from he norhern herd. 21
Appendi I: Developmen of a Sage-Srucured Model of he Yellowsone Bison Populaion Populaion model parameers and prior informaion. Prior disribuions of adul survival fecundiy and herd inerchange were esimaed from mark-recapure daa colleced during 1995-2011. We defined fecundiy (f) as he probabiliy of observing a calf in close proimiy o a dam during he paruriion period. Daa were aggregaed wih eising informaion on Yellowsone bison (Fuller e al. 2007 Geremia e al. 2009) and included 266 observaions of 132 female bison a leas 2 years of age. We reaed he number of observaions of dams wih calves (y) as a binomial disribued random variable such ha We assumed ha increasing snow pack diminished survival and coalesced recen daa wih eising informaion (Fuller e al. 2007 Geremia e al. 2009) o consider 377 observaions from 96 female bison a leas 1 year of age. We accumulaed snow pack merics (Garro e al. 2003) across each winer as our measure of snow pack esablishmen (Wason e al. 2006). Bison ha were culled or harvesed were no considered during he year of removal. Abbreviaions were s as he vecor of sandardized snow pack merics s a0 as he probabiliy of survival s a1 as he conribuion of snow pack esablishmen i as he subse of years ha each animal remained in he sudy and Y as he mari of observaions of survival saus. Each individual observaion was reaed as a random Bernoulli variable such ha Pulses of immigraion from he cenral herd o he norhern herd have occurred since he early 1980s (Fuller e al. 2007) and we assumed ha inerchange was unidirecional. We reaed annual numbers of dispersing cenral herd bison as random binomial variables. Dispersal was indicaed by a cenral herd animal ha was locaed on he norhern breeding range during he subsequen summer. We defined Y as he vecor of observaions and n as he vecor of numbers of cenral herd sudy animals where Feal gender raios were esimaed from several individual sudies of Yellowsone bison ha idenified he se of feuses associaed wih dams ha were harvesed during boundary reducions. Sudies occurred during 1931-1932 (n = 208) 1940-1941 (n = 263) 1945-1946 (n = 212) 1949-1950 (n = 238) and 1988-1989 (n = 82; Meagher 1973 Pac and Frey 1990). We defined g as he probabiliy ha a feus was male n as he vecor of numbers of feuses eamined during each sudy and y as he vecor of observed male feuses per sudy where These analyses provided prior disribuions for parameers used in he populaion model: Parameer Mean SD Prior disribuion f 0.66 0.03 Bea ( f 0 164 84 ) 22
s A0 2.40 0.19 Normal ( s A0 2.40 0.19 ) s A1-0.44 0.45 Normal ( s A1-0.44 0.45 ) i 0.05 0.01 Beal( i 10.69 216.83 ) g 0.55 0.02 Bea( j 340278 ) Esimaing harves composiion. Bison were removed near he norhern or wesern park boundary afer eiing he park during 1984-2011. Numbers of annual removals were known bu records were incomplee for age and gender classificaion (Whie e al. 2011). We assumed ha H was a mari of random variables where H = H W + H N wih H W represening wesern and H N as norhern removals. We needed o differeniae removals occurring a differen boundaries because bison from boh herds eied he norhern boundary afer approimaely 1992 while only animals from he cenral herd eied he wesern boundary. Inuiively our approach esimaed he number of animals removed from each demographic sage as he produc of known composiion of wesern removals and he oal removed from he wesern boundary and he produc of known composiion of norhern removals he oal removed from he norhern boundary and probabiliy ha a removal was a member of he cenral herd. Proporions of animals removed from each demographic sage were considered o be Dirichle random variables. We defined he mari r W as he rue composiion of wes boundary removals. Componens of r W for norhern herd bison were se o zero o aribue all wesern removals as occurring o cenral herd members. We defined y W as our observed annual oals of wes boundary removals from each demographic sage and evaluaed We defined R W as he vecor of oal annual wesern removals and esimaed wesern removal composiion as H W = R W r W. A similar approach was used for esimaing norh boundary removals during 1970-1992 when only norhern herd animals were speculaed o ei he norhern boundary. We defined y N as observed annual oals of norh boundary removals. Componens of r N for cenral herd bison were se o zero. We considered R N as he vecor of oal annual norhern removals and esimaed norh boundary removal composiion as H N = R N r N such ha Afer 1993 we needed o accoun for some unknown componen of norhern removals as occurring o cenral herd members. We defined he mari c as he proporion of animals removed a he norhern boundary from calf sub-adul female adul female sub-adul male and male demographic sages. We evaluaed r N = cp for componens of r N describing cenral herd demographic sages and r N = c(1-p) for componens of r N describing norhern herd demographic sages. We also defined y N as observed annual oals of norh boundary removals and incorporaed an informaive prior disribuion for p (he probabiliy ha a removal was a member of he cenral herd) such ha R N represened he vecor of oal annual norhern removals and we esimaed norhern removal composiion as H N = R N r N. The informaive prior disribuion for p was evaluaed from mark-recapure observaions of cenral and norhern herd collared bison during 1995-2011. Herd size affeced he number of cenral herd members migraing o he norhern boundary (Geremia e al. 2011) and we evaluaed p = invlogi (p 0 +p 1 C ) where C were annual couns of cenral herd animals. Sudy animals were observed a he norhern park boundary during si winers. We reaed y as a vecor of random 23
binomial variables indicaing he number of cenral herd sudy animals capured a he norh boundary processing faciliy and n as he vecor of all capured sudy animals where Noe: ne year we will aemp o updae his o a mulinomial o decrease uncerainy around he composiion esimaes. Esimaing numbers of bison in various demographic sages during 1970-2011. Wihin park gaher-andremoval operaions were compleed during 1964-1966 o reduce brucellosis prevalence which we used o esimae he saring composiion of he populaion during 1970. We defined z 0i as uniform random variables represening iniial numbers of animals in each herd and demographic sage. Wihin park reducions during 1964-1966 provided observaions of he composiion of each herd a model iniiaion. We defined he mari y 0 as random mulinomial variables of he observed number of bison in each demographic sage where he vecor n 0 was he oal number of observaions of cenral and norhern herd members. Vecors of mulinomial probabiliies (p 0 ) were defined by for cenral herd sages and disribuion as for norhern herd sages. We specified he iniial condiions componen of he poserior Process model. We defined Z as a 10 by 42 mari of lognormal disribued random variables represening rue numbers of bison in each demographic sage during 1971-2010. Rows of he mari Z corresponded o demographic sages wih row 1 porraying cenral herd calves (2 monhs of age) row 2 porraying cenral herd juvenile females (14 monhs of age) row 3 porraying cenral herd adul females (more han 26 monhs of age) row 4 porraying cenral herd juvenile males (14 monhs of age) row 5 porraying cenral herd adul males (more han 26 monhs of age) row 6 porraying norhern herd calves row 7 porraying norhern herd juvenile females row 8 porraying norhern herd adul females row 9 porraying norhern herd juvenile males and row 10 porraying norhern herd adul males. We defined he vecor ż as he log of he median of A (Z -H ) where Z was he h column of Z and H as he h column of H. H represened he mari of removals o each demographic sage per year. A was defined as he ransiion mari of survival fecundiy and dispersal probabiliies beween demographic sages where 24